I use my P500 as a speed controller through regenerated port. No issues whatsoever @ 33.3 (60 hz). When I adjust to 81, system takes on high pitched hum. Sound is only present when stylus is in the groove. Also, sound is eliminated when I lower frequency into the 70s. Any idea what gives?

Some systems, especially tube based systems, can reproduce those higher frequencies if their power supplies aren’t well filtered.

Is it a tubed bases system?

Thanks for responding Paul. Yes, I use an Aesthetix Rhea, which is a tube phono preamp. What puzzles me is why I only hear it when the stylus is on the record. Is it some kind of feedback issue, where the frequency is resonating through the cart and tonearm? Any fix?

That’s a good question and I don’t know the answer. The one thing you might want to do is have us check the regenerator to make sure it’s not doing something weird, though it really sounds more like the preamp. You might ask Aesthetix if their preamp uses a regulated heater voltage or not. Sometimes they don’t and this can lead to higher frequencies being reproduced through the tube - though I don’t know why it would only do it when the needle went down.

Perhaps the phono pre’s transformer is vibrating and this is being picked up by the stylus, or the turntable motor is unhappy and somehow oscillating.

Is the phone pre on the same shelf as the turntable? Is so, what happens if you pick it up with a record playing? Similarly, does the sound change if you touch/hold the cables from the turntable to the pre?