Motors spinning shafts that produce signals is a very old technique, dating back to the Telharmonium [1897], whose tonewheel technique was also used in Hammond

Motors spinning shafts that produce signals is a very old technique, dating back to the Telharmonium [1897], whose tonewheel technique was also used in Hammond organs [1935]. https://en.wikipedia.org/wiki/Tonewheel https://en.wikipedia.org/wiki/Tonewheel Speaking of spring reverbs: you can use a cheap piezo transducer mounted on the tremolo springs of an electric guitar as a passive reverb. Waylon MacPherson demonstrates this in his YT channel: it actually sounds good! https://www.youtube.com/watch?v=XP5pJLgHrgw https://www.youtube.com/watch?v=XP5pJLgHrgw