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

[harry]

I propose changing this thread to
"FatMan Hacking (and I don't mean hitting me with an Axxe !)

just to make it more Synthi.....

but seriously folks....

Someone on the list has a schematic for a "multi-pole" ladder filter...
I even remember a Moog title block on it, though I cannot tell if
that part is real...

This filter switched the diff amp to the various filter stages... so it gave
6,12,18,24 db outputs.

My simulations indicated that it didn't work very well... the shorter paths
had resonance problems not related to polarity. It looked like they simple did
not include enough phase shift for the resonance to occur.  We are looking for
180
degrees at the resonant frequency, yes ???

I experimented (sim) with tapping the full ladder. This works well, each lower
tap has less roll off, and more evident resonance.

Still... I have a tapped CEM3320 with the feedback around all filter stages,
tapped at the second stage. Works nice.

Have all the useful topologies been invented ?  Are we reduced to eternal
cloning ???   ;^P

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 18:41:41 -0500
>
> > 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.
>
> Hmm... maybe I should pick up that papper and pencil and destroy
> another otherwise wounderfull nigth?
>
> > So... we have Ladder, SVF, Sallen-Key.
> >
> > Anybody got another good topology ???
>
> The Leap-frog ladder anyone? ;O)
>
> I'm sure we can cook something out.
>
> Actually time for me to start some ladder experiments which have long
> been scheduled but never actually done.
>
> Hmm... there is a EMS ladder in that Synthi AKS there.... should I?
>
> Cheers,
> Magnus

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