[sdiy] Good 24db/oct HP-LP-BP-Notch filter Schematics ?? Moog type possible consideration..

[Tom Wiltshire]

Hi JP,

I recommend this Electronotes paper:

http://electronotes.netfirms.com/EN85part.pdf

In it, Bernie discusses how to get other responses from 4-pole LP filters. He usefully provides the tap values, so you don't have to work them out yourself, and if you look closely, there's 4-pole and 2-pole responses for HP, LP, and BP all provided, plus notches.

You could implement these if you build a Moog filter with an output amp on each stage. The output amp could be whichever design you like, from the discrete style of the 904A to the CA3080 of the Taurus.  You can then build as many mixers as you like to derive as many simultaneous responses as you want. Each mixer mixes some or all of the input and the four separate outputs from each pole. Alternatively, use a single mixer with switches to bring resistors in and out. Either way, you'd have a "Multimode Moog" filter which is good for the alliteration as well as everything else.

Personally, I'd do it using a SSM2164 since it makes everything so much simpler, but I'm lazy like that. The Moog version would certainly have its own sound.

Regards,
Tom


On 6 Mar 2014, at 13:47, Jean-Pierre Desrochers <jpdesroc at oricom.ca> wrote:

> Hi list,
> 
> Thanks for all your good comments,
> I think the topic is drifting a little...
> Here is my first post question:
> 
> 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...
> 
> --> If I'm willing to forget about simultaneous filter type outputs
> --> my love for Moog ladder VCF sound would drive me to build
> --> a VCF that would include Moog 904a, 904b & 904c (real 24db/oct).
> 
> Any suggestions welcomed.
> Thanks.
> JP
> 
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