VAC Preamp: Is my Phono stage failing?

My VAC Standard LE preamp is exhibiting a loud, strange hum, heard in both speakers equally when MC Phono is selected. However, the hum doesn't show up until about 10 minutes of normal sounding LP playback. It gets louder with volume.

I think it may have to do with the unit getting to a certain temperature, since it starts the process over again if I turn everything off for 30 minutes – quiet for 10 minutes or so, then Wham! a loud hum that has me diving for the mute button!

If I switch the selector to any other setting, such as CD... dead silence. Could it be a phono tube going bad, and if so, how is it in both channels?

Any ideas (aside from calling Kevin, which I will do)?
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?
If the VAC phono fits your needs and you love it, then the repair costs will likely be a fraction of what it would take to get a closely performing outboard unit . I bet you the cost of repair would not even be what you would want to spend on a good power cord for an outboard phono stage. Call Kevin or Brent and they will tell you if there is something obvious to check or do and the range of how much you are looking at in terms of repair.

The advantage of an outboard phono is that most have a great deal of flexibility in terms of gain and other settings that allow you to use many different cartridges. VAC might box you in a little with the phono but I am guessing it is extremely good for the carts that can be used with it.
Have you asked Kevin what he thinks the problem might be?
SOLVED! Well, almost.

Maineiac, Thanks, I really wonder how much I would need to spend on an outboard tube Phono Preamp to be significantly better than the VAC's.... sounds like it might be a lot. I would love to audition the Fosgate Signature, it's received good reviews and it looks so cool.

Pubul57, I spoke with Brent at VAC and he never heard of this problem and said to send it in for a check up. I guess the very notion of being without music for a few weeks was bad enough to kick my brain into gear and identify the problem's source.

My system is on two 20amp dedicated lines and all components are fed power from a AC regenerator that completely isolates the system from the wall power. I also have a hot tub in the back yard on its own separate 20a circuit.

Every time the hot tub motor turns on, the hum shows up in my phono stage. If I then turn off the tub, the hum disappears.

Considering the system and the tub are on completely separate dedicated circuits AND my gear is completely (supposedly) isolated from the wall power... how could this be?

I'm calling the electrician back in and I'm going to call PurePower and have a little talk with them. I don't think this has anything to do with my VAC.
The plot thickens:)
The techs at PurePower were awesome, and they're in Canada, so they worked on thanksgiving! We narrowed it down to a safety ground loop. The unit is fine, as is my VAC. Seems this safety ground cannot legally be disabled, so I'm counting on my electrician to at least separate the safety grounds for each circuit so they don't bleed over. What remains a mystery is how this hum got into the signal path... Any ideas?
My system is on two 20amp dedicated lines and all components are fed power from a AC regenerator that completely isolates the system from the wall power. I also have a hot tub in the back yard on its own separate 20a circuit.
I don't quite understand this. Do you have one AC regenerator or two? If it is only one, and all components are powered through it, how is the second dedicated line being used, if at all?

-- Al
Sorry Al, I should have clarified. My two channel analogue music system is my first priority. The PurePower regenerator is on this system plugged into the first dedicated line.

The other dedicated line is feeding the home theatre system which I keep completely separate. Although they are the same room, when I'm listening to vinyl, all power to the digital HT system is off. I use two Panamax power conditioners on this system.

When I'm in critical listening mode, i even turn off the refridgerator, which is quite loud in our open-plan home. Now, if I could only remember to turn the fridge back on, I would get fewer of those looks from my wife!
Alonski, FWIW, I have a dedicated line and a power conditioner and have found that the sound is improved (opened up) on my VAC integrated amp if I go straight into the wall with the amp. I have seen a number of threads that back up the assertion that amplification performance is better going straight to the wall. I know it is a bit of a risk but I take precaution to unplug during storms or if I am away for extended periods. Also, as a last resort, I guess my homeowners insurance will cover me if there is a sudden and accidental surge that wipes out my VAC.
What remains a mystery is how this hum got into the signal path... Any ideas?
Yes, that does seem counter-intuitive and mysterious. The only thought that occurs to me is along the lines of what you were speculating, that the safety grounds for the two circuits are not completely separate (both physically and electrically) all the way back to the point where the safety grounds and AC neutral lines come together at the service panel. Conceivably that could result in low-level leakage currents that can be expected to occur between the tub's AC supply and safety ground to couple onto the safety ground wiring to the audio system, which would put it on the chassis of the components, from whence it might couple onto the signal path. The MC stage, of course, figures to be more susceptible to that than any other point in the system, due to the low signal levels and high gain that are involved.

-- Al
Maineiac, Thanks, I tried having my Phi 200 amp direct to the wall and it sounded great. Then I tried plugging it into a Panamax power conditioner and it sounded like someone threw a wet blanket over the sound. Then i bought the Purepower AC regenerator and plugged the amp into it... WOW, it blew away anything I've heard from this amp. Surge protection of the highest order, clean power, lots of AC headroom for even more attack and a blacker background. A significant improvement from direct into the wall. But, to be fair, I'll A/B it again next time I move the 400 lb. armoire that's in front of the wall plug.

Al, I agree with your speculation on the pathway this rogue hum snuck through. I hope to have an answer on Monday when the electrician comes back.

Thank you both for your insights and help.
Looks like I've got some research to do on then Purepower. That is interesting to know.
Glad your problem has been solved.

Sorry to hi-jack your thread.

Maineiac & others.

Don't guess or assume that your homeowner's insurance will cover your gear, in the event of a catastrophe.

Many policies have limits on home electronics.

I have a rider that covers my, tv, computers, etc, with full replacement. Overall, the coverage is not terribly expensive.

It's worth reviewing with your agent.
In talking to my agent about this potential issue, I ended up increasing the overall coverage but was told that, at least for my policy, there was not a limit on specific types of items (i have some other toys too). It is a good question for sure.
Same here, increased coverage to $50K replacement value, but no special rider. Who do you insure with?