My tube amp causes isolation transformer to buzz

Geoff,

I wish this was as easy as you think it may be.

Here is what I did:

Step 1: unplugged everything in room but amp. Went to house circuit breaker, turned off entire house but room with amp. Remember, the only thing hooked up in house is the amp.

Step 2: Amp is plugged into power outlet - only the amp - no interconnects are connected to amp - no other components are even plugged in. Speaker cables are connected to loudspeakers. Amp on, no sound from speakers, almost completely quiet with barely a hit of the buzz.

step 3: plug in interconnects to amp, but NOT to preamp = buzz - relatively loud. Remember, nothing else in house has power but amp.

step 4: plug in interconnects to amp and to preamp = buzz - much quieter bit still audible, can be heard from sitting position. Also, Amp and Preamp plugged into same outlet and a ground wire connected to chassis of amp and preamp.

step 5: plug amp into Variac - amp still connected to preamp via interconnect = buzz almost completely gone. I have to put ear right next to speaker to hear it.

Ground is good at outlets, that is confirmed and cables are shielded.

last_lemming OP
Geoff,

I wish this was as easy as you think it may be.

>>>>>I don’t recall saying I thought it would be easy.

I guess what I’m saying is it’s easier said than done