Cayin RU6 Discrete R-2R USB-C DAC/Amp


100+ Head-Fier
Cayin Ru6 | Super Short Sound Review | 1:1 With The Vocal Chords
Pros: + Uniquely analogue tonality
+ Visceral & unapologetic in delivery
+ Fast & Unfiltered sounding (NOS mode)
+ Sounds raw and subsequently more "real", especially in the mid and highs
+ Pleasant warmth in bass
+ Quite wide expansive stage, immersive
+ Ameliorates BA timbre to large degree
+ Gets you closer to the vocalists emotion, has that naked touch
Cons: - Not as refined or microdetailed as competitors
- Slightly fuzzy imaging
- Sounds raw, rough, not necessarily unendingly desirable as it gets tiring after a while
Basically it should only be paired with non-warm IEMs or it turns too syrupy, lacking details.
What it does well I appreciate a lot. It has a noticably "unfiltered" or "unprepared" delivery of sound. This makes instruments
more convincing and authentic but less refined.
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I'm curious how well these will pair with the U12t, which is an all-BA iem.
I have found using the Ru6 with older CD flac files such as Deep Purples greatest hits brings out the old analog sound I used to get while listening from my home stereo. With my delta sigma dacs such as the Dethonray Honey the recording sounds flat. I must also say that I use the Ru6 with my IFI griffon and the have either the Cayin C9 or the Aroma A100 TB as the amplifier. With this set ups the older recordings sound great. If I just go from the Dethonray into the Aroma or the Cayin they sound flat and thin.


Reviewer at hxosplus
Resistive and Addictive
Pros: + Extremely musical and analogue sounding
+ Full bodied and visceral presentation
+ Lifelike mids - smooth, non fatiguing treble
+ Great technicalities
+ Holographic soundstage
+ NOS and OS modes
+ 4.4mm and 3.5mm headphone plugs
+ Very powerful can drive full sized headphones
+ Neat and simple operation
+ Hardware buttons
+ Not power hungry
+ Good build quality
+ OLED screen
Cons: - Technicalities not on par with the best delta-sigma rivals
- Could do with more extension and resolution
- A little bulkier than the competition
- More expensive than the competition
- Accessories pack is poor considering the price
- EMI interference can cause hissing issues
The RU6 was kindly provided by Cayin in exchange for my honest and subjective evaluation.
The selling price is $249.99 and you can order it from all authorized dealers across the world.
Full product specifications are available here.



The Cayin RU6 is a 24-bit USB dongle DAC/amp featuring a discreet R-2R ladder network.
The recent chip shortage, led many companies to revert back to the roots, the R-2R era where digital conversion was done with this particular method before the invention of the modern D/S DAC chip.

(The text includes comparison against the FiiO KA3)


Back to the basics

The Cayin RU6 features a self-developed 24bit discrete R-2R resistor ladder circuit that can decode up to 384kHz PCM audio.
The basic idea of the R-2R ladder is a matched pair of resistors, the first is “R” and the other is “2R'' which has twice the value of R.
To achieve 24 bit decoding, RU6 equips 48 units of resistors (23 x R and 25 x 2R), and that’s for one channel.
So for a stereo 24 Bit R-2R decoder, RU6 features 96 units of resistors for life-like audio reproduction.
With the advent of the R-2R circuit, Cayin RU6 establishes itself as master of the fully-discrete resistor DAC topology in portable audio.
Cayin is using only resistors that can deliver extreme precision and remain stable during temperature changes.
0.1% Ultra precision low TCR thin film resistors are used inside the RU6.


Oversampling and NON-Oversampling modes

Cayin offers both Oversampling and Non-oversampling DA modes in RU6. For Oversampling mode, the Digital Audio Bridge will upsample the digital audio data to 384kHz through digital filters.
This will enhance the resolution, reduce noise and improve the anti-aliasing of the digital signal.
The Oversampling DA mode will offer a noticeable improvement on details and frequency extension.
The playback is clean and sharp with a darker background.
On the other hand, NOS DA mode maintains the sampling rate of the original bit-stream and playback will become very musical with a natural and organic presentation.
This deactivates the digital filters and the signal is retained in perfect timing. That is, the phase distortion and jitter remain at a very low level with no artifacts in the output signal.

Analog resistor volume control

Most USB DAC/Amps will rely on the volume control of your mobile phone to control the volume of the headphone output.
Technically this was not a viable solution to Cayin RU6.
Understanding this issue, Cayin developed a fully analogue resistor array volume control circuit that provides 99 steps volume control through 9 segments of resistors and switching relays.
Resistor Array volume control features a very high-quality volume control design, extremely transparent when implemented correctly and it is found in a lot of high-end preamps and integrated amplifiers.
The resistance volume control includes a switching relay that mutes the output for a short moment in order to avoid crackling noises during level adjustment. As a result, however, a small delay in the volume adjustment has to be accepted.
Cayin therefore recommends a music player app for the smart device that supports Bit Perfect USB and thus bypasses the level control of the source device.


Board design

To minimise audio signal interference, Cayin has split the RU6's circuit into two 6-layers PCB, with digital and analogue circuits installed on separate boards.
This safeguards the audio signal integrity and ensures the noise from the reference clock and DSP do not bleed into the amplification circuit. This architecture in turn delivers artifact free audio every single time. This circuit design combined with the R-2R architecture enables the RU6 to support hi-resolution PCM and DSD audio formats with support for 384kHZ PCM and DSD 64/128/256 natively.


