A super compact and portable digital drum machine based on 12-bit PCM samples with a built in LCD matrix sequencer. The acoustic version of the DR-220a Dr.Rhythm was released by Boss in 1987.
Boss DR-220a Dr. Rhythm
Ace Tone Rhythm Ace FR-1
After the prototype rhythm Ace R-1 was shown at NAMM in 1964, Ace Tone released the Rhythm Ace FR-1. The first drum machine produced by a circuit called a diode matrix.