[sdiy] [AH] KORG 700S CV Hz/V / gate retrofit

[Richard Atkinson]

On Jul 25 2010, cheater cheater wrote:

>On Sun, Jul 25, 2010 at 21:15, David Bulog <d2ba at xtra.co.nz> wrote:
>> Korg 700S was used entirely for this classic track
>> http://www.youtube.com/watch?v=S5QErPDNcj4
>
>This demo... is not especially encouraging the purchase of a Korg 700S.

Try this one.

http://www.youtube.com/watch?v=_p7Ub1NDTVg

>>  
>> http://www.cykong.com/Synths/Korg%20700S/Images/Korg700-CVGateInModFull-Schmo.gif
>
>What you're looking for is an exponential converter. Those can be had
>in many forms and most VCOs with linear FM input have an exponential
>converter. You might want to look at a 2164 based one, they're
>extremely stable. I think David Dixon had some boards for his VCO, but
>not sure. You'd take the VCO and stuff just the exponential converter,
>basically, and maybe or maybe not you'd need to add a current->voltage
>converter with gain but that's not a big thing if it's needed at all.
>
>The DIY one you have posted doesn't seem to have any temperature
>compensation and does not use precision voltage references, so it'll
>be quite crap I think. That doesn't mean the Kenton's much better,
>it's probably just as bad. SSM 2164 based exponential converters are
>currently the best ones you can get, and the chips aren't expensive at
>all.

That's not an expo convertor. That's a hold circuit to pass the CV through 
to the oscillator while the Gate is enabled. When the Gate is released, the 
circuit holds the value at that point. The control voltage is in linear 
form (Hz/V) going into the circuit and in linear form coming out of it.