Power consumption

Discreet R-2R circuitry is a low power DAC circuit when compared to other highly integrated DAC chipsets.
This architecture minimises power drain from the mobile source allowing you to enjoy music without the need to worry about battery drain.
USB-C connection offers compatibility with a wide range of phones, consumer electronics and computers. The hardware has been designed in an intuitive manner, where the volume buttons double as menu selectors and the OLED screen displays playback information accurately.
The Cayin RU6 also offers two gain settings to enhance performance with various IEMs and headphones.
I measured the power draw with an inexpensive USB power meter and I found it was about 0.12A / 0.55W while playing music with the FiiO FD7.


Build quality and appearance

The RU6 has a rectangular shaped body which is bulkier and heavier than the usual D/S USB DAC/Amps like the EarMen Sparrow.
The net weight is 28g and the dimensions are 65x25.4x13.7mm.
Still for a device featuring an R-2R network and resistor array volume control, it is quite compact and lightweight, not that larger than the FiiO KA3.

The chassis is made from CNC aluminium while the side with the small OLED screen is protected by glossy glass.
The appearance is quite modern and minimalist while finish and build quality are excellent with the only negative being that the glass surface is a fingerprint magnet but if you ask me, I wouldn't care a lot.
The three physical buttons that are located to the one side of the chassis are of good quality and offer tactile feedback.
At the top of the device there are the two headphone outputs and at the bottom lies the USB type C socket.



The Cayin RU6 comes bundled with a short USB-C to USB-C cable and a USB-A adaptor.
The leather case for extra protection and a lightning cable for iOS users are sold separately.


User interface

The RU6 is plug'n play compatible with all USB-OTG devices (iOS and Android), Mac OS, Windows PC through the available driver and it can also be connected to Digital audio players that support USB out.
The DAC itself is power efficient so you don't have to worry about draining the host device battery.
The OLED screen will display sampling rate, volume level, gain H/L and whether you are using NOS or OS mode.
You can use the mode button to enter the menu and configure gain settings, NOS/OS mode and screen timeout.
While adjusting the volume, sometimes you can hear a clicking noise, that is instant and doesn't affect the performance.
Neat and simple it has the advantage of the hardware buttons and the OLED screen but it doesn't offer the same kind of customization as the FiiO KA3 does through the supporting application.

EMI interference

The RU6 is prone to picking EMI interference from a phone that causes background noise which can range from a faint hiss to a louder humming especially when using more sensitive earphones.
The effect is more pronounced when streaming and not as severe when playing music from local files but still there.
You can try using a longer USB cable or other DIY solutions, like wrapping the cable with aluminium foil in order to shield it but in the end I didn't manage to completely get rid of the noise.
This hissing noise is present when cellular reception is active.
In contrast the FiiO KA3 was dead silent with all mobile phones that I have tested.


Power output

I was asked to burn the RU6 for 100 hours minimum before listening and thus I did.
I used various earphones and headphones ranging from budget to more premium to find out that the RU6 not only scales very well but the use of higher quality partners is quite mandatory in order to get the most of it.

The RU6 with its full 4V swing and 213mW/32Ω of power output, is powerful and can drive a wide range of headphones with good grip and plenty of headroom.
This is one of the most powerful USB DAC dongles together with the FiiO KA3 and a few others.
The performance was very satisfying with headphones like the Sennheiser HD660S and the Focal Clear Mg while the gain setting proved very useful for driving more sensitive earphones like the FiiO FA7S.
Sometimes the faintest hissing was still present even with host devices without cellular antenna but it must be related to the host device power supply.
With my laptop was completely silent.
In contrast the KA3 which has a discreet power rectifying circuit remained dead silent under all circumstances.


The RU6 provided a great listening experience with the Sennheiser IE600.

Sound impressions

The sound performance of the Cayin RU6 is stellar with a touch of a pleasant, tube-like, euphonic warmth without lacking in transparency.
With the mode set to NOS, it sounds exceptionally musical with a very natural timbre, smooth texture and the presentation is realistic but still precise and true to the source.
Voices and acoustic instruments are heard organic with natural overtones and plenty of harmonic wealth, a wonderful combination which leads to an engaging and authentic listening experience.
At the same time, technicalities are good and close enough to D/S performance but not in the same ballpark as top D/S performers like the FiiO KA3.

The bass is visceral, weighty but still tight and well controlled, fast, clearly defined and multi-layered.
Attack and decay are very convincing as is the dynamic contrast but then it doesn't have the lighting speed or the boldness and ruthless impact of the KA3.
Nonetheless, with all my music the RU6 was punchy, full sounding with great macro dynamics from electronic music to classical.

The mid range is the star of the show, not because of the lack of linearity but due to some kind of a pleasant effect that seems to be imbued from the R-2R design.
It has a well sculpted texture with great liquidity, voices and solo instruments sound very engaging, fluid, articulated, large and three dimensional.
Timbre is utterly natural and so close to reality that in the end you forget about the technicalities as you are immensely drawn to the music, song after song as the time passes by without noticing.
One of my favorite albums is entitled "Hush", a fuse with Nora Fischer singing baroque arias accompanied by the electric guitar of Marnix Dorrestein.
With the RU6 her amazing voice perfectly blended together with the distorted guitar in the most charming way and I literally forgot how many times I listened to the track named "Cum Dederit".

