xDuoo XD-05 Plus Portable DAC / Headamp Review and Measurements

Discussion in 'Headphone Amplifiers and Combo (DAC/Amp) Units' started by purr1n, Jul 29, 2020.

  1. purr1n

    purr1n Finding his inner redneck

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    A few weeks ago @CEE TEE asked me if I was interested from anything in the Apos Audio catalog. A tube amp? Hmm, maybe not, well maybe that DarkVoice 336SE? Pass, I'm in SoCal which is swimming with DNA, EC, and ECP headamps, not to mention @Zampotech's stuff is just around the corner if I wanted to go budget. Topping A90? Sigh, another zero point zero zero zero zero type design. Uses the BB TPA chip. Hmm, at least it will sound different from the compressed square of the 789, THX, AHB2, 389, HP4 (thank you @dubharmonic for the visual analogy), but not sure what a slightly less expensive Sennheiser HDVA600 with lower output Z will do for me. Well at least it does offer under x1 gain for IEMs. Bah, pass, I'd rather deal with channel imbalance than an amp that imparts its sound so strongly that there's do difference between an iPhone or Wavedream as the source.

    So I got to thinking: Something that works with IEMs. That's what I need. I had a conversation with a member a while back regarding an small amp that would work well with hybrid DD/BA IEMs, namely the Solaris (OG or 2020). I've always ran CFA IEMs from the Sony ZX2 ever since I've picked it up. The reason is that the ZX2's organic sound, it's organic lows, mids, and highs, meshed really well with the OG Andromeda. I added the OG Solaris to the mix and it worked well enough. However, it wasn't as perfect as I wanted to be. While the organic highs of the Sony ZX2 player does wonders with the CFA BA drivers, the DD drivers, with their physicality, slower decay, and softer attacks, didn't gel so with with the ZX2. It wasn't bad, but it could be better. Similar issue with the Drop JVC FDX1. It's upper midrange emphasis is tamed by the ZX2, but it's bass really needed some help. So ahead I forged on the Apos website.

    IMG_20200729_182307.jpg

    Wait, what's this xDuoo boopy doop thingy? Hmm, the Force or Magic Eight Ball is telling me something here. "Hey, @CEE TEE, can you get me the iDuo duodenum X15 ZYX +++ mega version edition doodad?"

    "Sure thing" @CEE TEE replied.

    Well it turned out my hunch was right.

    The subjective portion of this review will largely be based on my use with the Campfire Audio Solaris 2020. I am also assuming that the CFA Ara will work well. It's suddenly occurred to me that more reviews should emphasize synergies with gear. Heck, Craig at Eddie Current has always said "I wish these assholes would stop complaining and get the headphone that works best with the amp or the amp that works best with the headphone". Right, headphone and headamp must be thought as one.

    Can someone advise the manufacturers to come up with a better name than xDuoo? It sounds like a dog ate something and left it on my front yard. Also XD-05 Plus is dumb. Dozens of people already have it confused with the non-Plus version. Also XD-05 sounds like something Elon Musk will name his next child. I suggest renaming the brand to Wolf. And this gimzo Warrior. Thus the product can be referred to by Americans as the Wolf Warrior. Or maybe Abbott and Cornelius. The "AC Five" sounds quite swell.

    Anyway, the xDuoo XD-05 Plus is Chi-Fi at its best. Extremely affordable, plain and unassuming (like the great Chinese leader Deng XiaoPing who laid the foundation for a greater society so millions of Chinese would no longer to have to eat tree bark soup), damn good sounding based on tried and true design, and opamp rollable (of course!). Do you guys remember the much heralded Leckerton UHA-6Smk2, well this is the next coming of it, except the DAC doesn't suck like on the Leckerton and it works straight away without a hitch with my Pixel 2 XL phone via USB C. There are a few niggles, but none of them were showstoppers, at least not to me.
     
