Some time ago we posted an odd video about an arduino-based synth. [DeFex] (arduino forum user) revealed a nice PCB design to get it shielded:

The arduino is a 4 oscillator phase accumulator, and does a few other things.

each oscillator has a separate DAC which are mixed in the analog realm (controlling an 8 bit DAC level with another 8 bit signal gives a lot better resolution than changing its level digitally)

The levels of the DACs are controlled VIA PWM > 4 pole filter > Vref. and then the DAC output is level converted to +- rather then +

Each pair of DACs has another 4 pole filter on the output to eliminate any aliasing.

And yet another 4 pole filter on an aux envelope out.

There are 2 Multiplexers (completely copied from the mux shield) which get the values for 32 potentiometers which control various modulation and wavetable selection etc.

There are no voltage controlled filters on board, but it can output envelopes and triggers for modular synth filters/analog envelope generators

And 2 inputs for external control voltages through a special ADA4091-2 op amp which can take +_25v over the rail input, and being powered by the arduino power, it automagically protects the inputs from the higher voltages existing in a modular synth (+- 15v)

I am planning to make a cut down version which would fit on a proper shield, but i still need to experiment a bit (especially trying to make a nice sounding 5 volt voltage controlled filter!) but it will still have to be a mega.

I will continue posting as it is built and tested along the way.
so far i attached the arduino and made sure the signals and power are going to all the proper places.

via [Arduino Forum]