Cayin C9, TOTL Tube/Solid-State Portable Amplifier

General Information

C9-01 .jpg

Cayin C9: TOTL Portable Headphone Amplifier

Cayin was founded in 1993 and is one of the largest audio tube amplifier development and manufacturing facilities in the world. We have developed over 400 products to date, ranging from CD players to speakers, all of which provide the same high-quality benchmark, but our amplifiers have been particularly well-received within the audio community. That's why when we venture into Personal Audio back in 2013, we started with C5, a portable headphone amplifier, because amplifier is always our purest achievement.

The N8 DAP marked our milestone in Personal Audio and laid down the foundation for a flagship portable headphone amplifier. The 2018 N8 was Cayin’s first cost-no-objective product in Personal Audio, but that does not mean we can ignore the scientific (physic and electronic engineering) constraints, so by the end of the N8 R&D, we pondered: what if we can find a way to relax the physical constraints? What if when we have more space, more battery power, more room for heat dispersion, …., we know we need to apply the law of subtraction and take away some features in order to stay focused. There were several ideas on the table: C8, C8DAC, ….etc, eventually we started off with C8 and today we delivered the C9.

As the model number has implied, C9 is the top model in Cayin product lineup. When we develop N8, we decided to use “8” because that is a lucky number to Chinese and we also visualized that there might be technology advancement to DAP down the road. For C9, we didn’t need to reserve that leeway because we know the analogue engineering inside out, it’s very mature and as far as Cayin’s concern, this is our ultimate.

The C9 will be available by 20 January 2021 and the suggested retail price is US$1999. Price and date might vary because of logistic and tax consideration. Please consult your Cayin dealer for local availability and price.


Highlights of Cayin C9 Portable Headphone Amplifier

1. Choice of Timber: select between Vacuum Tube and Solid State timber on the faceplate. This is no doubt the most attractive, most discussed, and most sought after feature of C9.
  • There are several portable tube headphone amplifier in the market, most of them are low power and with limited portability (microphonic effect from shock and vibration). C9 is a truly portable headphone amplifier, you can put it your backpack or hold it in your hand and walking around while listen to it.
  • C9 is designed around the KORG Nutube. This is a new generation vacuum tube developed by KORG in Japan. It is a Direct Heated Triode (DHT) but KORG replaced the traditional filament by LED technologies. It offers some advantaged that makes it a very good candidate for portable audio applications (flat form factor, low power drain, generated very little heat, …), but it maintain the microphonic problem of DHT vacuum tube, so the Nutube was not widely adopted in portable application.
  • Cayin N8 DAP is the first successful implementation of the Nutube in portable music player. We have developed a custom silicon housing and a spring-loaded suspension system to resolve the vibration, shock and impact, C9 has incurred the technologies from N8 (with modification). On the other hand, Cayin N8 used only one piece of Nutube so you can only listen to the Nutube with 3.5mm single-ended headphone, this is an inevitable limitation of N8 given we need to operate it as a DAP, but C9 has use a pair of Nutube so the Timber selection function is available to both single-end and balanced circuit, making C9 the first fully balanced portable tube headphone amplifier, to the best of our knowledge.
  • We didn’t overlook the important of Solid State option. We designed a discrete audio circuit around two matched pair Toshiba 2SK209 JFET as the alternative to Nutube in the Timber Circuit.

KORG Nutube.jpg



2. State-of-the-Art analogue amplification: C9 is probably the most sophisticated portable headphone amplifier for both earphones and headphones in the market. Cayin firmly believe that when the amplifier excels in control and equipped with appropriate volume management, there is no such thing as over-powered. Even IEMs will perform at a different level when we have ample power. Unfortunately, from what we observed, most, if not all, high-end headphone amplifiers are designed with full size headphone in mind, portable amplifiers are mostly DAC/Amp with emphasis on the digital audio technologies. Given the rapid development of high-end IEMs in recent years, Cayin believes there is a market for ultimate portable headphone amplifier that can bring out the best of these high-end IEMs, especially when they are equipped with demanding dynamic, planar magnetic and/or EST drivers, and yet versatile enough to cover a lot of full-size headphones in portable scenarios.
  • One of the very few fully Balanced portable headphone amplifier in the market
  • Dual Amplification Operation (DAO): allow users to switch between Pure Class A and Class AB
  • In-house developed Amplification circuit with discrete components, not IC or Op-Amp based
  • Selectable High/Low gain that is widely applicable to both input modes (LINE and PRE) and all amplification operation (Class A or Class AB), offer extra 6dB headroom when needed and enhance paring with different earphones and headphones.
  • High-precision and highly linear 130 steps volume control system that composes of a 4-channels ALPS potentiometer with a pair of MUSES72320 low noise, low distortion resistance ladder based stereo electronic volume.
  • High Power portable headphone amplifier (4,100mW to 2,600mW per channel at 16-32 Ohm loading, and same rating for both Class A or Class AB)
  • Special attention to make sure C9 can work with most, if not all, IEMs in the market satisfactory. Design a premium high power amplifier requires engineering and experience, but is attainable in general, make it enjoyable with both IEM and headphones are way more challenging.



