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It’s an analog, 20 note polyphonic, square wave synthesizer based on the 555 timer chip. The enclosure and keys are 3D-printed, its models were programmed in OpenSCAD, and its PCB was designed in Kicad.

A little history
The monophonic (one note at a time) OKAY synths I made a couple years ago also used the 555 timer as their oscillator, as a sort of homage to the ubiquitous chip’s long history within the electronics community. When I showed one to folks in the scene, “the best 555 synth ever” was an easy, understandable pitch.

But the first question I always got was “How can it play more than one note?”. To that I’d pop the hood and explain that since it has only one 555 to make one oscillator to make one note, to have more notes and still use the 555 I’d need… more 555s!

And while there are more economical ways to get analog polyphony (at the least, the 556 immediately comes to mind), I kept with discrete 555s because I thought it’d be fun to take this train of thought to its logical, if inconvenient!, extreme.

(I consider the POLY555 to be a spiritual successor to the OKAYs, which I haven’t abandoned yet but absolutely need to give some TLC…)”

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