VAC Preamp: Is my Phono stage failing?

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.

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.