iR2Resistible!

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.

Manufacturer website: Cayin.  Available for sale on MusicTeck.

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Intro.

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.

Design.

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.

Page 2 – Sound analysis, Comparison.
Page 3 – Pair up, and Conclusion.