9200000089683996 (1).jpg

Treble is silky smooth with the impression of being laid back, not too extended but very well behaved without a hint of brightness.
Natural is the word to use again, not only to define the timbre but also for expressing the decay, the notes are born and then fade away with the perfect timing.
High pitched percussion instruments sound full blooded with a convincingly natural decay, not splashy or thin.
In contrast the KA3 is more extended, faster, with increased clarity and more detailed presentation but it sounds somewhat leaner while it can't touch the naturalness and physicality of the RU6.
The tuning is very easy to the ear but it cannot be said that the RU6 is not resolving, missing in clarity and agility or lacking in energy as to sound dull or slow.
Tonality is very cohesive from top to bottom and there is great consistency of note intensity throughout the whole frequency range where the KA3 tends to lose some of its weight while reaching the higher frequencies.
A good example of the even treble performance is in the following album where the solo recorder can become very strident with some USB DAC dongles that I have tested.


R-2R DACs usually have the edge when it comes to soundstage and the RU6 certainly delivers.
The soundstage is not as extended and wide with the same laser sharp positioning of the FiiO KA3 but it has far better holography, a more dimensional shape and it is further convincing in communicating the ambience of the recording venue.
The FiiO KA3 might have the technicalities edge for electronic music and such genres or be better suited for ultimate detail and clarity lovers but the RU6 with its more natural timbre and grander soundstage is the obvious choice for classical and acoustic music.


Except for the timbre and texture qualities of the RU6, the next more notable sound characteristic is the complete absence of the so-called digital glare that is plugging a lot of D/S implementations.
No artifacts heard, no metallic harshness, no edginess to the sound which in contrast gets close enough to the analogue ideal at least as this is possible for such a USB powered device.
The FiiO KA3 is one of the best examples of a well implemented D/S USB dongle with the least possible digital imprint but the RU6 is a step above with a more organic and natural texture.

NOS or OS?

Switching to the OS mode doesn't induce extra digitus but the sound somewhat loses some of its analogue, organic magic.
To be honest, it is quite difficult to tell the two settings apart and it requires attentive listening and good headphones.
With the OS setting you give up some timbre, fullness and staging abilities in order to gain a little extra clarity, better definition between the lines, a leaner, tighter presentation and a touch of treble extension.
As said, differences are not night and day while the overall sound characteristics remain the same.


In the end

Thanks to the Cayin RU6, it is the first time that the user can experience the analogue like sound characteristics of the well designed R-2R technology from a USB powered DAC dongle.
In a market already flooded with delta-sigma USB dongles that sound more or less the same, the RU6 with its natural timbre and organic character is a welcomed addition.
Sound-wise the RU6 is an absolutely stellar performer and more than highly recommended especially if you are already a fan of the R-2R technology and you would like to experience it from a portable device or if you seek to discover the R-2R sound without breaking the bank.
Judging from sound performance alone, the RU6 is a five star rating without the slightest hesitation.
Unfortunately the possible hissing due to EMI interference would not allow for the full rating and is forcing a half star deduction.
But in the end, the RU6 is so good that it is fully enjoyed at home and not from your phone.
Without hesitation is one of the best sounding and most powerful USB DAC dongles available right now.

Test playlist

Copyright - Laskis Petros 2022.
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Sorry no experience with these but I am waiting for the Go bar.
Technicalities not on par with the best delta-sigma rivals - Who is the competition?
Could do with more extension and resolution - Like how?
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The FiiO KA3 that is pictured and mentioned in the review?
How could do with more extension and resolution?
You know, more resolving, as detailed and finer sounding?
More extension, like deeper sub-extension, sharper, better defined and splashing treble?
Thanks for reading.


100+ Head-Fier
Cayin RU6 : Arguably Best Dongle with R2R capabilities in $250 range
Pros: + Superb build quality
+ Small & Portable
+ Discrete R2R
+ Powerful enough to drive most IEMs
+ Analogue tuning
+ Great staging & imaging
+ Most Affordable R2R capable device till now
Cons: - Resolution may not be the best when compared to the other Delta-Sigma dongles
Cayin RU6 : Arguably Best Dongle with R2R capabilities in $250 range


Summary & Objective:

The Cayin RU6 is the first ever dongle to feature R2R in such a portable size. It comes with great build quality and some great sound performances. It has support for balanced output and comes with nifty features like NOS & High Precision Resistor Array Volume Control and is powerful enough for most IEMs.



The Cayin RU6 comes with great build quality and outstanding sound performance within the price bracket. It is the first ever dongle to feature Discrete 24 bit R2R capabilities and have some very nifty new features built-into it.
The Cayin RU6 is priced at $249.99.


Design, Build & Features:

I wouldn't want to make this a very long review by describing each feature but for people who want to know, here are some extracts from the Cayin website.






The Cayin RU6 comes with $249.99 price tag and the specifications are as below:







Items Used for this Review:


IEMs of different ranges:
$200-300: BQEYZ AUTUMN, @DUNU-Topsound Falcon PRO, @CampfireAudio Honeydew
$500-700: Campfire Audio Holocene, TINHIFI P2 Plus
$800 - 1200: @DUNU-Topsound ZEN PRO, @CampfireAudio Dorado 2020
$1500 - 2000: @UniqueMelody MEST MKII
$3000: @Vision Ears EXT

Well these are the ones I have with me presently... and have used for the review.


Source : iPad Pro, iPad Mini 6, iPhone 13 Pro max
Streaming Source: QOBUZ

Tracks Used:
The tracks I have used can be found from the below playlist that I have used and generally use for most reviews...


CAYIN RU6 Sound Impressions in Short:


The Analogue Discrete R2R tonality is something I have grown very fond of. The Cayin Ru6 delivers the R2R performance within a very portable size and the tonality is comparable to any R2R DAP. It has the warmth of any R2R typical tuning and can no way be considered bright.


