silicon chip/jaycar kit

how can i add modification?

a) build a bigger, more comfortable housing, which allows more distance between the volume plate and the pitch antenna.
b) do not use this thin telescopic antenna but replace it by a ca. 50cm long 10mm diameter aluminium tube.
c) replace the 1k resistor between the drain of Q1 and +V by a 1k potentiometer in series with a 470R resistor. This will allow fine tuning without modifying the antenna length.
d) connect a 1nF capacitor in series with an adjustable 10mH coil between the circuit board and the antenna in order to equalize the spacing between notes.

would you say it is a professional theremin than?

It comes nearer to that. There are still some modifications on the volume side and for additional waveshaping possible. All this will improve it. But it will not reach the Moog Etherwave Standard in terms of range and linearity.

There is an excellent article (not from me) which resumes most of the possible mods: click (http://www.thereminworld.com/silicon_chip_theremin_modifications.html)

thanks for the article! i just tried to connect it to an amplifier, with no result at all exept for a lot of noise. any ideas?

What comes from the internal speaker at the same time?

If there is a correct sound from the internal speaker, we have still to look for an error. If there is also no sound from the internal speaker, you must retune T2, since the better grounding shifted all parameters...