Cv/Gate for my SH2000

[Martin Fay]

I'm afraid I'm writing this a bit in fear of being newbie-flamed, but 
I want to get started and I have to start somewhere...

I've just been pondering how to most sensibly add external control to 
my SH2000, the complication being that as far as I've discovered so 
far the only easy control-voltage to tap into is -Hz/V. Seeing as I've 
got a BassStation rack that can do Hz/V there's no problem, and I'm 
thinking that the instability of an exponential converter would 
out-weigh the benefit of having CV input. What do you think? Going 
for Hz/V would reduce the input circuit to an inverter.

The internal gate I've located is positive so for a Hz/V Korg/Yamaha 
style interface another inverter would suffice to buffer that -ve 
gate input, again simple.

One thing I'm not sure of is what circuit to use to switch between 
the internal and external control...for the gate would a  diode on 
each of the internal and external gate sources suffice? This would 
seem to have the advantage of 'or'-ing the gate sources so both are 
active. Because the pitch voltage is Hz/V then summing the internal 
and external voltages would cause strange pitching if the keyboard 
was pressed at the same time as the external inputs were playing but 
I don't see that's too much of a problem.

I need to do a bit more multi-meter exploration to see if I can 
locate a suitable point to tap into the aftertouch, to connect that 
to a CV input, but with that this could become an expressive synth :)

One other point I've noticed is that Maplin's seem to be selling 
little breadboards for a similar price to veroboard so I don't see 
myself doing any soldering! I might as well chuck the prototype 
straight into the machine.

Finally, what are people's opinions on opamps? Seeing as this is all 
low frequency stuff I guess 741's would do?

Thanks for any help you can give me,


Martin