Cayin C9, TOTL Tube/Solid-State Portable Amplifier

Hello all, as per usual, I need to thank Andrew of Musicteck for the opportunity and the ability to do this review. For this product and all other Cayin products, they are available at https://shop.musicteck.com/collections/cayin.

The Cayin C9 was purchased alongside the Cayin N7, an excellent, unique, 1 Bit implementation DAP and my full review can be found here, I'll be referencing it throughout in order to save some repetitive nature between these two.

Through this review I'm going to do my best to strictly describe how the amplifier functions and it's effects on the sound itself, as such this review will be a bit different from my standard where I do direct comparisons between other products in the same space. Instead I'll do one reference area for Technicalities, Bass, Mid and Treble presentation attempting to describe the amplifiers effects with some references to different DAPs. Where the DAP is not referenced I'll be using the N7 as the baseline paired with the Nostalgia Audio Tesseract, Cleopatra II Octa cable and interconnect.

As expected of Cayin after the N7 unboxing, the packaging is well designed with an outside sleeve fitted around a flip up lid containing the C9 right up top with an inner drawer underneath housing the accessories. Nothing short of a nice little unboxing experience but also nothing over the top. and no extensively wasted packaging like some other brands.

The accessories included are two 8 wire interconnect cables, one 3.5mm to 3.5mm and another 4.4mm to 4.4mm. Both are quite large gauge wires and as such are quite thin and flexible despite a rather tight braiding. They appear to be full copper and are of a good quality, especially considering you get two of them. A charging cable, USB-A to USB-C very tightly wrapped with an attached velcro strap for storage. You also get a screwdriver for swapping the battery bay out if needed and an additional set of tiny screws, in case you happen to lose any on a swap.


The Cayin C9 is quite heavy and durable feeling with an excellent aluminum chassis for dissipating heat. Sticking to typical Cayin trend, they place nice viewing windows over each NuTube so you can see their gorgeous glow as they are in operation. The case, purchased as part of a bundle from Musicteck is also very well designed and thought out. Not only are the top and bottom vented aluminum to assist in heat dissipation while in operation (and it needs it!), the sides are also full vented aluminum and it provides a very nice, form AND function case that not only protects but will stop it from overheating. To note, I did do a bit of temperature testing with the case on and off, there was only a minor difference in temps with the case on compared to off, so it certainly isn't insulating the C9 too heavily.

On the topic of temperatures, the C9 gets TOASTY. I have not run the C9 for extensive periods in Class A and NuTube mode, but have run it for ~7 hours (until the batteries died) in Class AB and NuTube without it shutting down due to thermal protections and detected no performance loss or stutters. I found the best way to protect the C9 from it's own heat is ensure it is placed on a surface which will either be resistant to heat or dissipate it away quickly. My chosen method was 2 square glass coasters on-the-go and a home-made copper block with venting, 2 40x20mm Noctua fans hooked into my PCs power supply to keep it nice and cool when at home. Obviously not everyone out there is a mad man like myself, or has the access to building a custom copper block but the coasters will work just fine for you sane people, if another surface that isn't heat absorbing isn't available. All in all, I did not have any problems, I'm just a crazy person who hates letting their tech get hot. But as mentioned, I haven't run Class A and Tube for a long period but I'll assume the engineers at Cayin know their thing and planned for their product to be used as designed and thus created a proper thermal solution or, at least, used components that could handle those temps.

All the switches are clicky and responsive with no jiggle detected. The volume wheel is smooth and very responsive even in small increments. All ports are excellent, tight and no jiggle with the included USB-A to USB-C charger cable. My only slight complaints are the power button can be accidentally pressed in quite easily if not careful when blind reaching for the volume wheel. Other small nitpick is the placement of the pre-amp button, but luckily it must be held in in order to activate, so well designed accident protect.

All in all I'm very impressed with the C9's quality. It's a little heavy, thus "transportable" and not truly portable. I keep mine in an Effect Audio Chamber carrying case modded with the center cut out so the N7 and C9 can lay side by side without disconnecting any cables (again, I'm nuts and don't disconnect my IEMs unless absolutely necessary because wear and tear).

Technicalities:

The first thing I noticed when pairing with my Tesseract was an immediate hum. It is not terribly loud but it is definitely noticeable when no music is playing, but not present during playback. Immediately, I thought of my next most sensitive IEM and figured if the Tesseract was getting noise, the Empire Ears Odin would too, to my surprise I did not have any noise (paired via EA Horus+Cleopatra 8 wire). Both interconnects tried, Class A or AB and Solid State and NuTube timbre had the same hum. Neither my Ragnar, Indigo or Trifecta experienced any hum (possibly a VERY low level one on the Indigo but I'd really have to strain to hear it if it was there).
Other than that hum when no playback is occurring, the background is a nice solid black with details well defined and having distinctive lines. No complaints on this, other sensitive IEMs may experience the hum as well, unfortunately no other IEMs with low impedance and higher sensitivity sitting around.
Soundstage perception varies a bit based on your selected combination of amplifier class and timbre. I found the largest combination to be NuTube+Class AB for perception. This is because in Class A the bass is much less controlled, lending the perception of depth and air to not be as significant as the more controlled, dynamic speed of class AB. I also found solid state to be a little treble light compared to NuTube which had more sparkle and air leading to greater space and separation from bottom to top. I found solid-state to also contribute to a more forward bass impact comparative to tube.
When in Tube+AB I'd put the C9 well into the holographic soundstage presentation area, where with solid-state, class a, I'd put it in more of an oval, studio-like stage, with less head room and depth. Solid-state and AB is a middle ground between the two as it gains the dynamics and speed but has the greater impact from bass which hinders it's depth a bit.
When using the line-out to connect from my DAPs to the C9 I found the C9 to not have much impact on the staging of the DAP which was connected if it had a larger stage on its own. However, when connecting my iBasso DX320x, I found the stage opened up to be much closer to that of the C9 with the N7, which was an excellent find. I do not have too much experience using the C9 in pre-amp mode, but with the limited testing done using it, it 100% inherited the DAPs staging.

For this section, since it varies so much between combinations, I'll break each into an easier to read section.

Class A, Solid-State: I find the dynamics and transient speed of this combination to be the "middle ground" reference of the rest. Here, the C9 inherits the slower speed of Class A amplification, being warmer and having more reverb on either side of the note. This creates what I feel most bass loving listeners will be looking for. As a result of the warmer and longer note decay, the dynamics of the sound suffer, as there is far less air between and bass can (and will) bloom/bleed into the mids/mid bass. Solid-state also has much less emphasis around the treble and mids, focusing heavily on bass to me. Similar to my above statements, this will lead to bloom and bleed and micro-detail loss for a gain of high impact and rumble.

Class AB, Solid-State: Gaining a great dynamic sound, with much faster transients than class A but still containing some of the bleed (much less to no bloom) of the bass to mid-bass.

Class A, NuTube: Similar low end to Class AB, Solid-State with slightly better extension of the bass and treble. This allows the sound to sound faster than class A/SS but slightly slower than class AB/SS. Dynamics improve quite a bit over both of the above due to the top end extension and clarity.

Class AB, NuTube (Preferred!): By far the most dynamic with the best transients of any of the combinations. The bass is tighter, top end extension is greater and there is much more air between notes leading to a much wider, deeper sound. This lends itself to having much greater dynamic difference between notes as you're not suffering from either bass bleed, reverb and there are no shouty upper mids to harm the lower treble. Everything will sound appropriately leveled and discernable.



For the following sound profile section, I'm going to lead each section with my preferred combination, Class AB amplification, NuTube timbre and then briefly compare the differences the other combinations have from it. As with the N7, the C9 has both line out and pre-amp options, with the line-out to C9 from your chosen source resulting in a C9 leaning profile and pre-amp adopting more of the sources profile.
The bass of the C9 is excellently balanced when in Class AB/NuTube, there is next to no tilt toward sub or mid bass which is preferential to my tastes, especially with my paired monitor, the Tesseract. Despite being balanced, there is an excellent texture to the bass, all the while, still tight and well controlled. The dynamics are among the best out there comparative to other ToTL DAPs that I've heard. The C9 is able to tow a neat line between analytical and a touch of warmth that extends through the FR but puts the perfect touch on the mid bass into lower mids that is a pleasure to listen to. Due to the sheer balance of the sound, micro and macro details stand out excellently in anything I threw at it, even the most complex songs were excellently imaged and clear with zero bloom or bass bleed. For me, this might be one of the best bass presentations right next to the SP3K CU (CU has a slight more sub bass lean but in the upper sub bass, that helps bring forth the mid bass excellently).
Class A, Solid-State: Comparatively, this combination is my least favorite among the flavors available, especially so with the bass presentation. Bass is very forward, boomy, impactful but at the same time, will bleed and bloom through the mids, veiling micro details heavily at times. Bass heads will absolutely adore this as it is by no means a poor quality bass, there is a reverb and decay that bass lovers will die for. Your mids and treble will suffer as a result, but I feel anyone using this combination likely won't be bothered by that fact. Mids become recessed/veiled, lower treble is difficult to hear on some tracks and upper treble, especially if already softer, can disappear.

Class AB, Solid-State: As stated in the dynamics section, this is a great middle ground for those who love bass but don't want to have their mids and treble suffer as much. The control and dynamics offered by class AB amplification, as well as the speed drastically cuts down on reverb, bloom and bleed while the solid state portion helps keep a lively impact/punch.

Class A, NuTube: Similar to Class A/SS above but the NuTube presentation of the treble and mids help to recess the bass bleed slightly but don't cut the bloom too much. This profile will be for listeners who want their bass but don't want it to be TOO overbearing to the rest of the signature.
My reference point for NuTubes has always been the iBasso DX320 with Amp14, the presentation here is similar but slightly less warm than the Amp14. There is a clearer, more detailed image of vocals and upper mids here, from what I've read of the N8ii, this presentation should be similar, favoring a brighter, more revealing tonality without losing what makes NuTubes so special in the midrange (their ability to present emotion more accurately than solid-state, which is typically "drier". To me, there sounds to be an elevated slope from lower mids to upper mids where it levels off slightly and travels into the lower treble without any harsh canyons to make the upper mids sound shouty or nasally.
Class A, Solid-State: As I've covered in the Bass section, the mids in this combination are rather recessed, pulled back in the lower and upper mids due to the forwardness (lower/slight upper mid effect), bloom (upper mid effect) and bleed (lower mid effect) of the sub bass. Vocals will lose some detail here and as a result, can sound dry and lacking emotion. Again, as above, bass lovers would gravitate here, not many others.
Class AB, Solid-State: Keeping along the trend, Mids gain micro and macro detail and a bit more presence but this combo may also be the driest mid presentation of the lot. This is due to losing the warmth added by Class A, gaining additional speed but not gaining any of the benefits of the NuTubes toward vocals. This combination is a good balance for anyone looking to enjoy music in a more passive background state, as nothing will leap out or be distracting.
Class A, NuTube: This combination puts a stronger emphasis on the upper mids than any of the above in my listening, as the NuTubes will carry the upper mids/lower treble up but the Class A recesses the lower mids still (pretty heavily). I found this to be a decent listening experience for female vocals that were along the lines of melodic metal (Nightwish, Semblant, etc.).
The treble presentation of Class AB/NuTube on the C9 is simply outstanding. The treble is very well extended, airy, extremely micro and macro detailed. Where Class AB would normally make some cymbal reverbs a hair too short and unnatural, the nutubes come in and add JUST that last perfect little touch on the end to make the treble ideal. Very similar to that of the SP3K in that all of the technical aspects of the treble are perfect and then there's just that tiniest touch of smoothness to the end, where you still get all the sparkly and brightness but the last millisecond before it could become harsh, it doesn't. The treble from the C9 paired with the N7 is definitely on par with the SP3K and that's saying a lot (for me) given how much I love that DAPs treble. Any treble lovers will be extremely satisfied and those who may be extremely sensitive to any harshness might have a small issue but it would be heavily pairing/song dependent.
Class A, Solid-State: The weakest by a large margin in the treble and it was not a combination, as a treble lover, that I could utilize. There is not as much air up top, the bass reverb and bloom heavily harm micro details in the lower treble and can often drown out or at least heavily recess upper treble.
Class AB, Solid-State: Near a similar presentation to Class AB/NuTube but not as much air or extension. Also upper treble is slightly recessed (no where near as much as Class A/SS) so some detail is lost there. Lower treble remains decently detailed but if a track already has more recessed notes in this region, they may be difficult to detect but by no means absent. For those who may have sensitivity with their pairing, this sound profile would likely suit you.
Class A, NuTube: The extension and air here are good, but not as good as AB/NuTube due to the heavy sub bass lean. Lower treble suffers more here than in Class AB/SS and those quieter tracks may have previously heard details be missed. This presentation likely favors those who like air and extension but have a very high sensitivity to any treble peaky-ness or sibilance.
The C9 has been an absolute gem of a purchase for me and I've adored every minute with it. There is so much to love and so many flavors to choose from that there is a profile for everyone. The added ability to quickly swap battery packs for extended listening (especially great with the N7 as Class AB battery life is phenomenal), granted this is an added cost ($99 dollars MSRP for the additional tray and the cost of your chosen batteries) but the flexibility is a nice option. Also, to add to this, it gives the C9 essentially infinite life, never having to worry about a lith-ion battery going bad after some years or being unable to hold charge. Anyone looking to add an amp to their arsenal would undoubtedly be content with the C9.

As always, thank you for reading and I hope this helps any reader or prospective buyer come to an informed conclusion on if the Cayin C9 is right for them before diving into the deep end and if you do decide to purchase, remember you can find it at Musicteck's Cayin store - https://shop.musicteck.com/collections/cayin.

Cayin is no stranger to amps. In fact, they make some of the best desktop amps out there, including the venerable iHA-6 and the top-dog, the HA-6A (one of the best amps I’ve ever had the pleasure to listen to, by the by). The Cayin C9 is their flagship portable amp, meant to be more transportable than portable given the ~0.5kg of weight.

Being a flagship and perhaps the best showcase of Cayin's technical achievements so far, the C9 comes with a hefty price-tag of $2K. That's a pretty penny and demands top-tier performance. Let's see if the C9 delivers.

This review was originally published on Audioreviews.

Note: the ratings given will be subjective to the price tier. Cayin C9 was sent to me as part of the EU Review Tour (thanks Andy!)

IEMs/Headphones used: Dunu Zen/SA6, Final FI-BA-SS/E5000, UM MEST mk. 2, Campfire Audio Holocene, Sennheiser HD650, Hifiman Ananda

Price, while reviewed: $2000. Can be bought from Musicteck.

Click to expand...

PACKAGING AND ACCESSORIES​

In terms of accessories, you get two high quality interconnect cables (a 4.4mm to 4.4mm balanced cable, and a 3.5mm to 3.5mm single-ended cable). You also get a type-C cable for charging (supporting QuickCharge), a screw-driver (for removing the battery bay), and some spare screws. That’s about it, no carrying case or anything. The accessories aren’t plentiful given the price-tag but you do get all the basic necessities.
3.5/5

​

BUILD QUALITY​

Cayin C9 has a two part design: the front part has the amp circuit along with the controls/switches, and the back side has the battery bay which can be slid out. The top of the device is aluminium with CNC-cut windows (covered by glass) that houses the NuTubes, and the bottom of the device has a sheet of glass on it (I do wish this portion was also aluminium for consistencies’ sake). The tubes glow green when turned on and takes about 3/4 seconds to warm up.



The front of the device has… everything. Well, everything bar the pre-amp/line-in toggle button (on the left side of the device, you need to press it along with selecting pre-amp input mode on the front panel to activate the mode) and the USB-C port/battery indicators (on the back of the device, with the battery bay). Both the 3.5mm and 4.4mm inputs/outputs are on the front, along with the power switch/operation indicator LED button. There are toggles for (from left to right) line-in/pre-amp input mode, gain (High/Low), Timbre (Solid state/Tube), operation mode (Class-A/AB).

