He was the founder and leader of The Bobs before leaving the group in 1991, and has released several albums as a solo artist since then.
Madsen learned to play guitar as a teenager and studied classical piano at UC Berkeley.
Among other successes, Madsen was nominated for a Grammy award for their arrangement of "Helter Skelter" by The Beatles.
The title song from his CD Old Mr. Mackle Hackle was adapted by Madsen into a children's book for Little, Brown & Co.
A musical, "The Shaggs: Philosophy of the World", based on the life story of The Shaggs (co-written with Joy Gregory) was co-produced Off-Broadway by the New York Theatre Workshop and Playwrights Horizons in 2011, and was nominated for a Lucille Lortel Award and two Drama Desk Awards.