Cayin N6ii Replaceable Audio Motherboard R01

General Information

Cayin N6ii Replaceable Audio Motherboard R01

- R-2R DAC Resistor Ladder
- Discrete R-2R Network
- 768kHz DSP Oversampling
- 32Bit/384kHz, Supports DSD256
- High-powered Fully BAL head-amp
- 3.5mm SE / 4.4m BAL Phone Output


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twister6 Reviews
Headphoneus Supremus
Pros: R-2R discrete resistor DAC design (and at the time of writing, the first R-2R Android DAP), natural analog detailed tonality, breathes new life into N6ii.
Cons: add-on price of the module, lack of Line out.

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

Manufacturer website: Cayin. Available for sale on MusicTeck.


I often say in my reviews that non-Android DAPs have a greater longevity because they are independent of Android OS and don’t rely on trending SoC. With Android DAPs the shelf life is shorter because as time passes by, they can’t keep up with all the latest OS releases and faster processors to support it, and become dated sooner. So, in today’s competitive market where many audiophiles obsessed with upgraditis, a 2-year-old Android DAP doesn’t make the news, even if it has a modular design. Yet, Cayin managed to get N6ii back into the spotlight.


It was a smart move for Cayin to go with N6ii modular design when it was introduced. After the releases of A01 (AKM), T01 (TI/Burr-Brown), and E01/02 (ESS) motherboards, the A02 (AKM Line Out only) card was supposed to be their last module. But they left the door open, just a small crack, when they said “… unless a very innovative and feasible idea comes up down the road…” Nobody expected it, but this idea became a reality when Cayin announced R01 module with an all-discrete resistor R-2R Ladder DAC.

It was unexpected and did breathe a new life into their 2-year-old N6ii DAP, making it the first R-2R Android DAP. And apparently, Cayin was so proud of the design that to commemorate it they also released a limited edition N6ii Ti version with a stock R01 card in a matching Ti finish and a full backward compatibility with previous audio motherboards. Now, after spending almost a month with R01, I would like to share what I found.


Unboxing and Accessories.

The unboxing experience of R01 will be identical to all the previous modules.

The module arrived in a compact black box with a foam cutout to keep R01 secure during the shipment. When you remove the module, keep in mind there is a protective rubber cover over the connector, and you will need to remove it before inserting R01 into N6ii. And just like with E02, I was happy to see that a black protective tape sticker was removed from inner side of the module. I mentioned in my previous module reviews, the sticker made the fit very tight, and functionally this tape sticker wasn’t even necessary. Surprisingly, that sticker was still included in the box by itself.


Furthermore, included were 4 extra screws inside of a small plastic capsule similar to the one included with E01 and E02. Personally, I went through dozens of times with module replacement, and still using original screws without a problem. A premium colorful screwdriver with Torx T5 bit was provided as well. I don’t think everybody has Torx bits, so it is a good idea to include one as part of the accessories, and also a manual with detailed instructions how to remove and replace the module.



As it was already mentioned, in N6ii audio motherboard cards E0x stands for ESS DAC, just like A0x corresponds to AKM DAC and T0x name goes along with PCM DAC from TI. R01 name reference came from R-2R Ladder DAC. In R01 design there are no DAC chips, like popular AKM, ESS, TI/PCM, or CS DACs. Here, the discrete R-2R Ladder DAC is made of discrete matching resistors. Cayin decision was to design 24bit discrete R-2R precision DAC which requires 48 pieces of resistors per channel, a total of 96 resistors for both Left/Right channels. And we are not talking about some generic off the shelf resistor. They all have to be matching and with a high accuracy tolerance of +/-0.01% (corresponding to +/- 1/10,000).


But R-2R Ladder DAC implementation also comes at a cost where there is not going to be enough room on the audio motherboard to implement both headphone and line out outputs. And using PO as pseudo LO is not ideal either since usually R-2R background noise goes up at high volume. Ironically, the previous A02 module was Line Out only, while R01 is headphone output only. To understand better what is “under the hood” of R01 module design, I will refer to a very detailed explanation Andy Kong/Cayin posted during the R01 launch.

