[sdiy] What's going on in the M12 filter circuit?

[Colin Fraser]

----- Original Message -----
From: "DJ Marmalade" <djmarmalade at planetp.org>
To: "Synth-DIY" <synth-diy at dropmix.xs4all.nl>
Sent: Friday, March 29, 2002 12:06 PM
Subject: [sdiy] What's going on in the M12 filter circuit?


> In the M12 voice schematic, seen here :
>
> http://www.planetp.org/xpvoice.jpg
>
> The 3372 LPF is used as a multimode filter.  The circuit on the right
> apparantly sums at different levels, the signals available from the filter
> caps.
>
> I'm interested to know what is going on here, why does this work?  I also
> want to know if there is something unique about the 3372 or could this
idea
> be applied to any number of filter chips, say for example, the 2044?

There's a very good explanation here -
http://www.musicsynthesizer.com/Circuitry/Multi-Function%20VCF.htm

Colin f