I find this amp has quite a unique sound delivery. I had it my hands two days after my last post....Todd (TTVJ) busted his hump to get it right out!
It is quite balanced and has no noise....even with the Harvey JH13! I can listen at moderate, ear saving levels and still enjoy a terrific octave to octave frequency balance. I have had two of the HD800's in my time. The Beyer T1's and Audez'e LCD-2's. I don't have these phones any longer, these phones at those price levels, have to many flaws for my tastes.
Preferring instead the HD6XX's or Grados (PS1K's, Symphone Magnums V3 & V4's, or the HP2's two of those). The Harvey's (two of those also with various cables and terminations). I will add an HE-500 later.
The amp has been running continually for a month (the glory's of solid-state) and is well burnt in. The HA-501 is exceedingly well built, particularly for it's price. The sonic signature is very tuneful, much like, and is reminiscent of a good tube amp, with solid-state control for the driver. The damping factor selecting capabilities is very useful (IMO). The Grado PS1000 has the best middle I can recall, in its mid-bass through upper midrange. The bass-line of this phone can be overly exuberant and has big shoulders. Not so when I select the appropriate damping factor setting. Likewise the treble of the PS1000 is sweet, sometimes overly so. The control creates the proper amount of air with a wonderful sheen. I only used the PS1K with the Peak or Arete w/Volcano, in an attempt to control the driver for it's best performance...not any longer. The HA-501 has taken over this responsibility.
The Sennheiser 600-650's I own were driven either by my vintage Marantz 2285 or the Moth SA 2A3/45Hi for optimum playback. While both were different in sound because of the final output type, the control of each left little doubt that the Sennheisers were mated with amps that could coax the very best from those phones. The Teac does a most credible job, so I can keep the Marantz and Moth in the bullpen, not needing or wanting to make a switch for driving the Senns.
The Volume take-up from zero is unique with this amp. You have room to move, even when using the ultra sensitive JH13PRO's. No noises can be detected emerging from the amp output when I plug in the Harvey's...amazing! The Harvey's can be driven by any amp, yet very few make the Harvey sing like actual authentic instruments in real space. The Lisa XP with unity gain...or the L3 (both LaRocco designs) seemed best suited. Very fast and clean, with even response, exhibiting ultra fast TIM's (transient intermodulation). The Harvey makes typical amps sound....well typical. The Teac makes special noises here!
I have many....many amps, only because I'm a synergy seeker. When two components combine to reach heights that each couldn't be achieved either singularly/individually with other components? That's synergy! With the Teac....I have found an amp that I can leave in system and don't need to play amp merry-go-round. Unique... Is it the best of the best then? No, it is all the better for the ability to fill the needs of some very demanding phone types. Amps that handle the Sennheiser 6XX's don't sound credible with the Harvey (as example). Quite an achievement in my experience.
I use a Bel Canto stack, Transport and Dac w/ upgraded Bel Canto power supply for headphone source. Listening to mostly Jazz (Bop, Hard Bop and Avant Garde) or Classical and Opera (a bunch of Opera). The HP-2 was configured for Opera specifically!! Rock from my generation...I'm old... Blues to Blue Grass and any balladeer that makes musical sense. No Diana (make my skin) Krall, she has my permission to burn in the hot place.
Another unique feature....Yes, the "audiophile" recording is very well served. The clarity and definition with detail retrieval is exemplary. What is even more impressive is the handling of the less than stellar recording. Sifting through and framing the available sonic portrait quite credibly. The Complete Robert Johnson recordings as an example...those are some of the worst recordings that can actually glow with useful musical meaning....incredible.... takes my breath away....