Random number generator - what is it actually doing?

[Top Top]

I just built this and it is a fun little device. What is it actually doing though? There is some extreme distortion of transistors going on there, but there obviously has to be more to it than that. How is it actually providing the glitchy, note jumping sound? Seems like there is some feedback loop going on in there, but how is it then kept from just self-oscillating endlessly?

I did a lot of swapping transistors, and sometimes with certain transistors, it would provide a fairly reliable octave down (for a limited range), and other times, it can do a fifth down, which was really unusual though again in a limited range of the fretboard. It got me wondering how far off it was in design from octave down pedals, or if anyone has ever designed a fifth down pedal?

It is fun to use through a ring modulator, by the way, with one input as the straight guitar, and one as the RNG.

[earthtonesaudio]

The main action is happening with the last two transistors.  The two before are mainly just boosting the signal a lot.

If not for the .01 cap between "Q2" and "Q3," the "Q3/Q4" pair would essentially form a comparator with hysteresis.  The output reinforces the input, so you'd get a very square-wave fuzz with not much else going on.

But because that cap's in there, there is some phase shift going on and the output doesn't really reinforce the input exactly.  So you get cancellation and reinforcement, back and forth, which is probably where most of the "randomness" comes from.

A single RC network doesn't provide enough phase shift to make an oscillator, so that's why it doesn't keep going by itself.

[Top Top]

Thanks - your response actually gives me some things to look into to understand about circuit design. In other words, I didn't completely understand it, but it gives me some things to look up and read about. Thanks!

[tcobretti]

So are you saying if you pulled that cap and broke the signal you'd get fuzz, or if there was no cap but still a connection there would be fuzz?

I like square wave fuzz.

[earthtonesaudio]

I'm talking about shorting the cap.

[tcobretti]

Hmmm.

Thanks for the tip!