Lastly , there is the volume knob which is an ALPS rotary encoder and has quite high precision from my experience with no channel imbalance even at extremely low volumes (it’s electronic and resistance-ladder based with 130 discrete steps). The knob takes some force to rotate though, and it’s somewhat recessed into the housing to prevent accidental volume changes (which can be damaging due to the extremely high output power on the C9).

I don’t really have any complaints about build quality here.
5/5

USABILITY​

The Cayin C9 is more of a transportable than a portable device. In other words, they need to be stationed somewhere (a desk/bedside) and not really portable in a shirt/pant/coat pocket (unless you love unsightly bulges). Other than that, it’s quite easy to operate the device once stationed on a desk. Changing between modes is easy to do without looking once you get the layout memorized. However, due to all the controls being on the front, it can a pain to hook it up as a sole headphone amp with a desktop DAC (then you need to reach on the back to connect/disconnect headphones and IEMs). As of now it is more suited to connecting with DAPs than desk setups.



Another interesting aspect is that there is a slight delay every time you change modes. This is something you have to take into account for on-the-fly A/B comparison as the changes introduced by the tube mode, for example, won’t be instantaneous.
3.5/5

BATTERY​

The Cayin C9 uses four 18650 Li-ion batteries and apparently switching batteries may bring subtle changes to the sound signature (I did not verify this). It supports quick charge so recharging is quite quick, and I managed ~8 hours on a single-charge in class-A/High gain mode from the balanced out. This is not a stellar showing but given the power and performance here it is within expectations. Do note that Cayin have built several protection mechanisms in the battery powered circuitry (and you cannot bypass battery power here, not sure why would you want to anyway since the battery power is better than direct AC input for this particular use-case). You can read more about the power delivery method here.

AMP ARCHITECTURE​

The internal architecture of the Cayin C9 is fully discrete and fully balanced. Cayin also didn’t use a traditional IC/Op-amp based circuitry, rather opted for fully discrete design. The volume control is resistance-ladder based with 130 discrete steps.

Instead of trying to explain all the nitty-gritties in detail (which isn’t really my forte) I’d instead link to the Cayin head-fi thread (click here). There you will find amp schematics alongside a closer look at the internal components.


Toshiba 2SK209 JFET for the solid-state amplification. Image courtesy: Cayin

Korg Nutubes for the tube timbre. Courtesy: Cayin

TONALITY AND TECHNICALITIES​

The Cayin C9 is an absolute chameleon of an amp when it comes to tonality and technicalities. Between the class-A/AB mode and solid-state/tube timbre, you can have 4 different signatures, and this is quite helpful when it comes to pairing IEMs with a specific sound signature. Please note that due to the way the mode-switching works in this amp (has a 2-5 seconds delay depending on mode) some of the A/B comparisons below are based on auditory memory and listening notes. In other words: take them with some salt (though I am fairly convinced about the different bass reproduction in class-AB mode and the general characteristics of the tube mode).

CLASS-A (SOLID STATE)​

This is my most favorite mode, and apart from very bass-heavy stuff I preferred almost everything in my collection in this mode.

The best part about the class-A mode is the bass rendition. This is, by far, the best bass reproduction I’ve heard on a portable amp. The sheer grunt of the sub-bass (provided you have a suitably extended IEM) is unmatched. No DAP I’ve tried till date including the likes of Lotoo PAW Gold Touch, Sony WM1Z, Questyle QP1R, or the A&K SE200 could come close. I went through a huge portion of my library to simply enjoy the basslines in a completely different manner.

The sheer control Cayin C9 has over the sub and mid-bass is also uncanny. Snare hits are authoritative, sub-bass rumble is very much present, but it doesn’t overwhelm and actually corrects the bass-bleed issue in certain IEMs (Final E5000, for one). The best part about the bass: its density, given you got a good bass reproduction on the transducer side of things. The Cayin C9 isn’t a miracle-worker of course even in class-A mode. If you are pairing it with a BA-only IEM, the bass can only be so good. You’ll miss the texture and slam of good dynamic-drivers and that’s expected. Thus, the class-A mode is especially suited for dynamic driver IEMs/Headphones and the efficient planar magnetic ones.

All this talk about bass made me almost ignore the delightful midrange in the class-A mode. There is an analogue tone to the entire sound and vocals sound especially rich. However, transients aren’t softened at all and there’s a sense of transparency to the entire presentation. The stage depth is another aspect that seemed best on class-A mode, though I’d attribute it to the sub-bass response that is often perceived as depth while listening to tracks with an elevated sub-bass line. Separation was stellar with balanced out and I don’t think it can get any better in terms of perceived channel separation.

CLASS-A/B (SOLID STATE)​

If you found the class-A mode to be a bit bass heavy and the mids to be somewhat up-front, then the class-AB mode evens things out. The bass is less authoritative and the midrange esp vocals get slightly pushed back. So you end up with a more relaxed, wider presentation overall. I would recommend this mode with bassy IEMs or headphones. Channel separation was excellent in this mode as well.

NUTUBE + CLASS A, A/B
Last but not the least: NuTubes. The Korg NuTubes are miniaturized triode vacuum tube that uses vacuum fluorescent display technology to emulate the class tube distortion. Basically: you get the tube sound without having large, heat-generating, extremely microphonic vacuum tubes. More info can be found here.

That’s the sales pitch at least. In practice, I didn’t find Korg NuTubes to be as tonally rich and colored as traditional tubes. Cayin’s own N3Pro, for example, has a more drastic and noticeable coloration via JAN6418 tubes. The coloration here is subtler. When coupled with class-A mode, the bass becomes somewhat loose and lacks the texture, definition, and authority vs the solid-state mode. Resolved detail is also masked somewhat. Female vocals sound richer, however, and some harshness/shrillness is smoothed over. Treble detail is also masked to a degree esp the attack-decay of cymbal hits aren’t as pristine as they are on the solid-state mode.

In the end, I found the NuTube to work best with the class-AB mode for my tastes and gears. With some bright or neutral IEMs the tube mode works quite well in reigning down the harshness. However, don’t expect the stellar separation and resolution of the regular class-A mode with the tubes engaged.

PAIRING NOTES
The Cayin C9 made nearly every IEM/headphone in my collection sound, well, better. Given the numerous modes I think one can mix and match and make it work with any IEM. However, the Campfire Andromeda 2020 had audible hiss even at low gain, so if you own very sensitive IEMs you may want to use an iFi IEMatch in-between. Final FI-BA-SS, meanwhile, didn’t hiss much even though it can detect hiss on many sources.

There was a slight amount of hiss on the Dunu Zen but the end result was simply stunning when pairing the Cayin C9 with Lotoo PAW 6000. I used the balanced line out mode and the presentation was very dynamic. The resolved detail was desktop class and frankly – I can see myself ditching even high-end DAC/Amp setups for this combo (LP6K + Cayin C9). Cayin C9 + Questyle CMA-400i was less drastic a difference though the sound was softer and more rounded than the regular headphone out of the CMA-400i.



Lastly, I paired the Cayin C9 with the A&K SE200 and it was another excellent pairing. The A&K’s AKM output gained even better microdynamics and I could listen to the Sennheiser HD650 in its full glory. Many prefer this particular headphone from OTL tube amps so I decided to try the tube mode on the C9, but the end result wasn’t aligned to my tastes. Your mileage may vary.

Overall, I found the Cayin C9 to take on the characteristics of the DAC/DAP it’s connected to while enhancing some parts of it (mostly bass response, channel separation, and dynamics). As such, I’d recommend the Cayin C9 even for TOTL DAPs like Lotoo LPGT, provided you are willing to splurge for the diminishing returns.

SELECT COMPARISONS

vs iFi Diablo​

The iFi Diablo ($1000) is a powerhouse of a portable DAC/Amp that’s mostly intended to drive power-hungry headphones. It is excellent with inefficient planars (apart from the most demanding ones like Hifiman HE-6/Susvara) and as such works better in terms of powering planars than the Cayin C9.

That’s about it, though. The amp section on the Cayin C9 is superior to the Diablo in terms of tonal richness, bass reproduction, and powering IEMs and efficient headphones. The stellar separation of the C9 cannot be found on the iFi Diablo as well, and staging is more cramped as a result on the iFi Diablo. Moreover, it doesn’t have as many different modes as the Cayin C9 incl. the NuTubes.

As an amp, the Cayin C9 is indeed superior to the iFi Diablo. However, at half the price the Diablo also has a built-in DAC section and doesn’t rely on stacking as the Cayin C9 does, which is something buyers shall take into account.

vs Cayin iHA-6​

In the end, I decided to compare the Cayin C9 with other desktop amps because that’s what most of the target audience would be looking into (desktop-class performance in a more portable format). The Cayin iHA-6 ($700) is one of the best amps under $1000 IMO, and I love pairing it with the iFi Neo iDSD (review coming soon for the iHA-6 soon). The iHA-6 is huge and heavy so if the Cayin C9 can somewhat replicate the feeling of transparency you get with the iHA-6 – that’s a major win.



Turns out that the Cayin C9 is actually… better than the iHA-6. Wait, hear me out. It’s not better in terms of power, iHA-6 can push 7Watts (!) into a 32ohm load from the balanced out whereas the C9 manages a mere (!) 4Watts. However, when not driving super-demanding planars, the Cayin C9 simply has better imaging and dynamics (esp microdynamics). The iHA-6, despite being similarly transparent in the midrange, sounds edgier in treble and not as effortlessly resolving. Another issue with the iHA-6 is that it’s beyond overkill for IEMs and might even blow the drivers out if you’re not careful. Moreover, iHA-6 has very high noise-floor for sensitive drivers.

The realization that an amp 1/8th size of the venerable iHA-6 can outperform it in most scenarios is rather shocking for me, but that’s how it is. The C9 is almost 4x the price of the iHA-6, but it seems you do get your money’s worth of performance at a much smaller footprint.

vs Headamp GSX Mini​

The Headamp GSX-Mini ($1800) is one of my all-time favorite solid-state desktop amps and something I recommend everyone to try out. Given its desktop nature, it completely outshines the Cayin C9 in terms of output power and headphone driveability, though with moderately sensitive planars like Final D8000 Pro/Meze Empyrean you’re not really gonna need extra juice out of either of them.



I’ll skip over build etc. since it doesn’t really make sense when you’re comparing apples to oranges (desk amp vs transportable amp), but in this case there aren’t many competition to the C9 so desktop amps it is. However, one thing I must note: the volume knob on the GSX-Mini. It’s fabulous, class-leading. I want to fiddle with it for absolutely no reason, it’s that good.

With that out of the way, let’s talk about sound. There is a distinct difference in presentation between these two amps. The Cayin C9 goes for a transparent signature with slightly warm/analogue midrange and a sizeable increment in bass texture. The Headamp GSX-Mini takes a more laid-back approach with the bass but focuses on midrange and treble more. Outstanding detail retrieval is its calling card and there it does beat out the Cayin C9 marginally (when paired with full-size headphones).

However, the Cayin C9 strikes back with superior staging/imaging. The GSX-Mini can feel a bit closed-in in comparison. As a result the GSX-Mini works great with planars like Arya which have a naturally wide staging and the sound gains more focus with the GSX-Mini (if that’s what you want). The Cayin C9 meanwhile works better with IEMs and headphones that have relatively more intimate staging (e.g. Dunu Zen, Focal Utopia).

Overall, with the correct matching/pairing of headphones, the GSX-Mini does outperform the Cayin C9 in terms of resolved detail. That the Cayin C9 competes with a full-on desktop amp priced similarly is testament to what Cayin has achieved with the C9, and I am left even more impressed at this point.

CONCLUDING REMARKS​

If you’re someone who owns a premium DAP (>$1000) with a high quality line-out and intend to make the absolute most out of your IEMs and less demanding headphones (as in, less than the Susvara/1266 Phi/HE-6) – the Cayin C9 will pretty much be an endgame addition at this point. The weight of ~500gm makes it hard to carry around but I am mostly using it while on the desk/lying down and it works absolutely fine that way.

The biggest issue of the Cayin C9 is its price-tag of $2000. Only the most effusive of enthusiasts would pay that much for a headphone amp that improves upon the intangible aspects of the sound you get from a high quality DAP. However, once you hear it there’s no going back and the dynamism it brings is truly one-of-a-kind.

Cayin chased perfection with the C9, and I daresay that they came dangerously close to it. I’ll miss listening to it, but hopefully not for long as I plan on getting one for myself.

For me, and for many entrenched in this audiophile world, there is always this fascination with analog tube amplifiers. It's old school, it's cool and unique looking, and it has its own set of parameters to mess around with. It also provides a different listening experience for the curious ear. I've gone through a number of tube amps in the past: from hybrids, OTL, or SET-style tube amps for headphones and speakers, and I've also gone through a few portable tube amplifiers as well. While I've had some success with the desktop ones, the portable ones have always been mostly misses or more of "what's the point?"

The Cayin C9 was announced a while ago and has more recently just showed up for sale. It caught my attention when it was first announced due to its looks and its specifications. It features both balanced and single-ended input and outputs, a nice sized volume knob, a switch to activate solid-state or vacuum tube circuitry, and an additional switch to active Class A or Class AB circuitry. In addition, this is a pure amplifier, and does not have a DAC, which lets users choose which pairing they want to go with it. Many portables are DAC/Amp combinations and does not give users the option to choose, which for most cases is the only way to keep them portable and have a small footprint.

The C9 comes in at a $2000 price tag, and is definitely on the upper-end of the portable amplifier market. It does, however, make up for its price tag with a very nice and high quality build, featuring an all-metal chassis that is simple yet elegant. The input/output connectors have gold rings around them, as well as the power button and volume knob to provide both style and functionality to its design.



The C9's tube selection is powered by Korg NuTubes. These are unique and a relatively new tube design that glow with green LEDs and are laid flat on the board. The Cayin C9 has two oval-shaped window cut-outs on the top surface of the amp that lets the Nutubes shine their alien look when activated. When off, the windows are very dark and internals are not visible.

The C9 is pretty hefty, and definitely not pocketable. It may fit into a large coat pocket, but the weight would be pretty distracting and heavy to carry. Instead, this is definitely made for bag travel, and to sit on a solid table surface when in use. Due to the amp selections and metal chassis, the C9 also gets very hot in any of the combinations, and you'll probably want to minimize contact with it when it has been running for a short time. It will heat up the area around it.

Note: The Cayin C9 amplifier was provided on loan as part of a private review tour hosted by Cayin directly. I will be shipping the C9 amplifier to the next leg of the tour in Europe immediately after this review.

Sound Impressions​

The Cayin C9 has two "timbre" modes (solid-state and vacuum tube) and two amp circuits (Class A and Class AB), giving it a total of 4 combinations of user amp configurations. There is, of course, a high and low gain setting, but I'll just say that for headphones, I used high gain, and for IEMs, I used low gain for all my impressions.

I'll first take a look at some of the basic power demands and general observations and then go into the different configuration impressions and finally comparisons with other portables I have on hand.

Initial Stress Test​

When I first took out the C9 and got it setup, I connected my Lotoo PAW 6000 digital audio player with line-out enabled into the input of the C9. I used balanced 4.4mm interconnects, which are provided with the C9 and are quite stunning looking. The C9 also includes matching 3.5mm to 3.5mm interconnects as well.

My first stress test was to see how the notoriously hard-to-drive Hifiman Susvara planar magnetic headphone would sound with the Cayin C9, however only using the 3.5mm singled-ended output which has less power capability. I enabled Line Out on the PAW 6000 and set the switches to High Gain, Class A and Tube mode on the C9 and it was time to rock n' roll. I put on Grace Potter & The Nocturnal's modern classic rocker, "The Lion The Beast The Beat" and was happy audio came out, but I wasn't thrilled that I ran to the end of the line on the volume knob.

Now mind you, it got loud enough for me to enjoy music at almost my normal listening volumes (roughly 70-75dB SPL@ 1KHz), however for some, that may not be loud enough, and this specific headphone pairing didn't get it to even that level. Unfortunately with this, I did find the C9 to sound a tad bright, thin, and just lacking a great mid-range and smooth treble that I'd expect from the Susvara. The low-end held up fine though, surprisingly.

