Positive thinking

The dac/ino board, which is the heart of the Dual Quantizer, has a significant limitation in that the input CV range is 0–+5V. If you have a bipolar CV source — a Sloth Chaos, for instance — forget it, you can’t quantize it. Or you can, but anything negative gets “quantized” to zero. It’s a little odd that Synapse, the project dac/ino is based on, uses 0–+5V for the input CV range but produces output CV of either ±5V or 0–+10V. Someday maybe I’ll work up a new version of dac/ino that’ll input or output CVs in any of those three ranges. Not any time soon. But before then I’m planning to build another module that takes only positive CV, though up to 10V. It’d be nice to have it take negative CVs, but too much complication to be worth it. Of course VCAs often take only nonnegative CVs too. What to do if you have a bipolar source and a unipolar input?

Enter the Positivizer.

This is a very simple module that does one simple thing (twice, it’s really a Dual Positivizer): adds 5V to CV, and reduces the amplitude of the sum by a factor of 2. This means +5V becomes (+5+5)/2 = +5V; 0V becomes (0+5)/2 = +2.5V; and -5V becomes (-5+5)/2 = 0V. So a bipolar ±5V CV becomes a unipolar 0–+5V, suitable for Chaos or VCA or mystery future module.

If you think about it, what it’s really doing is averaging the input CV with a constant +5V. A voltage divider with equal resistances averages the voltages at its top and bottom, so put a +5V reference at one end and your CV at the other, and the output is the positivized CV. Add an op amp voltage follower as a buffer and that’s about all for half the module, and the other half too.

This is the first time I’ve used one of the prototyping boards I designed and had made recently. The board is optimized for Eurorack or Kosmo synth circuits, having footprints for a 2×5 shrouded header for power connection, two fuses on the rails (or you can put Schottky diodes or 10Ω resistors or craft store beads or whatever you prefer), and two 10 µF capacitors to ground. There are +12V, -12V, and ground rails along both edges and two isolated rails for whatever you want down the middle. The rest of the holes are connected in short strips like a solderless breadboard. I like it, it made for an easy layout.

And yes, I forgot to put in bypass caps. So far I haven’t noticed any trouble, but part of me nevertheless wants to add them in. Maybe I will.

3 thoughts on “Positive thinking

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