He was a pioneer of krautrock, playing and recording with his band Amon Düül II from 1969 when they released their first album Phallus Dei.

From the 1980s Karrer played as a soloist and with Embryo, a band that combined elements of rock and jazz with music from Africa and India.

[1][2] Karrer co-founded, with Peter Leopold, Dieter Serfas and others, the Amon Düül band and commune in 1967, in the spirit of the student movement.

[1][7] The group had begun in the late 1960s as one of the first to combine elements of rock and jazz, and had integrated ethno-musical influences before the term world music was invented, touring Africa, India and Japan, among others.

[6] Karrer explored the sounds of the oud and its music inspired by Sufism,[2] influenced by Sivan Perwer, Rabih Abou-Khalil and Abdul Wahab who played with him.