Senk, a 5v µModular

Been busy building a 5v µModular system for students to learn about and experiment with sound. Design should follow the classic synth setup like for example a Minimoog, with added patchpoints. Part of the design is finished, as follows:

senk1and2

Input of [1] is an Arduino PWM wave. This wave is passively filtered to a DC voltage (ranging from 0v to 5v). This resulting voltage will be one way to drive the voltage controlled oscillator. [2] is necessary to shift the voltage to a more musically interesting range including lower frequencies (-2v to 3v). The range is not amplified to i.e. -5v to 5v because the Arduino PWM only has limited resolution (10 bit = 1024 values). The shifted voltage is inverted because of the sawtooth oscillator under [4].

senk3

[3] shows the voltage scaler (1v -> ~18mV) and the exponential converter as already discussed on sinneb.net.  The 1k tempco should be coupled to the CA3046 array.

senk4

and finally [4] shows the sawtooth core for the Senk. Previous designs of me had an inverting schmitt trigger followed by an inverting buffer in the waveform reset loop. This design features a non-inverting schmitt trigger, sidelining the inverting buffer and a number of resistors. Deploying of the BC550 resulted in the best waveforms, as shown by this youtube video:

Next features I’m working on:

senkworking

Oscillator pulse out, oscillator sub out and mixer section.

Screen Shot 2015-12-08 at 22.23.45

Mixed waveform looking cool in simulation :) Output needs AC coupling.