I was hoping I don't have to measure the L and C of the transformer. He said you can use the frequency of oscillation (71KHz), but all his formulas involve either L or C.He is not overly clear, he does explain it all but he jumps around. It may help to read to the end and then go back.
Yes, the inductance of the transformer is measured and you know the frequency of oscillation, so there you go. Now you have the L (Lt) and the C (Ct) of the transformer (calculated). Of course Rt is the resistance of the transformer winding.
Then it just all plugs in. If you use 0.5 for the damping coefficient and 2pi to lower the corner frequency by about 6.3, all of the higher math can go away and you can just use the reduced forms.
Again, he could have been clearer.
I do not have ring at the big filter caps. I only look at the output of the amp. The scope picture is at the output of the amp with no input signal.To be clear, you see this ringing right at your filter capacitors?
The method that he explains, although I did not get it from him, has worked well for me.
I am pretty sure it's the diode turn off from the waveform of the sine wave.Sometimes it helps to ponder the fundamental source of the noise. If the source is rectifier reverse recovery current, ponder the path that current 'wants' to flow around; then minimize its loop area and keep it away from sensitive inputs. Adding the cap across the diode is a simple means to give this fast-risetime pulse of current a small, low-loop-area path.
BTW, are you hooking the amp outputs to your QA401 differentially? just curious...