[sdiy] Magnetic Bug squashed !

[harry]

Thanks all for the tips. The magnetic bug is now dead. As some pointed
out... it could be a grounding bug. It was BOTH... the magnetic hum was
masking a more subtle ground loop problem.

This was a rack mounted "360 Systems Slavedriver"... a semi-useless
Guitar/CV interface. I use it for the string select logic, with mods...
to get
a low note priority input to a custom octave dropper / bass synth. As
practice
starts in 10 hours (morning)... I had to fix it right away.

I removed one power supply and used a wall-wart. Then I opened the 360
box... it had a 723 based dual tracking supply... with a shitty little
24VCT
E-I core tranny... that was the major source of mag field... much more
than
the potted block supply. So I used the potted block (+/-15) to supply
the
723... eliminating half the AC in the box.

The I isolated the PCB from the box... I use nylon shoulder washers to
insulate
the 1/4" jacks... XLR connectors with the shield floating. The only
ground to the system is now at the output lead. Hum gone.

This also eliminated an isolation transformer in the bass output...
which SCREAMS
"I've got a ground loop problem" don't it. Should have listened
earlier....

Still, its nice to kill that bug after 20 years of buzzing...

Thanks again all....

H^) harry