Re: [sdiy] VCRs and OTAs (Re: saw-to-tri / Voltage Controlled Waveshape)

[Roman]

or rather:
http://www.sowa.synth.net/poly/f_vcf.html

I actually did try to make VC tri/saw VCO, using SSM2164 (what else...) as OTA and VCO core. By simply inverting control voltages to both OTAs I got not bad results. But only not bad for a LFO. It influenced tuning about the same, if not more, than standard pot solution, and had terrible temperature dependency.
The circuit was simple - VCO's linear FM input was fed from 2 OTAs, one for up slope, 2nd for down slope. AFAIR there were diodes on OTA outputs, and their inputs were driven from shmit toggle of the triangle VCO core.

Roman

---- Wiadomość Oryginalna ----
Od: john mahoney <jmahoney at gate.net>
Do: harrybissell <harrybissell at prodigy.net>
Kopia do: synth-diy at dropmix.xs4all.nl
Data: Sun, 3 Aug 2003 23:14:25 -0400
Temat: [sdiy] VCRs and OTAs (Re: saw-to-tri / Voltage Controlled Waveshape)

>> There are ways to use OTA's to simulate variable resistances...
>
>Looky here, a DIY polysynth using an OTA for voltage ctrl'd Q on the VCF:
>    http://membres.lycos.fr/romcio/poly/adsr.html
>
>> but a simple pot is still hard to beat
>
>Sure, knobs is good! ;-) I always liked the TG-33 for its little joystick,
>speaking of crossfades.
>But VC means never having to turn a pot, and manual control isn't for
>everything.
>--
>john
>
>