I found this box at a thrift shop a while ago and was trying to come up with a circuit to put in it. I finally decided on a circuit made from a NAND synth combined with resonant low pass filter. The controls are as follows:
Top row (left to right) Power on, NAND Osc 1 to output, NAND Osc 2 to output, NAND Osc 3 to output
Middle row (L to R): Starve (10 kOhm Pot on supply V), Q, Fco, Output volume
Bottom row (L to R): NAND1 Fqc, NAND2 Fqc, NAND3 Fqc, NAND input level to filter.
Back (not shown) Ext. Audio Input, Fco Cv input, Output.
Note: Below the glass plate are a couple of blinking diodes.
The control voltage mix op amp is to the left. It turns out this section did not function because apparently I forgot to tie some stuff to ground and -V. The NAND gate chip is on the right. In the middle is the VCF based on LM13700. This is the filter schematic. Note this has an error the transistors on the right need to be grounded. I think there is another error too. (The NAND synth section is not shown) The TL972 I am was using did not seem to work in this application. I am replacing it with a TL082 in future versions. Not quite sure why.
Updated circuit diagram and PCB layout. IC pin spacing should be .1".
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