The frequency response is load invariant within 1/10db from 20-20KHz, with 0 degrees phase shift at 20Hz and less than 1 degree at 20KHz. The invariance due to the output impedance being a few milliOhms, the low phase shift due to the feedback value, which allows the amp to correct for phase shift at the bandwidth extremes.
THD from 20Hz- 20KHz is < 0.1% at full power (200 W into 4 Ohms) and about 0.005% at 1 watt. We think it might be lower but finding a decent filter to knock out the residual has been tricky during the pandemic. We found one about a week ago and are interested to see how things differ once its integrated into our test setup. The distortion is lower into 16 Ohms.
The switching frequency is just shy of 500KHz, depending on load. The input is entirely direct-coupled.
The filter I mentioned is an Audio Precision device and is used to knock out the residual to prevent it messing with the distortion analysis. If I got this right its 8th order(!) and puts the residual down about 60dB... This is why we've not posted any more distortion data since the residual throws the readings off.
I understand amp pretty at the freshman college level. And I appreciate the new designs and designers bringing new stuff to market.
But I really appreciate venerable designers, like yourself, bringing their expertise to bear on these things.
[/scratching the chin(s) and watching]