[sdiy] SSM2164 state-variable filter PCB now available

[Scott Nordlund]

>From my (limited) knowledge of control systems, root locus, etc. I'd expect that as resonance is increased (or maybe even cutoff frequency since this is set by loop gain too), you'd get a pair of conjugate poles (2 pole resonance) and one pole that goes off somewhere- effectively a 2 pole filter with an additional pole that causes trouble by not doing what you want it to do.  I'm not familiar enough with this topology to make a particularly informed estimate at its behavior, and I haven't run any simulations, but it seems like an odd choice.  

How "well-behaved" is it in the end?

(by the way, has anyone analyzed the TB-303's "3+1 pole" filter in this light?)

> From: neil.johnson97 at ntlworld.com
> Date: Tue, 14 Oct 2008 23:00:15 +0100
> To: synth-diy at dropmix.xs4all.nl
> Subject: [sdiy] SSM2164 state-variable filter PCB now available
>
> Hi all,
>
> If I may be so bold... a little announcement:
>
> PCBs for my SSM2164-based 3-pole state variable filter are now
> available. Details, etc, here:
> http://www.milton.arachsys.com/nj71/index.php?
> menu=2&submenu=0&subsubmenu=1
>
> Note: I've decided to try a standardised form factor for my PCBs,
> 80mm x 80mm (3.15" x 3.15") with 70mm x 70mm (2.75" x 2.75") M3
> fixing centres. Should make it easy to stack them for large multi-
> PCB systems.
>
> It sounds quite clean - being state variable there isn't the
> distortion/character that you get with a ladder filter. As with any
> analogue system, drive the input hard and it will distort, if that's
> what excites you.
>
> Sometime this week (perhaps a job for the weekend) I'll put up some
> MP3s demonstrating this filter.
>
> Cheers,
> Neil
> --
> http://www.njohnson.co.uk
>
>
>
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