Vintage Synth Repair

On Saturday 04 February 2006 12:14 am, P........ wrote:
> Well hello, everyone! I have recently purchased a Arp Omni 1, but from
> the first moment on I kept having trouble with one note stuck at E in
> the first octave. Let me explain the symtomes: when switched to
> bass(synth) I'm able to play the notes from C1 to E1 then every other
> key I press after that makes the same sound. When switched to full
> strings/brass no matter which or how many keys I press or how I set
> the attack/sustain envelopes I always keep hearing E1 playing along
> with a long sustain. Did anybody else encounter this problem and how
> can I get that fixed? Help, please??

You're getting one note that just wants to bleed through the whole time?  I've 
hit that one before,  a few times...

ARP screwed up on the choice of one particular component in there,  the 
22uF/25V Tantalum caps they use to sustain a note.  That particular circuit 
has,  with extreme settings of the sustain slider,  up to 30V across those 
caps at times.  I guess it speaks well for the quality of the parts that more 
of them don't blow up,  tantalum caps have a way of doing that,  rather 
spectacularly at times.

You'll need to find out which cap it is (there are rows of them) that pertains 
to the particular note that's bleeding through -- easy enough,  it'll be the 
one note that plays cleanly without any _other_ note coming through.  Clip 
out that capacitor and the bleedthrough will be gone,  except of course that 
the note now won't sustain until you put a new cap in there.  Get a 35V unit 
to replace it with,  and you should be okay.

-- 
Member of the toughest, meanest, deadliest, most unrelenting -- and
ablest -- form of life in this section of space,  a critter that can
be killed but can't be tamed.  --Robert A. Heinlein, "The Puppet Masters"
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