I guess this explains why my Doepfer portable cases are so quiet.
The power supply is bolted to a piece of fibreboard, which probably
doesn't resonate as much as the metal.

--- In Doepfer_a100@yahoogroups.com , Florian Anwander
<Florian.Anwander@c...> wrote:

> Hi Pierre
>
> > Quick question: do your PSUs make an audible buzz/hum
>
> Yes it does. It is - as the others said - a mechanical hum from

the

> transformer. If you have a standard power supplies mounted to the

rear

> side of the rack, the hum will be louder than from a modul like

power

> supply, because the back plate of the housing works as resonator.
>
> To me this hum is quite annoying, because I always have to switch

off

> the modular when I do microphone recordings - and now guess where

the

> powerswitch is located and how reachable it is...
>
> A solution might be to mount the powersupply on a foamed rubber

plate

> and mount this rubber plate to the housing.
>
> Florian