The Bass sounds just Superb. Bass has details in the sub-bass region and is thick and creamy with enough muscle in the mid-bass to make the instrument attacks sound very natural and realistic. In tracks like : "Anna R. Chie (Remastered) - Konstantin Wecker" and "Dreams (2001 Remaster) – Fleetwood Mac" you can feel the the deep attack of the different instruments with just enough details. The thumps and slams are very enjoyable.


The Midrange is just great in terms of every single element. It is able to produce an good creamy smooth and textured midrange that is soothing to the ears while having enough details in it. The vocals are natural and both male and female vocals come with good amount of details. Instruments sounded natural and I love the analogue tonality and the sound seems very real. In tracks like: "Anchor - Trace Bundy" and "Ruby Tuesday - Franco Battiato" while you will love the overall midrange specially transients of the guitars, violins etc... instruments and the vocals.


The Treble is very natural with enough extension & air as the track commands. It has enough details and despite being very natural it doesn't come with any harsh peaks in the treble region.


The staging and resolution is just great and just the amount the track requires. Nothing artificial here. Tracks like: “ She Don't Know – Melody Gardot” or “Bohemian Rhapsody (live aid) – Queen” sound good & enjoyable. Resolution is amongst the best in the price bracket and can rival many full-sized $700-800 range DAPs easily.


The Cayin RU6 comes with good amplification traits and doesn't depend on the source for volume control. It has it's own Volume Control mechanism and is powerful enough to drive any IEM that I've tried so far.

The analogue R2R tonality makes it ideal pair with just about any IEM. It pairs well with most IEMs that I had tried from the various price ranges and various traits.



I have compared all 4 of the dongles I had in my possession for this review - @iFi audio Go Blue, Qyestyle M12, Luxury precision W2 and the Cayin RU6 dongles. Not because they had many things in common - but mostly because people asked for a dongle shoot-out and so here it is from me.


The Jack of All:

That would be the @iFi audio Go Blu. It comes packed with single Cirrus Logic CS43131 DAC chip and good build and some nifty features including BT and the volume dial.
However, when it comes to sound - it just lacks the iFi signature clean sound and also sounds quite thin when compared to others so far.


The creamy & buttery:

That would be the @Questyle M12 which comes ES9281AC ESS Sabre DAC chip.
While there's a general tendency of ESS Sabre chips to be slightly bright... this one is quite the reference grade with very smooth & creamy music performance specially the midrange & treble.
The bass response is also very good.


The Most Resolving:

That would the the Luxury & Precision W2. Powered by Dual Cirrus Logic CS43131 DAC chips, these are amongst the most resolving and powerful IEMs I've heard so far. Quite powerful and I've seen some reviewers compare them with $700-800 DAPs - while I have no comments regarding that, it is really the most resolving and very powerful with reference grade tuning.


The Musical Bliss:

That would be the Cayin RU6. the worlds ONLY full discrete R2R Dongle DAC/AMP.
While owing to the analog tonality of all R2R tech devices - this may not be the most resolving one but the Oversampling mode somehow takes care of it quite well and the resolution is just great.
While based on the specs mW stats this is slightly less powerful than the W2 - but in real life scenario I found this to be quite powerful and can easily power even power hungry IEMs.


CAYIN RU6 vs Luxury & Precision W2 vs Questyle M12 vs iFi Audio Go Blu:

Build quality:
This is a string trait found amongst all 4 dongles. All of them look very premium and come in great build quality. The W2 & Ru6 being amongst the larger ones while the M12 is the smallest sized.

Features & Amplification: BT features of the Go Blu not taken into account as that would be unfair for the others. All of the dongles come with great features and amongst them the W2 and the RU6 are the most powerful ones. Interestingly, while the RU6 has lower max mW power output than the W2, it seemed more powerful to me in most cases due to it's implementation.

Sound performance: While not going very deep into each category as that will make this review very long - I will comment on the overall sound performance here. The RU6 seemed the more musical to me while the W2 is the most resolving. However, the resolution of the RU6 is undeniably good by all means.

Resolution & Staging: While all dongles have equally good staging performance but the W2 and RU6 were better performing than the others. The Go Blu lacked slightly in terms of resolution to my ears while others did just great.


Conclusion :

The superb performance of the Cayin RU6 makes it an easy recommendation to anyone who is looking for a dongle with R2R capabilities. Just like the W2 - the RU6 can rival performances of many full-sized DAPs below $800 range. Such commendable performance in such a portable form is something many audiophiles had been searching for. I would be happy to recommend this to anyone in a heartbeat.
Nicely and most importantly concisely covered everything. How the RU6 compared with ifi HIPDAC in terms of sound quality ??
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@Rubai I don't have the Hipdac with me and hence wasn't able to compare. However, based on what I may recall from my previous experience with the 1st gen Hipdac... I would say that I prefer the RU6 more due to it's R2R based analogue tonality ... while the Hipdac comes with Burr Brown chip
Excellent review !