But, let me reiterate, this was just a stress test, and very, very few headphones require the amount of sheer power that a Susvara does and I also only tested it out of the weaker single-ended output stage. The majority of headphones and earphones I tried worked well within the bounds of the C9's power output.

Headphones Pairing with the Sennheiser HD600​

Now with that out of the way, I spent the majority of my headphone experience with the Sennheiser HD600. This is a classic reference headphone that many in this hobby have heard, and has a very well known and established tonality and timbre that appeases most people. It also pairs extremely well with most tube amplifiers, and so this was one that I had some good expectations for.

On this pairing, I kept the PAW 6000 in the chain, turned it to NOS mode, connected it as a DAC to my computer and turned on Roon and HQPlayer. I set HQPlayer to 768kHz oversampling with the Sinc-L filter and fired off some music.




First, I compared Class A and AB using the Tube mode on high gain.

In "Restless" by Alison Kraus & Union Station, I found the angelic voice of Kraus to sound really no different between either of the Class modes. In Class A mode, however, I did find the low end bass guitar to have just a slight amount of more impact, while the Class AB mode had a softer and brighter midrange.

Switching over to the live recording of Bill Laurence's "The Good Things" from "Live at Ronnie Scott's", I found there were some more noticeable differences between the settings. The Class A setting had a more warm sound but with a more muted piano strike, especially around 0:54 in the track. In Class AB mode, this piano attack was slightly more strained with more resonance in comparison.

I continued to listen and moved quickly towards the mid-point of this track, where the stand-up bass solo begins around 5:38 into the track towards the end. In this case, the amp settings did not seem to make any pronounced differences.

So, of course, I decided to mess around with the "timbre" switch. I flipped back and forth between Solid-State and Tube modes and found that the second half of the track, which is led by a bass solo, while drums and keyboard are still continuing in the background, had some more appreciable differences.

In Solid-State mode, I heard harder transients with more crisp edges, while also have more defined cuts. While in Tube mode, the transients became softer and sustain notes held longer with more decay and just an overall more euphonic sound.

At this point, I wanted to try some older music, and pulled out some classic Beatles music. On "Let it Be", Paul McCartney's vocals sounded much the same between any of the settings I messed with, but the most audible change between modes was how drums sounded. On Solid-State mode, drums sounded a tad thin and lean, and lacking the heft and weight I heard while on the Tube mode, which sounded more realistic and defined. I also felt the whizzing guitars and bass around the 3 minute mark sounded clearly better with the tube amp enabled.

There are many great Beatles tracks, but one of the more memorable introductions is the combination of drums, bass and buzzing guitars of George Harrison's "While My Guitar Weeps". In tube amp mode, this intro has a softer guitar presentation, and a smoother transition from the initial introduction to the guitar frenzy later. In Solid-State mode, the imaging is improved and things are little more separated, however, guitars are sharper but also more defined.

Some Time with In-Ear Monitors​

I also spent a bit of time with various in-ear monitors on the low setting with the Cayin C9. No matter which IEM I used, I did not find any issues with hissing or noise. All of them had black backgrounds, and no trouble with any sound anomalies. For reference, I used custom Hidition Viento and Unique Melody MEST, and also some time with the universal Shuoer EJ07M, Dunu SA6, and Kiwi Ears Orchestra.




I spent most of the time here with my two customs. With the Viento, I thought the pairing was alright. The Viento is a very neutral reference monitor, with a small bass boost. The Cayin C9 tube amp had a clean signature, that had just a slight amount of warmth, but a surprising amount of air and treble quantity to it that I wasn't expecting. It never felt harsh though with any of the IEMs, and that was good. It felt relatively sweet, especially after the initial brightness I found with the Susvara. Luckily, this isn't the case here nor was it with the HD600.

I thought the pairing with the Unique Melody MEST was quite nice. The MEST is a quad-driver IEM with dynamic driver, balanced armatures, electrostatic-tweeters and a bone conduction driver. The MEST's relaxed, yet exciting signature had some extra pop and reverbish sound to the low end while using the C9 in Tube, AB mode. Those Bill Laurence Trio live tracks had a nice amount of energy and an organic decay that felt very nice physically and mentally.

All in all, I think the C9 plays well with IEMs, which I will say, isn't a typical thing with many portable tube amplifiers. Many are just too loud for most IEMs or have loud feedback from amp noise or electromagnetic interference (EMI) from phones or other wireless signals. The C9 is quiet. Very quiet.

Comparisons with...​

Lotoo PAW 6000​

The Lotoo PAW 6000 is my current audio player of choice when it comes to portability since it has a lightning fast UI, easy touch interface, and a really nice sound signature that is resolving yet natural without sounding too stuffy or too bright. The sweet treble is probably my favorite part of the experience.

I spent a good chunk of time using it as a DAC for the Cayin C9 and then quickly A-B switching between the player directly and the amplifier. This worked well since I was able to use balanced cables for the I/O between the two devices and 3.5mm cable for headphone listening.

The PAW 6000 surprisingly sounded a touch warmer than the C9, with just a little bit more elevation in the lower midrange and a more relaxed treble range. As mentioned previously, I don't think the C9 is utterly bright, but I did notice it sounds like it has a little more energy up top than the other amps I have been using and own today. The C9 is also a little more precise in some ways, especially in solid-state mode. In tube mode, I do find these two line-up more comparably.

Chord Mojo + Poly​

The Chord Mojo + Poly combination is new to me. I only just received it a couple days after I got this C9 and intend to use it as a portable Roon streamer while in and around my home. In my brief time with both of these amps, I have noticed the Mojo plays just a bit more warm, a little more rounded in the edges, and a little more contained. The C9 has a little more pop and dynamic energy, and again, has a more lift in the upper range.

Both of these have equivalent power, though, I think the Susvara had a little more drive with the Mojo than it did with the C9. Again, this is a crazy ask for either of these amps so take that with a grain of salt. In other headphones play, I found power to not be an issue on either of these units.

Conclusions​

Ignoring the price tag, the Cayin C9 is a very nice addition and one of the better portable tube amplifiers on the market. It has a nice high quality build, pretty Korg NuTubes, and solid feeling switches and knob. The battery life also seems pretty good in my experience especially given how much heat this thing generates and the amp circuitry.

If I had to criticize anything, it would be that its a bit large, and heavy, and not super easily transportable without a bag. It also has a hefty price tag at $2000 USD, and puts it in the upper echelon of portable amplifiers.

But that said, I do like what I heard. It does not necessarily present the stereotypical warm and liquid sound that many think of tube amplifiers, but instead softens the transients just enough while keeping the upper range active and energetic to keep dynamics alive and resolution in-tact. It definitely outperforms other portable tube amplifiers I've tried, albeit, those were significantly less costly. So in the end, its a big dollar amplifier for those who can afford it. Its worth a demo for sure.

Cayin C9 ($1999): Tube sound from magic insides. 4.75 stars



Cayin C9

Intro: As part of the North American C9 tour, my turn came about while I was prepping for a working vacation. No better use for the C9 than in real world situations such as this. While I did not fly, I did have to accommodate the large box for my time would be up during that working vacation. No bother, I had another in house in the same situation as well.

The C9 follows to me on the heels of the quite good Fantasy tour. Coming with mixed reviews, the Fantasy was appreciated for the long-term vision Cayin was putting out to stay competitive in this market. I do believe some of the criticism comes about due to the full-on peloton of offerings at this price right now. My review showed that as well. The C9 was just about the polar opposite. With no marketed competition save for the more “equitably-priced” iFi Black Label, the C9 goes into Chord2 levels pricewise. Another reviewer compared those so I will not. I shall focus almost exclusively on the aspects of the C9 and compare to the BL.


Specs:

Other important info:

• Fully balanced, fully discrete, 4-channels high-fidelity headphone amplifier delivers up to 4,100mW (at 16Ω) or 2600mW (at 32Ω) per channel.
• Select between Vacuum Tube and Solid State timber on both balanced and single-end inputs.
• The tube timber circuit is designed around a pair of KORG Nutube vacuum tubes.
• Switch between Pure Class A and Class AB amplification modes.
• Dual input mode: regular LINE input mode and PRE-amp input mode (or known as pure power amplifier mode).
• Supports 3.5mm SE and 4.4mm BAL for both input and output, the amplifier will also optimize BAL to SE or vice versa.
• 4-channels ALPS potentiometer with a pair of stereo electronic volume.
• Removable battery module with 4x user replaceable Sony18650 rechargeable lithium batteries.

In The Box:

C9 portable headphone amplifier
C9 battery module (mounted)
Rear panel glass protector
Single-ended portable interconnect (CS-35C35, 3.5se to 3.5se)
Balance portable interconnect (CS-44C44, 4.4bal to 4.4bal)
USB Type-C charging cable
Backup screws for battery module
T6 screwdriver
User manual



Gear used/compared:

LCD-3
Empire Ears Legend X (Eletech Socrates cable)

Shanling M6 Pro
Cayin N6ii (E01 motherboard)

Songs:

Alex Fox
Stevie Ray Vaughan
Elton John
Twenty one pilots
Santana
Buena Vista Social Club
Jeff Beck
Pink Floyd


Unboxing:

The Cayin unboxing of items has become an event of sorts. Coming in larger well-protected boxes, the items of choice come not only safeguarded from bumps and bruises but with room aplenty for all of the accoutrements. The same of course holds for the C9. Mimicking the unboxing of an Empire Ears item, what with the “jewelry drawers” sliding out, you get the sense of care and commitment to the process. A well protected unit usually also comes with excellent build as a result.

Sliding the sleeve off the box just like with the Fantasy, you are met with a hard-cardboard box, including clamshell-type of flaps on two sides. While the Fantasy had an overlap on the top, the C9 does not. Pulling the top up, you are met with the C9 in a hard foam insert only. It is large and pushed deeply into the insert. It takes a good bit of careful force to extract the C9 as a result. No matter, I’d rather have it over protected than under.

Pulling the side flap down, you are met with one slide drawer as opposed to the two found in the Fantasy. The sheer size of the C9 means that ½ the depth of the case is used for the unit, including protection. Sliding the drawer out using the attached ribbon, you are met with an envelope-type paperboard, which contains the user’s manual and protects the contents below. HiRes stickers and an extra back glass screen protector is included as well. Under the envelope, you will find the 3.5-3.5 and 4.4-4.4 connecting cables as well as the charging cord, the T6 screwdriver, and extra screws WHEN you lose one. I have come to appreciate the included Cayin charging cables as some of the best around for sturdiness and use. Of a good length as well, you should have no problem.



Build/Finish:

Typically, Cayin products are very well built. This would not be an exception to that rule. The C9, especially for the price comes across as well as those high dollar desktop units, which cost as much or several times more. Black is the color of choice here, and frankly it would have been all right with me had it been hot pink or chartreuse. Utilizing an all glass back for heat dissipation as well as looks, the C9 is a stunning move forward in the plain black box. Since others were to follow, I kept the already mounted screen protector on, and it shows heavy wear. Once can assume that not using the screen protector would not yield such scratches. Also, you will want to purchase protective feet, as there aren’t any, so the unit sits on that glass back whether it has the screen protector or not.

A metal shell covers the rest, complete with a cutout of sorts on the top at the front. Application-wise for the volume pot, the inset looks clean and functional with the volume dial shows only marginally above the surface. Set back on either side of that inset are oblong holes, with glass inserts showing off the Korg NUTUBES inside. Looking like cat eyes, the green of the functioning Nutube looks pretty cool. Switch to solid state and the lights go away. I will cover the Korg “tubes” under the technical section, for there is much to discuss.

The front is dominated by two things: the in and out connectivity and the volume wheel. Along the top are finely tactile “toggles” for switching from (left to right) Amp to Line Pre-Amp; High and Low Gain; Timbre-Solid State or Nutube; and Class-A or Class-AB. Dead center with two toggles each side is the volume pot. Under that “row” are from left to right: the two inputs, 3.5se and 4.4bal; the power button (too tiny for me); and the two outputs, 4.4bal and 3.5se. Labels are clear and easy to read, something some desktop gear I have reviewed of late, should take note of.



The back seems absolutely barren compared to the packed functionality of the front. To the bottom right is the battery indicator, with four reddish-orange lights indication approximately 25% each. The last one will blink when charging is needed, or “death” is impending. Centered is the USB-C charging outlet. On each side is a single T6 screw for removing the battery packet. Cayin believes a couple of things about their batteries. For one, sound may deteriorate a bit as charge disseminates. I fully believe what their engineers propose here, I have no reason not to. And second, rechargeable batteries lose their power over time (think of your Smartphone and after about 2-3 years you are lucky to have 82-87% of the intended “full” capacity at 100% charge. So this makes sense, and the batteries can be replaced with a common Li battery as a result. Marcus’s Headfonics review of the C9 goes into a bit of detail regarding this and the choice of using Sony’s Murata VTC6 as an excellent one. He also mentions the battery quality and sound characteristics as well, so check that out (page 1) for more information on battery and the choice (https://headfonics.com/cayin-c9-review/). I was able to get a bit longer than the listed 5.5hrs on the tube timbre. This could be that the unit is fully broken in as well.

I do know that Cayin makes a case for the C9 as well as Miter or Dignis I believe. The Cayin case is $99, but when you spend this much, that does not seem inordinate to me.




Technicals:

To me Cayin has had a penchant for technology for quite some time. Witness their DAP’s and how they continue to fight for a spot with the “big boys” so to speak. As such, innovation comes as a result and this in turn leads to new products. The C9 is no different, but the technology used is not new, simply the implementation. And yes, Cayin has some proprietary material within that goes a long way towards bettering this product.

Using Toshiba’s 2SK209 JFET semiconductors (quad set) discrete and buffered amplification set up, the end result to me provides a typical richness of sound of which Cayin is known. Utilizing both Class-A and Class-AB in such a device draws its own issues, but with the Cayin N6ii, specifically the development of the E01 motherboard has given those engineers the practice needed for the C9. That warmth and rich signature is what I absolutely love about the E01 and the N6ii and do not even miss the balanced connectivity. In fact, that will be my baseline for testing the 3.5se source use here.



The Korg Nutube technology is fairly new (used in the N8), and I personally read about it a couple of years ago (I think). I am a bonafide tube-sound lover and when I heard Cayin was doing this, I became just a bit more intrigued. As Wiljen stated in his excellent C9 review (https://audiofool.reviews/2021/05/21/cayin-c9/) , the Nutube 6P1 “tubes” act similar to the actual 12ax7 tubes used in many tube amplifiers. Utilizing a Direct Heated Triode (DHT) and utilizing neon fluorescence for display purposes (licensed under Noritake Itron of Japan for Korg), you get that tube glow, and sound but with a miniscule amount of power compared to “real” tubes, which aids in battery life. As Will states, consider this a modern vacuum tube with improved power handling and decreased microphonics. Heat dissipation is also better since it is an enclosed circuit. But the unit does get fairly warm, so this would be another good for the foot idea-help dissipate heat. A new take on an old technology, even if I do enjoy “pinging” a good tube amp. I am also in the boat of loving a good tube-like sound, so knowing this beforehand may help to understand how I feel about what Cayin has done here.



Sound:

Summary: I will unabashedly state that over my two weeks, I used the C9 for all manners of testing from the economical IEM’s to a comparison with a similarly priced desktop DAC/Amp. From the first listen, I was taken. Using the Shanling M6 Pro (sacrilege!!!!) most of the time during the early moments for its 4.4bal connection, I was treated to a thoroughly envisioning time of full-bodied richness and warmth. Mind you not Legend X warmth, but that richness pervaded all comers. I would label this as a bit dark of signature, but not hindering if that makes sense. I have probably put close to 75 hours on the unit as a result. Mostly on Nutube and Class-A as my preferred signatory response.

This will be broken into four sections giving reference to all options available tuning-wise. You should find a preference as a result. I will note that mine differed from the two excellent reviews referenced above, which bodes well for those looking. While we three have similar tastes, coming to different conclusions about what the LIKED best is a good thing. Each will be treated separately.




