The Mellotron was a quite unique instrument built around 32 tape strips from a tape recorder, and had 32 tape recorder playback heads.

It powered the sound of a number of my favourite bands in the 70’s, including the Moody Blues.

A very good video explanation of how it works can be found here : https://blog.adafruit.com/2017/12/04/how-a-mellotron-works-musicmonday/