Vintage Synth Repair

hi Philip, i have Omni schematics & other info that might be useful for 
you on the "ARP Omni Resource Page"

http://peterunderdog.com/arp/

i did a lot of work on my Omni but it still has issues that keep it from 
sounding as good as the demo recording - can't get the String Controller 
to work right, and half of the bass section (16' bass synth and string 
section bass) doesn't work...the tants are a definite problem - i 
replaced mine w/aluminum electrolytics, which i later found out is 
probably not a good idea (i.e., should replace w/new tants)...however, 
it sounds better now than it did w/the old tants and an old weird note 
sustain problem that existed when i got the synth in "the 80s" (i.e., 
1980 :-) was apparently fixed in the process

if you find out any interesting info, let me know & i'll post it on my 
page...thanks, PB>>

Philip wrote:
> 
> 
> Cool...thanks for that...yeh I seem to remember
> something about the tants being a problem in that
> model.
> 
> Well I managed to fix a dead Quadra so I feel I could
> have a go at one of these..:)
> 
> Phil.
> 
> --- Malte Rogacki <gacki@... <mailto:gacki%40gacki.sax.de>> wrote:
> 
>  > At 17:08 Uhr +0100 08.05.2008, Philip wrote:
>  > > On the subject of arp stuff..Ive been thinking of
>  > > getting an Arp Omni but how come nearly every
>  > single
>  > > one I see is broken, not working, in need of
>  > repair
>  > > etc?
>  >
>  > There has been some discussion about this in the
>  > past few days. Some
>  > components inside the Omni are prone to failure.
>  >
>  > Here is a good description of the two typical
>  > problems:
>  >
>  > http://www.oldcrows.net/~oldcrow/synth/tips.txt 
> <http://www.oldcrows.net/~oldcrow/synth/tips.txt>
>  >
>  > The Omni uses quite a number of series 4000 CMOS
>  > chips; and also a huge
>  > number of tantalum caps. The one I'm currently
>  > trying to fix had a number
>  > of those chips and a number of those caps blown. The
>  > chips are very cheap;
>  > and I substituted electrolytic caps for the tantalum
>  > caps in the gating
>  > circuit. This got me about halfway to a working Omni
>  > - all voices produce
>  > sound now; and the gating circuits basically work
>  > (there are still some
>  > other problems, though).
>  >
>  > Anyway, it's a totally great sounding poly ensemble
>  > synth. The sound of
>  > those divide-down synths certainly is something
>  > special.
>  >
>  > The parts are cheap and mostly generic. I'm still
>  > learning all this stuff
>  > but I consider the Omni one of the easier to
>  > understand synths,
>  > circuit-wise. So if you want to learn to fix
>  > something a cheap non-working
>  > Omni might be a ticket.
>  >
>  > --
>  > Malte Rogacki gacki@... <mailto:gacki%40gacki.sax.de>
>  >
> ----------------------------------------------------------
>  > "Don't forget to TURN ON THE SYNTHESIZER. Often this
>  > is the reason why you
>  > get no sound out of it." (ARP 2600 Owner's Manual)
>  >
> ----------------------------------------------------------


-- 
Peter Brown
office: (413) 577-2747
cell: (413) 687-8287
AIM: pb0000math