[sdiy] Ray Wilson's SV VCF with +-15V

[Benjamín Velasco]

Hi All!!

Today i rechecked all the pcb, connections, components values and found no
error. I was about to give up when I decided to tweak some values on Rays
circuit. I compared the VC RES section on both the SVF and the 4 pole LPF
and noted there where very similar except for a value of a resistor
connected to pin3 of the OTA. In the SVF it is 30k and in the 4pLFP is 200k.
I dont know if this makes any sense but I replaced the 30k with a 200k  and
got a much better response of the RES pot. It oscillated near 3/4 of the
rotation. Finally I put a 390k and now it oscillates near the end. Maybe  I
have a mistake in my board but this tweak really solved the problem. It
sound really nice!!

Benjamín


2006/3/21, Benjamín Velasco <guatis at gmail.com>:
>
> Thanks Ray (and Roy) for your suggestions. I'll recheck the entire board
> tomorrow...now i'm a bit tired. Glad to hear that the filter should work
> fine under +-15V. I'll keep you informed.
>
> Greetings
>
> Benjamín
>
> 2006/3/21, Ray Wilson <raywilson at comcast.net>:
> >
> >  It must be this one:
> >
> > http://www.musicfromouterspace.com/analogsynth/STATEVARVCFFEB2006/STATEVARVCFFEB2006.html
> >
> >
> > Since its the only one that will oscillate.
> >
> > It should not be acting the way you have described. You should only get
> > oscillation near the end of the max resonance pot travel. Are you certain
> > that all component values are correct especially those around the Res and
> > COF pots. There are resistors in the circuit designed to limit the voltage
> > range that the pots can deliver (COF R1, R5) and (RES R48, R52). If you need
> > to adjust the range you can adjust them however when I tested this on +/-12V
> > and +/-15V and I saw normal behavior. Also check the values around the VC
> > resonance circuit. I'm not sure why you would be seeing what you've
> > described under normal circumstances. Unsoldered component? Unsoldered
> > off-board wire? Wrong value component?
> >
> > Here are some troubleshooting suggestions:
> >
> > http://www.musicfromouterspace.com/analogsynth/troubleshoot.html
> >
> > Ray
> >
> > ----- Original Message -----
> > *From:* Benjamín Velasco <guatis at gmail.com>
> > *To:* Synth DIY List <synth-diy at dropmix.xs4all.nl>
> > *Sent:* Tuesday, March 21, 2006 4:12 PM
> > *Subject:* [sdiy] Ray Wilson's SV VCF with +-15V
> >
> >
> > Hi you all!!  I recently finished this module from Ray's site using my
> > +-15V PSU. I seems to work but the ranges of the pots are too extreme. It
> > starts to oscillate as soon as I start moving the resonance pot, and also i
> > cover the entire CutOff freq range near the center position of the COff pot.
> > Can anybody help me figuring out what values to change so the response is
> > like the +-12V version?. Or maybe it's simpler to use a couple of voltage
> > regulators to get +-12V??. Thanks!!!
> >
> >
>
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