[sdiy] Multi-Input filters

[Grant Richter]

I have been working on the BIG filter chart. That is, take each filter
topology and cross it with each transconductor type.

Lots of mistakes here, please correct!

For example:

Typology: 24 dB Rolloff (mostly Butterworth lowpass)
Transconductor

Transistor: Moog 904A & later
Diode: EMS Synthi

OTAs
3080: Star Synare
13700: Wiard Omni
3280: Patchell
Discrete: Jurgens 20xx
Hybrid: Arp 4072?

CMOS VCR: ?

Opto-coupler: Wiard "Boogie" filter (shipping in March)

Typology: State Variable
Transconductor

Transistor: ?
Diode: ?

OTAs
3080: Aries 3xx
13700: Evenfall Mini-Modular
3280: Patchell
Discrete: ?
Hybrid: ?

CMOS VCR: ?

Opto-coupler: Wiard "Don't Bother" filter

Typology: Sallen-Key
Transconductor

Transistor: ?
Diode: Steiner-Parker

OTAs
3080: ?
13700: Korg MS-20
3280: Patchell
Discrete: ?
Hybrid: ?

CMOS VCR: ?

Opto-coupler: Buchla & Wiard Borg

Only one example is listed for each type, please add more info if you have
it. Each blank spot is a potential new filter design.

Since I like the sound of Vactrols I have been building each topology from
them as in the Borg and Boogie designs. A Vactrol State Variable or Biquad
sounds just as plain vanilla as any other SV implementation (IMHO).

I have noticed the topology is far more important to the characteristic
sound of a filter than the actual transconductor.