500+ Head-Fier
Cayin RU6 - The Analogue Champion
Pros: -
- Analogue neutral crisp timbre
- Mature & polished dynamics
- Reference level technicalities
- Clean background with zero floor noises
- Amazing driving power
- Reasonable battery draw on the host
Cons: -
- Expensive
- Occasionally the volume adjustment may exhibit stutter
- Could use just a little bit more of smoothness
Review Date: 12 January 2022



  • 24-Bit Discrete R-2R Resistor Ladder DAC
  • 1/1000 ultra-high precision TCR25 low temperature coefficient thin film resistors
  • Support up to PCM 384kHz and DSD 64/128/256
  • Low power consumption
  • User selectable NOS/OS DA Mode
  • NOS mode: digital filter-less, low phase distortion, low jitter, no ringing artifact
  • OS mode: increased sampling rate, enhance resolution, reduce noise, improve anti-aliasing
  • 99 steps Multi-segments High Precision Resistor Array Volume Control
  • Hardware Volume +/- button
  • TWO 6-layers PCB, digital and analog circuit on separate boards
  • 3.5mm single-ended phone output delivers 138mW per channel at 32Ω loading
  • 4.4mm balanced phone output delivers 213mW per channel at 32Ω loading
  • Compatible with Android, iOS, iPad OS, macOS, Windows 7/8/8,1/10 and DAP with USB Audio output
  • Type-C USB Audio, Shield USB-C to USB-C cable bundled.
  • High/Low gain control
  • Compact and seamless CNC aluminum chassis with 1” OLED screen at 28g.
  • Optional Leather cases: orange or blue
  • Optional USB-C to lightning cable

Test Equipment:

  • FOSTEX T40RP MK3 (Magnetic Planar, 50 Ohm, 91db Sensitivity)
  • Beyerdynamic DT880 (Dynamic Drivers, 600 Ohm, 96db Sensitivity)
  • Etymotic ER4SR (Single BA, 45 Ohm, 96db Sensitivity)
  • TRN VX Pro (8 BA + 1DD Hybrid, 22 Ohm, 106db Sensitivity)
  • TIN HiFi T3+ (Single DD, 32 Ohm, 105db Sensitivity)
  • Shure KSE1500 (Single Electrostatic 200V, KSA1200 Energizer)
  • VE Asura 3.0 FE (Single DD, 155 Ohm)
  • VE ZEN 2.0 SLQ (Single DD, 320 Ohm)
  • Windows 10, Foobar 2000 (Native USB Drivers)
  • LG V50 ThinQ (UAPP USB Exclusive Mode, Bitperfect)
  • Sony Xperia X Compact (UAPP USB Exclusive Mode, Bitperfect)
Comparative Reference DAC/Amp:
  • iFi ZEN DAC V2 + ZEN CAN Stack (15.1 Vrms)



Cayin RU6 is a very special Dongle. It is Cayin's first ever DAC/Amp in Dongle form factor and most importantly, it is the very first non Delta Sigma Dongle ever. Instead of building RU6 on the common DAC chips widely available out in the market now, Cayin opted for the much more complex R-2R design which was adopted from their highly regarded R01 Module for Cayin N6ii. Suffice to say that this has gotten me so pumped up that after completing #donglemadness 2021 with 100 Dongles, I have opted to conclude the adventure and "retire". Alas my morbid curiosity to try out this new innovation outweighs my reservation. And thus #donglemadness came back to life in 2022 simply because with the purchase of my RU6, the floodgates reopened for me to buy every prominent Dongles available out there that I have yet to test :D

Build, Functions, Usability​

RU6 is one hell of elegant device. For the asking price I expect no less from Cayin. Just like my previous DAPs of N6ii E02 and N3 Pro, black theme with glass faceplate implemented here to cement the signature look of Cayin. The unit offers standard accessories needed to run on the fly with any USB-C devices or PC with USB-A (via included adapter). iOS users may need to buy Lightning to C cable separately.

One most prominent feature that I find very interesting with RU6, it offers two switchable modes named OS (Oversampling) and NOS (NON Oversampling). What this does, OS mode toggles the RU6 to resampling of feeds to 384kHz through digital filters. NOS on the other hand, will not do any resampling and will allow the feed to be processed as it is. For my own extensive use, since I am almost exclusively on UAPP bitperfect or HiBy Music Player USB Exclusive Mode, the NOS option proved to be the better choice. It offers 100% source transparency and allowed me to enjoy my music unaltered. The usage of OS on the other hand, may proved useful if UAPP or HiBy Music Player are not used. For example playing Spotify or YouTube Music which does not have USB Exclusive mode, the OS mode will then override stock Android SRC and that to me is a much better option over native Android resampling.

Another great feature of RU6, the volume adjustment. High Precision Resistor Array Volume Control is implemented and I can attest this being one of the most refined volume steps adjustment that I have ever tested so far with Dongles. I must say that the refinement is on par with what I get from my all time favorite the CEntrance DACport HD. To be fair, Luxury & Precision W2, Lotoo PAW S1 and S2 offers similar type of volume adjusters (since all of them has LED screen), but I find RU6 and DACport HD being even more refined. I must note though, that sometimes RU6 will exhibit very brief stutter when changing volume level especially when used with UAPP and HiBy Music Player, so I would not place this as a Cons against RU6, because it did not behave that way on Windows or other non exclusive Android music players.

The other functions worth mentioning is the Hi and Lo Gain selection. This proved to be very useful as I am using my RU6 with anything from as high as 100db to as low as 91db of sensitivity listening devices with resistances up to 600 Ohm. The most powerful output being the 4.4mm BAL port at High Gain.

Other than that, RU6 thankfully is so very spartan as it does not have any EQ functions. And I am perfectly fine with this as I have never used any EQ for any of my gears since forever. For those wanting to alter or color the sound with EQ, then the W2 would be a better choice.

