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)?
Ag insider logo xs@2xalonski
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.

Regards,
-- 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.
Alon
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 electronics...audio, tv, computers, etc, with full replacement. Overall, the coverage is not terribly expensive.

It's worth reviewing with your agent.