VAC Signature 2a Preamp Question

Thanks everyone, your advice is appreciated. I would normally call Kevin or Brent, but it seems like in my audiophile life, the hum-chasing episodes only happen on the Weekends.

I know you're right, Maril555. With my components in a rack, it's difficult to find much physical separation of the Sig2a from its own power supply, which is one shelf below.

Today, in addition to the hum, I heard crackle and pops, so I went all Sherlock Holmes on my amps and found the bad tube in the right channel mono block that wouldn't take a bias adjustment. Replaced it, rebiased all the tubes, and now the pop and crackle is gone, but the hum is still there, so it's not the Phi 200 mono blocks. Everything is grounded well. It could be tube rush from the phono section tubes (the line stage is quiet). I'll probably call Brent for some advice and buy some really quiet tubes from VAC if necessary.

Almarg, I've been wanting to try shorting caps, so your advice seems well-timed to help find the source of the problem. I'll report back if I encounter some big audio life lesson that I can share!

Thanks again,
Alón

"Everything is grounded well. It could be tube rush from the phono section tubes (the line stage is quiet)."

In case you missed it, read my post from yesterday.

Alonski,
I can save your time and effort- I've had that EXACT same problem, called Kevin, and that's what he advised me to do- move PS away from the control unit. By doing so, you will get rid of 90% of the hum. And that is THE ONLY solution. I even played with some additional shielding with m- metal, no difference.

Zd542
You are right saying, that switching to MM will likely alleviate the hum. But for a different reason.
It has to do with the SUT in the MC section picking up EMI from the PS, and not with the higher gain of the MC input.

"Zd542
You are right saying, that switching to MM will likely alleviate the hum. But for a different reason.
It has to do with the SUT in the MC section picking up EMI from the PS, and not with the higher gain of the MC input."

I agree. But its just too simple not to try. Also, it can't be ruled out either because we don't know what the OP has, or how its set up. You're probably right, though, given this is a common problem with this model preamp.