This board was a long time in the making, starting off as part of a larger synthesiser project that had to be dialed further and further back with respect to available time over the summer it was going to be built. The original board had more than a few stages: the converter, two VCO’s that would be fed by it, a wave shaper for each VCO output and a mixer to combine these before output. While the mixer was successfully prototyped, as well as the VCO’s (as standalone breadboard circuits), the wave shaping circuitry proved more difficult and was left for a later iteration of the entire design.
In the end the converter and VCO made up the entirety of the PCB, this being the first iteration of the board, seen below, unpopulated.
VoltOk MINI Mark I
While the routing is somewhat messy I was very pleased with the layout, after going through about ten unofficial iterations in KiCAD. This was however irrelevant in the end, as pleased as I was with the layout (as it was) and graphic design, the thing did not work. Or at least it half worked, the converter behaving as expected but the VCO not at all, despite a working breadboard and SPICE simulation of the exact circuit laid out on the breadboard. It was suggested that stray capacitance in the board itself was perhaps throwing off the analogue feedback loop that made up part of the VCO however, I was also advised not to waste countless hours trying to trouble shoot this particular problem and at this stage, was happy to follow that advice.
In light of this, but still determined to have a working PCB by the end of the summer, I stripped back the schematic to just the converter and remade the board with only this circuitry in place.
VoltOk MINI Mark II
To no shock at all, this board worked, despite the routing making less sense now that a lot of the additional circuitry had been removed. Also, despite the focus of another project being power distribution (even more specifically bypass capacitors), not a SINGLE bypass capacitor made its way onto this board, something I realised after the population of the Mark II. This infuriates me but gives me something else to add to the full synth project when I get to it.