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

[harry]

Again... "guru mode off"

The Oberheim Matrix filter is more like a cascaded integrator filter... local
feedback around each stage, one global feedback path. very much like
the SSM2040, CEM3320, etc.  If you tap each section, and sum with correct
amplitude and polarity you can get "any" response you want.

They "kill" one filter by switching in such a small cap that that stage is
effectively
gone from the audio range (but still stable...)

This is NOT an SVF in any way I understand it.  Its closer to the Moog Ladder
in that the resonant gain will be fixed, and the passband will drop.

BTW a SVF can be configured to have constant peak response by putting the
input into the Q feedback, rather than the normal point.

So why can't you do the same with the Moog Ladder ???

Can any "mathy" types put this in "non-guru" form for us ?????

H^) harry

Magnus Danielson wrote:

> From: harry <harrybissell at prodigy.net>
> Subject: Re: [sdiy] FatMan Hacking ( and I dont mean hitting me with an Axe!)
> Date: Sat, 27 Oct 2001 15:47:00 -0400
>
> > I have not seen an 18db State Variable Filter...
> >
> > I do not have sufficient "guru" points to say that it cannot be done...
>
> Well, I don't know if I have sufficient guru points either, but I will
> stick out my big nose (I guess it is preferred over my big fanny) and
> say that it can be done, you can also set up a 4-pole if you really
> want to.
>
> I've seen loooooong leapfrog ladder filters, which to some degree is
> quite related, so it should indeed be possible.
>
> I would actually take a peek at the Matrix-12/Xpander filter section,
> I beleive they did something similar. That filter section is among the
> most flexible I've seen. Haven't spent quality time over the schematic
> thought.
>
> > but the SVF is basically a summing amp and two inverting integrators...
>
> Well, the integrators does not have to be inverters, that's just the
> variant of the SVF which saves op-amps and grown to become popular. If
> you run with OTA outputs with buffers (such as CA3094 or indeed the
> popular 13600/13700) you skip over the inverting side and run
> non-inverting mode.
>
> > If you add one more the feedback is going to get VERY funny... at least.
>
> Without another integrator? No, not that much fun...
>
> > Why not just build a clone of the TB-303 filter and ADD it to the fatman...
> > that would comemuch closer to the sound u want.
>
> Possibly.
>
> Cheers,
> Magnus

--
Jihad Terrorism Conspiracy New World Order
Revolution Black Helicopters Freedom of
Speech First Amendment Rights: Carnivore Bait
go ahead and READ my e-mail I have nothing to
hide... how about YOU ???