Cute synth circuit (with explanation)

Nice! It seems a little like a vocoder circuit, where the input is split into bands to form control voltages and then modulates parallel bandpass filters in the carrier signal path.

The CA3280 is superior to the LM13700 for synth circuits I think, unfortunately I believe Intersil sold off the fab capable of doing the old process circa 10 years ago, so the entire CA line was discontinued.

Nice prototype work too. Unfortunately I have lost the patience to prototype entire circuits of that size on plugboard!

Yeah, almost. It's the beginnings of something like that. It would need a good dozen or so more channels, and much higher Q on the filters, to get the CVs. Which would control the amplitude of independent oscillators, instead of two chained.

Reminds me, a friend and I have a "pet project" fantasy: rebuilding SIGSALY from what scant information there is on it. I'd love to hear what the transmissions actually sounded like, at various stages... all I've heard is "sounded like the Green Hornet".

That, or building a Fourier transform circuit out of period technology (tubes, or discrete transistors would be ok too). A retro-early electronic version of this,

Hmm, nice part (if it were still around..). I somewhat recently picked up some LM13700 (therefore having the unique distinction of still being in production and available from Digikey..) so it'll be fun to plop them into circuits in interesting places. I have one idea to stabilize a particularly ill-behaved control loop.

It's probably not obvious and I should've pointed a finger over the active bits, but... the top half (mostly red jumpers) was just the last project I breadboarded. Only the two bottom rows are active here.

This one used more area and jumpers,

Tim

The LM13700 can be used to make a voltage controlled inductance gyrator, if one can come up with a practical application for such a thing. I thought it up independently, and then discovered a similar circuit was in an application note somewhere.