Digital Theremin

Posted on Feb 6, 2014

The above circuit, whilst it works, is GREATLY INFERIOR to Lev`s Oscillator for Theremin use. The above simulation waveforms - Red Sine = voltage on L1:A, Black Sine = Voltage on Q1:D, Blue square wave is current through L1:B and Q1 (10mA, 5mA average) It should be noted that this current is through the `tickler` winding which has low R and L (100mR and 39uH max)

Digital Theremin
Click here to download the full size of the above Circuit.

so thermal and other problems should be minimal. Not physically built or tested in this form, but FET model is a good manufacturer supplied one which I have found reliable. Best to look at this schematic together with data on the RCA. Waveforms from first filters - Note, differential outputs have been genersted, but this is not strictly needed - one could take the lower [R4(2)] signal and use this directly: And finally - differentially combining the signals, and sharpening the filtering at the opamp, one gets clean audio (the above is shown with 170kHz and 172kHz input signals, giving 2kHz audio out: One can also add the 4-6 winding to any others giving additional range (for example, add 4-6 in series with 2-3 to extend somewhere around 50uH to this range available. great work!. but it appears the your tickler has a much lower inductance- whereas in RCA they are about the same. 170-180(ish) mH. and the RCA osc coils windings are in two layers with one on top of the other. The diagram for the 421F106 leads me to conclude that is is a single wind with multiple tap points. Fred, Im no engineer (should be my signature!) but couldnt these differences have an effect, albeit a subtle one, on the tone I dont think that I saved it, (and I may be wrong) but I recall another, or possibly followup email where Uncle Howie recommended against changing the coils at all. 76 turns of #26 magnet wire on a 1. 5" form X 2 layers (with about....

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