Solid-State/Class-A:

Running pure solid state gives a detailed vibrancy to the signature even with what Cayin calls the “low efficient” mode. A bit harder to push the Legend X than the Nutube, and to me a bit thinner of sound. That vibrant signature comes across as extremely clean but with a bit less energetic sound. This is not meant for reference tuning, but a more laid-back signatory. I found this to be good with uplifting songs such as Los Lonely Boys Heaven. But if energy is needed, a switch of tone was called for. With a fairly liquid treble note, and (to me) mids-push, this choice would be excellent for vocal presentations, or possibly string music. This is of course countered by the Class-A’s warmer signature.


Solid-State/Class-B:

If you want more energy and intensity, then this probably has the most of the four. Los Lonely Boys comes across like you are dead center of two excellent concert monitors listening live. An aggressive tone is the result, with more push of the bass down low, and sparkle up top. The pairing with a warmer, richer IEM or headphone would benefit from this set up and easily adds vitality to the sound. While this has less warmth (leaning towards cold), do not think of this as analytical but rather purity. Coming out as the cleanest of signatures through the Legend X says that it can take a dark, warmer, rich IEM and tame it a bit. But not in a bad way. This is also the closest to the E01 motherboard in punchiness, which seems a bit odd to me as I love the iteration in the N6ii, but less so here. Not that this is bad mind you, just a bit different. If vibrancy and a sparkling personality is your flavor, then this would be the choice of the four, to me.


Nutube/Class-A:

It should make sense that this is my favored signature here for it provides the listener (me) with the closest iteration of a true tube sound. The laidback nature of Class-A coupled with the tubelike sound of the Nutube provides me with a sound very similar to my iFi Pro set up. A certain sweetness permeates my cranial matter as I enjoy this. You get less bass response, but that is all right, for the mids sound sumptuous in response. This is like playing with your fine tube amp through floor speakers when no one else is home. Euphoria saturates you to the cellular level. One could consider the treble response as polite, but it isn’t. I would call it as softer response around the edges. That edginess is gone and replaced by a melodic flowing of note. As another reviewer mentions, this is tailor-made for those types of voice similar to crooners, such as Harry Connick Jr or Frank. Sumptuous.


Nutube/Class-AB:

Adding vibrancy to a tube sound may seem like blasphemy or sacrilegious, but here it is not. For that added vibrancy of the AB you get more (and better) bass response, with the mids pushed more forward than even Solid-State/AB to me. The softening of the treble edge still remains, but the Class-AB tries to accommodate this by providing an excellent platform for the rest to shine upon. Another reviewer (both posted here) states that this combination provides most likely the most detail and euphony. This is an energetic tube-like sound, which could very well be the best of both solid state and tube sound. The density of tube sound comes back with the Class-AB, which was lost a bit in the Class-A. This actually presents a dichotomy to me as I prefer the lush rich, warmth of tube sound the most, except here where I favor the Nutube/Class-A combination.



Source:

Using the Shanling M6 Pro (Turbo DAC, which is both Class A and AB; it’s a Shanling thing) for its 4.4bal connectivity, I could happily sell all other wares, except for my workout set up and be very, very happy. Tidal through the duo sounds sublime and full. Yes, I know Tidal “Master” has replaced MQA, but I like the bit of added richness Tidal provides to the signature. Both the Legend X and LCD3 shine on this set up and this makes me happy.

Using the Cayin N6ii with the E01 motherboard may seem a bit redundant, but for the four options on the C9. Utilizing the 3.5se connectivity (but both balanced and unbalanced headphone/IEM’s) I found the pairing to be quite complementary. The excellent rich tonality of the N6ii worked effortlessly with the vibrancy to richness of tone emanating from the C9. This allowed me to tailor each song as needed or each artist.

The C9 showed its mettle across some pretty fine DAP’s and could easily hook into a desktop set up as well.


Comparison:

Cayin C9 ($2000) v iFi Black Label ($599):

One would think this is a completely unfair comparison due to the price. Those people would be only partially correct. The BL provides massive amounts of power (but uncontrolled sometimes) for the price and includes iFi signatories such as Bass Boost and 3D+. this was the first quality headphone amp I purchased and for a reason. I could tailor to specific signatures using the settings listed above and the IEM-match switch, which accommodated various impedance IEM’s. A transportable amp, which came ahead of many others, the BL is a marvel of technology and can back it up beyond the gobs of abundant power. Good sound can be tailored using the Bass Boost and 3D+ yes, but the overall signature to me belies that richness, which pervades most iFi products. I fell for it upon review, and shortly purchased one after.

But as good as the BL is, you are limited by IEM connectivity, with no balanced option. That said, you have more connectivity options source-wise than the C9, moving it nicely into the desktop realm. There are more than enough positives to make the case for the BL, even sound-wise, but the C9 is simply superb, with on the fly (easier to use) options to tailor that sound quality, on a frame, which is more accommodating to usage. You decide, both are fabulous.



Finale:

At some point you must decide a level at which you should stop. What that level is, will be completely up to you. But I challenge you to add up all you have spent on audio goods in the portable demesne (those who are new are excused, and immune so far...). Tally every DAP, every DAC, every amp you have purchased over the years. My guess is that you have spent significantly more than the price of the C9 (I know I am guilty as all get out) or you are fast approaching that level. Now, I do not fault, in fact I applaud those who are satisfied with a more economical outlook in our hobby and are completely happy. In fact, I would be a bit (quite a bit) jealous of your self-control and appreciate that satisfying outlook. You will go far in life and much left over for you to thrive upon in your older years.

But for those who have spent more, much, much more; you may just be a target for the C9 (and others, please do not take this as a slight to anyone; it isn’t). For you see sometimes a device comes along that allows you to reach that level of satiation and you are content; much the way those who value economy over price (again applauded). I reached that level in IEM and DAP with significantly different purchases. I have heard “better” of each, but those better ones do not fit my tastes preferences of said purchases. The C9 is one of those devices that comes along and knocks you silly with a reorientation of what you feel is the appropriate level. A reorganizing of your cranial matter into semi-competent thought processes of needs tied to satisfaction. You hear it. You cannot believe something such as this can sound so delicious. You cannot understand why at this price you are re-evaluating what you have in order to quantify the C9.

It is indeed expensive. More than most would ever spend, and for good reason. This is a larger purchase. But if you tally all of your purchases in this segment and realize you have spent more, this may just be the device, which realigns those purchases into sales. Sales, which can fund the one device, which will satisfy the needs across those previous purchases. Even if you squirrel away a purchase of lower price for your everyday needs, the C9 could still very well replace and replace with exemplary sound qualities the other equipment sold and you will be satisfied. You will be thoroughly satisfied I say, and it will be all right. It will be all right for your journey has taken to this point where you can sell, without regret, those lower priced items (which may be quite fine and good) with the C9, and call it a net gain, or net even in the end.

Do I wax poetically too much about the C9? Maybe, but it is of such versatility that this can be justified. With the ability to run four sound options and two types of hook ups, you have pretty much all the versatility you need. It does lack those added connectivity options, but that will be all right for the sound signature is so good you will be fine. Just fine.

I again thank Cayin and Andy Kong for the inclusion in the C9 tour. It is a fabulous unit, which while expensive can function across many levels. On to the next lucky person it goes.

​

Cayin C9 is a flagship transportable fully balanced portable tube amp that can output up to a whopping 4.1W at 16 ohms. It’ll cost you just shy of $1999.

Introduction​

Cayin is a manufacturer that probably I don’t have to introduce anyone. They’ve been in this market for quite a while delivering a stellar price to performance audio equipment as well as unique designs such as tube DAPs or R2R DAC modules. However, this time what we’re getting is basically a transportable powerhouse. Portable Class A battery-powered amplifier that also has tubes and it can deliver almost 3W of power at 32 ohms… Ladies and gentlemen introducing, Cayin C9.

Packaging & Build Quality​

Don’t let this picture fool you. This amp isn’t THAT small.

Cayin C9 comes in a rather large box and to open it you have to slide out a smaller box from one side and open side doors from the other. Inside apart from C9 itself we also will find plenty of additional stuff, such as a nice braided USB-C cable, a screwdriver, a set of screws, and two very well-built interconnect cables. 3.5mm for single-ended, and 4.4mm for balanced.

Let’s proceed to the device itself because we have a significant amount of things to cover. Starting with the build quality, it’s just top-notch. Beautifully machined metal brick that you certainly can kill a man with. On the top, we can find the Cayin logo, top of the potentiometer and small windows where you can see your Korg Nutubes glowing green when working. At the back all you’ll find is a single USB C port as well as a battery indicator with tiny orange LEDs. The front is where all that fun stuff happens.

Here we have numerous amount of different options. Starting with Line/Pre switch. It changes the device between being able to control the volume by potentiometer or being fixed at a max volume all the time. However, Cayin was clever while implementing this. If you want to switch to Pre you have to put the switch to Pre mode and then click the button on the side. Such double step procedure in my opinion is very clever, because you don’t want to accidentally blast 3 Watts of power into your IEMs. They will be destroyed, as well as your hearing. Next up we have Low and High Gain switch which is pretty self-explanatory. On the right side though we are getting Timbre and Class switches. Timbre changes what source we are listening at the moment. Solid State or Tube. They do have their own pros and cons and none of them work well in every single case scenario. The class switch is pretty simple. It changes between Class A and Class AB amplification. If you do care about power then you should stay with A. If you’d like to preserve slightly more battery, AB is the way to go.

Look at these connectors. And they come with an amp!

Last but not least all inputs and outputs. Cayin C9 has 3.5mm single-ended and 4.4mm input on the left side and output on the right side. We also do have a small power button with tiny white LED that indicates if the amp is ready to listen to. Last is going to be that potentiometer. It works smoothly and even. It does have a moderate amount of friction so it’s not that easy to accidentally bump it which is a huge plus.

I also have to mention the battery. Inside we have 4x Sony VTC6 18650 batteries that will give you in total 3000 mAh and can work up to 15 hours while using Class AB Solid State and Single Ended. The most power hungry-setting which is Class A Vacuum Tube Balanced mode will decrease playtime to about 6 hours. It also takes about 6 hours to charge the C9 with your standard charger. However, if you have a Quick Charge 3.0 charger then the charging time will be decreased to about 3 hours.

Oh, do you still remember about that screwdriver and set of screws? Well, it turns out that those batteries are swappable. If they’ll start to give up you can simply open your C9 and swap them for something else. This is a great feature that’ll make this device last literally for years, maybe even decades. Cayin, you’re getting a huge thumbs up for that.

Trip companion.

Tech​

The Cayin C9 packs a lot of very unique tech. Let’s start with the star of the show, the so-called Timbre circuits. For Solid State, we have 4 Toshiba 2SK209 JFET’s and for Tube – 2 Korg Nutube 6P1’s.

THD+N measures at around 0.003% on SS and 0.03% on Tube. In terms of Dynamic Range, we’re getting 123 dB on SS and 114 dB on Tube. And last which is Signal To Noise Ratio:
125 dB on Solid State and 114 dB in Tube mode. I have to point out that for a circuit mainly based on tubes these are some stellar measurements.

If we are talking about the amplification section already I also have to mention that this amp requires a little bit of warm-up especially if you are turning it on for the first time during the day. If you’ll start to listen to C9 right after switching it on, you’ll experience a massive channel imbalance, but don’t worry. About a minute and it will balance itself out. Also, I do not recommend carrying the C9 in a pocket or especially trying to sandwich it and then carry that in a pocket. It’s a small powerhouse that also has tubes inside. It is normal that it gets a little warm at times.

And speaking about being a powerhouse… it can deliver up to 4.100 mW of power through Balanced output at 16 ohms. For a portable amp that is… A lot.

Sound​

Lots of I/O and different switches on the front.

There’s one thing that I need to clarify first. The Cayin C9 offers a true stationary level of audio quality on the go, which is a great thing. With so many options, including two timbre modes and A/AB class sound, it is a true powerhouse. It’s not too easy to review such a unit, having in mind that it basically has many sound signatures. That’s why I’d be focusing more on the actual quality of the frequencies, instead of telling you about its timbre, as it really, really depends.

Starting with the bass, it’s not really surprising. It’s big, bold, powerful, and well-controlled, with great textures. The main thing worth mentioning is that it’ll be able to power almost every single pair of headphones in the world (with very few exceptions, like the Susvara by Hifiman). Thanks to that, you’ll be getting a big, saturated, and dynamic sound from top to bottom.
It offers a very high quality of the low frequencies, which are filled with details and different textures. There’s absolutely no sign of any sloppiness, lack of definition, or being overpowered.
It works exceptional with my HEDDphones (review here), providing them enough juice to really shine, without sacrificing their beautiful timbre. Class A and Solid State is the way to go here in my opinion, as it keeps that thick, fun, and saturated performance, without really changing their type of performance.
What’s the most important here is that the HEDDphone isn’t really that easy to drive, and the C9 handles them better than both Cayin N3Pro and iBasso DX220. As I said, you’re basically getting a stationary-level quality on the go. Not really portable, but transportable, and that’s fair enough for many hard-to-drive headphones on the market. You won’t be taking them for a walk in a park anyway.

One of the nicest battery indicators I’ve ever seen. And it’s orange!

The midrange is probably the most impressive thing about the C9, together with the bass. Even while using it in A/B + SS mode you’re getting that slightly warmish, highly natural sound that is basically Cayin’s trademark.
While using it with the Hifiman HE1000se, I actually prefer to switch to the tube mode. It gives them that additional warmth in the midrange, that could help with their non-forgiving sound performance.
No matter which mode you’ll use though, you’re always getting a highly resolving, textured, and rich midrange performance, that’ll suit basically anything that you’ll plug into it.
The star of the show is the vocals here, as the C9 really grasps you by its superbly natural voice timbre. It’s not a device that’ll dictate the way of recreating the sound to your headphones, as all it does is making sure that you’re getting a properly tuned and superbly-layered midrange performance. Because of that, you still need to rely on your headphone’s type of sound, as it won’t really change much while using the C9. Don’t treat it as some magical tube amp that’ll make your dry-sounding pair of headphones into a lush and warm one, as it’s not the case here. It’s not a 300B tube AMP at the end of the day, and its goal is quite different – to give you vast flexibility when it comes to the pairing, and giving you the possibility to use your power-hungry headphones on the go.

This thing is kinda a weapon.

The treble is very clean, coherent, and shiny sounding, and depending on the choice of timbre and class switch, you’ll be getting different results. Switching to the tube output, you’re getting a more delicate, smooth, and more forgiving type of experience with high frequencies, ideal to some harsh sounding pair of headphones. You can also use it with poorly mastered music, as it tends to hide some slight details that you don’t really want to hear.
If you want a more romantic and lush sound performance though, Class A and Tube is the way to go here. It gives the upper mid/lower treble a slight creaminess and warmth, that’ll suit some pairings perfectly.
Have in mind though, that the C9 is never a slow-sounding or overly warm type of amplifier. The changes you’re getting with all those options are noticeable, but it’s not a night and day difference. Thanks to that, every single switch setup gives you a saturated, detailed and crisp treble performance, which you can simply tune to your liking or current mood.
One thing that sounds exceptionally great on the C9 is an acoustic guitar. No matter which sound preset you’ll choose, it’s able to give you that insightful, shiny and physical treble response on the strings, that is pretty necessary for the acoustic guitar to sound the most natural. The whole album “Acoustic Live” by Nils Lofgren is a perfect example here, as it sounds natural and aggressive in the upper frequencies, no matter what headphones you’ll use. It’s well controlled and highly-textured though, and you don’t have to worry about any harshness or unpleasant spikes.

Rock-solid.

Overall, while the C9 has many options when it comes to the sound reproduction, they all share a refined, rich, and natural tone that’ll suit the vast majority of headphones on the market. The flexibility lets you tune the sound a little bit, which is a great thing when you’re in the mood for a specific type of playstyle, while only having one pair of headphones at your disposal. That’s why it’s the perfect companion for any trip, as it’s a 4-in-1 type of experience, giving you the choice that is often lacking in its competitors.

Pairing

Hifiman HE1000se


Even though the 1000se isn’t a demanding pair of headphones when it comes to the power, it sounds so transparent and detailed, that you don’t really want to plug it into the first amplifier you’ll see and call it a day. The C9 is a brilliant choice with the 1000se though, as it easily outputs a very high-quality signal, and all the sound presets are there to tune it to your liking or to the music you’re currently listening to.