3. Dual input mode: on top of regular LINE input mode, C9 can also operate in PRE-amp input mode (or known as pure power amplifier mode), with volume control disabled and all stages operate at full capacity.
• When operate in LINE input mode, which we presume will be the primary input mode of C9, it will receive audio signal from the line level output of DAP, DAC, or from any reliable audio source.
• The PRE-amp input mode is designed to work with variable level inputs (e.g PRE-amp or DAC with variable-level line out).
• Alternatively, if you have a DAP with high quality low distortion phone out but no line out, you can use the phone out as PRE-amp output. Switching between Line input and PRE-amp input is an unique feature, the first of its kind to the best of our knowledge.

4. Versatile input and output options: C9 supports 3.5mm single-ended and 4.4mm balanced for both input and output, the amplifier will also optimize balanced inputs to single-ended headphones, and from single-end input to balanced headphones. The following interconnects are bundled in the C9 package:
  • Single-ended Portable Interconnect CS-35C35 (3.5mm to 3.5mm)
  • Balanced Portable Interconnect CS-44C44 (4.4mm to 4.4mm with GND)



5. Replaceable battery: the removable battery module houses 4 x Sony US18650VTC6 (3000mAh 3.7V) lithium batteries. You can charge the 18650 batteries while the battery module is attached to C9 or after you detached it from the amplifier. The battery module supports standard, PD and QC3.0 battery charging through USB-C connector.
  • Users can acquire and replace the batteries conveniently to extend the battery duration when needed.
  • User can acquire extra set of battery module.
  • In case the original battery are run down after extensive used, user can replace the battery conveniently, making sure the C9 can serve a very long time without worrying the 500 charge cycle of lithium battery.
  • Changing to different make and specification of 18650 battery might introduce small changes to the sound signature, audiophile can enjoy battery rolling as an additional tweak to their system.


C9 Faceplate Temp.jpg

C9 Functional Framework.jpg

C9 Specification.jpg

FAQ and Resources
Charging and Protection Circuit
Burn in Setting
Gain Control, Volume Control and Input Sensitivity
Dual input mode: LINE input vs PRE-amp input

Latest reviews


100+ Head-Fier
Excellent Amp with many "flavor" options
Pros: Tube Amp
Class A and AB
Excellent Treble presentation
Flexibility (Line In/Pre-Out potential)
Swappable battery
Cons: Gets hot
Class A Bass is bloomy for my tastes
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

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.


Build Quality:
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).


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.


Sound Profile:
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 -


500+ Head-Fier
Chasing Perfection
Pros: Great build quality
– Stellar bass control, slam, speed, and texture
– Transparent midrange and treble rendition without any coloration
– Channel separation is pretty much perfect
– Timbre switch (solid state/nuTube) is handy
– On-the-fly switching between class-A/AB
– Quick charge support, decent battery life, replaceable batteries
– Will replace most desktop units in this range for powering IEMs and dynamic driver headphones
Cons: Cayin C9 is rather heavy
– Very faint amp hiss with sensitive IEMs
– Gets warm in class-A mode after more than an hour of operation
– NuTubes don’t sound like classic tubes, tube purists may feel disappointed
– Won’t replace desktop setups if you’re running inefficient planar headphones
– Eye-watering price that gives you a pause

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.


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.



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.


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.


Size comparison vs the iPhone SE

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.


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.



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


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).


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.


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.

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.

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.


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.


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.


Last edited:
Thanks for posting! Could be exactly what I am looking for.
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Great work on this review mate 👌🏻
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Headphoneus Supremus
Cayin C9: One of the Better Portable Tube Solutions for Portable Gear
Pros: Nice sound quality with no lack of treble air or low end grunt
Good Battery Life given the Amp configuration
Lots of Settings!
4.4mm Balanced Option
Nice build and feel
Cons: Gets pretty hot
Big and Heavy for pockets
Pricey ($2000)

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.


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.