Prophet 5 Power Supply Question

Mark Pulver mpulver at
Tue Oct 8 18:24:55 CEST 1996

>I have a question for all of you knowledgeable types out there.  I recently
>purchased a Sequential Circuits Prophet 5 (rev. 3.3); upon playing it in a
>quiet situation (away from the sounds of the music store and band practice),
>I noticed it was emitting a hum.  The hum comes from the machine itself, and
>can be felt as a slight vibration in the music stand.  The output seems to
>be free of this hum, so it is not a simple ground loop problem (the hum can
>be heard without an amplifier).

My rev 2 has a decent hum going... I have a couple of piece of gear that
do. And, many of the bench power supplies here at work do as well.

>From what I've learned, it comes from the windings inside the transformer
vibrating at the line frequency (60hz). Most transformers with age will do
this... The heating/cooling cycles loosen up the windings and the epoxy
holding the windings to the transformer frame. Some transformers (read:
more expensive) tend to show less of this in the same amount of usage than

If it's a real drag, you can try replacing the transformer with a new
one... Make sure to match the specs!


 Mark Pulver/Chicagoish, IL          The home of "Son of The MIDI Wall"
 mpulver at              
    Check out the EMP CD -->>>

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