[sdiy] Oakley Moog filter

[Magnus Danielson]

From: pfperry at melbpc.org.au
Subject: [sdiy] Oakley Moog filter
Date: Thu, 18 Oct 2001 01:01:12 +1000 (EST)

> Just built up the VCF-1 issue 2Oakley ladder filter.
> Very nice board (& I expect the new product that obsoleted it is even better!).
> What I wonder is, can it oscilate below 200Hz? 
> As I run the osc freq down, it falls off pretty sharply around 200Hz & won't
> osc. But, I seeem to remember that the Moog ladder doesn't osc at low freq anyway.. is this true?
> I wanted to just sledgehammer it by putting a bit of a LP filter in the feedback loop, but the EE I was with turned white & said something about
> "The poles! the poles!" so, if anyone has an idea about this, let's hear!

Yes? You add another pole if you add a simple RC LP link in the
feedback path, so? Do it and let us know. It does screw things up, but
you don't learn if you don't try it, do you?

You know that I could drag you through a tough mathematical derivation
of the properties, but I won't. Just recall that adding that LP will
toss in a fixed pole into the mixture, which may or may not work.

Cheers,
Magnus