[sdiy] IR3109 (OTA-based) filter question

[DCMagnuson at aol.com]

Hi List,

I've got a few questions regarding OTA based VCFs.  I've made a sketch of the 
IR3109-based VCF in the Roland SH-101. (PDF) It's located at:

http://www.hoohahrecords.com/temp/sh101vcf.pdf

It's a series of 4 OTA/Buffer stages...  Basically, I'm curious what is 
possible with this filter.  From what I understand, pins 4, 7, 12 and 15 are 
essentially 6, 12, 18 and 24 dB LP outputs, correct?

Is there a way to change this filter to BP/HP?  Any info or links to relevant 
schematics would be greatly appreciated...

Also, if anyone can supply a little info on how the CV input should connect 
to the gain stages (internally on the 3109 chip), I'd like to add it to the 
diagram

Dave Magnuson