Ground loop ain't always the guilty one

[Stabist]

Hi!

My Zen v4 had a little hum - I've tried different ground connections - but is stayed and stayed ... So I just tried to ignore it ...
But I'm quite known beeing annoyed 'cause of little detailes ...
So I've decided to locate the reason - I've noticed that the trannie has "it's moments" - when it produce hum - and bingo - at the same time the hum in speakers increased ...
First thouht was - it's only 360VA trannie - maybe I should implement bigger one ...
But since trannies don't lay around for small bucks - that was not the option to start with ...
Then I've decided to find a logical explanation - and voila - I've found it
The thing is - the trannie is mounted on "fake"/internal bottom plate - the bottom consists of 2 plates - with 8mm space betwwen them ... And both of plates are pretty thin (2 and 3mm) - I guess a perfect way to produce a resonance - so today I've damped the first plate with Dynamat - and VOILA!!! It's almost quiet now To damp the one with trannie - I'll have to dissamble the amp - so I'll need a bit more time to do it - but I'm almost convinced it will become dead silent then

[Magura]

Funny you mention it, I've had similar experiences with inductors for the PSU. If not potted and mounted proper, they can sing along as well, with pretty much the same problems as the result.

Magura