[sdiy] ARP Omni 1 and 2...similar but different effect..

[Bob Weigel]

Well I worked over the Omni2 yesterday.  A little easier than than the 
Mark I though the diagrams were harder to read (I should post a little 
text help on which chip is which on the schematics now that I've traced 
them all on that bass board that is unique to the Omni 2) and though 
somebody didn't keep this one totally indoors all the time I'd say :-).  
And the TOP where the tuning hole is?  Looks like they used a stinking 
roto-hammer to adjust it or something!  I mean...man it's tweaked and 
that is some thick metal up there!  Hehe. Does make one wonder. Oh well 
I have a guy doing some body work on my sigma too here soon...might as 
well give him that one too.
    ANyway recall I said the bass sounds were, upon release, going to a 
low C on omni 1?  Well after getting everything else fixed (op amp that 
mixes 4' voices dead, op amp that mixed string and synth damaged and 
3086 which I've been swapping in MC3386's for damaged also...along with 
lots of interconnect dirt causing keys not to work) THIS Omni2 now works 
great until you move release past 1/2.  Then..you quickly start hearing 
on the string sounds a note that will kind of randomly trigger for no 
reasons and swell and very gradually decay.   It's always a lower middle 
D and or E.  There is interaction all over these machines which..is part 
of the reason they sound kind of cool.  It's analogous to a piano where 
you have all the other strings responding in a subtle way to whatever 
undamped strings are resounding.  But it's just a wee bit out of hand on 
both of these machines it seems :-).  Anybody run into this?  I don't 
think it has to do with the release caps.  I've monitored the voltages 
and they all seem to do exactly the same things and there's nothing 
happening there on the notes that I'm hearing when these false triggers 
occur. -Bob