I've got a Studer amp to keep my Stax menagerie under control via the SRD-7 Spritzer. It has always had quite marked mechanical hum when run at 240V (Australia's mains voltage). I have a 240 -> 110V transformer and the Studer is able to be configured to almost any possible mains voltage via a rotary switch and with a change of fuse. Did that. NO FREAKIN' HUM! $2.50 for 2 new fuses! Love it.

Edited October 5, 201114 yr by John Buchanan

That means you likely have a larger problem. I'd guess you have a significant DC component on your AC lines.

DC on the mains? How does that get sorted out?

DC on the mains? How does that get sorted out?

That's one possibility, there could be others. Just letting you know that it's likely not the amp's transformer, but poor filtering on the amp PSU combined with some really bad mains voltage.

I thought it may be a mains related problem, as the hum was not consistent.

If you've got a hum on 240, the mains plug may be wired the wrong way round.

I would get hum on my amp when the mains voltage would drop below 200V(and that happened often during the summers).

The issue was that the LM317 would drop out of regulation, fixed it by getting a bigger transformer.

If you've got a hum on 240, the mains plug may be wired the wrong way round.

Hmmmmm interesting thought - might try another IEC cable and see if that makes a difference.