[sdiy] SVF problems

[Magnus Danielson]

From: patchell <patchell at silcom.com>
Subject: Re: [sdiy] SVF problems
Date: Fri, 02 May 2003 17:33:57 -0700

>     That circuit won't work as drawn...there is a positive feedback loop around
> U1 and U2 through the Q pot....Move R5 from the Negative input of U1 to the
> Positive input, and it should work....

That's correct. I spotted the mental breakdown in my reduction of the
schematic. If you look carefull on the ASM-1 VCF schematic you see that the
OTAs use the negative input instead of the positive input, which makes each
section double sine reversed, i.e. no sign is changed. Now, for the total
loop that doesn't make a differance, but the feedback term of the shorter form
it will make a differance. Well spotted Jim!

I will fix the schematics (it's just that I have to do some Postscript hacking
and eh... I have yeat to make a good generator for this stuff, so it's hardcore
Postscript and I need to move the R5 in the code and handle all the stack
effects as a result of it).

Cheers,
Magnus