This flowchart should give a general idea of how things are interconnected:

Each component is closely linked to its modular synthesizer namesake, except that I use a digital potentiometer (MCP4251) to control the amplitude. The low pass filter is an AS3320, which is receiving control voltage from the inbuilt DACs of the ESP32. The vacuum tube is a Soviet 6n2p (12ax7 "equivalent") that I snagged from an old radio, and miraculously it still worked. I'm using a PT2399 to create an echo, and the delay time is modulated with the same digital potentiometer that I'm using to control the amplitude of the audio signal. The signal is fed back into the ADC of the ESP32, translating the audio to light through four PWM controlled LEDs. Finally I bridged two LM380s to create a 5W amplifier, which makes this thing quite loud.

This was also the first time I tried to create a speaker enclosure. I didn't have high hopes for it, and was expecting it to have a much sharper resonance frequency, but it turned out fine.

You can watch the whole build in this video if you are interested in learning more:

The project is powered from a single +12Vdc wall wart, but I'm using various regulators to create +5V for the digital circuitry, 6.3V for the tube heater, and a 7660S charge pump configured to invert +12V to -12V for the negative rail used by the opamps and the filter.