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My tube amp causes isolation transformer to buzz

So I have an ARC Classic 60 tube amp that was causing a hum/buzz on my speakers regardless of volume.  In an effort to eliminate variables I plugged the amp into a Variac Transformer.  The sound from the speakers was almost completely eliminated, however once the power was turned on at the amp the transformer, which was otherwise silent, started to buzz.  Not super loud but audibly.  My amp draws 350 watts at idle. My Variac can handle up to 800 watts. 
So my question is, does applying a load to a transformer cause it to buzz, or can the amp cause the transformer to buzz?
last_lemming

Showing 2 responses by erik_squires

erik_squires
15,657 posts
 
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.
erik_squires
15,657 posts
 
It does sound like you might have a ground loop, but testing on a variac isn't how it's normally diagnosed.

Disconnect all inputs from the amp, see if the hum persists. Alternatively, lift the ground with a cheater plug (temporarily only).
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