basic experiments

Now some results of the volume control. Here please find a short mp3.

JPascal Theremin volume control test mp3 sample here

"The practical results are good." - JPascal

Interesting. What about the repeatability? (the FETs have a noticeable spread of parameters).

The jFETs I use have about 150 to 200 Ohm respective to a gain-source-voltage = 0. Below - 1,5 V they are high resistance, more than 1 MegOhm. The knob for adjustment the volume control would easy compensate parameter tolerance of the Fets. 

Спасибо за интерес.

Now I have posted a little 2 minutes video, shows an unusual replacement of antennas...My jFET divider is used for volume control. The banana and the little melon are the pitch and the volume antenna. You can see that their functions are not generally coupled to geometry like a plate or a rod form nor to a solid metallic material.

The high content of  - non destillated - water in the fruits guarantees the electrical behavior.  This is the same reason why our human body is able to produce a hand capacity.

The human bodies consistence is much more like fruits than metal. (Do not confuse this with the apple or pear shaped body you have :-) Therefore it is no problem to make a Theremin with "fruity" antennas. 

https://youtu.be/ZZYaoMSDtao

Now, back from my short excursion to the antenna fruits, vegetables and berries, which allows a lot of basic experiments, the next subject waits for solution. 

To give the theremin a sound like a classical instrument the envelope of theremin output signal should be shaped by parameters Attack - Decay - Release - Sustain as used in synthesizers. The initial part performing a tone on a violine or a wind instrument is an example for this.

Volume pegel pushed by hand distance to the antenna and the dynamic movement of the hand allone do not produce an suitable adrs envelope in many cases. I look for simplest ways in combination with my voltage controlled resistors with FET-Cascade.

Tips are welcome.

The Discussion about using plates ore rods for pitch linearity is a really serious topic. And there remain some questions for me. But before I go on with my basic experiments here is the funny sight of it. Volume best with a plate, pitch with a loop!

Using a single two transistor LC Oszillator I tested some antenna forms. The picture shows three antennas who have the same static capacitance: a rod, a loop, a plate. Estimated using frequency difference with and without antenna. The hand capacitance is of course at the same distance quite different.

But is the linearity generally better with rod or by plate?

Some experiments shall help answering that.
Just before getting started I briefly have to explain the used hand model: a bottle filled with normal drinking water!

Why that? Well, the human body mostly consists of conductiv water. Therefore you can calculate approximately the quantity of your body capacitance by considering a big conductiv cylindar which has the same hight and surface as you have. Arms or legs in a similar manner. A bottle as fist plus forearm too.

For example: To get your surface area use the well investigated medical formulas here, inputting your hight and weight:

http://halls.md/body-surface-area/bsa.htm

So I myself am such a cylinder with about 180 cm hight (length l) and surface area 2 square meters. My "radius" r is thereby about 17,7 cm.  The static capacitances formula with good approximations is:

You can find this formula in a russian book "Calculation of Electrical Capacitance" by Strunski, Kotschanow, Nossel, 1969. A translated book is available using a surching machine.

My static capacitance results than  - calculated with the formula above - in 50 pF. That seems plausible. My best wife of all has only a body capacitance of 44 pF. And what is yours? This body capacitances are - as expected - much higher than the hand capacitance to the rod or plate. 

And now the hand with forearm: you can take a big bottle as a fat man hand and a little bottle for a small woman, or vice versa. You could connect it via a suitable capacitor (instead rest of body capacitance) or directly to mass potential of the circuit.

To simplify the experiment and to reduce the influencing parameters, a grounding of the bottle is not made. The frequency behavior without grounding is analogous to the use of a coupling condenser to the antenna. For this qualitative and comparative basic experiment is grounding the "hand" not necessary. The one liter bottle I used has a static capacitance of about 8,5 pF. The capacitance value between the bottle-hand and antenna (rod or plate) is less then 1 pF, because only the front area is relevant here.

The results are following soon...

The wooden antenna support is somewhat capacitive, as is the wood you have your breadboard sitting on.

I think the bottle should contain somewhat conductive water and be more or less grounded.  The shape of the end is perhaps not the best to simulate a hand.  I've found the thing closest to the antenna does most of the interactive work.  I don't want to discourage you, but I find these kinds of experiments at best only demonstrate bulk/rough behavior, and aren't super convincing when it comes to "proving" (if only to yourself) various real-world scenarios.  Why not use your own hand/arm?  Not the best for teasing out exact theoretical formulas and constants (not that there's anything wrong with that), but the best for knowing & modeling actual LC frequency behavior.

Linearity for a Theremin that is conventionally heterodyned will be more linear with a rod antenna than a plate antenna.

I like this kind of experiment, if someone already had done it with a bottle please let me know the results. (but I won't ask for severed arms in the accident hospital ). The wooden equipment is so relevant for my experimental work here like plastic cabinets are for tube radios or theremins. Forget the low influence in this comparative experiment, take a plastic ruler if you want. The shape is the best plastic bottle I have and very appropriate here. If you want to use flexible houshold gloves - do it, but freeze them before use. To take only my hand with my arm and my body would be a very limited experiment. What is the difference with a small or big person?

I look forward the evidence of your supposition concerning linearity. In the moment I have now more asks, please let the other user a chance to read my post before reply again.