It sounds as if the strayfield magnetic radiation from your power
transformer may be inducing hum into the signal traces of the PCB.
Try this experiment: remove the transformer from the PCB and
make the connections to it temporarily using long (~1 metre) wires.
If the hum goes away, there's your problem.  Let us know what
happens.

Brian Aase

----- Original Message -----
From: "Tal Bejerano - AMC" <kooter@ZAHAV.NET.IL>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Saturday, June 22, 2002 5:51 PM
Subject: [EE]: Hum problem


> Hi 2 All
>
> Attach a quick schematic that I draw to explain my problem.
> The problem is a hum I can't rid of.
> I try to increase the 1000uf capacitors with larger ones (4700uf) but no
> change, only the hum sound changed to lower. I try to increase the output
> caps' from 100uf to 470uf but no change at all.
> what I can do more? maybe the bulky transformer that on the pcb can cause
> this hum problem?
>
> if you think the component placement is important I can send the pcb
> picture/drawing (even I put it in the way that unregulated / unfiltered
> traces will not be near the audio circuit)
>
> I really need your help!
>
> Tal
>

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