    Last edited: Jul 29, 2020
  2. purr1n

    purr1n Finding his inner redneck

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    This is the back of the unit. The digital in on the right is a combination TOSLINK optical and electrical SPDIF. There is a USB C input for digital. It's my understanding that the Plus version has the USB C stuff and with some rearranged buttons on the front panel. Another USB C port is available for change. Finally, these is an analog in port. So far, all of my use has been with the USB digital input from my Android Pixel 2 XL phone running Qobuz. Since I've become a Qubuz subscriber, I've been using my ZX2 less and less. It's all about the music and exploration of content. Qobuz makes it easier. xDuoo provides a short USB C to USB C adapter, Velcro tape to affix my phone (or my iRiver, now Astell and Kern, H340). I think iPhone users are SOL. Additionally, extra small screws and the appropriate Torx screwdriver is provided for weirdos who like to roll opamps like myself.

    IMG_20200729_182322.jpg

    The front panel (see photo in above post) has a clear display that tells me what I need to know. There are three switches on the front panel. A impedance boost, a bass boost, and gain, of which there are low, medium, and high. I preferred the sound of medium gain with the volume of my phone turned down. There's probably some digital attenuation going on in the Android OS, but honestly, I'm way past worrying about the bits being perfect*. All this neurosis just gets in the way of enjoying music.

    On the side are three toggle buttons. One is for input selection. The next is for switching the filters (there are four, but there appears to be a bug when using the USB input where filters 1 and 3, 2 and 4, are the same. The last button is for SRC, which does not appear to work with USB input.

    IMG_20200729_194504.jpg

    *The Android Pixel 2 XL also upsamples 44.1 output from Qobuz to 48kHz. Oh, well.
     
    Last edited: Jul 29, 2020
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  3. purr1n

    purr1n Finding his inner redneck

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    IMG_20200729_195213.jpg

    XMOS and AKM4493. Yes, it's an AKM Velvet Sound DAC. But it doesn't sound Velvet! So far, only Schiit and xDuoo have discovered the secrets behind the AKM Velvet DACs so they don't so sound Velvet. Topping doesn't seem quite to be there yet. For those who do not understand, the AKM Velvet Sound has been much maligned, and for good reason IMO, although some people do like the sound. In short, the the mids are recessed, the attacks are soft, the top octave over-emphasized, and the mid-bass warm and mushy: https://www.superbestaudiofriends.org/index.php?threads/akms-velvet-sound.2356/

    While I do not intend to use the XD-05 plus as DAC, it does have some qualities that I find superior to the Modius. The tonal response seems flatter without phat upper bass (Modius SE) or emphasis in lower bass (Modius BAL) and the bass is less one-note with more texture. I don't think it resolves any where close or stages as deep as the Modius though, but really we are talking apples and oranges here.
     
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  4. purr1n

    purr1n Finding his inner redneck

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    The design of the amplifier section appears to be two-stage. Voltage gain with opamps and an output buffer. I do not know if the these opamps are also part of the analog LPF after the DAC. I'm too lazy (and blind - gosh I wish I had my vision when I was my son's age) to trace the board and I do not want to do sloppy work like Amir on Audio Science Review who thinking he knows everything confuses opamps used for DC servos for other purposes, especially when there's an opportunity to rag on Schiit.

    The output buffers are the classic BB BUF634. It's not the bestest in the world, but I can see now see why the XD-05 works so well with the CFA IEMs. The BUF634 measures great, but like everything, does have a sound. BB makes a newer version higher bandwidth "A" version of it which is supposed to be pretty good, but I have not played with it or heard designs based on it, and it may not have the synergies as the OG BUF634 with the IEMs that I have been using.

    IMG_20200723_172229.jpg

    As an aside, I urge any of you to build a PIMETA: https://tangentsoft.net/audio/pimeta/

    Tangent was the OG nwavguy of chip designs. He just wasn't an ass, a measurement fascist, like nwavguy. Nwavguy only made waves because he was an ass and played up the objective thing ragging on people who could afford to buy $10k audiophile gear as dumb if such gear didn't measure with zero point zero zero zero zero.

    The PIMETA uses a BUF634 as the output buffer and opamps for gain. There's no need for a ground channel. A two channel design will suffice, but definitely play with the active ground channel if you have time. This breadboard is all you need to get started: https://www.amazon.com/1660-Point-Solderless-Breadboard-Prototyping-Classroom/dp/B00B8862FA. It's basically Lego of electronics. You will learn so so so much, understand how feedback affect the sound, and realize how so many of these pure measurbators talk out of their asses! To encourage true understanding of audio science and the hands-on application of it (engineering), I will pay the first person who was never DIY'd before $200 to post a YouTube video of their first successful PIMETA build.

    Tip: Get extra caps, just in case you accidentally install them backwards and they start steaming right before they explode! Also get cheap PortaPros to test, in case you have a brain fart and gave the drivers 18V DC.
     
    Last edited: Jul 29, 2020
  5. purr1n

    purr1n Finding his inner redneck

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    Now this was a weird and positive twist that I did not expect. I had heard that the opamps were rollable on the XD-05 Plus, but what I did not know was the the XD-05 Plus supported both dual and single channel opamps! Woohoo. See the unique arrangement below. The sockets are high quality DIP, not the cheap leaf spring loaded type. Surface mount opamps will need an adapter. Be sure that the pins of the adapter are of of the skinny type so that they will fit into the sockets. The thicker pins will not fit into these types of sockets.

    IMG_20200718_233433.jpg

    The included opamp is a TI OPA1612. I did my initial listening with this opamp for a few days and its quite good. The highs of the Solaris 2020 weren't so "BA" from the XD-05 Plus. The unnatural timbre was addressed just as well as with the Sony ZX2, but the XD-05 PLus was able to do this with less of that organic, almost tubey coloration of the ZX2. As for the bass, wow. That is were the biggest difference lie. The XD-05 was impactful, so much more controlled, more articulate, faster. If the overall presentation of the ZX2 was maybe a bit too rounded, the presentation of the ZD-05 with the OPA1612 was perhaps a bit too straight, to the point where I feel there might be something missing. Zippy, fast, clear, clean, but too simplified. Think of the OPA1612 like a Drop 789 amp, but with balls, slam, less edge, and richer timbre.
     
  6. purr1n

    purr1n Finding his inner redneck

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    I then moved on to the AD744 x2, which is the single opamp version of the AD823. This is a brighter presentation that is zippy clean lean and energetic. It was too much. The CFA IEMs tend to be lively and energetic because of their sensitivity. The AD744 was a bit too much for the Solaris 2020. To make a driving analogy: too much oversteer, the rear anti-roll bar is too stuff, and can't get the power down. However for IEMs that are bassy and bit sluggish (thinking Shure SE846 or MEE Pinnacle P1 (triple-flange tip with deep insertion), the AD744x2 or AD823 would be a good choice.

    So what opamps did I eventually settle on for the CFA Solaris 2020? The overpriced audiophile approved OPA627. See below for how two singles plug into the socket arrangement. F, I love the xDuoo engineers. How do you think of this stuff? The most ingenious things are simple.

    IMG_20200729_211526.jpg

    I really hate saying that I preferred the OPA627. These suckers are $29 a pop at Mouser and we need two of them. It doesn't make much sense for a $250 DAC/amp. And even then, I don't necessarily like the sound of the OPA627 in most circuits. But here, they just worked. The OPA627 follows the characteristic sound of many BB opamps of that era, mellow, and in the case of OPA627 dark. Those of you who know me that I'm good with a darker presentation. The OPA627's presentation isn't quite as vivid as the the stock OPA1612, but it doesn't lose much. The heft in the lows is still there, it's not over-bloated at all (always a concern with IEM DD bass), maybe the articulation is a nick behind, but oh, the OPA627 brings so much more to the table. The presentation is more rounded with microdynamics and microdetail more fully fleshed out. I don't get that sense of simplification anymore. At times I thought it may have been to dark, but after switching back to the stock OPA1612, I was like F this shit, OPA627 all the way. I don't miss anything from the OPA1612. There's a reason why the OPA627 has a reputation and is priced the way it is, despite, or because of its niche.

    Now given the price of the OPA627, I definitely do not recommend immediately going for it if you think this is the direction you want to go. I would suggest a single dual-opamp the OPA2134. It has the same characteristic mellowness of the OPA627, maybe less dark, a tiny bit less resolving. Spend $4 before going stupid. Honestly, I wouldn't have gone stupid had I not already have my cache of parts from building CMOYS, METAS, PPA, on the breadboard when I was too poor to buy expensive gear (around the time after my first kid was born).

    By the way, some opamps need a bit of voltage to work, and most in my experience sound better when the voltage rails are higher than that provided by most batteries. Out of curiosity, I measured the rails. +/- 13.5V, which is pretty beefy. No wonder the XD-05 sounds good. Looks like xDuoo did a voltage multiplier circuit from that single battery. Kudos to them for not forcing the opamps to run at low voltages.

    IMG_20200723_172048.jpg

    Next up, measurements (boring).
     
    Last edited: Jul 29, 2020
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  7. purr1n

    purr1n Finding his inner redneck

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    My cat is so weird. He sleeps like a human.
    IMG_20200726_153755.jpg
     
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  8. purr1n

    purr1n Finding his inner redneck

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    Before we embark on measurements, here is the state of "audio science" today:
    upload_2020-7-29_21-44-7.png
     
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  9. purr1n

    purr1n Finding his inner redneck

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    Imagine what I can do with an AP555. Can one of you guys call Audio Precision and ask them gift me and @atomicbob one? Not being full of myself, but I think Bob and I are much more deserving of the AP than Jude or Amir.

    Let's take a look at the pot (volume control) of the XD-05 Plus. It's a cheap pot. One thing about channel imbalance is that it's almost always going to be dependent upon the pot. Pots always have problems. There will always be a channel imbalance issue near the most counterclockwise positions. What more expensive pots gets us is less imbalance and better consistency. It's actually possible to get a fantastic pot that is cheap, but it's the luck of the draw. When Ray Samuels was around selling portable stuff, one of the things that he supposedly did was buy a bunch of pots and pick out the ones that had the least imbalance. This time sorting pots and expense of buying extra pots was one of the justifications of his pricing. He sure got a lot of grief from the guys at Head-Case back in the day.

    Below are three (actually four) measurements taken from near the most counter clockwise position at 0830, 0930 and 1000 positions of the clock. Channel balance is close at 830 and 1000. However that spot in between at 0930 is off by 5db! The good thing is that everything after 1000 seemed to be within 0.1db (not shown - this is why need an AP555 - much easier to do, more automated).

    The volume knob / channel imbalance was a non-issue for me using the Solaris 2020 with the amp set at medium gain and the output on the phone set down a few notches.

    pot.png
     
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  10. purr1n

    purr1n Finding his inner redneck

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    Relative gain among the settings, as we really can't determine a gain unless we know the output of the source. The source or DAC in this case is built-in. However, below are the outputs in dBu for low, medium, and high gain with the XD-05 Plus being fed a 0dbFS signal via TOSLINK.

    gain.png

    A subjective note: Like the Leckerton UHA-6S, there are some differences in sound depending upon the gain (and how open loop the circuit is). Higher gain sounds more lively (be sure to volume match). I preferred the middle gain position. The high gain was too much for the Solaris 2020 IEM which is super sensitive. As far a noise, I think any hiss or noise is a bit less than the ZX2. I can hear faint noise with the Solaris 2020 from the ZX2 for sure. On the XD-05 Plus, I am not totally sure I can hear it. I would say that I can maybe "sense" it, because I don't want to mislead those with younger more sensitive ears. I should have my son test it and report back.

    This is what the bass boost does. One word: tasteful. Personally I would have liked to see the rise start at a lower frequency, but it's good for the consumer who wants moar bass in general. And what person doesn't want more bass? Sean Olive's research agrees.

    bass boost.png
     
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  11. purr1n

    purr1n Finding his inner redneck

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    As I mentioned, the filters look broken in USB mode with filter 1 and 3, 2 and 4 being the same.

    Filter 1 looks like minimum phase steep slope
    FR filter 1.png
    IR filter 1.png

    Filter 3 looks like minimum phase steep slope, the same as filter 1
    FR filter 3.png
    IR filter 3.png
     
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  12. purr1n

    purr1n Finding his inner redneck

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    Filter 2 looks like linear phase, gentle slope
    FR filter 2.png
    IR filter 2.png

    Filter 4 looks to be the same as filter 2
    FR filter 4.png
    IR filter 4.png

    Before I forget to mention, the filter settings don't make a huge difference in terms of sound, like on the Topping D70.
     
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  13. purr1n

    purr1n Finding his inner redneck

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    The following are measurements into 300-ohms. For AIO units, I tend to do these differently from others. The XD-05 Plus was fed a 0dbFS digital signal. I then used the volume knob to adjust the output to what is indicated.*

    NOTE: ALL MEASUREMENTS BELOW WITH OPA627

    Not as super clean as others which have been part of the latest objectivist fad, but it's still a zero point zero zero zero amp. Just not zero point zero zero zero zero. Seriously, SINAD -100db or so down. This number by itself will have no zero correlation to human subjective experience.

    Harmonic distortion pattern tends to be equal parts D2 and D3. When pushed a bit, the odd orders D5, D7, and D9 pop out. Curiously so does D6, but lower in level to the odd orders. Whether this pattern exhibits a sound is up for debate: https://www.superbestaudiofriends.o...hd-n-or-why-both-tell-us-almost-nothing.9544/

    -3dBu at output 300-ohm load. -3dBu is approximately 0.55Vrms. This is very very loud for a Sennheiser HD650 and likely to overheat the VC if left on an extended period of time in a hot environment.
    -3dbu 300-ohm.png

    -10dBu at output 300-ohm load.
    -10dbu 300-ohm.png

    -20dBu at output 300-ohm load.
    -20dbu 300-ohm.png

    *This is almost about as real world as it gets (well, other than the dumb steady-stage single sine wave). Not pictured anywhere, but the DAC section of the XD-05 PLus performs at bit worse at 0dbFS than -5dbFS. This happens with a few DACs (the Topping D70 is an example). I think maybe a -5dbFS or even -10dbFS input may be a better method in the future. Musical signals don't always reside at the 0dbFS point.
     
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  14. purr1n

    purr1n Finding his inner redneck

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    The following are measurements into 32-ohms. Think Grados or IEMs. Planars too.

    Not too different from above, except that the odd orders rear their ugly head earlier. 32-ohms wants more current, more juice. The BUF634 are doing what they can to keep up. Still, in the overall scheme of things, distortion at expected usage levels are low. Seriously dudes, 100db down. There's more microphone noise in the recording you are listening to (well, unless it's nuked via a plug-in).

    -3dBu into 32-ohms. This level will probably blow out your eardrums with CFA IEMs or Grados. Some of the less sensitive DD IEMs can take this though.
    -3dbu 32-ohm.jpg

    -10dBu into 32-ohms.
    -10dbU 32-ohm.png

    -20dBu into 23-ohms.
    -20dbU 32-ohm.png
     
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  15. purr1n

    purr1n Finding his inner redneck

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    Here is THD+N vs frequency for a -3dBu signal into 300-ohms.
    300-ohm -3dBu.png

    The XD-05 Plus distortion is fairly flat across with a rise starting from 5kHz. I set the bandwidth to 22kHz, hence this is the reason why the distortion drops shortly after 7kHz. Limiting the bandwidth cuts off third harmonic, so that's why we see a drop after with a continued rise (it would appear that while D3 gets cut off, D2 keeps rising). Note that the rise in distortion below 24Hz is real. I wouldn't be worried about it unless your music had a lot of content below 24Hz. In reality, 99.99% of music won't have much signal below 30Hz.

