Diy synth workshop was based on NAND (cmos 4093) synth. Participants first prototyped their own version of the synth on protoboard and then soldered it to a copperboard. Synth circuit is really simple (+- wires, 1 resistor, 1 capacitor, output wire) and perfect for beginners to learn how to make their first oscillator.
Amp workshop was based on lm386 opAmp chip and it had x20 amplification (example from Nicholas Collins : Art of Hardware Hacking book and various internet sources). Amp has 0.5 watt power and it can feed a small speaker. Participants first made working prototype of the amp circuit and then soldered it to a copperboard.
Putting soldered amp and synth circuit into a box was left as homework. I thought to leave flexibility for participants how to use their built synths and amps in the future projects.
Photo by Victor Khashchanskiy
Here is sound sample of solar powered NAND synth: