Monday, January 28, 2013

DIY modular synth panel

Hey, it's a modular synth. Very low-cost, -fi, -skill, etc. Generally low. I don't know what I'm doing (e.g. transistors were avoided, because what do they do?) but no flames so far, therefore success! I wanted something that would work with eurorack adding much needed triggers and lfos, but that could also stand alone as a 9v battery powered patchable weirdo noisebox. The circuits are all pretty simple - either CMOS or passive - so very light current draw. Quite a few homemade vactrols in there, as vactrols are expensive, but easy to make with an LED, a photoresistor, some tape and they will look kind of like molluscs, which commercial vactrols do not really - so added bonus there. It's housed in a most-reasonably-priced tool box from the home-improvement center, Bauhaus. It's made of aluminum, probably a little over 1mm thick. Cost about 9 Eurobucks.
 I drew up a plan and drilled holes in the back with a hand drill. Not the fun part.

 Filled it with the following curcuits:
  • A quad-oscillator which is based on the 40106 hex-inverter chip. Each oscillator has a range switch to select between audio and control frequency and an input for voltage control via a vactrol.
  • 3 input logic gates based on the MFOS Mickey Mouse Logic circuits. Switchable between AND and NAND; and Or and NOR. Wow, ridiculous sentence (but logical, maybe?).
  • A pulse divider made with CMOS 4040 chip and diodes.
  • A Ring Mod-ish kind of thing similar to these.
  • A CGS Ring Mod because I had the pcb laying around and it's passive. It doesn't work that well with the levels this box puts out but sounds great with signals from stronger eurorack oscillators.
  • 6 "low pass gates" or slews. These are passive and have voltage control via vactrols. Switchable capacitor size gives either slew or filter/vca effect.
  • A 3x3 matrix mixer.
  • Multiples
Components are from Tayda which is very cheap and somewhat offbrand in certain cases, but there is a recession, and this is how we must roll. Maybe cost about 50 Euros for the parts.

Here is a demo of the box making noises with a bit of reverb and synced to a kick and snare from the octatrack.

And here is a short demo of the box making noise on its own with no reverb or anything else helping out.

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