AW: Re: MIDI -> CV and state var VCF resonance cont

gstopp at gstopp at
Mon Mar 10 19:33:49 CET 1997

     The 3080 works fine as a VC resonance control in both state-variable 
     filters as well as 4-pole designs. Just watch out for little DC 
     offsets that may be added by it in state-variable filters - any 
     offsets may mess up the loop. There's a circuit in EN#37 that shows 
     Also with state-variable VCQ circuits, you can add an audio input to 
     the VCF at the Q OTA. When you use this input as the signal input to 
     the VCF, the signal will be attenuated as the Q is increased, so that 
     the VCF will be less prone to be nudged into runaway oscillation by 
     transients at the input. This is covered in the EN#37 circuit too.
     - Gene
     gstopp at

______________________________ Reply Separator _________________________________
Subject: Re: AW: Re: MIDI -> CV  and  state var VCF resonance control
Author:  chordman at at ccrelayout
Date:    3/10/97 10:10 AM

On Mon, 10 Mar 1997 10:50:00 +0100, you wrote:
>>Could an OTA be inserted into the feedback 
>> loop to do this?
>But careful: maximum OTA control current means minimum 
>resonance, zero current means maximum resonance.
>For a good start, get the OB-X (not OB-Xa) schematics. 
Thanks, I knew that the CV would work 'backwards' so I intend to put a 
switch on the panel to have an inverted as well as non-inverted CV to 
control it.  Would the OB-X schematics be on the net somewhere or is 
that a snail mail issue?  I can't wait to try this!

More information about the Synth-diy mailing list