The R01 audio motherboard consists of digital and analog sections with R-2R Ladder DAC bridging them. On a digital side of the design you have 4 main functional blocks: 1) Digital Audio Bridge – where you receive audio files in all supported formats from the main N6ii FPGA, 2) Oversampling Interpolation Filter – where you convert the digital data into left and right channel 24bit/768kH serial audio data, 3) Serial to Parallel Shift Register – where you convert serial data to parallel bits that going to control gates of R-2R DAC, and 4) 24bit Discrete R-2R precision DAC where you actually convert that parallel digital data to analog as it goes through resistive ladder of 48 resistors per channel. For a greater accuracy and less jitter, instead of using the master clock from the main board, a local reference clock (24.576MHz) was provided for blocks 1 & 2 above.


When we talk about DAC chips, we often refer to each one having its own sound signature. When it comes to Resistive R-2R Ladder DAC implementation, you are dealing with discrete components and the choice of Resistors will be the one affecting the sound signature. Apparently, Cayin went through months of trial, testing different Resistor values until they settled on R=5.1ohm and 2R=10.2ohm resistors from a brand name manufacturer (Viking), all ultra precision, low tolerance, and low TCR (temperature coefficient resistance) thin film resistors.


As many are probably aware, the final sound is shaped by the amplifier section of the circuit that follows the DAC. In R01, Cayin implemented the same head-amp design as they did in A01 and T01 cards with single ended and fully differential amplifier outputs. And similar to A01 and T01, they used a set of four opamps to increase the output current and to lower the output impedance which translates into a Spec of 4.4mm BAL output with 430mW power and 0.68ohm output impedance, and 3.5mm SE output with 240mW power and 0.45ohm output impedance. Furthermore, I was able to verify 10hrs 50min battery life using 4.4mm BAL output with med gain while playing FLAC files at normal listening volume.


The modular design and the handling of the audio motherboard modules is very straight forward.


Sound Analysis.

Before doing any critical sound analysis, I had R01 w/N6ii on burn-in for about 4-5 days playing various tracks in the loop. Afterwards, for a critical listening I used Oriolus Traillii to analyze the sound using my usual test tracks, such as Agnes Obel “The curse”, Sandro Cavazza “So much better” (Avicii remix), C-Bool “Never go away”, Ed Sheeran “Shape of you”, Alan Walker “Darkside”, Galantis “Hunter”, Iggy Azalea “Black widow”, Indila “Boite en argent”, Counting Crows “Big yellow taxi”, David Elias “Vision of her”, and Michael Jackson “Dirty Diana”.


In my opinion, the best way to understand and to describe the tonality of N6ii modules is by comparison of one to the others. And while it is convenient to have access to two DAPs for a true A/B comparison, I was actually able to do a module hot-swap. Cayin doesn’t recommend swapping modules while powered up, but it works without a problem and the DAP even remembers the last volume setting for that specific module. It took me literally a second or two to swap between modules when doing the comparison. But as a DISCLAIMER, do it at your own risk.

R01 vs E02

E02 has been my favorite N6ii module, so I was very curios how it will compare to a new R01. The first thing you notice is a more analog tonality, with the sound being noticeably smoother. I never found E02 to sound 'digital', but when you compare these two side by side, I find R01 to sound smoother and more natural. This is not the type of smoothness where you lose resolution or retrieval of details, and you shouldn't expect the sound to become warm and colored. The signature and the technical performance are on the same level as E02 with its Class AB amp, but the tonality of R01 is more analog, more natural, and smoother.

A closer listening shows E02 bass to have more impact, hitting stronger, and treble to be crisper, while the decay of notes being faster, making the sound tighter and the background blacker. In contrast, R01 sound is more relaxed, more natural and smoother due to a decay of notes fading into the background instead of being sharply cutoff. R01 bass has more weight, still an impressive impact quantity, but a little less than in E02. And the same goes for treble, R01 is a little smoother in upper frequencies, nothing rolled off, just taking the edge off the crisper treble I hear with E02. The soundstage expansion and imaging are very similar.

