[sdiy] Looking for 2164 12db/oct slopes bandpass filter design.. more detailed..

[Tom Wiltshire]

On 8 Mar 2014, at 23:25, Jean-Pierre Desrochers <jpdesroc at oricom.ca> wrote:

> Tom,
> 
>> Olivier's designs on the Mutable Instruments site are still a good starting point.
>> His Dual SVF Shruthi board would do what you want - you could use the 12 dB LP from one filter in concert 
>> with the 12dB HP from the other.
> 
> I cannot find any 12db Highpass design using 2164 in both links you gave
> me..
> Sorry..
> 
> JP

It's a standard SVF design, so the HP output is from the first mixer stage on each filter core. IC8A on the top filter, IC8D on the lower one.
The BP outputs are on the next op-amp, and the LP on the final one.

Obviously a state variable filter isn't the only possible 12dB high pass design that's possible, but it's convenient, and it's tested so it seems like a good fit.
Olivier's board has two SVFs with analogue switches to select between the three responses, and to alter the filters from parallel to series. It can already do what you suggested (HP and LP to make variable width bandpass) but it goes quite a bit beyond that too, so you could simplify it quite a bit if that's all you need. The basic filter core design is good though, and would serve your purpose well.

HTH,
Tom