Review Date: 12 January 2022

SPECIFICATIONS

• 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

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Test Equipment

LISTENING EQUIPMENT USED IMPARTED HUGE INFLUENCE TO SOUND IMPRESSIONS & RATING

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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 😀

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 110db 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 neutral, 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.

VERDICT

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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