After the Droid show last night, I realized I really should get my butt in gear on those hardware synths I’ve been pondering about for a while now. It would be pretty sick to be able to make and sell really cheap but still useable Eurorack synth modules at those types of show.

So today I laid out a trial run of a simple LM13700 VCO. These chips are in way too many of the modules already on the market but I’ve always been surprised at how simple they really are. They are really nice to work with… but I already fried one by allowing too much current into the Iabc pin. Oh well…

And now I’m realizing why these modules are always rather more expensive then I thought they should be. Getting it stable isn’t as easy as I would have guessed. Still, I’m sure a transistor based logarithmic convertor would get the input stable enough… and if I get this LF353N OpAmp’s feedback network dialed in then the output should be pretty stable as well.

Maybe. I’m no electrical engineer. I know this stuff, but I’m not gonna sit down and do the math out quite yet. Plus, what I’ve got so far would work wonderfully for a simple noise toy anyways.

… which may fit the Droid crowd better anyways…

Breadboard of the LM13700 VCO I’m working on: