Let's get the thread back on track. I'd like to present an important point regarding this amp and the use of the TL1210 in particular -- as well as a few other personal opinions.
Asr had requested to hear "any Portaphile model", simply to hear how the 8610 opamps sound. I could have sent him a base X3 and he would have been satisfied.
However, I was very interested to hear his impressions of the current amp at its very best, which had to be the Maxxed version with all updates, INCLUDING the TL1210 as virtual ground. I can't emphasize that strongly enough, that if anyone wishes to order the PV2^2 Maxxed, it is essential to request that the TL1210 be included -- in order to hear the beautiful and unique sound it is capable of, after (like the M-Hornet) 350+ hours of break in ("burn in") to reach its optimal sound.
If I had sent him even one upgrade step earlier, with BUF634 as virtual ground, he would only have heard incremental improvements over the original PV2^2.
Cesar's discovery and implementation of the TL1210 as virtual ground in the power supply turned out to be a brilliant application and a very significant improvement. "Out of the box" this final version of the amp literally startled me with the level of improvement (which I expressed to Cesar in no uncertain terms). Based on experience with "burning in" many portable amps, and Portaphile amps in particular, I was literally apprehensive that the HF sparkle, extension, definition and imaging would be subdued and overwhelmed by huge bass when the caps fully burned in -- which did not happen.
I've also experience weird "burn in curves" with various amps, and so I was prepared to tough it out and not be more than a little anxious if the sound quality took odd turns along the way -- which it did.
I've urged a few amp manufacturers to listen to it "just for fun" and with no strings attached -- and they were startled at how good this unassuming and unheralded little amp sounded.
The only small area of reservation or question I have -- hinted at by Asr -- is the frequency range in the mids that involves throat and chest resonances of voices. It's my impression that other portable amps present voices with more warmth and fullness of throat and chest resonance. That aside, I love this amp. I brushed aside my fear of withdrawal symptoms, knowing it's in good hands.
Either the PV2^2 Maxxed-LT1210 has a small dip in this part of the mids, or other warmer amps impart a euphonic warmth to voices. The M-Hornet presents voices with a marvelous warm full character that is wonderful and satisfying to hear. I really would love to have a portable that can combines the best of this Portaphile with the best of the M-Hornet, if that's possible. So far such an amp doesn't exist.
In every other regard, I find this amp to be remarkable and very seductive, so that even though the M-Hornet, as a very good example, is IMO easier to listen to for long periods, and possessed of greater bass punch and overall warmth -- this Portaphile has incredible bass definition/articulation, great HF sparkle and nuance, sometimes startling front-to-back layering of instruments/voices, and great clarity that enables the listener to hear deeper into the sound space with spatial volume around performers with solid placement in space. This is a very transmissive amp that will let you hear much more of the recorded information than portable I know to date. I don't like to use the word "transparent", because every amp I've heard does impart something to the sound, and I don't expect that there will be a truly transparent audio tool for at least a few technological generations.
In terms of timbral complexities, it adds to percussive instruments more of the actual note and complex waveform of each stroke and a greater impression of the material makeup and character of that individual instrument.
Of course if you find this much "detail" overwhelming, then you'll need to choose an amp with a less complex character.
Granted, it doesn't quite create the gorgeous spatial clarity, lush sound or timbral nuance of the best home amps (even the "modest" RKV-MkII with OPA627 upgrade excels in all regards) -- but for a modest little portable I couldn't ask for much more, other than the midrange warmth and bass punch of the M-Hornet, the super micro-dynamics of the SR-71, the great soundstage width, big sound and smooth/well-integrated frequency spectrum of the Headroom Micro+desktop module -- and I'm sure there are a few other specialties that other portables excel at, but I haven't yet heard them all.
All in all -- I believe this truly maxxed-out Portaphile is absolutely a must to hear.