Ground Loop?

Work your way back from your amplifier and disconnect all other inputs to your main preamp.

If you just have the JC3 Jr, with no inputs, and your preamp and amp do you get a hum?

Also, if given the chance to use the balanced connections, do so and lift the ground on the destination if possible.

Thanks, I'll give that a try in the AM 9 930 I'll give that a try in the AM tomorrow I got to get some sleep I was up with it all night trying to fix this till around 430 am EST. and iy's 1030 now.

Since you mentioned two dedicated circuits, are you using isolated ground receptacles? If so, check the ground wires. Remember, an isolated ground requires an insulated ground wire. You should not use Romex. The ground wire is not insulated. I’m not an electrician but when I installed a new receptacle for my system. Based on my readings, an isolated ground has different grounding specs. In my case, I could not use an audio grade receptacle like PS Audio or any other brand that required an insulated ground wire for an isolated ground. I ended up using a Hubbell 8300 hospital grade receptacle. Hope this helps.

I tried with only the 2 pieces hooked up, nothing else just the Moon 350P preamp and the JC3 Jr phono preamp plugged directly into the dedicated 20 A line. Using 4 different pair of balanced or unbalanced connectors makes no difference. I hated doing this with full intention of returning it, but I ordered a less expensive MM/MC preamp, and it does the same thing too. It's like I'm cursed on vinyl playback.