My tube amp causes isolation transformer to buzz

It’s probably obvious but transformers generate magnetic fields that produce....you guessed it, distortion!

It’s probably obvious but transformers produce magnetic fields that produce....you guessed it, distortion!

I dunno, without magnetic fields there would be no loudspeakers, so I'm actually a big fan.

Yuk, yuk! 😬

I am confused when you say you can't find the cause of the ground loop.

Disconnect all inputs to the amp.  Turn on amp.  Noise through speakers?
yes? amp is the problem.  Try a different outlet or use a conditioner. No noise? Plug in input from pre-amp (with no other connections to pre-amp).  Noise?  yes, pre-amp or interconnection cables are the problem.  no noise?  not the pre-amp or cables from pre-amp to amp.

Plug a source into pre-amp.  Noise?  yes?  Source or interconnects from source to pre-amp the problem.  no noise?  plug different source and so on.

Check to see if outlet has ground connected.  

some cables aren't made very well, so better  cables with better shielding helps.

Also, don't run interconnect cables near power cables.

I agree with many hear that if it is a ground loop.  Find the cause and fix it.  masking the sound with cheaters (not ever a good idea because you actually lift the safety ground and now in the event of a fault, you, your kids, your pets, etc.  become a better path to ground).

take the time to find find the problem.

enjoy

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.