Spring Line Hum

[Harry Bissell]

And not only THAT !!!

I bet all those "low profile pcb mount" transformers made a shitload of
ACOUSTIC noise as well.  My Matrix 1000 is the noisiest piece of gear
I own. The magnetic field of that tranny is enough to buzz the steel cover
of the unit !!!

Toroids usually help in acoustic (airborne) hum also.

H^) harry

jhaible wrote:

> > So the hum problem certainly must be preventable
>
> Sure it's possible. The spring reverb I've built for my CX-3 organ
> does not produce any noticable hum at all. But only after I've removed
> all these ugly 19" 1U boxes with internal low profile pcb mount transformers
> from the same rack. Replaced transformers with toroidal ones, "outsouced"
> the transformer of one particularly bad device (Miditemp PMM88) - yes
> making a wall wart from an internal PSU !
> If you don't have a complete Mu-Metal shield around the pickup, hum
> or no hum is mostly determined by the strength of the stray field of nearby
> transformers. That Miditemp box produced a stray field to interfere with
> the reverb tank over a whole meter !
>
> JH.