21 + 5 accidental treble buttons, 3 voices, 3 voices instrument with 5 automatic couplers, located behind the fingerboard, allowing 5 possible sounds : – 1 voice : concertina (single medium reed) – 2 voices : double medium reeds. (dry, swing or musette, according to voicing) – 3 voices : double medium + single low octave reed – 2 voices : Bandoneon. (single medium + single low octave reed) – 1 voice : single low reed 12 basses with 3 stops.