Synth restoration, spare PCBs

[mikekelly]

I made this DIY synth many years ago - it was my first music project. It stopped working so I did quite a lot of work in my spare time over the last months getting it running again, with the benefit of a bit more experience.

I fixed up the original wiring, but also had to replace a couple of the circuit boards, one of which (power supply) was home-etched and not good quality, the other (Midi -> CV) was not working properly and was also not of good enough quality to be reliable in the long term.

So I designed a couple of PCBs based on some open source circuits and got them made up by JLCPCB.

I have a few spares of each, if anyone is interested. The power supply is +12/-12V and has a space for a Eurorack header, so could be good for a small Eurorack box or a test setup. There is more info about the Midi->CV circuit here. It’s based on an Arduino nano.

Now that it’s working I recorded a few sounds for posterity. Gives an idea of its capabilities. It’s mainly a noise machine but it can be quite musical too.

https://vimeo.com/544051229

[Gawain (Gawain Hewitt)]

Hi, I’d be interested in one please. I’m thinking of making some synth modules at some point so they’d be really useful.
Great project too btw!

[mikekelly]

No problem, if you DM me your address I’ll send it out to you.

[Dermot (Dermot Jones)]

Is the PSU a ‘capacitor dropper’ circuit? And if so: what current can it supply?

[mikekelly]

No, it’s a ‘half-wave rectifier’ circuit - I should have mentioned it doesn’t connect to the mains, it needs a 12 or 15V AC wall wart. I try not to mess with mains power!
So it uses diodes to split the AC signal and the capacitors are for smoothing. It uses LM7812 and LM7912 regulators which I think max out at 1A. With the four capacitors you might get close to that but it also depends on the spec of your wall wart.