Another difference when comparing to E02, R01 background is quieter with sensitive IEMs. And in R01 when comparing 4.4mm to 3.5mm outputs, balanced output has a wider soundstage and a blacker background which is quite noticeable. But when looking for background hissing, while using CFA Solaris ‘20 and switching between E02 and R01, the background "waterfall" hissing is more noticeable with E02. Another thing to keep in mind, while lacking LO in comparison to E01/02, it was more convenient to have both SE and BAL output in R01 card.


In my E02 review I covered comparison with all the previous audio motherboards. To make R01 review fully complete, I decided to include copy’n’paste of that section below.

E02 vs E01 (AB) - E02 soundstage is a touch wider, and while I was impressed with soundstage expansion of single ended E01 output, E02 spreads L/R a little bit further apart. Bass (E02) has a bit more impact and more rumble with a velvety texture, mids have a little more body especially in lower mids while E01 mids sound more transparent and E01 treble is just a little bit smoother, making E02 signature more organic, placing E02 performance between E01 (A) and E01 (AB), though being closer to E01 (AB). But in general, E02 is not too far off from E01. Also, despite a rated difference in output power, regardless of IEMs or headphones, I hear a difference of about 5-6 volume clicks.

E02 vs T01 - T01 soundstage is a little bit wider, perhaps due to a brighter tonality with airier treble. T01 bass is faster and tighter, with shorter decay, mids are brighter, more revealing and micro-detailed while E02 mids are more natural and smoother, and have more body. The treble of T01 is crisper and brighter. The preference here will depend on the signature of IEMs/headphones and how it pairs up with either of the modules.

E02 vs A01 - E02 soundstage is a little wider. Overall tonality is similar, but there are some differences I’m picking up. E02 bass has more rumble and more analog texture. Mids are similarly smooth, but E02 has more organic layered natural texture. I went back and forth many times comparing these, focusing specifically on mids, and that texture and better layering and separation is what makes E02 stand out, especially when it comes to vocals. Also, E02 treble has a little more sparkle and airiness. Overall, E02 sounds like it has more analog texture, better layering, and improved sound dynamics in this comparison.



In every comparison I used Oriolus Traillii, volume matched while listening to the same test tracks between DAPs. Furthermore, I mostly focusing on the difference in sound as I hear it without going too deep into the design and functionality differences.

N6ii w/R01 vs A&K SE180 ESS – In my recent SE180 review I compared their ESS module against N6ii with E02, and found tonality to be very close. Moving up to R01 from E02, the tonality is not too far off either, though I do find R01 to be more analog, more natural, and with a tighter bass punch. But those are all fine-tuning details. What really does stand out and quite noticeable is a wider soundstage of R01 with a more realistic imaging in comparison to SE180/ESS which has more depth and less width relative to R01. Another difference was a blacker background of R01, giving overall sound a better definition. I also find fully open Android OS with access to Google Play in N6ii to be an advantage over A&K limited side-loading of apps.

N6ii w/R01 vs Lotoo LPGT - This was another interesting comparison because I use LPGT quite often in my testing due to its relatively neutral transparent sound quality. Comparing it with R01 demonstrated that R01 analog smoothness is not a result of extra warmth or additional coloring. It is due to a technical performance enhancement rather than changes in tonality. This comparison also shows that, unlike E02 with its slightly elevated bass impact and treble sparkle, R01 is more balanced in tuning and its smooth analog textured sound is still neutral and natural like LPGT. Last, but not least, have to keep in mind that N6ii is Android DAP while LPGT is audio playback only.

N6ii w/R01 vs L&P P6 Pro - If we talk about discrete resistor R-2R ladder DAC, you can't avoid the comparison with P6 Pro which also features R-2R discrete resistors DAC. To my surprise, these had a few interesting differences. They both share the same natural analog tonality, but while R01 has a slightly more laidback presentation of the sound with a little longer decay of notes, P6 Pro sound is tighter, faster, and with a blacker background. Another interesting observation was with vocals, where using Traillii I heard vocals being pushed slightly back with P6 Pro, and brought a little forward with more focus with R01. You do have to keep in mind P6 Pro cost 2x more and audio playback only non-Android player.

