[sdiy] Bandpass Filter Recommendations

[David G. Dixon]

Tom,

I'd definitely like the schematics!  Wow, that Sowa dude does nice work!

> Hi Scott,
> 
> I did some work towards a similar thing, but never got to a point I
> was happy with. I decided to use an SVF based on the SSM2164. I
> started out with Roman Sowa's design, but only used the filter part
> of his circuit:
> http://www.sowa.synth.net/modular/vcf.html
> 
> This uses two OTA stages for the filter and one for the resonance. I
> used the spare stage for the gain control. This makes a convenient
> total of 1 SSM2164 and one quad op-amp per filter.
> 
> I had some difficulty with the resonance. You'll find the discussion
> on this in the archives. Ian Fritz and Neil Johnson gave me a lot of
> help, but I never did get it going how I wanted, although I think
> this was a fault, not the design per se. It's currently a project on
> my "things to go back to" shelf.
> 
> If you want more details, ask me and I'll mail you the schematic.
> 
> Hope this helps,
> Tom
> 
> 
> On 24 May 2009, at 19:23, Scott Juskiw wrote:
> 
> > I'm working on a programmable filter bank and am asking the group
> > for recommendations on a suitable bandpass filter. The filter
> > requirements are:
> >
> > 1. voltage controlled frequency
> > 2. voltage controlled resonance
> > 3. voltage controlled gain
> > 4. analogue circuit
> >
> > Some solutions I've come up with:
> >
> > 1. state variable filter
> > 2. cascaded lowpass/highpass filters (using cascaded OTA stages)
> >
> > #1 is relatively easy but I'm less than thrilled with the 6db/oct
> > slopes. #2 seems to be better for my needs since I can get 12 db/
> > oct slopes.
> >
> > Are there any other filter topologies that anyone can recommend?
> > Hopefully something that won't require 400 components per filter
> > since I'd like to have a bank of these on one PCB. But maybe that's
> > asking for too much. I would also consider a digital filter
> > solution, if it would be easier to build and if (big IF) I could
> > figure out how to do it digitally.
> >
> > Thanks
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> >
> 
> 
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