Their first album - Silver Apples. This technology predates any of the commercial synthesizers - Simeon was playing a collection of homemade oscillators, tape decks, reverb machines and guitar effects.
As Trebuchet Magazine says:
Silver Apples are THE electronic group of all time…
Silver Apples are to electronic music what Thomas Edison is to Facebook."
Website here: Silver Apples
This post at Dangerous Minds brought up the subject and prompted some digging. Funny how close their sound is to current EDM and trance music.