[sdiy] what makes a transformer vibrate?

[Ingo Debus]

Am Freitag, 28.01.05 um 15:21 Uhr schrieb The Peasant:

> Some causes of transformer hum are undersized core, loose core pieces, 
> and DC
> or noise on the power line. It may just be a low quality transformer.

A piece of steel close to the transformer can also hum. I once built a 
PCB-mount transformer into an 1U rack enclosure, pretty close to the 
top lid. It was humming loudly. Moving the transformer away from the 
lid helped a lot.

Ingo