N6ii w/R01 vs Hifiman R2R2k (red) - Both have a similar wide soundstage expansion and imaging. The tonality difference is the first thing I noticed, with R01 being smoother, more laidback, while Red being more revealing, still natural but not as smooth, even a bit more digital when you do a close A/B comparison. One difference that really stood out for me was a high level of hissing of many IEMs with Red in comparison to R01 that handle it a lot better. Even with something like Traillii, zero hiss with R01 while it was quite noticeable with Red even in Low gain. I’m not even going to touch functionality comparison since R2R2k is very limited and primitive.


Pair up.

For consistency, all earphones and headphones were tested in Med gain (MG) unless noted differently. Volume level is noted with “V”, and please keep in mind that max volume is at 100.


Oriolus Traillii (BAL, MG, V34) – holographic soundstage expansion with 3D imaging. The sound sig is very balanced with a natural detailed tonality, deep sub-bass rumble, tight articulate mid-bass punch, natural, layered, detailed, revealing vocals, and natural well defined crisp treble. Traillii shines in every pair up, and here with R01 it demonstrated a natural detailed tonality, maybe just with a touch more revealing upper mids shine. No hissing.

Empire Ears Odin (BAL, MG, V31) – holographic 3D soundstage expansion and imaging. Deep and slightly elevated sub-bass with a tight mid-bass punch, above neutral quantity. Bass it tight and articulate, with a great sub-bass extension. Mids are very detailed, layered, more revealing, with a bit thinner lower mids and more focus on upper mids. Treble is also crisp and natural. I was very impressed with extra depth of sub-bass rumble and smoothness of EST treble. With hissing, I can't hear it in either of the gains. Often, I hear some waterfall hissing with Odin and other DAPs, but not here.

Cayin Fantasy (SE, MG, V38) - holographic soundstage expansion with nearly 3D imaging. The sound sig is close to J-shaped where you will find a neutral bass which extends and goes down to sub-bass level and has a fast mid-bass punch, but the quantity is neutrally flat. Lower mids are neutral as well, there is not an ounce of coloring to add to the thickness or warmth of the sound body. Where this pair up shines is in upper mids and treble, being micro-detailed, layered, very revealing, and with treble being crisp and airy. The benefit of R01 here is that upper mids/treble tonality is less sterile and a little more natural. It is analytical, no question about it, but R01 takes the edge off the digital coldness of the sound. No hissing, even with my "The curse" test track.


Vision Ears Elysium (BAL, MG, V43) – soundstage width is above average with a good height and depth, I typically complain about stock cable contributing to narrower soundstage, but here even with a stock cable it was surprisingly wide. Sound sig is balanced, even a bit u-shaped due to deeper bass extension and natural crisp treble energy which puts its detailed organic vocals slightly behind, relative to lows/highs. But vocals still come through as a shining star of this pair up. Also, Ely's treble can get hot, especially at higher volumes, but it was quite natural and non-fatigue here. No hissing.

Empire Ears Legend X (BAL, MG, V36) – wide soundstage with an imaging slightly out of your head. L-shaped sound signature with a hefty bass slam that extends down to an elevated sub-bass, stronger mid-bass punch, north of neutral lower mids, clear natural vocals, and natural clear treble sparkle. Bass is big, bold, heavy, speaker-like. But even with this level of bass, you can still keep a clear focus on mids. No hissing.

CFA Solaris 20 (BAL, MG, V22) – wide soundstage with a matching height/depth and close to holographic imaging. The sound sig is balanced with a little more emphasis on mids/vocals. Bass has a decent extension, goes deep and with a noticeable mid-bass impact, but it is scaled down, definitely above neutral but not as elevated. Mids/vocals are truly exceptional here, being clear, detailed, natural, layered. Treble is clear, crisp, and airy but not as bright as in some other pair ups, sounding more natural here. With hissing, if you are playing instrumental or vocal tracks with minimalistic instrument arrangement, you will hear some waterfall type of hissing. To reduce it, switching to Low gain helps.

