AW: Prophet 5 Power Supply Question

Haible_Juergen#Tel2743 HJ2743 at
Wed Oct 9 21:49:00 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 
>I noticed it was emitting a hum.  The hum comes from the machine itself, 
>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).
>Is this normal?  Any idea what could be causing this hum?  I presume it is
>something in the power supply, but I don't know what it would be.  Is this
>something that I should have serviced?  Will it cause damage to my Prophet?
>Does this sound too much like a letter to Dear Abby?

I had exactly the same problem with my own P5.
(this is btw a quite common problem, at least in Europe, where the mains
voltage is higher than it used to be 15 years ago, especially if you have
a transformer that was designed for 60Hz ...)
IMO, the best way is to throw out the old transformer and put in a
modern toriodal transformer. It's easy for a tech, so it shouldn't be
too expensive. Calculate with $50 for the transformer and half an
hour of work.


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