🚀 go-pugleaf

In article <15DEC199216354453@almach.caltech.edu> shoppa@almach.caltech.edu (TIM SHOPPA) writes:
>Hello,
>	I have been building some low-level audio circuitry, and have had
>problems with hum from nearby AC transformers.  Currently, I have the power
>supply located a great distance away from my circuitry in order to eliminate
>the hum.  The sort of transformer I need is 120VAC to around 20 VAC
>center-tapped, at a few V-A's. As I understand, Toroid transformers can have a
>much smaller radiated EM field than usual transformers. 

I used to think so, but after building an amplifier using two 500 VA toroid
transformers I am not so sure anymore.
I had several problems with radiated EM fields - one of these resulting in
a 7-9 A (!) current though the chassis.

I have discussed this with one of my friends who works with power supplies
(and transformers) and in his opinion toroid are not as good as originally 
claimed regarding radiation of EM fields.

His experience is that a well constructed 'normal' transformer can be
as good.

Another way to solve your problem could be shielding - enclosing the 
transformer or the low-level equipment in MU-metal (best) or just plain
iron could be a cheep and probably better method to get rid of the EM field.

>	There are several manufacturers of toroidal power transformers,
>but they all seem to want an arm and a leg ($50+) for even the smallest
                                             ^^^^
 This will give you at least a 200 VA toroid transformer here in Denmark.


Kind regards

Martin Berg

Employed by Oracle Denamrk, but this reply are my opinions.