[sdiy] 1v/oct expo converter front end for SSM2164 quad pole vcf..

[David G Dixon]

> Does anybody have a schematic for a
> 1v/oct expo converter front end in a SSM2164 based quad pole 
> low pass vcf ?
> Some circuits around but they seem to be with linear front end summer.
> I'd need 1v/oct for the VCF span.
> I found this:
> http://userdisk.webry.biglobe.ne.jp/000/024/65/N000/000/000/12
> 5151002153016326829_Exp_SSM0908.PNG
> But the front summer uses half of the SSM2164 as an expo converter..
> The best would be to use the SSM only for the quad low pass 
> part of the VCF..
> Thanks
> JP

I have an entire circuit schematic I can send.  This is the basis of the
Intellijel Dr. Octature filter in eurorack.

The 2164 has an exponential voltage-to-current response already, so all you
need to do is send the CV summer output directly to the 2164 VC pins (all of
them tied together).  In other words, no expo converter is required for VCFs
with 2164s.  The proper CV gain for 1V/oct is about 20% (or slightly less).
You can expect about 5 octaves of tracking in this case.