While the A/B / Tube setup made the 1000se more forgiving and lush sounding, it is a great choice for some older recordings or some late-night, chill listening sessions. Fair, you’re losing a bit of that crispiness and detail, but remember that the 1000se is a very unforgiving and neutral-sounding pair of headphones, that often doesn’t sound that great with poorly mastered records. With the options to tune the sound on the go, you’ll be able to comfortably use the 1000se as your only pair of headphones, and you won’t have to worry about the poorly mastered stuff as much.

On the other side, if you’re in the mood for a very detailed sound, or you’re simply listening to some really well-recorded albums, you can easily switch to the AB/SS setup and enjoy every single detail and spark in the music.

Keep in mind that it’ll never sound dry or harsh, as the C9 is a natural and rich-sounding amplifier no matter the type of sound you’ll choose. That makes it a fantastic companion for the 1000se, as it’s able to unleash their full potential, while giving you a choice to slightly adjust the tune.

HEDDphone



The HEDDphone is more demanding when it comes to the power than the Hifiman HE1000se. While you can plug the latter into any modern DAP and get a really good result, the HEDDphone really improves when it’s used with a powerful amplifier.

I’m not gonna lie, taking such heavy-duty equipment on a trip is nowhere close to what I’ll ever do, but I know there are some hardcore audiophiles that want to have an ultimate experience everywhere, and they don’t really like IEMs. For all of those people, the C9 could be a life-changer. It definitely has enough juice to run the HEDD in a great fashion, giving you a very juicy, natural, and extremely fun sound performance.

The setup I actually like the most is Tube/AB with this specific pairing. It gives as that slight tube-ish timbre with superb layering and detail retrieval of the AB class. That setup sounds refined and technical at the same time, providing you with gorgeous vocals and an outstanding soundstage wherever you are. The amount of textures and dynamics you’re getting with this setup is spectacular, and it’s definitely one of the best pairings with the HEDDphone that I’ve heard.

Summary​

Powerhouse.

The Cayin C9 is a very flexible and functional powerhouse. It has enough power to run most headphones on the market, and it has this classic Cayin sound, which is natural, rich, and very dynamic. It’s big and heavy, making it a more “transportable” device, but if you’re a regular hotel visitor, it could actually be the best audio companion in your arsenal. Also, thanks to having four different sound outputs to choose from, you’ve got plenty of choices when it comes to the music and headphones you’ll be using. Brilliant device.


Absolutely recommended.

THE CAYIN C9 REVIEWED ABOVE IS A LOAN UNIT AND IT HAS BEEN RETURNED TO THE SENDER.
THANKS CAYIN FOR SENDING US THIS DEVICE. ALL OF THE ABOVE IS MY HONEST AND UNBIASED OPINION.

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Gear used during this review for the sake of comparison and as an accompanying equipment:

• Headphones – Beyerdynamic DT770 Pro, DT1990 Pro, Campfire Audio Solaris 2020 LE, Audeze LCD-3, Hifiman HE1000se, HEDDphone
• Sources – Sony ZX300, SMSL M100 Mk II, Schiit Modi 3+, SMSL SU-9, Cayin N3Pro

It seems this year I’ve been in a rather extended audio review rut. Not by there being a lack of offerings but for personal indifference. That is until I was presented with the opportunity to review a new product from a company I’ve immensely enjoyed everything from them I’ve had the honor of experiencing. Cayin has a new portable amp that offers many impressive qualities that sparked a little excitement in me that I haven’t had in a while. So, without further adieu, allow me to share my thoughts on the product that put some pep in my step; the Cayin C9.



The Opening Experience




Construction



As a product that costs 2 grand, one would naturally assume that the construction and build quality of said product would be premium, right? Well, at least with the Cayin C9, you would be absolutely correct. The C9, seemingly inspired by its DAP design, makes the C9 using machined aluminum along with a glass back to add a touch of elegance. Now, that also brings up the first negative and that is that glass, as I’m sure all have experience with, scratches. As seen in the pictures attached in this section, my tour unit has a fair few. I cannot comment on how long this unit has been on tour throughout its life, but still an unfortunate side effect of glass that users will need to keep in mind.
The top of the unit is beautifully simplistic with only the Cayin branding and 2 sight glasses showing off the lovely tealish hue of the 2 tube amps the C9 can utilize. The right side has nothing aside from a screw to remove the user replaceable batteries, but the left side has the preamp button which I’ll discuss further in the following section. The back of the unit has the LED battery level indicator as well as its type C charger (thank you). The glass bottom of the C9 too has the Cayin logo as well as the product model name, website, etc… The front end is where the business happens. From left top to right bottom, you have the mode indicator switch from line or preamp mode (which I’ll discuss further in the next section), high and low gain switch, headphone inputs (3.5 and 4.4mm respectively). The buttery smooth 4-channel ALPS potentiometer knob followed by the power button (which has a slight warm up (couple seconds) period before the C9 can be utilized. Following them are the Timbre (tube/SS sound) selector switch, the class A and A/B selector switch and then lastly the output jacks (3.5 and 4.4mm respectively).
So, in summary, the Cayin C9 is a wonderfully simplistic portable amplifier in terms of its construction but still offers the users many different options to fit their individual tastes. Additionally, it’s solid construction gives me no worries about its ability to last for many years of proud ownership.

Features



Lately a portable amp is absolutely weighted down by having every possible feature than anyone could even fathom they may want. Whether or not this is a good thing or not is definitely up for debate but at least with the C9, they’ve done a solid job and presented a quality portable amp that can just about offer everything sub bluetooth. The first feature that I personally would like to highlight is that the C9 has the capability of sounding like a tube amp as well as a solid state amp that is changeable by the simple flip of a switch. This allows users to get the audiophile grade accuracy in their music and headphones that allow them to be as analytical as possible though its SS mode and also the creamy lushness of a tube sound (personal favorite choice) when they just want to relax and enjoy the musical experience presented in front of them. Adding to that, the C9 can also operate in class A or A/b power mode which further changes the sound characteristic to further suit the listeners preferences (class A all the way). Next is the ability to have the C9 operate as either a pre amp or a power amp. By selecting the premode and holding the pre button down for a few seconds, the C9 will function completely as the power amp and the volume will be completely controlled by the source (MAJOR NOTE: Please don’t do what I did and have your source at max volume when switching over. It was painfully loud, in very much so, the literal and physical sense [obviously this is nothing on the C9 but an oversight on my part. Just wanting to warn others to not experience my pain]). The last and possibly the most appreciated feature that will add many years of longevity to the C9, is the ability for the user to replace the rechargeable batteries. Simply unscrew and slide out and replace with either new Sony VTC6’s or equivalent.
To conclude, the C9 offers features that I believe many audiophiles will greatly appreciate but also not feel intimidated as to not understand them or be confused on how to get the C9 into the desired mode of listening. Or, when I wasn’t critically reviewing the product and just experiencing it, being extremely satisfied leaving it on 1 setting. The Class A, tube timbre for me personally.

Sound




Similar to all Cayin products, that I’ve listened to at least, the C9 has an overall warm, musical and even somewhat “slow” sound to it. Whether I’m listening to my Empire Ears Hermes VI ciem’s or my Sennheiser HD650 this presentation has remained the same. I guess I should’ve started by saying that for the majority of my review time I utilized the C9 in tube timbre and Class A modes because they personally sounded best and I enjoyed that most. However, even in SS and Class AB modes the Cayin house sound was still there but was noticeably more tighter and even colder sounding.
The two main products I used throughout my review is my hyper sensitive EE Hermes VI and the renowned HD650 that neither is very difficult to drive, but the C9 was able to power them very easily ESPECIALLY when using the 4.4 cable from the HD660S, dear gosh the power this thing pushes. This is VERY evident when I’ve my EE’s in. While single ended, the C9 is pushing 1.2Watts into these extremely sensitive iems so I do need to make certain that the volume is minimized on both this and my source (this was critical when in pre mode). To further touch on my EE’s when using the C9, there was very little hiss I’ve become all too accustomed to hearing on just about any device. The C9 was all but a pitch black background, on both SS and tube timbre.
I will close this section by generally comparing the SS and Tube timbres. As stated above, the tube mode has a very warm and musical tonality, especially when paired to the Class A mode, and was the mode I personally prefer the most. I can understand “traditional” audiophiles not leaning towards this mode due to the music sounding a little slower and the bass especially being looser than what the SS mode is. I feel the mid range boost allows me to enjoy the music vs dissecting it. On the flip side, SS mode is very clean and the bass is noticeably tighter and one can really take in all the detail that your source can push through this impressive amp. I do, again, wish to warn about the volume levels. Even if you’re using this in pre mode, ensure that you’ve turned down the volume on both the source and the C9 to minimum just in case something happens and is switched to either mode and you’re blasted with a painful level of volume. But any further and I’d just be rambling. I really enjoyed the sound the C9 gave to my headphones and iems. Subjectively speaking, I seriously understand why this brick has the 2 grand asking price. It can give any portable rig on the market a serious run for its premium money.


Conclusion



My final thoughts on what is the Cayin C9 portable headphone amplifier is that it, very much so, lives up to the continued love I have for the Cayin products. From the build quality to the ease of use to the simplicity of its design to the warm and inviting Cayin house sound I have no qualms with it outside its very premium price tag, but that’s a subjective opinion. I also believe that the C9 is on the very borderline of being a reasonable portable option because it is quite large. But in relation to the ability to drive my portable headphones (which, I mean, seeing as my “hardest” to drive headphone is a HD650, wasn’t able to really be pushed) I absolutely have no complaints to offer. Also, I don’t think I mentioned this anywhere yet but the battery life on this thing is absurd. I listened to this all day (aprx. 5-6 hours straight in technicality) while writing this review and the indicator only went down half. Hot. Dang.





Also, make sure to check out my unboxing and review videos. They’re pretty awesome AND you getta put a face to the Army-Firedawg name. If this review helped you out at all, please hit that thumbs up button! It really helps me out a lot. Till next time my friends, stay safe.

Disclaimer: Cayin needs little introduction as a long time player in the Tube amp, DAC and DAP market and this latest product combines some elements of all of that backstory. I received the Cayin C9 as part of a review tour and spent 10 days with the C9 as my primary amplifier both home and portable to give it a good workout before sending it on to the next reviewer in line. I have no financial interest in Cayin or any of its distributors, nor have I received any remuneration for this review. I own several other Cayin Products and have reviewed several of their DAPs and IEMs previously in these pages. If you have an interest in the C9 or other Cayin products, see their website and follow them on Facebook.



Packaging:

The C9 is a premium product with a price tag to match so one expects a premium experience from start to finish and largely the packaging works although the sticker with the specs on the package reverse was not smoothed out well and air gaps can be seen in the photos, a little more care there would be appreciated. Once the slipcover is removed, the packaging is nicely laid out with the C9 tucked in a foam surround in the top compartment and a pull out shelf with cables (3.5 interconnect and 4.4 interconnect), USB charging cable, disassembly tool, extra screws and storage container for same all hiding under the manual. The kit is complete with everything one needs to take it out of the box and start using it without having to go search for a interconnect which is a nice touch. Likewise, my test unit came with the batteries at resting voltage (3.7V) so was usable out of the box even if not topped off before using. (How many of us resist the urge to try out a device before fully charging it?, I suspect many don't).








Build:

The C9 uses a three sided (top and sides) cnc milled anodized aluminum housing with two oval openings cut in the top surface for tube visibility. The bottom surface is a glass plate with a protective cover attached at the factory. Unfortunately no feet are provided so it would likely be worth investing in some felt or rubber stand-offs to keep from scratching the unit on the desk. Dimensions are about the size of an average cell phone in height and width (roughly 3.25 x 6.25 inches) and roughly 3 times as thick as phone (1 inch). Heft is significant at just over a half kg. Most of the controls are on the front panel except for a button on the left side that is used to activate pre-amp mode. On the unit's front there is a row of switches that sits atop a row of ports. From left to right the top row is line/pre-amp, gain, volume knob, solid state/tube, and finally Class A/AB switches. The bottom row contains the single ended 3.5mm input port, 4.4mm balanced input port, power button, 4.4mm balanced output port, and 3.5mm single ended output port. Some of that heft is because of the battery arrangement. Unlike most devices that use a LiPO foil pack battery, the C9 uses a removable battery tray with four 18650 Lithium Ion cells. The unit ships with Murata (formerly Sony) VtC6 cells installed (more about these in the battery section later) and makes it easy for the user to carry a spare set when recharging is not an option or to replace the battery when the originals inevitably wear out. The battery tray can be removed by using the provided tool to remove a screw from either side of the case about 1.5 inches from the rear, and then sliding the tray out of the rear of the unit. Be sure the unit is off before doing so. With the USB port and charging indicators being part of the battery tray, it may be used to charge the tray outside the unit. Cayin offers spare trays as well for those who want a quick change option. I'm glad to see a product that is acknowledges the need for user serviceable batteries as this is one of my biggest pet peeves with things like air buds. Planned obsolescence due to not having the ability to replace a battery with a known life-cycle of 500 or so charge cycles has kept many products off my recommended lists. One other note, this unit gets warm which shouldn't come as a shock when you see class A and tubes in the mix, but Cayin has done a good job of controlling the heat build up and the unit while warm never got hot enough to be uncomfortable to touch or carry.





Internals:

Circuitry:

This is a loaded discussion as the c9 has so many different options. The signal starts with the choice of tube or solid state balanced preamps (what Cayin labels as timbre circuits). These are followed by a split. One path remains balanced while the other is converted to single ended. From there both paths pass through the primary gain stage (voltage gain 6dB) followed by the secondary gain and a Muses 72320 electronic volume control (±18V). After leaving the volume control, the signal passes to two fully discrete headphone amplifier circuits in opposite phase (Those familiar with the Cayin N6ii and particularly the E01 module will recognize the discrete amplifier design as it seems to be a near copy of the one used in that module. Both of those circuits pass output to the balanced port while only one (the positive side) is used to feed the single ended circuit. This can all be seen in the attached diagram below. Just remember this is for a single channel so in reality the diagram would be doubled if looking at the entire C9 design. On top of that, the unit is capable of impressive power (4,100mW (at 16Ω) or 2600mW (at 32Ω) per channel) which makes cooling those amplifiers even more of a challenge.




Battery:

The C9 ships with four VTC6 cells made by Murata of Japan (formerly Sony). These are 3000 mAh cells that are slightly lower capacity than the market leaders, but lead the market in sustained current throughput with a 20Amp rating. That combination of 8.4V (2 in parallel 2 in series) at 20Amps gives the C9 the ability to run without needing a boost converter to dirty up the output. While 18650 type batteries can be found at pretty much any vape shop, there are very few cells currently on the market capable of support 20Amp continuous power draw so when sourcing replacement batteries, ask for the Sony VTC6 by name or make sure to purchase cells capable of sustaining a high current load from a reputable seller. Other compatible batteries include the Sony VTC5 cells, Samsung 25R, the LG IMR 18650 HE4, and Sanyo NCR2070C but all except the Sanyo have lower capacity than the VTC6 so will result in shorter battery life than the table below shows. The Sanyo NCR2070C is actually a bit higher capacity than the VTC6 cells (3475 vs 3000 mAh) so will extend charge life by rough 15% when using the 2070C cells in the C9. Also note that when charging lithium ion cells they will take an initial charge of 4.2V but will slowly self-discharge back to a resting voltage of 3.7-3.8V where they will then stabilize and can sit for an extended period at 3.7V. A cell that self-discharges below 3.7V is going bad and should be changed. When replacing batteries in the C9, always replace all four with a new set at the same time, do not mix old and new as this can have disastrous results. I found the numbers provided by Cayin on battery life to be pretty accurate and while 5.5 hours is a little disappointing as one can't get through an 8 hour work-day on a single charge, switching to class AB loses very little performance and nearly doubles that so is an acceptable trade off.