As for battery consumption, I have measured my RU6 on Sony Xperia X Compact (Android 8, 2700 mAH, UAPP bitperfect mode, Low Gain driving TRN VX Pro) and the results yielded 6 hours of continuous play by the time the battery reached 3% (from 100%). Admittedly nothing too impressive here. But assuredly much better than DACport HD which only manage a measly 3.5 hours. On par with Lotoo PAW S2 driving the same load.

Sound Impressions​

This is the most important part. To me, the biggest appeal of RU6, it was designed with a legacy Rail to Rail Array Resistors audio processing which clearly revealed the intent by Cayin on why they choose it - True Analogue sound. Why bother with Analogue sound anyway? you see there was a time audio were all non digital and during those days there's certain appreciation for sound quality that is as real as possible. With Delta Sigma audio processors, what I am hearing today is sound presentation that is very clean, detailed, resolving and analytical - and I can understand that many love it that way. However, they often ended up being too clean sounding that they lacked musicality and some even lacking realism altogether. Real life isn't that clean. Try spending time listening to actual live music or even studio sessions, they are anything but sterile clean. And this is the essence of Cayin RU6 - it is one of the most analogue sounding Dongle I have ever tested so far. Perhaps from critical standpoint, I find Ovidius B1, Apogee Groove and CEntrance DACport HD closer to being organic sounding, but RU6 is definitely there among these three Dongles that I loved so much.

Timbral signature and tonality of RU6 is definitely natural - devoid of any coloration. It is neither warm nor bright - it sounds correct. Analogue presentation with a hint of organic crispness and smoothness. It is wholesome as it is rich in density, no hint of being digital or lean sounding. This is evident when tested with Etymotic ER4SR and Shure KSE1500, my most trusted reference listening devices that will reveal the nature of the source truthfully. ER4SR being Diffused Field Neutral, exhibited the flatness of RU6 sound, which indicated that there's no manipulation of sound frequencies beyond what is normal, no attempt by RU6 to spice things up unnaturally. KSE1500 on the other hand, reveals the natural organic side of RU6. That airy and life like presentation that literally place the listener INTO the music.

Despite being Analogue, RU6 exhibited exceeding competency with technicalities. Tested with my listening gears, what I am hearing is super transparent resolution throughout the dynamic range. Being Analogue sounding does not mean it has to be fuzzy. Details articulation is crisp and convincing, so is the resolution of imaging. The more resolving the pairing partner the better it is. In fact when paired with my ER4SR and Shure KSE1500 I am hearing every micro details that are available in the recordings.

On the other hand, the staging is amazingly spacious as it is wide. It is undoubtedly up there among the very best. For example with my TRN VX Pro which is already natively wide sounding, I am hearing effortless headroom of soundstage that can make me forget I am listening to an IEM. The same can be said for the rest of my gears and even the normally "narrow-ish" Fostex T40RP MK3 sounded sensibly spacious.

However if I am going to be nitpicking, I would say that I would have preferred RU6 to exhibit just a tiny bit more of smoothness. Don't get me wrong, it is already admirably smooth, but comparing it against Lotoo PAW S2, Ovidius B1, Apogee Groove and CEntrance DACport HD, I can hear that RU6 favors crispness slightly more over smoothness. The good thing is, this crispiness approach is still very polished and mature if I am to compare it against the likes of Hidizs S9 Pro, E1DA 9038SG3, TempoTec Sonata E44 etc. - of which these dongles focuses primarily on "modern sound" reproduction. This is not a matter of right or wrong, it's a matter of preferences and I can understand some listener prefer it that way. Audio is still a very subjective passion after all.

As for the presentation of the three major sound frequencies, Mids, Treble and Bass. I would say that being natural RU6 does not color the sound spectrum. A great source should always strive to be transparent and natural. What this means, when I use a specific listening device I expect it to sound as it is. With sound extensions, resolution, textures and details presented in the most truthful way. That being said, I am assuredly happy with the quality of RU6 dynamic range handling. Treble sounded realistic as it is naturally vibrant, Mids as rich as the listening device capable of emitting, Bass having visceral density which is real and engaging. Details and textures present as how they should be.

Driving Power, Gain Control and BAL-SE Differences​

So how does RU6 performs on driving power delivery? To find out I have conducted exhaustive tests with two of my most difficult to drive Headphones. And RU6 does not disappoint. This is where I use my desktop stack of iFi ZEN DAC V2 + ZEN Can (15.1 Vrms) to ascertain how close RU6 able to drive those two monsters. With the ZEN stacks providing 100% experience, this is how RU6 compares: (done on 4.4mm BAL, NOS, High Gain)
  • Fostex T40RP MK3: 90% (Vol 75/100)
  • Beyerdynamic DT880: 80% (Vol 85/100)
The percentage being indication of how close RU6 to that iFi ZEN Stack. Of which the criteria for comparison as follows:
  • Listening loudness (proper level)
  • Dynamic transients and density
  • Headroom spacing and staging
  • Imaging strength
  • Details articulation
The percentage scored by RU6 is truly mind blowing. Comparing this against Luxury & Precision W2, that W2 only managed to score 70% (with Fostex T40RP MK3) at the very best. Clearly RU6 is a much better device for hard to drive partners.

On the other side of the spectrum, RU6 is as amazingly competent driving super sensitive stuffs like multi drivers hybrid IEMs. My TRN VX Pro, having 9 drivers per side and with super sensitivity, does not exhibit any unsavory floor noises nor does it sounded edgy or shouty.

