My New Year gift to TW: A new theremin circuit

Well thank you very much for the explanations :) i'll give the most dusty part of the library a try.

"Nowadays, where everything has to be cheap and integrated, and at the best digitally controlled or compensated, most engineers have forgotten about technologies which achieved the same or even better results by using a few "tricks" like building stable harmonic oscillators in common gate configuration."

 It's a shame, in my very humble opinion. In fact that's exactly what got me into theremins : i wanted to build something that showed the power of analog electronics. 

"Nowadays, where everything has to be cheap and integrated, and at the best digitally controlled or compensated, most engineers have forgotten about technologies which achieved the same or even better results by using a few "tricks" like building stable harmonic oscillators in common gate configuration."  - Thierry

Do I love analog or digital?  It's all the right tool for the right job IMO, though the field keeps expanding so you need to be a polymath just to keep track of the various tools.  The synth field exploded when processors were able to auto-calibrate the analog circuitry, enable polyphony, track the keyboard, and implement MIDI.  If those guys were able to pawn it all off on the very stable processor they most likely would have, but the early digital hardware just wasn't up to it.  Most of the negatives of digital today are due to shoddy programming, not any inherent superiority of analog.  Corps are too stingy to pay anyone to do it right, so we all get what they won't pay for.  Analog still has its place, but it's increasingly a god-of-the-gaps as digital covers more and more of the design space.  Emotions are wasted when it comes to the analog / digital issue, a good designer will pick the best division to handle the job at hand.

hi everyone! 

I made this project for the oral part of my high school exam( I'm studying electronic). I made the pcb and everything is working but i have some problems with the theory behind this project. I can't get how the oscillator works, I only saw wien bridge oscillator and phase shift oscillator at school, and in my books i can't find something exactly like that, just something similar. i thought it was an resonance rlc circuit and the transistor eas used to keep the damping coefficient ζ=0 but this phrase in the beggining part of the post confused me a lot: "R11/C11 and R41/C41 decouple both oscillators which gives the circuit a nice low audio frequency response, together with the small coupling capacitors C14 and C44.".  Can someone explain to me how it works? if you can link me something or give me the name of this oscillator will be fine too. thanks a lot :)

It's a common gate Colpitts oscillator.

The way I understand it is L1 forms an LC tank with the combined capactiances of C1, C2, and Cant. The oscillation point is the drain of J1, with the other ends of the LC connected to low impedance (ground & VCC).

Think of it as already oscillating, with the drain of J1 swinging from ground to 16V or so.  As it swings towards positive, the voltage divider formed by C1 and C2 pulls the source up, which makes the gate more negative with respect to the source, which tends to turn off J1, which decreases the drain current.  The fancy term for decreasing current with increasing voltage is negative resistance, so instead of damping oscillation like a normal resistance would do, it actually encourages it.  This is in-phase sense & stimulation.

R2 and C3 smooth out and therefore decouple the inductor currents so the two oscillators don't interact through the power supply.  The two oscillators are coupled via 3.3pF caps to a non-linear FET amplifier which performs mixing / heterodyning, and that's pretty much it.

(Sorry, I write through the Google translator :-))

Thank you for the scheme. I collect it. Pleasantly surprised by good "vulture". In the absence of complex inductance.

But at the low sounds (the low end of the range) distortion and dirt. What could it be? It's unavoidable? Or it is necessary to work with modes?

Martel, а можешь описать какого характера эти искажения? И попутно -- насколько низкие "басы" может выдавать твоя схема?

Recorded Audio - http://rgho.st/6h6dNyK5y

I specify particular. The mixer I have is the Russian field-effect transistor KP303 (I have little 5484)

Coils homemade circuits to the factory, but exactly 1 mH.

The values of capacitors and resistors matched exactly.

I recorded the audio and explain the scheme, but my post moderator reason not approved.

"...but my post moderator reason not approved."  - Martel

I've had posts rejected in the past, it's a bug here at Theremin World.  Contact Jason.

Recorded Audio - https://www.youtube.com/watch?v=8xnz62GoKqU&feature=youtu.be

I specify particular. The mixer I have is the Russian field-effect transistor KP303 (I have little 5484)

Coils homemade circuits to the factory, but exactly 1 mН.

The values of capacitors and resistors matched exactly.