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.

IEMs.

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.

Conclusion.

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.