Complex sentence: Around this time, Pinder was employed by Streetly Electronics, a firm that manufactured the Mellotron, a keyboard instrument that produced sound when each key pressed a magnetic tape head onto a short strip of magnetic tape.
Split into simpler sentences: Around this time, Pinder wound up employed by Streetly Electronics, a firm that manufactured the Mellotron. The Mellotron was a keyboard instrument that produced sound when each key pressed a magnetic tape head onto a short strip of magnetic tape.