R01 paired up great with every IEM I threw at it without any exceptions. But the one that truly stood out for me was EE Odin and how their pair up with R01 enhanced its sub-bass rumble and added a smoother touch to its EST treble. Along with a hiss-free performance, it stood out over a number of other DAPs.


Full Size headphones.

Meze Empyrean (BAL, MG, V52) - I was able to reach the optimal volume output without a need to push it harder. I noticed right away the expanded width/depth of the soundstage where the sound was more out of my head. The overall tuning was balanced, smooth, leaning more toward the warmer side, but still with a lot of clarity in mids/vocals. Bass was softer and more laidback, treble was clear, natural, rather smooth in tonality. Upper mids is where it was shining with more clarity and transparency, bringing vocals more forward.

Audio-Technica ATH-R70x (SE, MG, V65) - This is my most demanding 470ohm open back headphones, and R01 was driving them loud enough and to their full potential with surprisingly good transparency. As expected, the sound is very open and expanded, but with many other sources R70x sounds warmer and smoother. Here, the mids/vocals are more transparent and less colored, bringing more clarity and higher resolution. And as result of mids transparency, the bass has more focus and better articulation. The biggest surprise here was the clarity of mids.

Beyerdynamic T5p 2nd (BAL, MG, V42) - I hear soundstage with a good width and even better depth/height. I have heard T5p2 with a wider soundstage in other pair ups; here the width was a bit shy, but still above the average. The sound is very clean and detailed. Not bright, just very transparent, detailed, and layered in mids. Bass extends deep but the rumble and mid-bass are not as boosted, north of neutral but not too elevated, more polite and less aggressive. Mids/vocals sound natural, transparent, smooth and detailed, and treble is smooth and airy. In this pair up I felt like mids had more focus and better definition in comparison to some other source pair ups with T5p2.

It is true that I don’t have a big collection of full-size headphones, but with the one I tested above I absolutely loved how in every pair up the mids/vocals sounded natural, transparent, and detailed in comparison to many other DAPs. That revealing transparency is what really stood out for me.



One of the main ideas behind modular DAP design is being able to futureproof your investment. So, when new modules become available, you can upgrade the sound of the original audio player instead of buying a new one. But even a modular design has its limits, exactly how it felt after the last Cayin release of A02 Line Out only audio motherboard. The R01 with its R-2R discrete resistor ladder DAC was a big surprise, giving a two-year old N6ii Android DAP a second wind with a new level of natural sound finesse.

This natural smooth sound tonality didn’t compromise resolution or retrieval of details. Instead, it gave N6ii w/R01 a more natural analog tonality, and truly set it apart from previous N6ii modules. Every N6ii module, except for A02, has a unique DAC/amp combo which offers a different signature and tonality. But especially between E02 and R01, it felt like listening to two different DAPs, and I didn’t even care about losing LO because I gained 3.5mm output, something I actually missed in E02.

There is also another plus when it comes to R01. After the AKM factory fire and recent shortage of electronic components following the pandemic year, using a discrete resistor DAC design frees you from being tied up to DAC chips and their procurement. Of course, you still need to get a supply of resistors, but you have more flexibility to choose different values and no longer have to compete with other DAP manufacturers fighting over the same DAC chip. I hope more manufacturers will follow this route.
Very crisp and detailed review as always, now am again intrigued to buy my dream DAP after reading it!:tired_face:
@abheybir : my suggestion, if you already have N6ii and other modules, R01 is a must have to breath in a new life into your DAP. But if you are only after that discrete R-2R dac sound and want a fast Android DAP, Hiby RS6 is just around the corner. From what I understand, it is like R6 2020 with a discrete R-2R resistive dac ladder.
Nice review...Thanks for the comparison to Hifiman R2R specially!


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