BTW, SVS Director of engineering to me NEVER to test their speakers using constant test tones as that runs the very high risk of burning the voice coil, as I did on my first SVS SB4000 sample. I kept running tones in the 10 to 30Hz range to 'feel' the bass. Afterward it just stopped working...
There is no buzz or other kinds of noise on my A30 Pro. It's a very powerful and extremely clean headphone amplifier, able to handle super low impedances. It also has an excellent set of outputs. I have no complaints!
That explains why the THDN specs don't specify if they are measured from balanced or unbalanced outputs. But many audio devices have balanced outputs for mechanical convenience only.
A transplant from California (and never to return!) ... but I came here (UML) to start and finish up my PhD in Biomedical Engineering this year, which I started Fall of 2017.
1. What is the impedance of your headphones? The DO400 HA provides 6 Watts per channel into 32ohms at ultralow distortion. It can drive all headphones out there with ease.
2. The Do400 sounds excellent to me and the change in my setup was obvious. Hard to find a credible competitor at their...
Finally...an amp that is able to play 20Hz signals at full power without shutting down. Its unfortunate I have to say this but I'm still not sure why the NCore amps and maybe Purifi ones have this issue.
BTW, for DO400 owners (like me:)), please see the noise and distortion plots of the 4mm and 6.35mm HA outputs here. Russian language but easily translated into English by any modern web browser.
Eye-opening to see how the 6.35mm output measures significantly worse than the 4mm output...
I take issue with you last statement about the DO400 sounding worse and has issues. I have had this DAC for 2 months now, having upgraded from the Topping EX5/A30 Pro and it was quite an upgrade. I have never had issues a few have mentioned and the SQ is amazing, imho. Plenty of online reviews...