Best synthesizer for theremin

Posted: 8/30/2020 5:31:51 PM

From: Berlin Germany

Joined: 4/27/2016

Thierry, thank you for this insight. Do I understand correctly that the E-Pro creates its sound by reproducing mixed sharp rectangular signals? How is the excellent temperature stability achieved?

Posted: 8/30/2020 8:32:11 PM

From: Colmar, France

Joined: 12/31/2007

I wrote everything above: Both pitch oscillators’ sine waves are sent through LM393 comparators to transform them into 5Vp square waves. These are fed into 74HCT393 dividers. Then, the original signals, their divide-by-two, and their divide-by-four outputs are sent to 3 respective 74HCT86 XOR gates as mixers. Their three raw output signals (original pitch, one octave down, two octaves down) go to the register switch whose return goes through a passive 12dB/oct 2xRC low pass filter with a corner frequency of ~14kHz which gives a relatively clean but slightly rounded triangle wave. Afterwards, it’s some biasing and the LM13700 wave shaping stuff which we know already from the E-Standard. Finally an additional LM13700 acts as a voltage controlled filter, before it goes to the VCA section which is again LM13700 based.

The temperature stability is achieved by 3 means: First, both pitch oscillator transistor pairs are fed through current mirrors on their common emitters. This makes that when they drift, they’ll drift together and the heterodyning difference will remain the same or almost. Second, the same ugly capacitance multiplier (variable reactance stage) which replaces the variable capacitor to tune the fixed oscillator like in the E-Standard by a potentiometer is also not simply controlled by the tuning pot in the emitter circuit, but the potentiometer is followed bu a unity gain op-amp as a buffer which drives again a current mirror to feed the reactance transistor. Third, the reactance stage as a virtual variable capacitance does not act in parallel on the full LC parallel resonant circuit like in the E-Standard, but only on a part, there are two inductors in series.

Posted: 9/12/2020 11:21:52 AM

From: Rockville, Maryland

Joined: 9/12/2020

Having played three of those magnificent beasts I am unimpressed. Tube amp and baffeledspeaker improves it.  How you play it makes the sound more than the waveform.

For that great sound -mel 9 and talking machine.

But you can waste your time doing what you desire so the only thing I can say about this is that it is affordable:

Mooer tone capture has a sample of an rca sweep, load it into the box and then play your theremin matching the sweep and see if you wasted time and money. If you want dynamic harmonics a distortion box can do that. I use the kmise crunch 22 bucks. I think the kmlise will do more for you.

If you get it to work let us know, then I might buy one and give it a shot

Good luck and happy theremining!


Posted: 9/12/2020 11:45:54 AM

From: Rockville, Maryland

Joined: 9/12/2020

"At that time, there was no other Theremin which could play in such a deep bass register down to 30Hz besides the rarely available Russian tVox tour theremin."

Harrison Instruments theremins have a rich deep bass that goes down to sub audio.

Thierry, you are an expert, but until you get familiar with the easiest and best theremin, you have a rather large lacuna. There may be a model 302 still available.

Probably not for long - like the tvox.

I would have bought one . . .

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