Parts clarification for Etherwave Theremin build

There are oscillator peripherals on both sides: The antenna circuit at the VPO and the tuning/reactance stage at the FPO. As the Etherwave Pro demonstrates with ease, these do not contribute to drift.

Drift can be observed from temperature differences between FPO and VPO. The Etherwave Pro has a simple mechanism to keep both oscillators at the same working point: Feeding them through a current mirror (That could also be added to the Etherewave Standard and Plus theremins, but it is not necessary). The tVox tour has the transistors of both oscillators glued from different sides on the same cooling/shielding element which makes also sure that they run at equal temperature.

Stop theorizing in abstract spheres, guys. Every professional musician is used to giving his instrument some time to acclimate and to eventually retune it after a short warm-up time. Be rather happy that a theremin has only two tuning knobs and not around 190 like a grand piano... ;-)

_{-- offtopic --
Alesandro, just remind you if interested:}

_{tomorrow,  sept  21 at 19:00,  White Hall of Saint Petersburg State Polytechnic University -- 
The only concert "Theremin returns". Masami Takeuchi+ "Dа"+"Mable"+Natalia Thermen+Peter Thermen etc.}

Hello everyone! I have been a little bit away off the topic for some days with other work, but finally could read all of your informative and interesting replies. This goes to all who contributed to my query! 

I appreciate the comments about the PCB design. I have mostly designed digital boards for microcontrollers and DSPs running at frequencies on which the PCB design has minimal effects, and have mostly 0 experience with any radio frequency signal routing. As I mentioned, I basically used the layout from the hotrodding document with an intent of staying close to the original design and routing best I could from my personal experience. For the first theremin built, I will try and build it with this layout, but I am definitely interested in getting further into it and design my own circuit and layout with all of the ESD protection details considered and enhancements as possible.

I understand that plenty of diverse VCA designs are available and many others come to mind, as well as oscillator configurations, parts selection (DIY and commercially) and their arrangement and layout - every one of these things and their combination will create a certain type of sound, antenna sensitivity and linearity slightly different one from another, which at the end adds to the uniqueness of each owns theremin (this said from a more artistic perspective). I like the idea of that! A digital system with an automatic frequency compensation and drift elimination scheme sounds attractive, with whole lot of additional ideas and possibilities come to mind, some sort of a digitally controlled analog hybrid (mind you, I have not dwelt too much into research of that side of the theremin universe).

On the engineering side, I really appreciate the tips about linearizing coils placement, self-capacitance, and drift minimizing - will definitely keep all the information in mind and study more on the subject.

It is indeed true that every instrument will have a certain re-tuning from time to time, be it days or months for some instruments like a piano or minutes for a violin or alike - my father being a violinist, I know that they re-tune the instrument every few musical pieces at a concert, so it is always part of the performance hehe.

Thierry 

Sorry, the "cores" of the VPO&FPO is the same, really... But!.. for thermal stability "Pitch tuning" circuit shall be added to VPO and... antenna coils shall be added to FPO (with screen...) (with small C - about 10 pF as antenna capacitance equivalence)!..

Being honest, the Korolyov' design is'nt "totally identical" in oscillator part. An antenna on the one side, and a small cap on the other. The different parts -- the different thermal coefficients.

As for the EtherWave, the main contributors of thermal instability are: 1. ferrite 2. p-n junctions. At this point EW oscillators (VPO and FPO) are symmetrical.

Let me remind you about NP0 thermal k of the cap. And about Q5 p-n junction in EW.

Let me also remind about a non zero temperature coefficient of antennae.

Q5 could have the same coefficient as the Q3. The resulting  temperature coefficient of two identical capacitors in parallel is the same as the separate ones.

Hello everyone, I am new here, so this is my first post.

I want to ask if anyone has had any experience with using smd elements for their builds. I am also building an EM theremin and I'm using smd resistors and capacitors. So my question is, whether I should be caucious about anything when desining the pcb.

Thank you very much in advance