[sdiy] Multi-Input filters

[Theo]

My QUAD filterbank uses a multi input filter based on the MS50.
However a number of changes in where made,
most notably two section are cascaded to get 24dB LP/BP and 12dB HP.

The filter is based on a diode bridge as variable resistor element.
When you input the signal though the caps on the "+ and -" sides of the
bridge you get BP.
How it works is very easy to see when you replace the diode bridge with two
resistors in the schematic.
This simple structure:

in--C--+--R--+--buffer
       R     C
       |     |
      gnd   gnd

can often replace/outperform a statevariable when it is used for BP only.

Theo

BTW Please DO come to hall 5.1-A64/B67 on the Musik Messe if you want to
hear the filter ;)




From: Osamu (Sam) HOSHUYAMA <houshu at rogers.com>
<snip>

> A Japanese diyer said he developed a BPF modification based
> on the MS-20 filter, which results in almost the same function
> as the Synthacon filter.  I'll try to ask him to put the
> schematic available online.
>
> Best,
> Sam Hoshuyama
>
> Tim Ressel wrote:
> >
> > Yo,
> >
> > I was fascinated by Ken Stone's description of his
> > Synthacon filter.
> >
> > http://www.cgs.synth.net/modules/cgs35_syntha_vcf.html
> >
> > Especially the part about having different sources
> > driving the various inputs. I was wondering if this
> > trick could be applied to a state-variable filter? I'm
> > thinking the inputs would be applied to the integrator
> > summing node or buffer, depending on the filter
> > design.
> >
> > Thoughts?
> >
> > --Tim
> -- - ---  - -- ------ - -------- -- - ---- -
> Osamu (Sam) HOSHUYAMA      houshu at rogers.com
>                               Ottawa, CANADA
> --------------------------------------------
>