​

Korg NuTube 6P1:

I gave the tubes used here their own section as they are quite a departure from the tubes I grew up with and most here recognize. The Nutube looks like an IC with a couple blue/green LEDs embedded. In reality, it is a modern vacuum tube with improved power handling and microphonics and it behaves similarly to a 12ax7 in use. The 6P1 is a directly heated dual triode tube using vacuum fluorescent display technology and is made under license by Noritake Itron of Japan for Korg. Compared to the 12Ax7 that has a heater voltage/current of 12V/0.15A, the Nutube uses a heater voltage of 0.7V/.017A. Likewise plate voltage of a 12ax7 is usually somewhere around 200-250V vs the nutube's 12V. One big difference though is mu (kind of gain in the tube if you will) where the 12ax7 is a good bit higher output than the Nutube. Still we don't see 12ax7's used as pre-amp tubes often due to the fact they are too high powered for that role and instead they often are the 2nd tube in a circuit following a 12au7 or 6922 preamp tube with a mu similar to that of the Nutube. So here we have a modern take on the classic preamp tube with lower power requirements, better stability, and a 30,000 hour rated life. For more information, see Korg's guide.





Sound:

There really is no way to discuss the C9s sound in a single section as it has too many options to tune the sound to do that. I have broken it down a bit based on modes so I can cover at least most of the options. So first lets look at Class A vs Class AB as that actually makes more difference than many will expect and will impact our tubes vs solid-state discussion that follows. The C9 in class A mode is a bit less impactful than in AB mode but remains a little closer to neutral as well. AB mode is more aggressive from bottom to top with more impact in the sub-bass and more shimmer in the treble range, but a bit less warmth than in pure A. This is particularly notable in the mids and lower treble with AB having a bit tighter sound with a bit more edge to it. The Class A by comparison is a bit warmer in the mids, but a bit more laid-back as well. These qualities show through in both solid-state and tube modes. For example in class AB switching from Solid state to tubes doesn't make this huge jump that many will expect, instead it softens the sound a bit and gives the C9 a more relaxed feel with less of that assertive edge in the treble heard in solid state. Overall the AB tube mode is probably the best combination of detail and euphony and is what I would leave the C9 set to were I listening for pleasure. Class A tube sound is smooth, warm and provides that creamy signature that pure class A tubes are known for. It is a little thinner than the Tube AB which I found carried a touch more weight in the mids compared to Class A mode. I preferred the detail of the AB mode with the tubes but for those looking for pure tube sound, the Class A tube setting will provide what they are after. In solid state, the Class AB mode has the most impactful bass and treble of all the modes but also has what I thought was the worst mid-range tonality with strings presenting a bit too much energy at times. It would likely pair well with a headphone that needs a little mid push to do its best work. Class A solid-state loses a little of the impact of AB but gains a better timbre to the mids and treble that makes it a better option to my ear. Vocal performance was best of all 4 modes in my estimation in the pure class A solid state setting. Class A solid state is a good pairing for headphones that already have a V-shaped signature where it calms it a bit.

You can see that modes on the C9 are not gimmicks, they do actually give the user enough tuning options to use the C9 with a wide variety of sources and headphones and coax the most out of them. Regardless of mode, the C9 had good clarity and instrument separation. I have a hard time attributing things like stage and imaging to an amp as I find the headphone is mostly responsible for these qualities but I can say at the very least the C9 did nothing to detract from stage and imaging and in most cases it did seem to have a beneficial effect with improved stage dimensions.

The C9 also has the option of Line in or preamp input. The issue here is if using the line-input mode and accidentally switching to preamp input where the c9 is set to maximum possible output level one could destroy both the headphones and their hearing in a matter of seconds. For this reason, switching to preamp mode requires that the button on the left side of the unit be pressed and held as well as moving the switch to pre position on the front panel before engaging the preamp mode (smart!). I tried the C9 in pre-amp mode and generally found that I preferred using line-in mode as essentially you are amping the sound twice in pre-amp mode coming from the likes of the WM1A or Cayin N3 Pro and in both cases I felt it lost a little bit of dynamic range as a result.



Pairings:

As mentioned earlier, the C9 is quite capable with nearly 2.7 watts into a 32Ω load so one would expect it to be best suited for full sized headphones or high impedance/low sensitivity in-ears. I tested with the normal murderer's row of 600Ω beyer dynamics, the He6 (balanced), and the HD800 (also balanced) and it handled all as well as I expected it would. The tube mode seemed a particularly good match with the HD700 as it added a little body to the mids with its warmth. Once I got through testing every headphone I could throw at it without finding any it really hated (from the Cascade and T5p at the easy to drive end all the way to 600+ Ohm AKG and power hungry T60rp and He6), I turned to in-ears. Surely this beast with enough power to light up an He6 was going to hiss when I plugged in something like the Andromeda and indeed it does. Plugging in an iE-match solves the issue, but it is fairly clear that high sensitivity in-ears were not the intended target of the C9.



Comparisons:

Let's face it, there are not too many competitors for the C9 as most are either half the cost or twice it. I used the two closest things I had at the house for comparison sake. Those are an iFi micro iDSD Black label which puts out similar power to the C9 but lacks the modes and costs a good bit less, and the Chord Hugo 2 (a borrowed unit) which again, similar form factor and portability, but at a substantial increase in cost vs the C9. The iDSD Diablo might be a fairer comparison but having not had the opportunity to get my hands on one yet, I'll have to save that for a later date.



ifi Micro iDSD BL-

These two have similar shapes with the ifi having a less convenient shape for stacking should the need arise. The iDSD is a DAC/Amp vs the Amp-only C9, but offers similar power at 4 Watts into 16Ω (in turbo mode) and also has similar battery performance when set to equal output levels. Sound wise the iDSD does not offer A/AB switching, or tube/solid state but does expose the dac filters and offers 3d and Xbass boost so does provide the end user some tuning ability. The iDSD has an additional gain level that lets it drop lower than the C9 as the mid and high on the iDSD are roughly comparable to low and high on the C9. iDSD also has the iE-match built in that will be needed for use with in-ears with the C9. What the iDSD does not have is as rich and full a tonality as the c9 when on tube mode or the dynamic range of the C9 on solid state. The iFi has become a very popular dac/amp for price performance, but Cayin clearly has outclassed it with the C9 and a quick listen will show any would be naysayer why the C9 commands the price it does comparatively. The battery in the iDSD is non-removable and charging requires a male to female USB cable that is much more difficult to source than a replacement USB type C used with the C9. While I still find the iDSD good value in the $600 range, it doesn't fit in this comparison as build and sound both favor the C9 by a good margin.

Chord Hugo 2 -

Here again, its dac/amp vs amp with the Hugo 2 having Chords FCPGA as its centerpiece that operates as both dac and control unit. Unlike the previous compare, the Hugo 2 comes in at roughly $500 more than the C9 so we have both a functional and price disparity. I might have mentioned the market for $2k amps is pretty thin. In order to do a valid compare I used the Hugo 2 dac output to the C9 via a 3.5mm to RCA cable so as to only compare amp to amp. Both are more transportable than pocket material with the Hugo coming in at 400 grams and the C9 at 550, neither is a lightweight and both are fairly large footprints for portables as well. Construction favors the C9 as it looks more premium while the brushed shell of the Hugo 2 looks a bit unfinished by contrast and don't get me started on the controls on the Hugo. Whoever thought it was a good idea to wrap controls all the way around the unit has obviously never tried to use the Hugo 2 on an office desk where you either expose the controls or the headphone jack. And on top of that you have to wrap the USB cables around the front to connect a source via USB or charge the unit. Ergonomics very much favors the C9. The Hugo 2 is a class A only amp with no option for tubes or class AB so the ability to change its tonality is only through the dac filters and changes are more subtle compared to mode switches on the C9. Power handling is quite similar in single-ended between the two units with a slightly advantage to the Hugo as we get above about 300Ω headphones. Having said that, the balanced output on the C9 is not even an option on the Hugo and easily outperforms the Hugo's single ended output (even including 300-600Ω models that slightly favor the Hugo2 on single ended). The other oddity here is despite power being roughly equal, the C9 has less hiss and noise when using things like the Andromeda or K5 and the Hugo 2 is about unusable with these same in-ears without adding the iE-match to the mix.

Soundwise, the star of the Hugo 2 is the DAC as it is super detailed and very near neutral so sorting out the amp differences was a bit of a task. The c9 has more weight and a bit more low end grunt with either a slight sub-bass emphasis or simply enough power to get all of it out of the connected headphone. The Hugo2 is slightly less impactful, but a little tighter and a little more linear. Above the lows, the Hugo 2 seems a bit thinner while the C9 is a bit fuller and more lush. The Hugo 2 is the better technical performer but the C9 is more engaging of the pair with vocals being notably more musical via the c9 and more analytical via the Hugo2. These two obviously target different things with the Hugo going for absolute neutrality and cleanliness and the C9 going for a more organic musical experience. If listening for review purposes, I'd choose the Hugo 2, if instead listening for pleasure, I'd use the Hugo 2 dac output to the C9 and pair it with the HD800 all day.

As a final note, the Hugo 2 battery life is even less than that of the C9 so if you plan on using the Hugo 2 for any extended period, plug it in.



Conclusions:

Cayin has been in this game for more than a few years and has made premium products in the tube amplifier space for years. More recently they got heavily into the portable space and have now produced some fantastic products in that space with innovations like being the first premium DAP with modular dac/amp modules, the first budget DAP with tube/solid state amplification options etc. Seeing them combine their design chops from portables and tube amps into the C9 was a natural extension of their business and it shows. There is nothing about the C9 that isn't well thought out, well designed, and equally well implemented. From the removable, replaceable battery pack, to the location of all controls centrally, to the options of sound signature, the C9 shows that Cayin did their homework. The C9 is expensive for sure, but it shows all the polish and capability we expect from a product in that space and for those who can afford it, it's a helluva product. I was honestly sad to see this one go as it rivals the best options I have on hand and is more portable than things like my Auris Euterpe that compete with it in performance. The other nice thing is being a pure amp with a tube lifespan of 30,000 hours of continuous use, and replaceable batteries, this could well be the last amp you need to buy for the foreseeable future since while DAC and OS functionality seems to change weekly, a pure Class A tube amp has been around since the 1940s and is still going strong today.

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The product was provided to me free of charge for the review purpose in exchange for my honest opinion. The review was originally posted on my site, and now I would like to share it with my readers on Head-fi.

Manufacturer website: Cayin. Available for sale from Musicteck.

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Intro.

Some of you are probably going to find it a bit surprising that I’m reviewing an amplifier. I had to take a walk down the memory lane, trying to remember the last time I tested portable amps, just to realize it was 6 years ago, and coincidentally one of them was Cayin C5. Back then DAPs were not as powerful, their internal amp sections were more basic, and battery life was subpar, thus using external amp was beneficial to boost output power and to extend battery life of your portable source. But you also had to compromise the portability of your setup.

Then, DAPs evolved, becoming more powerful and more advanced, with some of the manufacturers offering modular design solutions with interchangeable amp modules or more advance interchangeable DAC/amp cards like in N6ii. It all comes down to having more choices and being able to use your favorite source with different sound-shaping options. And speaking of more options, another example would be N3Pro and N8 from Cayin where you don’t even have to replace the module, just switch from Solid State to Tube.

So, what is next for Cayin after DAPs with Solid State and Tube timbre or DAC/amp cards with Class A/AB amp modes? The announcement of A02 module for N6ii with Line Out only output was a big clue. At first some were confused about release of LO only card without headphone output, just to realize later that A02 was a preamble to the upcoming C9 portable amplifier. I was skeptical at first, thinking why do I need external amp, regardless of its advanced design. But this skepticism turned into a bit of an obsession in the last few weeks. Here is more about it.



Unboxing and Accessories.

The unboxing experience of C9 reminded me of the premium IEM packaging. The giftbox quality packaging box had a magnetic top cover to reveal a non-removable foam insert with a secure cutout for C9 and another magnetic side door for a sliding tray with accessories. I know, some will say, what is a big deal. But I found it to be very convenient to access the accessories without digging through and removing layers inside of the storage box.



In addition to the main attraction, C9 with its battery module already mounted inside, other accessories include pure copper single ended (3.5mm to 3.5mm, CS-35C35) and balanced (4.4mm to 4.4mm, CS-44C44) interconnect short cables, usb type-c charging cable, a capsule with 4 spare screws for a battery module and T6 screwdriver. Plus, you will find a user manual and rear panel glass protector.



Design.

The overall dimensions of C9 are 160x80x28mm with a weight of 550g. It’s a rectangular box, borderline on being portable/transportable due to its weight and considering it has to be stacked with a source (if you go with a DAP). A big part of its weight and the size is due to internal battery module and 4x included Sony VTC6 18650 batteries (3000mAh, 3.7V). The battery module tray alone has a weight of 282g and extends 82mm in length. Thus, half of the length and the weight of C9 is due to its 4x rechargeable 18650 premium batteries inside of a module tray.



The back of C9 has usb type-c connector for charging of batteries, and it supports anything from a standard 5V/2A charger to a higher voltage fast PD or QC3.0 chargers which cut down the charging time by almost a half from 6hrs to 3hrs. Also, next to usb connector you have 4 battery status LEDs to indicate charging status and remaining battery capacity. The unit is fully charged when all 4 LEDs are solid and stop blinking. Both, usb connector and LEDs, are part of the removable charging battery tray which you can use standalone for charging. Of course, you can buy your own battery charger, but Cayin will be offering spare charging tray for sale soon which should make it very convenient to be able to charge another set of batteries outside of C9 and then just slide in and out a new tray.



The bottom of the C9 has a glass surface with a protective film that was already applied on my review unit. I would have loved to see included some stick-on rubber feet to make sure the amp doesn’t slide across the surface. The top of C9 was crafted with two glass oval shaped “eye” openings to reveal a pair of Korg NuTube directly heated triode vacuum tubes when in use. The right side doesn’t have anything, and the left side has a Pre-Amp activation button, used as a safety measure in addition to Line/Pre-Amp switch. You will have to press and hold this button for 3sec until the blue led indicator next to it lit up, letting you know that Pre-Amp input mode is activated.



The front of the C9 is where you will find all the ports and switches placed around the volume wheel in the middle. The volume wheel, which controls 4-channel ALPS potentiometer, is 15mm in diameter and rotates clockwise to raise the volume and counterclockwise to lower it. The knob of the wheel is flush with the front of the C9 to prevent accidental turning, and easily accessible from the top through a generous cutout to be able to turn its diamond-cut wheel knob. The rotation of the wheel has a fluid motion and a nice resistance, just enough so you don’t turn the wheel by accident, and still easy to operate with a thumb.

Looking closer at the front of C9, you will find at the top left corner Line (controls output with volume wheel) and Pre-Amp (output is set to fixed level and you control the input to C9 from the source) input mode switch, H/L gain switch (6dB boost), Solid Stage (quad set of Toshiba 25K209 JFETs) or Tube (Korg NuTube 6P1 vacuum tubes) timbre switch, and Class A and AB (dual amplification operation – DAO) mode switch. In the lower left corner, you have Input ports, 3.5mm SE and 4.4mm BAL, and in the right corner you have Output ports, 3.5mm SE and 4.4mm BAL with a design allowing you to mix SE to SE, BAL to BAL, SE to BAL, and BAL to SE. In the middle of the front under the volume wheel you will find a power button with a status LED that blinks for a few seconds when you turn C9 on when controller initializes the device, and also when you switch between Solid State and Tube timbre.



Under the hood.

You can already get a good idea of what to expect under the hood from the Design section of the review. Cayin been in business of audio electronics for almost 3 decades, especially with a focus on personal audio products in the last 7+ years. C9 amplifier looks like a combination of their best design elements combined together in one package. And speaking of the design in general, some already asked on Head-fi “why amplifier only?” and if “Cayin planning to release DAC/amp version of C9?” The response from Cayin was clear, due to DAC and sw/fw dependency, DAC/amps get outdated faster than a pure amplifier that can stay relevant for a much longer time and be used with many different sources. And here is what you will find under the hood of C9.