BAL and SE Comparisons:

Etymotic ER4SR (Low Gain)
- SE 3.5mm - Vol 58/100
- BAL 4.4mm - Vol 50/100

TRN VX Pro (Low Gain)
- SE - Vol 35/100
- BAL - Vol 30/100

Marginally crisper dynamics density on BAL, perhaps by 5% of which the SE is no less impressive, in place of pronounced crispiness, less bite with more smoothing. Otherwise from quality perspective I found both to be quite satisfying, there are times I want to have solid crispness and solid imaging and the 4.4mm BAL will do the trick, there are times I enjoy articulated smoothness, switch to 3.5mm, Easy-peasy. In comparison, Luxury & Precision W2 is a disaster with the 3.5mm SE, where everything sounded subdued and outright uninspiring. W2 defacto SQ only to be had from the 4.4mm BAL - and even so, W2 trying too hard on being neutral and clean sounding making it less than realistic (Hi-Fi indeed but lacking soul), of which RU6 has that analogue timbral hint which keeps thing believable.

What I can conclude from this test, RU6 SE will be excellent for sensitive IEMs and the 4.4mm perfect for something a bit more stubborn like my ER4SR.


There's not much I can add to what has already been said. I love this Cayin RU6. Everything that it is, RU6 epitomize near perfect Analogue sound in a very compact form factor. But yes, that's the appeal of RU6, for those seeking the balance between musicality and technical competencies. Not an easy balance to attain. But RU6 did it. However I reckon that being Analogue it would probably mean RU6 will likely score terribly with measurements. So for those prioritizing measurements, RU6 may not be suitable unit.

In the end, finding myself using RU6 regularly alongside my all time favorite DACport HD proved to me that RU6 clicks to my heart. I spent no less than 6 hours daily listening to music. RU6 has found its way to the top segment of #donglemadness.


⭐⭐⭐⭐⭐ ($250)​

Best Pairing: Anything up to 600 Ohm

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Great review. I’m really interested to hear an R2R dongle.
This is starting to sound like a must have device. Nice review 👍
Expensive? No really


1000+ Head-Fier
Portable R-2R DAC/Amp
Pros: R-2R
3.5 & 4.4mm
Flexbility of a DAC/Amp dongle
Stunning level of detail and musicality
A Return on Investment (ROI) difficult to beat
Cons: Can be sensitive to EMIs when streaming but nothing major

Short of raw power and holding your music on a dedicated device, the gap in-between DAPs and DAC/Amp dongles has never been so small since the introduction of Lotoo's PAW S1/2, Luxury & Precision's W1/2 and, more recently, Cayin's RU6.

The RU6 exhibits a level of detail and musicality which is absolutely stunning. I personally prefer it in NOS as I find the OS mode to sound more like a delta-sigma DAC but that's just me — there's no wrong choices here.

I bought and received Cayin's RU6 shortly after I got the FiiO M11 Plus LTD. Compared to the M11 Plus LTD, the RU6 set in NOS breathes a bit more, has a bigger soundstage and is overall more organic and effortless.

You'll have a small interruption/pop every 10 volume steps but it isn't much of an annoyance and is normal. One can hear EMIs, especially while streaming, but it depends on the wireless equipment around you.

With sensitive IEMs such as the Campfire Audio Solaris 2020, background noise wasn't an issue for me but I'm not the pickiest about this.

Power draw is similar than via L&P's W2 which means there's consequent drain on the battery of an iPhone XR which will impact you if you genuinely need to use your phone during the day.

Unless one specifically seeks a DAP, there's hardly anything at fault here. Cayin's RU6 is a safe bet for a high-end DAC/Amp dongle with all the flexibility DAC/Amp dongles bring, an excellent foray into R-2R technology as well as into genuinely portable Hi-Fi — without breaking the bank.

IEMs: 64 Audio U6t (MX and M15 module), stock cable, medium silicone tips | 7Hz Timeless, KBEAR 4.4 8 Core Single Crystal Copper UPOCC cable, Final E tips | Campfire Audio Solaris 2020, stock cable, medium silicone tips

Headphones: Grado RS2e with G-Cush pads
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100+ Head-Fier
Cayin RU-6 - the Portable Bliss to Enjoy an R2R Replay!
Pros: - Solid and elegant build
- Combines natural replay (especially vocals) and very good resolution
- Wide soundstage (especially depth)
- Good imaging and instrument separation
- NOS and OS like two different sound signatures
Cons: - Might be prone to scratching
- Delay when volume increase (especially when not warm)
In the portable music world, Cayin is well known brand that offers product range from the budget N3 Pro up to the flagship N8 with the N6ii sitting in the middle. Now Cayin offered portable R2R dac/amp at affordable price that, according to me, will win many fans. For me it is a bit a game-changer since the price you pay for getting into the R2R replay is peanuts.

Cayin took a bold step and built the RU6 with thin-film resistors with 0.1% precision and a 25ppm temperature coefficient and brought the price tag inline with some leading MQA dongles thus setting a challenge to other premium brands. And according to me it achieved building a very solid product and R2R replay.

The RU6 offers two gain levels and 3.5mm single-ended and 4.4mm 'balanced' outputs (the 4.4 is not a real balanced, it has 4.4 balanced power). The RU6 also offers oversampling as an option that increases the bit-rate of the input sample to 384kHz - it decreases noise and increases detail level; according to me, both NOS and OS have very solid replays.


One of the achievements that surprised me most is that RU-6 drives successfully not only demanding iems but also demanding headphones - it drivers perfectly the Z1R iem but also the Z7M2 headphones, it also drives very well the P1 but also even the T60rp (for the headphones I used the 4.4 output). Meanwhile, I do not hear any hiss even with sensitive iems like Thieaudio Voyager 3 or Andromeda.

