I tried ground loop breakers also, with no effect. That's why I'm started to think that maybe this is not a grounding problem? Well, I will try adding another R to my psu. If it doesn't work, I will build F6 or something. It seems I have 6 matched IRFP240 pairs left over and 6 more from Aleph 5.
Hum is almost always a ground loop issue especially if the amp PSU has reasonable ripple control and the amp has good psrr. Try this, disconnect PSU from one channel and disconnect source from it. Is there still hum?
If you connect your source as battery powered floating source - like your phone or other portable device. Is there still hum? If so then might be mains trafo electro-magnetic field modulating your front end or VAS stage. Noise pickup basically.
I had this problem with M2 amp. Moving trafo outside case fixed it. Not an option though practically.
I had this problem with M2 amp. Moving trafo outside case fixed it. Not an option though practically.
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