Creative differences that had arisen during the production of the Holy Moses album No Matter What's the Cause (1994) with bassist Dan Lilker and Ryker's drummer Meff lead to Andy Classen leaving the band.
Among others he produced records for the bands Dew-Scented, Tankard, Disbelief, President Evil (all from Germany), Asphyx (Netherlands), Legen Beltza (Basque Country), The Old Dead Tree (France), Graveworm (Italy) and Deafness by Noise (Croatia).
From the year 2000, he has found increasing recognition for his work in the international scene, with bands like Rotting Christ from Greece, Criminal from Chile/Great Britain, Dark Embrace from Spain, Krisiun from Brazil as well as Mantic Ritual and Solace of Requiem from the USA recording with him.
In 1997 Andy Classen was founding member, songwriter, producer and guitarist with the German Neue Deutsche Härte industrial metal band Richthofen.
In 2003, Die Apokalyptischen Reiter's Have a Nice Trip was the first album produced by Andy Classen to enter the charts, reaching number 95 in Germany.