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

Jean-Pierre Desrochers jpdesroc at oricom.ca
Thu Mar 6 17:29:25 CET 2014


Hi Tom,

You are very close of what I'm looking for.
My first wishes would go to an 'enhanced' Moog ladder VCF
with addwed features.
I just have to do my studies now...
First I build a lowpass ladder filter on breadboard
and buffer any of the 4 matched transistors stages
with FET opamps, then see what I can do with all
the 4 opamp's outputs to generate HP, BP & notch simultaneous outs.
The electronotes will be VERY handy !
Thanks.
JP


Le 2014-03-06 10:18, Tom Wiltshire a écrit :
> 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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