Just got this one completed and working. Uses the classic (reissued) CEM3340 chip as used in so many classic synths like the Sequential Prophet 5, Roland SH-101 and many others. The PCB wasn't quite right so I had to bodge wire a resistor and capacitor into the CV mixing section, not really worth fabricating a new PCB though as the finished module works very well.
After several failed PCBs, we now have a working version that reads frequency from the modular! So far I've burned out four Arduino Nanos and a 20x4 LCD display module but we're getting closer to a working unit all the time. Next step is writing the rest of the firmware for the Nano to control the DAC and the 4066 switch.
I stumbled across a video demo of a clone of the Buchla LPG on Youtube and was phenomenally impressed. So much so that I knew I had to build one. It's an ancient type of filter using Vactrols, a combination of an LED and a light-dependent resistor to effect a frequency response change. And it sounds wonderful.
The first PCBs aren't quite right, I managed to omit the two voltage tracks to the ICs so this first version is patched up with a couple of bodge wires to make it work. Only smoked one opamp making it, a new record.
To assist in my electronic endeavours I have treated myself to the very wonderful Rigol DS1054Z digital storage oscilloscope and BLIMEY, it is good. This machine does everything from FFT analysis to SPI bus decoding in realtime (almost). It's a four-channel scope, brilliant for watching the channels of something like an SPI or I2C bus.
So naturally the first thing I'd want to connect up was my modular synth. Here's the MakeNoise DPO oscillator outputs running in hard sync mode. FFT shows the harmonics and already I can see that I need to turn up the sweep extent trimpots for the pulse width modulation on two of my other oscillators.
The scope has LAN connectivity, PNG waveform saving to USB memory stick, hundreds of features you might normally expect to pay twice the asking price for.
And by illicitly googling "RIGLOL" you can find a page that lets you enable the paid performances for free.
Not that I condone such behaviour.
Currently on the production line is another kit from Rick Holt at Frequency Central. This one is the fabulous Meth Amp, effectively a clone of the EHX Big Muff in Eurorack format for those insanely distorted TB-303 squelches. Should be ready within a week if the Alpha pots arrive soon.
Having made a complete fuckup of two previous boards by putting the voltage regulators in the wrong way round, I've rattled through building this new version. One more board to build then the modular cases will finally be ready for me to transfer the synth modules into.