For my project I decided to make simple analog synthesizer using an oscillator circuit using the reverse avalanche mode of a transistor — specifically the 2N3904 transistor. I found the circuit from Look Mum No Computer on YouTube as well as his website.
The picture below is my redrawn schematic of the circuit, with the capacitor value changing — I used 10uf, 20uf, 47uf, and 100uf. In total I made six separate circuits that all combine into a common power, ground, and audio out bus.
Below is a video of five of the circuits bussed onto a breadboard.
Finally I soldered everything onto the ‘bus’ proto-board, and planned out a basic enclosure and cut it out on the laser cutter.