Hi I have been working on my first revision of my amp and been spending a lot of time on it the pass few weeks. It is still in working progress, but at least today I reach a mile stone of doing the first FFT test. I am still working on lowering the distortion and still have to put into the chassis and test in real listening. This is my two chassis, I first bought the smaller one, but determined the heatsink is too small, so I got the second one which is a clone of Krell 50W class A chassis. The power dissipation is about 70W/ch, so I need all the heatsink I can get. The amp is only going to be about 70W 8ohm or 140W 4ohm. I sacrifice peak power for big class A region. I get about 16W of class A for 8ohm or 8W for 4ohm load This is the set of pcb. I separate the OPS board from the IPS/VAS board so I can swap to different designs in the future. I have a board for voltage regulation to get rid of the ripple from the transformer and separate filter board for each channel. I use separate bridge rect for each channel. Each channel has total of 80,000uF (40,000uF for each rail) This is my test setup, I use +/-31V bench supply to power the amp. I still use 20,000uF per rail. The bias is quite stable, it drops about 10% from stone cold to fully warm. I tested by driving with large input signal, then remove the signal to verify the current does not change. I use burst pulses to keep the power down and I can use large signal. This picture shows a positive pulse from 0V to 15V( as seen on the display). I use +/-30V to power the amp. I also show the width of the pulse of 9.335uS to compare to the next picture. You can see the rise time is less than 700nS and very little overshoot and no ringing. I don't know how important is group delay. The top trace is the input signal, from the picture, the delay from input to output is definitely less than 0.2uS, maybe even shorter. This picture shows way over drive. You can see the recovery is about 1.2uS. The display show the original 0.9335uS width for a non clipping pulse, you can see it just get about 1.2uS wider, there is not funny wave shape on the clipping on the top. This picture shows the slew of the rising edge during clipping. This shows 25V/uS. This shows slew rate of falling edge, about 25V/uS. The closed loop gain is 21. I tested the stability by lowering the closed loop gain down to 9 and show it's stable. I also put a pole at about 300KHz to take away 45 deg phase margin at around the -3dB crossover point. It passed both test. And you can see the square wave looks good.