MIDI -> CV and state var VCF resonance control

Berenger Enselme benselme at imaginet.fr
Sat Mar 8 03:59:45 CET 1997

> I just placed an order with PAiA for a MIDI->CV converter and I was
> wondering if any of you have one of these (or another type) and what
> you did with it.
We own Kenton Pro2's and a MCV8, and all our synth are thus
MIDI-controlled, at least for CV/Gate and cutoff fraquency, which is great
because you can write all this stuff in your sequencer, and once you get it
right, it's there to stay !

> I am using a FatMan and I already have a voltage controlled PWM output
> device attached to it that I will connect to a CV.  I know that I can
> also easily voltage control the filter cutoff with a CV and also add
> some VCA tricks with CVs.  I am really interested in CVing resonance
> on the FatMan VCF (state var).  I'd like to learn what methods people
> have used to do this with a state variable filter.  I know of only two
> myself, those being voltage controlled resistors (I have a circuit
> from the LM13600 spec sheet) and optically coupled types.  I am
> leaning toward the LM13600 right now, but I'd like to hear of other
> ideas before I commit.  Could an OTA be inserted into the feedback
> loop to do this?

That would work in theory, but we had strange surprises, when we tried to
use the LM13600-based Voltage-controlled resistor to put CV on LFO-rate
knob... So chances are it won't work for resonance either... I think a LED
and a photoresistor could be just the simplest and best solution for this.
The resonance on our miniKorg 700s is "CV'ed" that way, and it works fine.


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