[sdiy] Power Supply Noise Tip of the Month...

[patchell]

    One of the problems I encountered at yesterdays DIY meet was that my
VCO's exhibited some un wanted FM.  I had just recently (2 days before
the meet) put in new transformers to power the board, and suspected that
this had something to do with it.

    There were two transformers, a 30 VAC CT and an 18VAC CT
transformer.  The AC goes to power supply via a 6 pin connector, three
pins for each supply (a +/- 15V and a +5V).  I used my ohm meeter to
determine which ground wire was which, or, at least, I thought I did.
After I got the supply wired up, I realized that I had my meter on
Volts, instead of ohms, and I wondered at the time what great luck, I
guessed the wires correctly the first time.  Turns out this was the
problem, I guessed wrong.

    While the circuit was electrically correct (both wire did after all
eventually go to ground), it was electronically incorrect.  There were
60 hz currents flowing through trances that wasn't supposed to have
these currents flowing.  I just fixed the wiring, and it fixed the
problem.

--
 -Jim
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