The schematic for the Microsynth is out there - there is a hand drawn one that is different, but I used the one that is more easily out there drawn by Fabian Hartley. If you connect the LM13X00 OTA to a discrete version of this two resistor and transistor circuit, properly as per the schematic, the filter really does work the same. Note that this is just a snippet from the CA3094 datasheet circuit itself: For this part, I realized I can simply used the OTA onboard the LM13X00 chip, added the two transistors & two resistors that you can see here, that function as pins 6 and 8 of the CA3094 circuit. The hard part here is the triggering circuitry which uses a CA3094 OTA to 'drive' the filter sweep. Most if not all of Ray Wilsons filter and other noteworthy filter designs use 13X00 chips - they're not missing any filtering mojo. Plenty of great filters use non-CA3094 OTAs in the synth world the CA3094 has nothing ‘special’ for filters. It's a standard OTA filter, it uses 3 OTA sections, and each section utilizes output buffering. How I see it, the filter itself is 'nothing special' in terms of needing CA3094s. I did it this weekend, and I did it with two LM13X00. I'm not going to screw around with modding mine, and I will not even 'true bypass' it (since I plan to sell it and it’s unusable on my pedalboard), even though a 3PDT switch sits in there, stock, but with only one pole in use if I'm not mistaken! Moreso I've always wanted to build/imitate the triggered filter for a long time. Likewise, it’s just too big to leave on the board. The internal gain boost/buffer is necessary for good tracking, but when ‘bypassed’ the gain boost, and hence the clean signal reaches self-distortion at that point, and too hot a signal for all gear following it. I’ve enjoyed it, but there are some things about it I've always wanted to tweak, the bypass scheme makes it useless. I have a Microsynth I got used in a store trade for some gear I didn’t want. I say that at least from an audible perspective - So, after a bunch of simulation, that this weekend I spend time making the Microsynth filter a reality. Each OTA has an extra pin for a 'dual diode' drop functionality or whatever if you ignore that pin and leave it unconnected, again, it's more or less the same as a CA3080/CA3094 OTA. The 3080 did not have output buffering capabilities, but the LM13600 adds simple darlington transistors onboard, or less one for each OTA, a slightly different (simplified) configuration than the added circuitry the 3094 has, but in most cases and for most of our purposes, functionally equivalent. The LM13600 (LM13700) chips, to my understanding, are more or less a chip that houses 2 OTAs - which are fairly primitive - and similar to the 3080 OTA. A lot of that is beyond me, and I suspect, beyond our uses (and the microsynths). The CA3280 are 'the best of the OTAs' according to Don Tillman and spec, a dual chip with OTAs that meet better specs than the CA3094 and buffer, and possibly some additional capabilities.

The OTA portion CAN be used without the benefit of its 'buffer' or additional when preferred, but rarely is.but the option is there. The CA3094 type OTAs are slightly less primitive 8 pin OTA which utilized extra pins for a basic transistor circuitry, most often used as an output buffer. It has not buffering, which comes in handy seeing as an OTA more or less acts as a variable (and sometimes high value) resistor, which can load following circuitry.

The CA3080 type OTA is basic/primitive single OTA (think 741 op amp) on a 8 pin package. Any other OTA can be implemented to do the same, and I would dare I say NO tweaking needs to be done in the majority of cases. The rest are all acting like standard voltage-controlled (variable) resistors, more or less. With a little understanding of OTAs, really, only one of seven CA3094/OTAs in the microsynth is doing anything particular to that part. I've been looking this dilemma over a lot recently.

Eh microsynth schematic