VAC Preamp: Is my Phono stage failing?

Since you mentioned it, have you tried changing tubes?

Yo Alonski, hope all is well. I have a pair of low noise 12ax7 tubes that i received from VAC that you are welcome to borrow to see if that will isolate your problem. I currently have a pair of NOS Mullards in my phono section and they sound great by the way. The stock VAC tubes sound wonderful as well. Drop me a pm if you would like to borrow them. Peace

One could guess a grounding issue but hard to imagine how this would work with a warm-up. It might be worth playing with different grounding options to see if that is the problem.

Tpreaves, I would, but I neglected to have spares on hand.

Ghasley, Thanks Geoff – I'll PM you.

Maineiac, Yeah, I've been scratching my head about whether this could be a ground issue because it came out of nowhere. Just started happening a few days ago.

Wearing my Sherlock Holmes hat, I disconnected the tone arm while the hum was happening, but in stages: First I disconnected the right channel... hum was reduced. Yanked out the left RCA, hum reduced even more. Removed the ground wire... even more reduction. However, even with no tonearm connected the hum was still loud and unacceptable when selector was set to Phono. Then I tried every other source selection on the knob... dead quiet. Using one of the quiet settings, I switched the other selector from "Source" to "Cinema Bypass," which is connected via IC to my Marantz HT receiver, and the hum comes on strong as ever! So I disconnected my VAC from the Marantz and yes, the hum is still there!

Any tech wizards out there have a diagnosis?

Just rolled a pair of NOS Telefunken 12AX7 to replace the stock VACs. And for about 40 minutes of horrible sounding crap coming out of my speakers (how long does it take to break in new tubes?) the hum started again – it took longer, but it did show up.

So it's probably not the tubes after all. If my phono stage is indeed needing repair, which means packing up and shipping my pre to Kevin way across the country, which would be another expense on top of the repair costs... I may consider an upgrade to an outboard phono stage instead of fixing the internal phono stage.

Does anyone know what outboard phono stage would be equivalent to the VAC's built in (which is awesome BTW)? And once I get a bench mark, what would you recommend as a significant upgrade from there?