AS2164 pole mixing filter

[craigyb]

This design is taken from the electric druid multi mode filter discussion pages. Here Tom Wiltshire outlines various filter types used in several polysynths and monos. Amongst them are a pole mixing filter similar to the Matrix 12, but rather than use the CEM3372 or the modern AS3372E, Tom as put two designs together, one that uses the AS2164 and the other that uses the CEM3320 or AS3320. I decided to go with the slightly more complicated AS2164 design as I had a bucket load spare, so I have built a dual voice card with the same pin out as my other AS3372E dual cards. This should allow me to test the card in an existing synth.

My high accuracy 330pF caps arrived today so I added a lot more components and realized my mistakes and added 2 more TL074 to cope with various functions.

Left to right

ADSR chips, ADSR inversion, buffering.
Input VCAs
Control switching, EG invert, velocity, key track etc
Filter cores
Resonance and final VCAs
Pole mixing resistors and pole selection and output buffers.

[analogoutput]

Nice, I did a Kosmo format filter based on the Electric Druid AS3320 version:

Electric Druid pole mixing filter

I don’t have the final front panel yet, but this module seems to be working: [PXL_20230503_231205738.MP] It’s a multimode VCF based on a (partial) design by Electric Druid. I made a number of modifications but the basic design is not really changed. It uses pole mixing to achieve different filter responses. The Shape rotary switch allows selection of two different low pass, two high pass, two band pass, and two notch filter shapes. The latter two can be altered by changing resistors on the P…

[craigyb]

Yeah, I saw a post that you did a while back that we had conversed on. Then realized I was probably repeating your work but with the AS2164.

[craigyb]

Here’s the finished version of the AS2164/V2164 filter card. Ready to be tested in my existing PolyKit-16 chassis. Hopefully it will work ok without too much fuss. I might build an extension card so I can debug it out of the synth. I’ve got two spare VCAs and two spare opamps.