    Measurements are tricky. See how Audio-GD is bragging about the excellence of their Master 10 design with the sudden drop of distortion after 5kHz: http://www.audio-gd.com/Master/Master-32019/M3-8R-10W.JPG
    Note the bandwidth setting. Now I'm not saying it's not impossible for this behavior to be real (i'm not sure this behavior is even desirable), but this result could be very much the result of the Master 10 exhibiting a high level of D3 and higher harmonics, and no D2. We need more information (FFTs at appropriate levels with appropriate signals) or higher bandwidth measurement, to be certain.

    Here is the THD+N vs frequency for a -10dBu signal into 32-ohms. It's a portable that will be used with easy to drive headphones, hence why I decided on a -10dBu signal.
    32-ohm -10dBu.png

    Same pattern as with 300-ohms, but overall higher distortion with a greater rise as we go up in frequency.

    +3dBu into 32-ohms. Here I decided to push it a bit. There is when the CFA IEMs start to light on fire.
    32-ohm +3dBu.png

    We are getting lower THD+N (better SINAD) in some spots from before, but the signal is higher. How is this possible? It's because the distortion hasn't gone up significantly, but the noise floor is lower. Moral of the story: a single SINAD number is dumb, utterly moronic. It leads to simplistic thinking such as this:

    upload_2020-7-29_22-47-28.png
     
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  16. purr1n

    purr1n Finding his inner redneck

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    Well that's it folks. The Abbott and Cornelius Model Five, I mean the xDuoo XD-05 Plus, is highly recommended. Chi-Fi at its best.

    Pros:
    • Low price, affordable for people who are not crazy rich asians
    • Great sound, harmonically rich with plenty of slam, articulation, and clarity
    • Can roll an F-ton of opamps, singles and duals, grants us the option to listen to opamps instead of music, I mean allows us to tailor the sound for different IEMs
    • Solid tried and true design using opamps for voltage gain followed up a BUF637
    • Three gain settings
    • Quieter than Sony ZX2, so good, or at least better with CFA IEMs.
    • USB C DAC
    • Includes extra screws in case you lose in the carpet while changing opamps. I hate it when that happens. F! Son, can you find that screw for me?
    • Did I mention low price?
    Cons:
    • No <1 gain for super sensitive IEMs
    • Half the filters don't work in USB mode
    • No iPhone adapter included
    • Pedestrian Hammond like chassis with PCB that slides in on rails instead of Astell and Kern like sci-fi device from the future
    • Too large to be pocketable
    Miscellaneous notes: Been secretly using this with Solaris 2020 (waiting for my Ara to come back) ever since it's arrived by my bedside with my phone attached playing from the Qobuz app. Wife got annoyed at the open Grados from the uber tube amp. While I am always wowed but the Grados and EC, this does good enough where I fall asleep drooling with the music playing.

    P.S. BTW, I got an OPA1656 opamp, one of them TI next-gen deals coming in. Also an OPA828, which is supposed to be the second coming of OPA627 used here. Will report back.
     
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  17. Priidik

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    I see what you are doing here. Helping to build a sustainable and healthy future for personal audio.
     
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  18. Baten

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    I'm excited that we're having an op-amp swapping discussion because of Apos sending you the Xduuo! :) wondering how you'll like that modern OPA1656 sound! You sure got me curious about the OPA627.
     
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  19. Biodegraded

    Biodegraded Friend

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    "Measurements can be trickery", I think your first sentence should have read. Great stuff.
     
  20. Captainsubtext

    Captainsubtext Rando

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    @purr1n how does this compare to the ifi nano bl or the fiio q5/q5s?

    I’ve been using the zx2 with my andros but I find the ifi nano bl to be a better fit for the fdx01. The zx2 is getting a bit long in the tooth now (though the battery life continues to be astoundingly good).
     

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