Technicalities, Replay and Timber
The RU-6 has a very natural tonality (especially for vocals) with good detail retrieval - I find it very natural R2R sounding and do not miss resolution:
- Bass is tight, sub-bass goes deep, there is good detail and separation between sub-bass and bass.
- Mids and vocals are naturally warm, naturalistic and have very good details. They are a little bit forward but in a very good way that doesn't overpower the bass and treble. These are mids that give you the entry level to R2R signature - do not expect Ares II performance but the level produced is far different and higher in naturalism than leading MQA dongles.
- Treble is done perfectly well for me, no roll-off, good resolution and airiness, details are not attacking your years but are well articulated. They fit the whole signature very well and play good role for the sound staging.

The sound stage is wide, especially in depth; the layering is impressive; the separation between instruments is solid and I even find that RU-6 has 3D presentation. Attack and decay on/of tones is fully Ok.

I cannot give description how the RU-6 matches the 100s of iems from my collection but I will do short descriptions with some favorite of mine iems from the last 15 years:
- Sennheiser IE80 - a great pair, RU-6 opens the big sound stage of the IE80 more and brings forward the vocals;
- Sony XBA-A2 - a great pair, RU-6 controls the XBA-A2's bass very well, increases sound staging and vocals enjoyment;
- Sennheiser IE800 - RU-6 makes the vocals come forward and makes the highs more natural and airy;
- Blon-03 - RU-6 enhances the natural replay of the iem and shows that it deserves a better iem :)wink:
- Tin T2 - a very good pair, RU-6 makes the T2 even more unjoyful and shows the value of the T2;
- 7hz Timeless - OMG this combo is as impressive as the that with the Drop JVC HA-FDX1;
- Thieaudio Voyager 3 - O-o-o-o musicality bliss, mid-price perfection, endless enjoyment;
- Moondrop B2 Dusk - finally the sometimes dull Dusk gets some emotion and bigger sound stage without loosing technicalities; the pair shows the beauty of Harman tuning;
- My two top pairs - IER-Z1R and UM Mest - so perfect: well controlled bass, improved vocals , enlarged sound stage and 3D.

I will not fall in so many details on headphones since I think the point is to explain how RU-6 enhances different replays but I will outline that RU-6 pairs well with Sony MDR-7510, CAL! SE, HB560s, Sundara, Focal Listen Pro, Focal Elegia, T60rp, Z7M2, HD800s. And I really enjoyed it with the CAL! SE, the Z7M2, the Austrian Audio Xi-55 and Denon 5200 and the Sundara.

The RU-6 also pairs very well with the Burson Soloist 3X and the TEAC HA-501 enhancing the natural replay of the first and the musicality of the second and paired with these two gives me same but also a bit different enjoyment vs the Mytek Liberty DAC.

I will cover only dongles that I know very well and are good benchmarks and will make it short but you will get the point:
- vs HiBy FC3 - the RU-6 is far more naturalistic and smooth and has far better staging and layering;
- vs THX Onyx - well think that the Onyx has blacker background but in A-B test sometimes it sounds very analytical, close to clinical, and cannot compete in naturalism and sound stage wideness; I would always choose the RU-6 vs the Onyx;
- vs Hidizs DH80s - the DH80s is having good musicality but favors analytics vs naturalism of RU-6; these two are really a good pair if you like musicality, power and want a good value performance.
Also what is worth noticing is that streaming MQAs from Tidal via the RU-6 works highly satisfactory and unjoyfully for me.

I think Cayin did a great product - RU-6 is the 2021 dongle for me, a dongle that will make premium brands sweat. RU-6 value is its naturalism of replay and presenting the flavor of R2R w/o dropping technicalities. NOS and OS are giving different replay and the power is enough to have enjoyment with any iem and most of the headphones up to 300 ohms.
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Hello, sorry for my ignorance (I'm kind of new to the hobby) I own MEST MKI coupled with a FiiO BTR5 - Does the Cayin RU6 offer bluetooth capabilities? Or is it exclusively an inline DAC/AMP.

And how is the quality of the overall system compared with the FiiO BTR5?

Hello, sorry for my ignorance (I'm kind of new to the hobby) I own MEST MKI coupled with a FiiO BTR5 - Does the Cayin RU6 offer bluetooth capabilities? Or is it exclusively an inline DAC/AMP.

And how is the quality of the overall system compared with the FiiO BTR5?

What options are there better than the FiiO BTR5 - I am looking for a small form factor with bluetooth capabilities - I've heard great stuff about the LP W2. Any recommendations?

Hi, I also have the UM Mest mk1, so you get my first hand (ear) impressions. The RU6 is only inline dac/amp and fits extremely well the UM Mest mk1. And: 1/ no BT is not a deal breaker - how would you listen to music with the UM Mest and use BT, BT is crippling your music; 2/ the BTR5 is a good dac/amp but it is quite below the level of the UM Mest and the RU6. I was so satisfied by the RU6 that I immediately started choosing a big R2R dac and got the Ares II. I gave to friends to try the RU6, friends that use tubes and R2Rs and Stax-es and they were not believing to their ears. Its a gem! The only regret for me is that RU6 is a bit power hungry, like 1 hour with it from my Note 10+ is equal to -10%. So use an old phone like a player for your library, install USB Audio Pro Player app (small payment) to get a bit perfect sound out (a way around the Android/iOS modifying the music), attach the RU6 and you are well done. Can't speak about LP W2 since do not have it. But is it R2R?!