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

Tom Wiltshire tom at electricdruid.net
Wed Mar 5 19:23:43 CET 2014

On 5 Mar 2014, at 17:22, Oren Leavitt <obl64 at ix.netcom.com> wrote:

> On 3/5/2014 9:58 AM, 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 only filter I found that do such things is the following:
>> http://www.analoguesystems.co.uk/modules/rs110.htm
>> But no schematic available...
>> Any suggestions welcomed.
>> Thanks.
>> JP
> That design is most likely two tracking state variable filters connected in series for the 24db/oct response.
> I believe there were some ideas for this in Electrontes.

I doubt it, because it provides simultaneous 4-pole HP and BP outputs. The 4-pole HP requires the HP output of the first filter to be sent to the input of the second filter, but the BP would require the LP output to be used, as would the LP.

Sure, you can do these responses with a pair of 12dB/oct SVFs, but not simultaneously. You'd have switches to select the modes.

I can't see a simple way (that is to say: actually likely) that they've built this. It's starting to bug me!


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