[sdiy] Filters

[Grant Richter]

on 1/2/04 5:58 PM, Linium at intent at netpratique.fr wrote:

> On Vendredi 2 Janvier 2004 14:50, jbv wrote:
>>>> Is there a (easy) way to modify this VC-BPF design :
>>>> http://www.cgs.synth.net/modules/cgs35_syntha_vcf.html
>>>> to add VC-Q to it ?
>>> 
>>> Replace the Q pot with a LDR+LED (and 1k resistor parallel to the LDR) ?
>> 
>> Mmh... I guess there my be a slighly more hi-tech, OTA-based
>> solution...

That is called a "Sallen-Key" filter. Buchla implemented it using a Vactrol
for the transconductor. Neil Steiner used diodes as the transconductor. The
Korg MS-20 implemented it using an OTA.