How to add jacks to an old synth for a modular?

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How to add jacks to an old synth for a modular?

Post by acid-legpress.exe » Tue Feb 16, 2010 1:08 am

I want to add several 3.5mm jacks to an old Roland SH-2 to interface with a modular I will soon be buying. I don't know anything about electronics so can someone show me the way? I would like to add just these few simple connections to both of the oscillators:

FREQ MOD IN (I don't know anything about circuits so I wonder if I can do this. FM is not a feature on this synth. )

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Dave Kendall
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Post by Dave Kendall » Wed Feb 17, 2010 4:40 am


Modding something like an SH-2 is not a simple task. As you've said you're not experienced in electronics, the best thing to do would be to contact a specialist synth repair/mod company, and have them do it.

One such firm in the UK is Analogue solutions. A list of their mods is here;
They do not mention the SH-2, although the SH3 and SH09 are listed. They probably could mod the SH-2 though - it might be worth calling/emailing them. The list is for kits that you have to install yourself (tricky), but they can also do the work for you - there are some notes about international shipping schemes at the bottom of the page.

There is a link to a service manual with schematics here; ... 27277.html

There are probably quite a few similar firms worldwide that can do these sort of mods....

hope this helps,

(edited for spelling)
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Post by andrewF » Wed Feb 17, 2010 8:50 am

Probably Dave's advice is the best
and you already have CV in, no need to do anything more, unless you want two CV inputs?
but if you are keen -
heres my half-arsed opinion formed from staring at the schematic for 2 minutes:

look at page 4
on the bottom right you can see the connector OP64, you could tap outputs of VCO1 and VCO2 here, look up op amp buffers and build two, a TL072 will do.
will need to connect it to the +/- power supply
Having the buffers will mean you can get outputs from the VCOs and still have the synth operate as normal.

From the manual pole of the PWM switch a 68k is connected to +V. break the connection between the 68k and the switch pole. connect two wires to a jack. The wire from the 68k goes to the switch tab on the jack, the other wire from the switch pole to the jack's main tab. Maybe you need to add protection to this mod.....

have a look at the CGS VCO here, the FM inputs in particular.
compare to the core sections of the SH2 VCOs, they are very similar.
possibly you could mod the SH2 using Ken's VCO for inspiration.

be careful, don't fry those five BA662s in the filter, if they die your synth is virtually fkd!
:despair: good luck

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Post by wetterberg » Wed Feb 17, 2010 11:22 am

Like Dave said; send it to a tech.

Also, FM *is* just normal CV in. The Control Voltage Modulates the Frequency of the oscillators. Adding a second input should be doable as well.
in fact, the things you mention look really doable... to a tech. I'd never recommend futzing about inside it if you "don't know anything about electronics". An SH-2 is a lovely synth and shouldn't be sacrificed as a "learning experience", imo ;)

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Post by acid-legpress.exe » Wed Feb 17, 2010 12:35 pm

Thanks everyone for the great information!

I was pretty sure I was way in over my head but now I know for certain. I'll just take it to someone, but now that I have an incentive to learn electronics (the modular I'll soon be owning) I'm definitely going to get my feet wet with some DIY projects.

Thanks again and take care.

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