SX-151 Synth Guitar

We wanted to play a synthesizer with less traditional input system and more opportunity for expressive control, so we built this.

The idea is not original; we were inspired by a similar model made by Japanese innovators Maywa Denki involving a taut cable system coupled with a pick-shaped stylus, and this YouTube video.

The neck is a pressure-sensitive strip that sends note data to the synthesizer. The left hand controls note input while the right hand can modify the synth modeling such as LFO, cutoff, resonance, etc. The unit makes noise when pressure is applied to the strip, and the higher you are on the neck, the higher the note. We have ‘tuned’ ours by placing color coded markers on the neck to indicate note placement. This ‘fretless’ style input system allows for both traditional chromatic and dissonant noise performance.

The synth module is the Gakken SX-150 Mark II. They are extremely affordable and very easy to modify. Originally, the input system relies on a stylus completing the circuit through tapping on the 3-inch ribbon.

The ribbon has 3 solder points – the start of the strip (lowest note), the end of the strip (highest note) and the stylus (effectively the ground).

The softpot (touch-sensitive strip) was soldered on with the stylus solder point going to the center pin, and the left/right pins connecting with the lowest note/highest note solder points.

If you are going to try this for yourself, we recommend purchasing the Gakken SX-150 Mark II (red model), not the original SX-150 (black model). Not only are they much cheaper and easier to come by, they have a different configuration on the circuit board. Most important to this project, the octave range with the softpot is at least 3x the range given on the Mark I, due to different strength of resistors used around the ribbon.

For the body, we mounted ours onto a 12″ vinyl record, and mounted that onto a kids toy ‘PaperJamz’ guitar, seeng as it had the shape we needed and already contained guitar strap mounts.

We encourage anyone curious about synth hacking, instrument modification or alternative input systems to try this project. It forced us to think through alternative writing and performing in our band.