Boss / Roland Dr Rhythm DR-55 Vintage Analogue Drum MachineBoss DR 55 Vintage Analogue Drum Machine. The DR 55 Dr. Rhythm was released in 1980 and was one of the first step write style drum machines, and it was the first rhythm machine in BOSS' successful Dr. Rhythm Series. It was small and easy to use perfect for musicians at any level. Incredibly basic controls and sounds made this drum machine an instant hit among guitarists and other musicians looking for drum accompaniment to practice along with and even