First of all, you have a dual Input mode where you either select Line Input with the incoming signal from the source being fixed and you vary the amplifier output using C9 volume wheel, a more traditional headphone amplifier operation. Or you switch to Pre-Amp Input where C9 functions as a power amp with a fixed max gain level and you adjust its output by varying the input from the source. Some DAPs offer LO with an adjustable output controlled by a volume wheel, thus a name of “Pre-Amp” since you are adjusting the amp volume in pre-amplifier input stage. And because Pre-Amp output will set C9 to max gain level, as a safety precaution in addition to a switch you also have to press and hold pre-amp activator button on the side of C9.

After the initial input stage, signal gets timbre treatment depending on a selection of either Solid State (2SK209 JFETs) or Vacuum Tube (Korg NuTube 6P1). Yes, C9 is Solid State/Tube amplifier, but that part of the circuit is responsible for “coloring” of the sound prior to the actual headphone amplifier section. And as I already mentioned, this sound “coloring” will be applied to either SE or BAL inputs and C9 has a clever design to process audio directly through single ended or balanced path, as well as being able to switch from BAL to SE and SE to BA, considering amplifier offers both of these inputs and outputs.

The amplifier gain control is done in two stages. Primary Gain control is between Low (0dB) and High (6dB boost) gain selectable from the front panel switch. Secondary Gain control uses 4-channel ALPs potentiometer (volume wheel) with a pair of MUSES Series low noise, low distortion resistance ladder electronic volume (MUSES72320). Especially when using sensitive IEMs while keeping the volume low, I never experienced L/R imbalance with C9 volume control.

And last, but not least, the fully discrete headphone amplifier section with a selectable (by a switch) Class A or Class AB dual amp operation (DAO) mode. Many are probably going to remember that Cayin featured Class A and Class AB in their E01 card for N6ii. With E02 there was not enough room to have fully balanced circuit and both A/AB, thus E02 only featured Class AB. Here, C9 will give you both Class A and Class AB.

So, how does C9 amplification translate into the actual output power? C9 is rated at 700mW (@ 32ohm) from 3.5mm SE and 2,600mW (@ 32ohm) from 4.4mm BAL output jack. Of course, depending on headphones, with higher impedance the rated output power will scale down accordingly since it is inversely proportional. Considering this is a portable battery-operated amplifier, the power output parameters are quite impressive. And speaking of battery, the rating it from 5.5hrs to 15hrs and will depend on a mode of operation. Vacuum Tubes consume more current and will drain battery faster in comparison to Solid State. And you should expect to drain more battery in power hungry Class A or when using Balanced connection.

Thus, you can expect to go from Balanced Tubes and Class A with 5.5hrs to Single Ended and Solid State Class AB with 15hrs of battery life. And don’t forget, we are talking about components that generate a lot of heat, especially combination of discrete Class A and Tubes that make C9 feel quite warm. That is a reason why Cayin paid close attention to component layout to improve the air flow, even attaching PBS (pyrolytic graphic sheets) to those parts generating more heat. But overall, my typical C9 use was Balanced, Tubes, and Class AB where I was getting a little over 9hrs of playback time.

I have talked about Korg NuTube 6P1 (a dual channel triode vacuum tube) back in my N8 review. Just as a recap, while NuTube operates exactly like a triode vacuum tube, the tech behind it is based on a vacuum fluorescent display technology, like LED. These NuTube modules require less power than a traditional vacuum tube, smaller in size, have a much higher reliability with 30,000 hours of continuous life expectancy, all that while still providing a sound characteristics of vacuum tube sound. And just like with a vacuum tube, there is a warm up period, thus when you switch to tubes there is a short “warm up” delay. And similar to N8, to eliminated microphonics associated with these tube modules, Cayin designed a custom-built shock-absorption silicone housing and a spring-loaded suspension system.



Sound Analysis.

I analyzed C9 sound with Oriolus Traillii and Audio-Technica ATH-R70x while playing a variety of my favorite test tracks, such as Agnes Obel “The curse”, Sandro Cavazza “So much better” (Avicii remix), C-Bool “Never go away”, Ed Sheeran “Shape of you”, Alan Walker “Darkside”, Galantis “Hunter”, Iggy Azalea “Black widow”, Indila “Boite en argent”, Dua Lipa “Love again”, Counting Crows “Big yellow taxi”, David Elias “Vision of her”, and Michael Jackson “Dirty Diana”. I let C9 burn in for about 150hrs before starting my sound analysis.

Similar to my DAP reviews, I prefer to describe amplifier sound based on comparisons and pair ups, but not in the same way as DAPs. People buy amplifiers to replace internal amp stage of their DAPs with an external one through Line Out connection. In the follow up sections I will bring up a lot of brief pair up examples with various IEMs and headphones, as well as different examples of DAP comparisons with and without C9.

This sound analysis section usually serves as a summary of my findings in the follow up sections. And across all my comparisons I found a common improvement of soundstage being more expanded, both in stereo separation and improved 3D imaging. Also, as expected, overall tonality changed with a more natural fuller body sound, thanks to vacuum tubes, though solid stage amp also adds some organic coloring, though not to the same extent as tubes. Furthermore, while some might expect sound coloring with vacuum tubes to make the sound thicker and more saturated, to my surprise I actually found improvements in micro-dynamics with layers of sounds being more separated and less compressed (improvement in vertical dynamics).



The flexibility of C9 design gives you many different sound shaping options, like going between Class A and Class AB and of course, Solid State and Vacuum Tubes (Korg NuTube). I’m already familiar with Class A vs AB from E01 card, and quite familiar with AB from E02 card. In C9, you can clearly hear the difference when switching between Class A and Class AB where AB sounds tighter and faster with notes having cleaner edges, while A is smoother, more relaxed, with notes having longer decay. It is up to a personal preference, and I preferred AB since I like a punchier sound.

When switching between SS and Tube, the difference in tonality reminded me of switching between Class AB and Class A. SS timbre gives you a faster and tighter sound, with shorter and faster attack of the notes, while Tube timbre gives you a smoother and more analog tonality, also slightly laidback and less aggressive. The sound with Tube timbre still packs the punch, especially when you use it in combination with Class AB. That is a beauty of C9, you have lots of different options to customize your sound.

I’m sure some will be wondering about 3.5mm vs 4.4mm comparison. Here, I found tonality to be the same under consideration of using either SS or Tube, or Class A or Class AB. But 2 noticeable differences were the soundstage width, with BAL output sounding wider and more expanded, and the other one with BAL output having a blacker background which is also quite noticeable, most likely due to grounding of 4.4mm BAL TRRRS jack.

Also, I saw a discussion on Head-fi about different rechargeable 1860 batteries. Cayin already includes premium Sony batteries, and for comparison I “borrowed” 18650 batteries from Broadway S, “rolling” between stock Sony VTC6 3000mAh and replacement Panasonic NCR 18650B 3400mAh. I did hear with Panasonic the sound to be a little smoother and more laidback, while with Sony the pace of the sound was faster and the sound was a little more revealing. Of course, there is a little delay when you have to slide out the tray and replace the battery, but it was relatively quick for a “non-blind” A/B comparison.

As I was writing this review, a few people asked me if Interconnect Cables (IC) make a difference. Cayin includes a rather nice pure copper short ICs, both 4.4mm and 3.5mm, so I wanted to test it with a few other ICs I have on hand.

IC comparison:

Cayin stock copper IC (CS-44C44), DHC silver IC (Clone 22awg OCC Silver Litz x4, coaxial cable with 2 conductors and rhodium Eidolic plug), Romi Audio encryption series Sensation IC (pure silver core with silver-plated copper shielding), and Eletech Iliad 6W IC (24awg, 6wire with a full TRRRS connection including GND, Monocrystal Silver & Palladium Plated Silver & Gold-Silver alloy). I know, it is just a short piece of wire, but nevertheless, there is some difference in sound that I hear, maybe not night’n’day, but I do hear it.

Cayin to DHC - DHC IC sounds a little dense and warmer, giving the sound a thicker tonality while Cayin original cable has a little more air between the sound layers, giving it a little brighter tonality.

Cayin to Romi Audio - the improvement is quite noticeable here, and I actually had to lower the volume a bit since it was louder, most likely due to lower impedance of Sensation IC. The soundstage is a little wider, the sound has more air and sparkle, bass is a little deeper, and it also felt like I’m hearing further improvements in vertical dynamics.

Cayin to Eletech Iliad 6W – the improvement is also noticeable with sound having more air and sparkle, bass deeper, but overall tonality was still natural and organic. One interesting observation which I confirmed multiple times is that in addition to improvement in width I also hear some improvement in depth. This is the only interconnect cable I have with a proper wiring that has both signal pairs and GND connected between the plugs.



Comparison.

I know for some the comparison to other amps using demanding headphones will be very important. Unfortunately, I don’t have too many demanding headphones, or too many portable amps for comparison. But I was using ATH-R70x (open back, 99dB sensitivity, 470ohm impedance, 3.5mm SE termination) which is my hardest to drive pair of cans. Also, I used N6ii w/E02 as my source while switching between C9 ($1,999), Romi Audio BX2 ($850), and XI Audio Broadway S ($1,599) amps. With C9 and BX2 I was using stock 4.4mm interconnect to N6ii, while with Broadway S which has RCA inputs, I was using Audioquest RCA to 3.5mm cable and DDHiFi single ended to 4.4mm adapter (the one which uses only L+/R+/GND side) to connect to E02.

All three, C9, BX2, and Broadway S were able to drive R70x without a problem with enough volume headroom. I had all three amps in low gain and approximated the volume % by looking at the volume knob. Under all these conditions and with ATH-R70x volume matched, BX2 was at about 20%, C9 was at about 50%, and Broadways S was at about 75% of volume setting. BX2 has too much power for IEMs and optimized better for demanding headphones, while Broadway S (Single ended) was optimized for IEMs. This puts C9 to be somewhere in the middle, optimized for both IEMs and headphones.



Using R70x and a few other IEMs, I found BX2 to be more transparent, clean, uncolored, and maybe even a little colder while C9 (SS timbre) and Broadway S were being warmer, richer and more analog in tonality and also having a fuller body sound. When I switched C9 to Tube, the sound became even more analog and smoother, pushing farther ahead of Broadway S. Of course, these types of sound changes will depend on your IEMs and headphones, their sound signature and power requirements, and their pair up synergy with these amps. For me personally, it was a clear choice. BX2 has too much power and Broadway S only one “coloring” option. C9 was versatile to use with either IEMs or headphones and it gave me different options of coloring the sound, using either SS or Tubes and Class A or Class AB.

Another thing to keep in mind. Something like Broadway S (I only have single ended version since it is more IEM friendly) is definitely not a portable amp, and also not in a category where you will carry it around. It will be transportable to move from one desk to another without interrupting the playback since you are not plugged into the wall. Romi Audio BX2 is a portable amp, though in comparison to C9 it is only solid state and Class A. And while BX2 is shorter than C9, it also 10mm wider and a little thicker which puts it in-between portable and transportable. For my own personal preference, the width of the stack up is one of the deciding factors between portable and transportable because it makes it easier to grip.



Pair up – IEMs/Headphones.

When I was testing and taking notes of C9 pair up with various IEMs and headphones, I received a few questions from my readers asking about benefits of using C9 w/tubes vs N8 w/tubes. Thus, I thought it will be an interesting pair up comparison. Here, I was using N6ii w/E02 + C9 (Low Gain, Tubes, Class AB) 4.4mm BAL vs N8 (Low Gain, P+, Tubes) 3.5mm SE, volume matched in every example.

Also, the reason why I thought N6ii w/E02 + C9 vs N8 will be good in this pair up comparison because due to a similar pricing some might find adding C9 to N6ii to be a more cost-efficient upgrade than going to N8. The DAC choice is important, but from my personal experience I find the amplifier section of the source to make it or break it!

IEMs.

Here are some of my favorite IEM pair ups with C9.

Oriolus Traillii - Both C9 and N8 have a wide soundstage expansion and holographic imaging with Traillii, but the width spreads more L/R with C9, depth/height the same but stereo separation is wider. C9 tonality is a little warmer, with a fuller body, but it doesn't affect the resolution or retrieval of details. Another thing, while both have excellent macro-dynamics of vertical expansion, I hear better micro-dynamics with C9 when analyzing layering and separation of the sounds. When switching SE of C9, the soundstage is narrower in comparison to BAL, but it is still wider than N8 SE.

EE Legend X - Interesting comparison here. As expected, the soundstage is wider with C9 vs N8, while imaging is similar. Also, I hear a smoother and warmer tonality of mids in pair up with C9. But it wasn't just the tonality, being more analog and fuller body, but also the quantity of mids that came up, making the sound more balanced in comparison to N8 pair up where mids/vocals are pushed a bit back with bass being more forward. With C9 the signature of LX is more W-shaped than L-shaped. Also, in LX pair up with C9 the bass had more analog texture.

64 Audio U18t - In addition to C9 soundstage being wider in comparison to N8, C9 also improves the U18t imaging, making it more 3D holographic, positioning sounds not just wider but also with more 3D depth. Both C9 and N8 pair up well with U18t, give the sound more bass texture and even extra bass quantity, and they both give the mids/vocals more body and help treble with more natural tonality. Actually, C9 was a little bit smoother in this pair up, but to my big surprise, U18t had more clarity and better resolution with C9 than N8, despite being smoother. N8 is also quieter when it comes to hissing, C9 has a little more hissing with U18t, but I personally preferred a pair up with C9 here.

VE Elysium - Ely really does come alive with C9. Both have a similar 3D imaging on a holographic level, but there is something interesting about the soundstage. C9 is definitely wider than N8, but I hear more width in vocals. But the most noticeable difference is in tonality, with C9 mids being warmer and having a fuller body, while still being very detailed and layered. Ely strength is in the reproduction of vocals, and C9 scales up its quality relative to N8, giving vocals more analog vacuum-tube flavor. Also, adding more texture to the bass, especially to sub-bass rumble.



Here are a few IEM surprises where I actually preferred N8 over C9, in most of the cases due to hissing. But if you use iFi iEMatch, hissing goes away, dead quiet!

DUNU Luna - I do hear a wider soundstage when comparing C9 to N8, and the soundstage was even wider when I switched to 3.5mm of C9. I actually preferred using 3.5mm of C9 because 4.4mm had a bit too much power for Luna and hissing level was higher. With 3.5mm of C9 the hissing is lower and when music is playing, it is not even noticeable. When it comes to tonality, C9 does add more body and makes Luna smoothers, but I wasn't 100% sure if I like that because it took away some speed, making sound more laidback. Between C9 and N8, I preferred more transparent and revealing pair up with N8.

VE Erlkonig – this is a more sensitive iem where I do hear some hissing with C9 and N8, a lot more with C9 (BAL). Both have a very similar wide soundstage expansion and close to holographic imaging; I was expecting to hear a bigger difference, but it wasn't too far off. The tonality of C9 is warmer, especially with fuller body and slightly more textured bass, while resolution and retrieval of details is the same. Unlike Traillii, here the vertical dynamic expansion of the sound is very similar as well. The main difference is in tonality with C9 being warmer. Switching to C9 SE only yielded a slightly narrower soundstage expansion, while tonality remained the same, and it was still hissing.

EE Odin - I had higher hopes for this pair up with C9, but it wasn't exactly the best match in comparison to N8. C9 soundstage is wider than N8, even when I tried both 4.4mm and 3.5mm C9 outputs. But I was expecting a warmer and smoother tonality with a fuller body when comparing C9 pair up to N8, but surprisingly found the opposite where N8 pair up was smoother. That was one of the reasons I switched Odin to 3.5mm output of C9, but it didn't help. And on top of that, Odin hissing with C9 was noticeably louder than with N8. I preferred Odin pair up directly from N8.

Campfire Audio Solaris – this one going to be short. If you have high sensitivity IEMs, there is no way around it even if you switch to low gain. The hissing is there and it is noticeable. Of course, you don’t need amplifier for high sensitivity IEMs, but if you are still considering it, I wouldn’t recommend it if you are into instrumental or classical music where a black background is a must. Otherwise, you will get all the benefits of expanded soundstage and more natural body in sound.



Headphones.

