[sdiy] Filters

[David Reichert]

Now that this has been mentioned, are there any good sources explaining
how to implement diodes as transconductance devices?

-----Original Message-----
From: owner-synth-diy at dropmix.xs4all.nl
[mailto:owner-synth-diy at dropmix.xs4all.nl] On Behalf Of Grant Richter
Sent: January 2, 2004 10:12 PM
To: Linium; jbv
Cc: synth-diy at dropmix.xs4all.nl
Subject: Re: [sdiy] Filters

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.