I decided to interface a Moog moogerfooger MF-101 Low Pass Filter with my G2X to use with mono synth patches.
I needed to get a DC control voltage signal out of the G2X to plug into the fooger external voltage control jack for the filter cutoff. But, the G2 outputs have DC blocking capacitors in the way. So, I opened up the G2X and used my o'scope to find a point before the DC blocking cap for the G2X Output 4 from which I could get a DC signal. I soldered a cable to the G2 circuit board to bring out the DC control signal to a plug for the fooger. I found that the G2 produces a signal maximum swing of less than -4 to +4 VDC. According to the fooger specifications, the MF-101 uses 0 to +5 VDC for the external control voltage. But, this turned out not to be the case, the fooger filter cutoff will work with a bipolar external signal (the fooger filter cutoff knob produces a signal swing of -5 to +5 VDC). I traced the external cutoff signal on the fooger circuit board to the circuit that buffers and mixes the signal and modified it to increase the gain to work with the -4 to +4 G2 signal.
I connected the necessary cables between the G2X and the fooger and then created a tuning patch to trim the gain of the fooger external cutoff circuit so that the filter cutoff frequency would track properly.
The moogerfooger LPF sounds great with the G2X! Maybe not as good as a minimoog or modular 904 filter, but better than the G2 "FltClassic" module (sorry Clavia!).
This is not a perfect setup. There are a couple of "issues":
1. Currently, there is no way to program the fooger filter resonance setting in a G2 patch, it must be set manually. This would have required using another G2 output for this CV signal, leaving only one for the patch audio output signal (no G2 stereo output, too high a price to pay).
2. The G2 Master Level and the Patch Level settings also affect the DC CV signal output level. The workaround is to set these levels at maximum and adjust the patch audio output level within the patch itself.
I think that the same interface could also be made to the NM1.