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Bringing CV/Gate into the Roland SH-3A?
MUFF WIGGLER Forum Index -> Music Tech DIY  
Author Bringing CV/Gate into the Roland SH-3A?
I am looking to add CV/Gate, and possibly filter cutoff into my Roland SH3a. I managed to find this info by Colin Fraser:

I since had a brief discussion with Colin about this, it seems he would go about this a different way now...

"IIRC, I used an opto-isolator to drive a shorting negative voltage trigger. I would use a couple of transistors now. The CV input just needs an op-amp, or a couple of stages of op-amp maybe. The scaling control internally sets the voltage on the keyboard resistor ladder. You need to override that CV with external CV, with a trimmable gain to scale the external CV correctly. You may also want to defeat the sampling of the key CV by gate, or at least make the effect switchable."

I sort of get what he's saying, but not to the point where I could design anything, nor would I know where to wire it to internally inside the synth. Eventually I'd like to make it MIDI (I have a couple of the Highly Liquid MIDI retro boards), but I understand I need to sort the CV scaling first, and also have the option of CV inputs too.

I wish I knew more about retrofitting, If anyone has done this, or could provide a schematic/wiring diagram I would be eternally grateful.[/img]
I`m very interested.
If anyone could explain that last part further, I offer myself to design the PCB.
I did the opposite: bringing various CVs out. I think it is easier to make a controller of it than to control it. The SH-3A has so many CVs floating about (CV, gate, 3 LFOs, S&H, Noise, ADSR, the two fixed EGs, plus you could bring out the 8' for syncing or the 2' for high-speed waveshaping.

If I was doing it today, I would break it out to a Eurorack module.

(The big thing, especially if you are just starting, is to stay away from the divider circuit like the plague: it uses a fragile divider chip that is rare and expensive to replace: if it dies, no sound! So probably best to leave the chorus LFO and the 2'/8' alone if you are unsure.)
Been curious about a solution for this, myself.

Hope to see it get sorted out and shared.
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