It's early.. I guess I'm still in the honeymoon stage (though, I've heard enough (good and bad) gear to pretty quickly know if I've got something worthwhile).. but I'm absolutely smitten with the V4. The soundstage, is quite simply, amazing. Stunning depth, width, and height.. unlike anything I've heard from a portable.. that's for damn sure. In terms of sound quality.. the transparency is the first thing that jumps out at you (after the soundstage). This is especially apparent with the ADA4627.. which makes this amp sound like a chameleon of sorts. The sound can go from bright, open, airy, and crisp.. to warm, smooth, full, and intimate.. all in a whim. It "gets out of the way," so to speak.. and gives you a very clear picture of what's up- & downstream the V4. What the V4 offers is extremely precise control, stunning dynamic ability, a life like presentation, and crystal clear transparency.
I haven't had a chance to run IEMs w/ the V4 all that much.. cause I've been flat mesmerized by how well it drives full sized phones. The HD800 is away getting tweaked to run off a speaker amp (will be back on Monday), so my full-sized can use has just been with the excellent FA-002w "High Edition." On the V4 product page, Neco mentions how the V4 is particularly suited to drive full-sized headphones. From my experience so far.. he's wholly delivered on that statement. Aside from being able to 'go loud' with inefficient phones (which practically any amp can do), the V4 separates itself from it's portable peers in that its presentation possesses a robust elegance that one would expect to hear from a very HQ desktop amp. The FA-002w-HE is fairly sensitive (but has ~160 ohm impedance).. though it's QUITE picky with amps and DACs..in much the same way the HD800 is. The V800/V4 combo has the 002w HE sounding positively majestic. The accurate timbre, terrific speed, clarity, and resolution makes me want to listen for hours and hours on end.
As I mentioned earlier, I had the gain lowered on my V4. Even on low gain (which it comes set on, by default), this phone has more than enough power to drive full sized phones w/o breaking a sweat. I have the V800 feeding ~2Vrms (6dB) gain to the V4.. and I don't need to go much past a quarter turn to reach my max listening volume. The excellent quality (Alps) pot the V4 utilizes makes for very clear and smooth volume tracking. W/ the JH13, I'm able to listen at low volumes with any channel imbalance.. and still have sufficient control over the pot.
More coming in a dedicated thread. I've got no more than ten hours on this amp.. Neco recommends at least 100 hours of use before making any final assessments.. I can hardly imagine it getting too much better than this, though.. but I'll spend more time with it this weekend and report back.