VAC Signature 2a Preamp Question

I've had Signature 2a before, and can tell you with confidence, that the problem you are experiencing, is the EMI induced. And its generated by the power supply. EMI affects SUT in the MC section of the phono stage. If you switch to MM, or any other input, the hum disappears.

The only cure is the physical proximity from the control unit.
Keep it as far away, as the umbilical will allow.
This is "normal" for that design.

I think you have told us. I hear what I think is tube rush! There may be a bad tube in the phono circuit, which BTW can also make humming or other baseline noise. Check your tone arm wires and check the tubes. You can get very quiet tubes from Jim McShane at his website McShane Design over at audio asylum. I have no connection to him other than being a customer.

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.