The Solafide Forbes Nash Organ


A few years ago, [Chad] wanted to build a musical instrument. Not just any musical instrument, mind you, but one with just intonation. Where modern western music maps 12 semitones onto a logarithmic scale per octave, just temperament uses ratios or fractions to represent notes on a scale. For formal, academic music, it’s quite odd especially if you’re building an analog synth for this temperament. In a remarkable three-part write up (parts one, two, and three), [Chad] goes over the creation of this extremely strange musical instrument.

The idea was for this synth to produce sine waves for each of the tones on the just intonated scale. [Chad]’s initial experiments led him down the path of using strings and magnetic pickups to produce these sine waves. These ideas were initially discarded for producing sine waves electronically on dozens of different homemade PCBs, one for each tone.

The keys are an extremely interesting design, working on the principle of light from an LED shining on a photodetector, blocked by a shutter on a spring-loaded key made on a laser cutter. The glyphs on the keys seen above actually have meaning; each one describes the ratio of the interval that key plays, encoded in some schema that isn’t quite clear.

What does it sound like? There’s three videos below, but because this synth isn’t tuned to the scale you’re used to, it doesn’t sound like anything else you’ve heard before.

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