Envelope controlled filter question

[menome]

http://sound.whsites.net/articles/st-var-f1.gif

SFV Filter-

"r6 and r7 set the cutoff frequency"  which of these would you replace with a pot if equal value to adjust cutoff frequency, or would one be cutoff, and the other resonance?

[Kipper4]

I guess it depends on which output you use.

Read further down here.

http://sound.whsites.net/articles/state-variable.htm


Then look at some other SVF autowah schematics.

In the sabrotone version here replace the ldrs with a dual pot. To change the corner freqauncies.


http://www.sabrotone.com/?attachment_id=3192

[ElectricDruid]

http://sound.whsites.net/articles/st-var-f1.gif

SFV Filter-

"r6 and r7 set the cutoff frequency"  which of these would you replace with a pot if equal value to adjust cutoff frequency, or would one be cutoff, and the other resonance?

You'd replace *both* of them with pots - e.g. a dual pot is required, like Kipper mentioned in the Sabrotone pedal. The resonance is controlled by the feedback paths through R3 and R5. You can make one of those variable. Since the integrator stages U2 and U3 are inverting, the Bandpass feedback is out-of-phase and acts to *damp* the resonance, whereas the Lowpass output is in-phase and acts to increase the resonance. This is worth pointing out since it means the control works the opposite way around depending if you use R3 or R5 as the resonance control.

HTH,
Tom

[menome]

may i interject, and mention a problem im having with a ratted-out eh microsynth.  first off, the trigger (input gate) slider pot is physically broken, it does not glide smoothly thru the range, im not sure where its stuck, but no matter how low i turn down the output of the source, all the way down to near nothing, it sounds distorted- especially inn the square wave.  Is that just the result of a wide open trigger gate or physically intermittent connection in the pot, or should i examine anywhere else in particular in the circuitry while changing the pot?  Otherwise, id change the pot, put it back together, and then, possibly, take it apart again and test every resistor, and examine every cap for swelling.