I have received my unit. With HD650, loud enough on low gain (pegged). On max gain, I was using at about 1:00 position. Nice power boost (and headroom increase) when used with my SMSL Idea dac/amp, which outputs at a good line level (approx 2VRMS). So by extension, at Gain=1, at same loudness IDEA, now with headroom. With weak laptop output (not using external DAC), am left wanting for more power.
I have no experience with amps with ample power, this is my first. Bass incredibly more defined, rest of spectrum seems clean. I think unit has good noise spec. Funny how now that bass is where it should be, I am noticing the veil on the other end more. I need to adjust to this. Also, so far listening on with youtube videos, so don't count me as an expert. Will try with flac files later, don't have on my chromebook.
This unit sure is cute.