The circuits in the synthbots are pretty straight forward. Send me an email if you’d like to learn how to build your own – it’s cheap and choice!

4-Stage Gated Oscillator
The first one is the 4-stage gated oscillator, which is explained in an earlier post.

Build notes: any small value (<2k) will do for R1-R4, experiment with different caps from 47n-1u, and outputs 1-3 are optional.

Slacker Melodygen
The second bot is a melody generator which I discovered on this forum.

When you send an audio or super-audio clock to the input, the output oscillates at 1/2, 1/3, 1/4, 1/5, 1/6, 1/7, or 1/8th the frequency, depending on the states of control inputs A, B, and C. If you drive those three control inputs with oscillators (e.g. the 4093 circuit shown above), the output moves through a sequence of tones.

Tone Sequencer
The third bot, with all the arms and legs sticking out, is an 8-step tone sequencer, based on this design.

In the bots I replaced R2-R9 with 10k log pots and put C2 on a rotary switch so you could select between a range of frequencies (I think I used 5 steps about 68n – 1u).

Output
If you build any of these you’ll need some kind of output module, the simplest being a 1k resistor followed by a 10u capacitor to drive headphones directly (not ideal), or you can use a voltage divider to approximate line level (330K on the chip output, then 160K to ground). In my noise machine I use an opamp mixer stage as the output, according to this diagram:

Filter
Finally, because most humans don’t like square waves, I built a little filter bot. It is pretty lofi but it does the trick for taking the sting out of these tones.

I believe I used 100kB for the level pot and a dual gang 10kA pot for the frequency control, with 8k2 for R1 and R6, and 47k for R2.

If you’re in Wellington and you’d like to build things like this, I give classes in my workshop, drop me a line if you’re interested: richdecibels (at) gmail.com