[sdiy] FatMan Hacking ( and I dont mean hitting me with anAxe!)

[harry]

OK here's what I did....

I took a simulation of a moog ladder, and added a diff-amp
at the 2nd cap (12 db).  I could take the resonance output from
the end of the ladder (normal) or the 2nd tap.

With the feedback tapped from the normal position, the tap
gave a 12db output, and looked a lot like the 24db.

With the tap as the feedback point, there was similar effect
if the polarity stayed the same... and with reverse polarity it
turned into a sort of VCA... once Q was raised past a certain
point, the amplitude at both outputs fell sharply. Not too interesting
IMHO.

So... we have Ladder, SVF, Sallen-Key.

Anybody got another good topology ???

H^) harry

Magnus Danielson wrote:

> From: harry <harrybissell at prodigy.net>
> Subject: Re: [sdiy] FatMan Hacking ( and I dont mean hitting me with anAxe!)
> Date: Sun, 28 Oct 2001 14:06:19 -0500
>
> > I've played a little with the Moog Ladder... and trying the feedback from
> > other than the last stage is not too useful (IMHO).  If you tap the second
> > stage and put the
> > feedback there... the last two stages still LPF the signal.
>
> Yes, but you migth want to swap polarity. You want a positive feedback
> instead of the normal negative feedback.
>
> > I guess a way of looking at it is that the filter section of the SVF can
> > have
> > gain, where as the Ladder is loss only (gain is added back in the post
> > amplifier).
> >
> > I have to play more....
>
> Indeed. Try to swap the feedback polarity and comment back... why not
> try that for the evening?
>
> Cheers,
> Magnus

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