Not to pile on because I'm not electronically very knowledgeable, but this was my experience in dealing with a phono hum: After much experimentation, I got a tip from the Tweak Shop to wrap my unshielded phono IC with aluminum foil. Gone! Obviously, the phono IC was picking up hum from my big Audio Valve Baldur 300s sitting within 2 feet side-by-side of my phono preamp. Also, one of more tubes went bad in my Kondo KSL DAC a year ago causing the left channel to reduce in output. So, tubes can cause erratic things to happen. Good luck in finding the solution.
Hum problem
Been chasing a hum in my VAC Ren 30/30 for quite a while. My technician has been all through it and does not find a problem. Says he cannot hear it in his system, but it's quite apparent on my Horning speakers (94 dB maybe?). As soon as the soft start relay starts to open, it begins to be audible and when it clicks open it's fully audible, maybe from 5-6' away, with the pre-amp fully attenuated. Once you advance the attenuator past about 9 or 10 o'clock, it starts to get louder, but not before.
It's not a transformer mechanical hum; no sound at the amp but clearly audible through the mid range of the speakers.
Present w no other components turned on (or any/all turned on). No change after swapping out power cords, lifting ground, swapping interconnects. Changing the position of the ground switch on the amp has no impact. Same w AC straight from the wall or w AC from a Dodd Audio Balanced Power System iso transformer. Since this is a transformer/tube amp (not an OTL), I assume there can be no DC offset, and cannot really check that because I don't think I can operate it w/o a speaker load and the info I find on the web says it must be checked w/o a load.
Any ideas before I ship this 85 lb beast back to VAC?
Any ideas before I ship this 85 lb beast back to VAC?