Krell KSA-50 not quite a clone (Hum Breaking Resistor)

[ctrlx]

well, the HBR proposed at the beginning doesn't work. It actually make it worse!

either your problem is not cross-channel or you have fitted hbr wrongly

 

[Harry3]

If you haven't already read this:
Earthing (Grounding) Your Hi-Fi - Tricks and Techniques

I assume you do not have a ground wire going to C101, as the schematic you showed is confusing.