Back in the day I added a D25 female connector to the side of my C64, wired up a 3.5 octave keyboard (which I built for the 'Formant' [1] synthesizer I made whi

Back in the day I added a D25 female connector to the side of my C64, wired up a 3.5 octave keyboard (which I built for the 'Formant' [1] synthesizer I made while in high school) with a diode matrix [2]. Made some programs to make it easy to access SID 'patches' and voila, I had a 3-voice polyphonic synthesizer. It surely beat the way I used the C64 before that, the thing lying on the stage as if it were an effect pedal with me playing some pre-programmed notes with my toes. I still have the stuff around somewhere, the keyboard looks quite snazzy in its triangular Meranti multiplex housing with the shoulder strap. I could play it on stage but could of course not move far from the machine since the cable was only 3 m long... [1] https://sdiy.info/wiki/Elektor_Formant https://sdiy.info/wiki/Elektor_Formant [2] which I more or less 'invented' myself after I found out I could not play chords without adding diodes since a single key press would light up a whole column of keys... it was only later I found out this is the canonical way to do this.