[sdiy] Good 24db/oct HP-LP-BP-Notch filter Schematics ??

[Andrew Simper]

On 6 March 2014 02:21, Tom Wiltshire <tom at electricdruid.net> wrote:
>
> On 5 Mar 2014, at 17:13, Neil Johnson <neil.johnson71 at gmail.com> wrote:
>
>> Jean-Pierre Desrochers wrote:
>>> I'm looking for schematics of a good 24db/oct HP-LP-BP-Notch VCF.
>>> All the filter modes outputs should be available simultaneously..
>>
>> The Oberheim matrix 12/Expander multimode VCF might give you some clues.
>
> That was my first thought, but the Xpander pole-mixing design doesn't do 4-pole HP. It'll do 3-pole HP, but only by switching the first stage out.
>
> T.

You can generate a 4 pole HP from summing output taps, you just need
to include the input signal as well as the 4 one pole cascades in your
sum.