The full-size headphones pair up coverage is not as extensive, since I’m mostly use IEMs, but you can get some idea how it pairs up with demanding high impedance (ATH-R70x), planar magnetic (Empyrean), and classic Tesla dynamic driver (T5p 2nd gen) headphones.

Audio Technica ATH-R70x - These are my hardest to drive headphones (470ohm impedance, 99dB sensitivity) so I was looking forward to this comparison. Right away I noticed soundstage being wider with C9, not just subtle difference, but quite noticeable, especially for open back headphones. Next, N8 in low gain wasn't driving R70x properly, and I had to switch to high gain and still raise the volume to 56 while C9 remained at low gain, though volume was at around 50%. Comparing the tonality, you can clearly hear N8 being a little brighter and less colored, while C9 added warmth and body to the mids without affecting its technical performance. As a result, pair up with N8 was more transparent and a little faster, while with C9 R70x sounded fuller, warmer, and slightly more laid back.

Meze Audio Empyrean - The soundstage expansion and imaging have a lot of similarities between C9 and N8, just a little bit wider in C9, especially when focusing on mids/vocals. Tonality had a bigger gap until I changed N8 gain to high, otherwise bass was very soft and mids were lacking clarity in low gain. But even in high gain, N8 doesn't reach the same level of sub-bass rumble as C9 which pushed Empyrean to have a better low end extension, which is noticeable. Still, with either C9 or N8 the Empyrean sounds smoother and more laidback, and C9 has a lot more headroom to drive these planar magnetic headphones more efficiently while N8 has to be pushed harder.

Beyerdynamic T5p 2nd - The soundstage width in this comparison is quite noticeable, stretching T5p2 width more to the right/left, giving the sound more holographic soundstage and imaging. Tonality didn't change as much, both C9 and N8 paired up with T5p2 give you a natural smooth balanced sound with extra velvety bass texture, natural organic mids/vocals, and just enough tremble sparkle to maintain natural clarity and resolution, but I hear improved micro-dynamics and a little more clarity with C9 and wondering if this could be due to improvement in soundstage width and imaging which gives vocals more room to breathe. It's not a night'n'day difference, but I did enjoy T5p2 more with C9.



Pair Up - DAPs.

When I started to share my C9 impressions on Head-fi, quite a few people also pinged me with questions about what is the best source/DAP for pair up with C9. It’s not a simple question because C9 will be connected to LO of your source, so in theory you have to determine which DAC output you like better. Different DAPs will have different DACs, and it will be a matter of a personal preference with quite a few variables in that equation. So instead, I decided took at a number of my sources (N8 was borrowed) and to compare each one directly between headphones output vs connected to C9. For this test I was using Oriolus Traillii, volume matched in every pair up comparison. C9 was set to Low Gain (LG), used with Tubes timbre and Class AB amp. I know these are brief impressions, but it clearly shows how consistent the performance of C9 when it comes to enhancing the sound of every DAP I tried it with.

Let’s start first by looking at Cayin “family” since I’m sure many will be curious about their N8 tubes/solid state DAP comparison or N8 vs equally priced N6ii w/C9 stack up.

Cayin N8 (HG, P+, tube, SE) vs N8 + C9 - more holographic soundstage and imaging, in both width and depth, fuller body with more textured analog tonality, improved dynamics. One thing I was truly surprised here is the change in the tonality because in theory we are talking about going from a single NuTube to a dual NuTube, but the discrete Class A/AB amplification modes of C9 in combination with dual NuTube have a different effect on tonality when compared to N8. Plus, Cayin acknowledged that NuTube circuit in C9 was redesigned.



Cayin N8 (HG, P+, tube, SE) vs N6ii w/E02 + C9 - after going back and forth, I can confirm that to my ears N6ii w/E02 + C9 (tubes, Class AB) is an improvement over N8 (tubes, P+) where I hear a wider soundstage, improvement in micro-dynamics, and a more analog textured tonality. The sound of C9 with a fuller body and warmer mids creates a perception of a more analog textured sound without losing resolution or retrieval of details.



If streaming is important to you, here are a few pair up examples with Android DAPs, where R8 and DX300 are currently the fastest open Android performers and SP2000 SS can be side-loaded with popular streaming apps.

Hiby R8 (HG, BAL, Turbo) vs R8 (BAL LO) + C9 - soundstage width expansion was noticeable, not exactly night'n'day, but you can definitely hear the difference. Also, the tonality change was more subtle but the improvement in retrieval of details and layering and separations of the sounds was the first thing I noticed right away after switching to C9 connected to LO of R8. The sound was cleaner, tighter, more resolving, and with improved dynamics.

iBasso DX300 (HG, BAL) vs DX300 (BAL L0) + C9 - improvement in soundstage width is probably the first thing I noticed, and not just the soundstage but 3D imaging. Tonality change was there, not very drastic, but C9 does add more analog texture to the sound and a little more body. The biggest improvement was in dynamics which improved the layering of the sounds, literally felt like more air between the layers of the sound.

A&K SP2000 SS (BAL) vs SP2k (BAL LO) + C9 - while comparing direct HO output of SP2k vs paired up with C9, I hear the improvement in soundstage width, quite noticeable, and also tonality got more analog with a tube flavor when using C9 with NuTube output. SP2k by itself has a very clean precise sound, C9 adds a nice analog texture touch to it.

If you don’t care about running apps directly from your DAP and OK with Bluetooth/LDAC pair up to your smartphone, P6 Pro, LPGT, and WM1Z are some of the non-Android top choices which can also benefit from C9 stack up.

L&P P6 Pro (HG, BAL) vs P6 Pro (BAL LO) + C9 - in this comparison the change was more subtle. I do hear the improvement in soundstage width when paired up with C9, it is noticeable but not necessary night'n'day change. Also, with C9 one improvement I did notice was bass texture, impact, and articulation improvement. Connected directly to P6 Pro Traillii bass was a little softer while gaining more authority with C9.

Lotoo LPGT (HG, BAL) vs LPGT (BAL LO) + C9 - the improvement here was noticeable. Soundstage width expansion was definitely expected, with C9 the sound is more holographic. The tonality change was more subtle, but the technical performance improved with a noticeably better retrieval of details, improvement in layering and separation of the sounds, and also improved dynamics.

Sony WM1Z (HG, BAL, direct sound) vs WM1Z (BAL HO) + C9 - since WM1Z doesn't have analog LO, I had to use BAL headphone output, so we are talking about double amping here. Adding C9 to BAL HO did widen the soundstage and of course boosted the output power, but also improved the bass impact, giving it more authority with a little mid-bass boost, and adding more analog texture to the mids/vocals. I had all the effects off when comparing to direct WM1Z connection, and the effect of adding C9 reminded me of Vinyl Processor "standard" preset, just a little bit clear and more resolving. But the biggest surprise here came when I switched to Pre-amp, letting WM1Z volume control the output. I heard a similar improvement in soundstage and bass, but in additional to a more analog texture, the sound was also more resolving, cleaner, tighter, and with improved retrieval of details. In general, WM1Z and 1A are underpowered DAPs thus adding amp is no brainer. But I also found C9 to benefit 1Z more than some other DAPs, especially using Pre-Amp input.



Conclusion.

I have a little confession to make: when I received C9 amp, at first, I wasn’t sure how to approach this review. As many are aware, I have a lot more experience with DAPs and IEMs, don’t have desktop or portable tube amps, and don’t use power hungry high impedance low sensitivity headphones. Yet, in the last few weeks while listening to music when working from home at my desk, I found C9 to be so addictive that I couldn’t stop swapping different DAPs to see how C9 enhances their performance with my favorite IEMs.

And then it dawned on me. While not exactly the same as cable rolling, it was a very similar experience of trying to improve the synergy between various DAPs and IEMs, except the variable here was the source. And instead of a subtle refinement, I was able to hear a more noticeable improvement with an expanded soundstage that pushed the sound to a more pronounced stereo separation and 3D imaging, a more natural fuller body detailed tonality colored by vacuum tubes, and improved micro-dynamics.

If you think about it, the two main audio building blocks of any DAP is the DAC and the amplifier section, and manufacturers have to deal with a limited board space which puts a constraint on the design of amp section. That is one of the reasons why audiophiles look into external amps to enhance their source. C9 offers many different options for such enhancement, from a solid state to a vacuum tube, Class A or Class AB, single ended or balanced, serious output power, and even replaceable batteries. With a price tag of $2k C9 does cost more, but also offers a lot more than any other portable amp. And while DAPs come and go, C9 should last you a while to enhance any source you pair it up with.

This is going to be a long review so I will break it into two parts: The first for C9's functionality and general performance (this post), and the second for its specific pairing with my various gears.

I think it will also be useful that I open this review by giving my conclusion of C9. It is a truly TOTL amplifier for IEMs and headphones. It has the ability to bring any DAPs one or two levels up in their performance. This is true not just for mid-tier DAPs, but even for TOTL DAPs like Lotoo PAW Gold and AK SP2000. The improvement is comprehensive. With it, the sound opens up, the veil is lifted, and the performance of both the DAP and the IEM is brought to their full potentials.

In general, I consider the combo of a decent DAP + C9 to be at least at the level of Hugo 2, which I considered as the king in driving IEMs.



Some Background Info of Portable Amps

If you are quite familiar with portable amplifiers, please feel free to skip this section.

So what is a portable amp, and why do I need it? A portable amp is something that can be connected with your DAP (or any source component) to further enhance its performance. In a super general level, you can consider any DAP as doing two jobs simultaneous: (1) it has the DAC portion that helps to decode the music; (2) it has the Amp portion that takes the input from the DAC portion, amplifiers the input, and then delivers it as the output from the DAP.

Most modern DAPs have the line-out function which, if it works as intended, will bypass the Amp portion of the DAP and only outputs the signals from its DAC. With this function, the DAP can be connected with a dedicated amplifier to achieve a performance upgrade. C9 is such a dedicated amplifier. In principle, an additional, dedicated Amp should do a much better job in taking up the Amp job: It has an independent power supply, better components/circuit design, and potentially better functionalities.

General Introduction of C9

I want to start with a simple personal experience in my journey of DAPs. Back in the days, I got my first DAP from Lotoo: LP6K. I really like its functionality and sound signature. However, I find that it could not really drive my LCD-i4 or IER-Z1R very well. So I thought, OK, let me upgrade the DAP to get better performance out of the two IEMs. I then sold the LP6K and got the LPGT. LPGT did have better performance and I was quite happy with it for a while, but I still have the feeling that there is still room for improvement. I then continue my journal of searching, go through a couple of other DAPs, and eventually come to Hugo 2 which I am finally happy with its performance in driving virtually any IEMs I have.

Does this experience sound familiar to some of you? I think a lot of people have had similar experiences. When C9 came out, I in fact don't really need it as I am quite satisfied with Hugo 2. But I keep thinking this: If C9 were available back in the days when I wanted to upgrade LP6K, maybe all I needed was to buy a C9. No more need for DAPs exploring, and I get to keep my favorite Lotoo sound signature. So, I bought the C9, and I am happy to report that it not only does such a job, but it accomplishes it extremely well.


Functionality

C9 is a tube/solid-state dual-mode portable amplifier. Besides these two modes, it has two classes as well: A and AB. Just from this, you can see that C9 gives you a lot of different sound signatures to explore. It takes both 3.5mm and 4.4mm input and outputs in both 3.5mm and 4.4mm - so again very flexible in how you want to connect your DAPs and IEMs/headphones to it.

An additional interesting point is that, unlike many portable amps that only take line-in signals, C9 can also take pre-amp signals. Its pre-amp mode is designed when your DAP does not really have a line-out function. In that case, you can simply use the regular headphone output and connect that with C9. C9 will then serve as a "power amp" that dramatically increases the power of the signals from your DAP. Unlike the regular line-in mode, where C9 takes up most of the job of delivering the sound signature of the output, in pre-mode the signature of the DAP is mostly preserved. This is ideal for DAPs like WM1Z, which has an excellent sound signature but has been known for its relatively weak output (in today's view). Then, the pre mode of C9 allows you to preserve the sound signature of the 1Z, but gives it a lot of power.

When I say C9 has a lot of power, don't worry, it works very well with sensitive IEMs. In fact, C9 is designed with such a goal in mind. In its low gain mode, C9 works well with virtually any IEMs. In its high gain mode, you get huge power that is enough to drive planars like Abyss Diana V2.


Performance

Here I am going to give an overview of C9's sound performance. Its pairing with my specific gears will be covered in the second part of the review (in a later, separate post). My source gears for this review include Cayin N6ii (E02/A02, both in line-out), Lotoo PAW Gold (line-out), and Hugo 2. My IEMs are Fir M5, UM Mest (with Iliad), and 64 U18t (with Socrates).



In its solid-state mode, I think the best term I can use to describe C9's performance is that it helps to reveal the music. With it, the sound is cleaner, the imaging and placing improve dramatically; you hear ALL the details of the music but in a nice and not "all in your face" manner. I think this is what impresses me the most. Different DAPs/sources I currently own could have different weaknesses in their sound. What C9 does (in line-in mode) is that it "reorganizes" the music and produces a well-rounded, comprehensive presentation of the music. I generally feel like the music coming out of C9 is what the music producers want it to be, and it is no longer limited by my DAPs.

In terms of general IEM pairing, it works really well with the three IEMs I own. I am happy to report that C9 does not work like Hugo 2 in giving a dominant sound signature such that different IEMs sound more or less the same (although in a good way). Instead, it helps to preserve the signature of the IEM rather well but pushes them to their full potential.

Meanwhile, I would say C9 does add some coloring to the music. I would say its signature is between LPG (which is extremely neutral IMO) and Hugo 2 (which adds color to the music and in a very pleasing way). In SS mode it gets closer to the neutral end, and with tube mode, it gets closer to the lush/coloring end. I haven't had the time to compare Class A and Class AB. I mostly just go with Class A because it is my favorite, and it sounds fantastic. I did briefly try Class AB and it sounds almost as good, but it seems a bit softer to my ears than Class A.

Detailed Pairing with DAPs and IEM/Headphone

To be continued in a follow-up review post.

Short Conclusion

In my own experience, C9 is the single biggest improvement I have brought to my system. Before getting C9 I have been listening under the assumption that TOTL DAPs should most likely have competent Amps, at least for IEMs. It was after getting C9 that I realized how much these DAPs are limited by their Amp section. I also want to quote the feedback from @KickAssChewGum which I totally agree with.

"I’m in total agreement with this. I couldn’t believe the improvement with my SP2000 plugged into the C9 and absolutely wasn’t expecting it to be anywhere near as drastic as it is. I’d go as far to say that the C9 is actually the one component that I’ve ever bought that has the most significant effect on sound (for the better). I’m massively impressed by what Cayin have achieved here. The C9 has made me a Cayin devotee for life and it’s literally the first Cayin product I’ve ever bought. I cannot recommend the C9 enough!"

To me, if you are quite happy with your current DAP, but want to upgrade your listening experience, C9 is an excellent choice. You get to keep what you enjoy with your existing DAP, such as its functionality and sound signature; meanwhile, C9 helps you to transform it into a world-class listening system. You also benefit from the great versatility of C9 for its various modes and sound signatures - You can always find one that suits your need, and you will never get bored,



Finally, I am really pleased that Cayin builds C9 with the goal that it is built to last. The VP of Cayin said that Cayin wants C9 to last for 5-10 years. In this process, the technology, especially the functionality of DAPs, will likely evolve quite dramatically. Think about what we had 3 years ago for the Andriod DAPs and the DAPs we have today like DX300, R8 that are at the same level in system functionality as flagship smartphones. So, when you are upgrading your DAPs in the future, with C9 you don't have to go from one flagship to another flagship. You can simply focus on getting the one that has the best functionality and suits your daily needs, and be confident with the fact that when paired with C9, it will always bring you a world-class music experience. C9 has really solid built, removable batteries for easy replacement and future upgrades, and TOTL sound performance. If you have the chance in the coming months, I will strongly recommend to reach out to your local dealers and request a demo unit to try it out yourself. I am sure that a lot of you will be pleasantly surprised by how the C9 can help you bring your current favorite DAPs to the next level.

Edit: For further questions and discussions, please join us in C9's discussion thread.