Modified Mid-Fi Random Number Generator

Heavily modded & not-quite-so modded versions

My first DIY project, a Mid Fi Random Number Generator by Doug Deeper that I've modified the tits off of and stiched some fresh tits on. Minor tweaks to this circuit can produce a bellyful of easter eggs including a bass simulator and filter sweep.

Noise reduction

The main drawback with the 2006 schematic is the fuzzy crackle that splurts out after a few seconds of not playing. I've seen other people complain about this on forums as well. I've worked out you can fix this by connecting a 47k resistor from the negative leg of the 10uf electrolytic capacitor to ground and syphoning off those superfluous juices.

Bass simulator

You can hack a fairly fat synthy bass sound by removing the connection from Q2 emmitter to ground. I added a footswitch to connect/disconnect these two points. I call it a "simulator" as it can only produce about 8 notes, recycling through them as you move up the fretboard. You get a similar effect by reducing resistance between Q1 emitter and +9V or removing/reducing the 470k resistor between Q3 base and collector. I spliced pots onto these connections for my 'beef' and 'snark'* controls to emphasise lower or higher harmonics. Essentially these controls have very similar effects but interact interestingly together. If I had to recommend just one modification (other than the noise reducing resistor) it would be the 'snark' knob, as it most elegantly controls the low to high note favourability of the pitch-glitching. A large pot in place of the 470k resistor from Q2 base to collector does this yet again.

More knobs

The additional knobs control feedback and gain ("crank"), both easily chopped into the circuit. I've seen a couple other people have added a feedback mod to the RNG by replacing the 100k resistor that connects the collector of Q2 to the output capacitor with a 100k pot, so that's easy enough. For a gain control, add a 100k pot from Q4 collector to +9v, with a 51k limiting resistor, which is useful to turn down when the other settings kick out a squeel.

Adding a voltage starve has interesting effects with this pedal, at a certain setting (around 1 or 2v) you get a downward filter sweep effect that's triggered when you play a note. Voltage starving often works well with fuzzes but I didn't really have room in the enclosure this time, same goes for a tone knob.

Final word

During my aimless tinkering I managed to eke out a volume swell effect, but I'd wired things outrageously at this point. Nevertheless, it's further testament to how many hidden gems lurk in this pedal's circuitry if you're willing to poke and bend it.