The Mellotron was the original sampler. Invented in 1963, it was a keyboard instrument that played back sounds stored on magnetic tape. When you pushed a key, the tape would play, and when you let go, it would spring back to its original position. It was big, it was impractical, and now that we're well into the age of digital synthesis and laptop-based sound production, there's no reason to go back. Right?
Invented in Brooklyn, the Crudman is a modern take on the Mellotron. The sounds come from a cassette player playing a tape all the way through. That tape could contain a single droning tone or something a little weirder, like a spoken word track. The players are re-engineered with an Arduino-based Teensy microcontroller so that they respond to MIDI signals from a keyboard. When you press a key, the tape motor speeds up or slows down with enough precision to generate a specific musical note.
If you have one tape player hooked up to your keyboard, the Crudman is monophonic, meaning that one tone can be played at a time. If you have a few hacked players on hand, you can arrange them to generate polyphonic sounds, like a chord, with multiple notes being played at once. The sounds coming from the tape can also be sculpted using the envelope controls—attack, sustain, decay, and release—that come standard on most synths.
Engineering the Crudman posed some thorny technical challenges, which its inventor lays out in a technical document available online. For example, the volume of an audio signal decreases dramatically when a tape is slowed down, and Sony Walkman motors were not designed to change speed very quickly or precisely. The Crudman wasn't exactly an intended use case for Sony's iconic portable cassette players.
The volume issue was solved with a dedicated gain circuit that measures how fast the motor is running, and adjusts the signal's volume accordingly. The second issue was a mechanical one, and a little tricky, but the Crudman's creator happened to come across a Sony model called the TCM-200DV. The TCM-200DV contained a three-phase motor, which was more precise and quick to respond than those in standard Walkman models. Still, its motor driver circuit needed to be tinkered with.
Hack it all together, and you've got yourself a batshit little DIY Mellotron that you can play like a synth. Rad.