Vintage Synth Repair

Hello there,

I bought an Arp2600 two days ago and there seems to be a little 
problem with the osc-pitch.

As long as I press a note on the arp's keyboard the tune stays 
stable. If I release the key, the oscillator pitch tunes down slowly 
without stopping. But, if I plug a dummy in the cv keyboard-in on 
any of osc, the pitch stays stable at 110hz. the keyboard is a 3604 
model, the arp is version 3.

Any ideas?

Another question: the jacks for patching in are 3,6mm instead of the 
common 3,5mm. can anybody tell me, where I can get those jacks, 
preferrably in germany?

Does anybody know who repairs analogue synthesizers like the arp in 
germany?

Thanks in advance.

Michael

Or a leaky capacitor in the Keyboard Sample and Hold.  It should work 
fine if you use it with a MIDI to CV converter (while the original 
ARP keyboard is at your local analog synth guru repair shop) or one 
of the more knowledgeable types on this list might be able to tell 
you which capacitor to try changing.


--- In vintagesynthrepair@y..., mtcasino@c... wrote:
> It sounds like a broken or stuck contact in the keyboard if the 
keyboard is any thing like an Odyssey setup.
> 
>   ----- Original Message ----- 
>   As long as I press a note on the arp's keyboard the tune stays 
>   stable. If I release the key, the oscillator pitch tunes down 
slowly

I just rebuilt a 3604 keyboard.  It definitely sounds like a hold
problem.  Mine had a potted module from Dynamic Measurement
Corporation.  The sounds would fall back immediately on release.  I
never could find any information on the module so I replaced it with
a National LF198A S&H with a 1 uF capacitor.  It really holds the
control voltage now.  Funny thing about that Dynamic Measurement
Corporation module.  There was no gate signal going into it anywhere
so I don't know how the sample function would have ever worked.  I'm
going to try and un-pot it and trace it out someday.  If anyone has
the schematics for the 3604 keyboard I would appreciate a copy. 
Email me off list if you want the information on the circuit.  It
works great.

Dave

--- In vintagesynthrepair@y..., "mfox2011" <mfox@m...> wrote:
> Hello there,
> 
> I bought an Arp2600 two days ago and there seems to be a little 
> problem with the osc-pitch.
> 
> As long as I press a note on the arp's keyboard the tune stays 
> stable. If I release the key, the oscillator pitch tunes down
slowly 
> without stopping. But, if I plug a dummy in the cv keyboard-in on 
> any of osc, the pitch stays stable at 110hz. the keyboard is a 3604 
> model, the arp is version 3.
> 
> Any ideas?
> 
> Another question: the jacks for patching in are 3,6mm instead of
the 

> common 3,5mm. can anybody tell me, where I can get those jacks, 
> preferrably in germany?
> 
> Does anybody know who repairs analogue synthesizers like the arp in 
> germany?
> 
> Thanks in advance.
> 
> Michael

> Hello there,
> 
> I bought an Arp2600 two days ago and there seems to be a little 
> problem with the osc-pitch.
> 
> Another question: the jacks for patching in are 3,6mm instead of the 
> common 3,5mm. can anybody tell me, where I can get those jacks, 
> preferrably in germany?
> 

The original ARP jacks were made by Switchcraft in the USA.  The jacks
are actually 1/8" (English system), not metric.  The best answer is
to order some Switchcraft 1/8" connectors from an electronics place
like Mouser, or Farnell, or Maplin and make some cables.  You can
also order pre-made cable using Switchcraft connectors, but you have
to be careful to specify the 1/8" (not 3.5mm) jacks.

The real problem comes when you try to interface the 2600 with other
gear made in different parts of the world and need cables that can
securely connect to 3.5mm and 1/8"....

> also order pre-made cable using Switchcraft connectors, but you have
> to be careful to specify the 1/8" (not 3.5mm) jacks.
> 
> The real problem comes when you try to interface the 2600 with other
> gear made in different parts of the world and need cables that can
> securely connect to 3.5mm and 1/8"....

The other problem is to get patch cables of varying lengths so that 
you can have a bit of 'cable management'.  BigCityMusic 
(www.bigcitymusic.com) has ones available (made by Analogue 
Solutions, I think) that are different lengths and colors.  I bought 
a few and am very happy with them.

---Dean