The Poly-9

The Poly-9 from the front
The Poly-9 Polyphonic Chorus Synthesiser

After I'd built the Delta Seven I wanted to put together a polyphonic machine. At the time I had no knowledge of microprocessor designs, and not enough money for something like that either. So I put together a design based on a String Ensamble from Practical Electronics, cut out the string instrument filters and added a 12dB/octave state variable filter with lowpass and bandpass settings together with an ADSR envelope instead. The String Ensemble was based on top-octave-divider organ technology which means full polyphony but no real means of individual articulation of notes, especially not with the common filter to all notes that I had.

To put it shortly, the machine failed miserably. In my eagerness to get the machine together I didn't test the parts individually (especially unwise since I'd changed the original design quite a bit) and once it was all in the case nothing really worked properly. So, after a while I tore most of the insides out, leaving only the keyboard circuits. If you look carefully at the picture above, you can see that there are quite a few empty holes in the front panel. I re-built the chorus generator which then worked properly, and the machine then stayed in pretty much the same state. This means:

...and that's about it! No filters. Whatsoever. Which means the machine has a bit of a harsh (and largely unmodifyable) sound; nevertheless, the fixed lowpass filters in the constantly operating chorus generator tend to cut down on some of the top-heaviness.

I've used the machine as a background string machine but that was a while ago and lately it has never been used much. It never really was completed. The insides of the machine are as unfinished as the unpainted too-thin wood used for the cabinet. Mostly, this machine is a reminder to me to test each part of a design before going on with the next part. In fact, after several years of disuse, I finally sold the machine to fellow DIY:er (who I don't think has done much with it since either).

The Poly-9 from the front
Poly-9 with covers off

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