My New Year gift to TW: A new theremin circuit

Dear Thierry, can you recommend a simple addition to your circuit that changes the timbre? (but so as not to significantly worsen the thermal stability of the circuit) Something for a small, but timbre control? At least in the direction of softening, reducing high and mid frequencies, sounding flat and dry. I tried different options, but only adding one amplification stage (I took it from the network) with changing the potentiometer of the transistor base mode worked (not significantly).

I still have not learned how to accurately select transistors for your circuit, although I assembled a set-top box for measuring the parameters of the cutoff voltage and current. But the transistors I bought (specially for these parameters) did not meet the parameters required for this circuit (?!!). But (the circuit works with them) at the same time, some of them produce a sharp, unpleasant, dry sound, and some - a pleasant, soft, musical one.
(you have to select transistors by trial and error, finding a soft, musical set.)
But, the secret of the soft, musical mode, with the presence of low frequencies, remains undisclosed)).
So I decided to ask you, as the creator of the circuit, for advice on timbre.

Hello. I'm a beginner so i apologise if my question may seem a little stupid haha. But I was wondering, whether we could use a BJT instead of a JFET

Hello. I'm a beginner so i apologise if my question may seem a little stupid haha. But I was wondering, whether we could use a BJT instead of a JFET

Hello. I was wondering if I could use a BJT instead of a JFET. Could you also let me know, what types of capacitors were used for the theremin. 

Hello Electro,

A basic theremin design is just two RF oscillators operating between 200 khz to 2 mhz. A lower frequency will have less thermal or pitch frequency drift. JFET’s I found to be “less” desirable than BJT or NPN transistors. My design days are over but here is my own authentic analog theremin design using two 2N3909.

The Theremin Phenomenon is so simple in design that it kicks the ass of most engineers . . .
This why they go with digital imitation which is more of a fluty whistle.

The authentic design does require special knowledge, often referred to as being invited.

Best of success 

Christophe S Becker