Abstract: An electronic circuit connected to and operated by the bass buttons of an accordion to simulate a string bass instrument. The circuit can be disposed in the accordion or remote from the accordion. Each button has a switch associated therewith which couples to means for generating a fixed frequency signal indicative of the actuated button. Signals over a two octave range may be generated and logic circuitry is provided to effectively expand the single octave of available buttons to greater than the single octave such as by a half octave expansion. Output circuitry shapes the output audio signals to allow more or less of the harmonics to pass. A special bass pluck circuit is also provided.