VCF and VCO problems

[Grant Richter]

Your design is a variation on a two pole
lowpass/highpass switchable by changing
the circuit topology. The capacitor for the
second integrator stage has to connect to
the output of the first integrator stage
in highpass mode. Also the feedback for
resonance control should not go to the
first stage capacitor but to the summing
node of the first stage.

Remember, both capacitors go to ground
for lowpass mode or to the output of the
previous stage for highpass mode. Resonance
control is a multiplier (pot or VCA) feeding
the correct polarity signal from the output
back to the input summing node.

The 220 ohm resistor is a low enough
impedance to treat it as a summing node.

Best of luck,

Grant

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> From: Niklas Rönnberg <nikro at itn.liu.se>
> To: Synth Diy <synth-diy at mailhost.bpa.nl>
> Subject: VCF and VCO problems
> Date: Monday, January 31, 2000 2:43 AM
> 
> Hello!
> I have some problems with a vcf...
> http://www.itn.liu.se/~nikro/littleman/vcf.gif
> The Hi/Lo switch works fine, but the cutoff does not effect the sound
> that much. Yes, I can hear a difference but not enough. It's the same
> with the res-pot, it don't do its work! Maybe I should use different
> values of the cutoff and init-freq. pots, maybe it would be better to
> use another sort of diodes? Any comments? Please

> The whole project is here:
> http://www.itn.liu.se/~nikro/littleman/littleman.html
> I has also some problems with the VCO. I think the FET is the problem

> Is this correct?
>        |---  S
> G  --->|
>        |---  D
> Does anyone know the correct "pin-layout" for the BF256C? I think I have
> reversed mine

> The dist works fine, soft and crispy. :-)
> Thanks for your help!
> Regards 
> /Niklas
> ______________________________________________
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> | Niklas Rönnberg, Lecturer                  |
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