Hello. I have constructed this Jaycar kit and applied some of Max Baars ideas. Max Baars mods
The electronic part of the kit seemed to be very well done. As a relative newcomer to electronic construction I found it to be quite doable. Cosmetically and functionally the external parts of the theremin are poor. The plastic box, extendable aerial and aluminium plate are all hideous.The aerial and plate are too close together. It must be interesting trying to keep your hands away from the aerials when doing the setup adjustments! The speaker is ridiculous. I decided that it needed a better case so I made one. I can post some pictures if someone tells me how.
I am running it on a pack of 8 AA batteries at present. The kit document claims that it only consumes 30mA with no sound from loudspeaker so the AA batteries should last, 50 hours? Because I am not using the speaker I replaced the volume control with a fixed 10 K resister.
The only other electronic modification I have made so far is to add potentiometers in series with the resistors on Q1 and Q3, as explained by Max Baars. The Mark 2 has a 1K resistor on Q3 rather than 100 ohms so I replaced the 1 K with 800 ohms fixed in series with 500 ohms potentiometer. I'm not sure if these Q3 volume adjustment values are the best. These modifications make the kit into a much more useable theremin. I have discovered that the theremin action needs to be set up on each startup and then it drifts over time. It is not practical to manage this by removing the cover and adjusting the inductor coils, and in any case the adjustable coils are too difficult to adjust and repeated adjustment would quickly destroy them. The ability to adjust the pitch range from the front panel is wonderful.
My main musical theremin inspiration is Carolina Eyck. My current practice sessions consist of trying to get those lovely vibrato cello tones. Just one note at a time lasting about one second, then try to hit the octave or fifth. Repeat many times. The sound that comes out of one stereo channel is quite nice. Apart from the synthesised tone there is no nastiness in the way of buzz or hiss. I have ideas of running the output through filters on my computer then out to a stereo. I am also considering running it through my electric guitar effects and amps.
I can see some possible value in trying to "linearize" the pitch range as described by Max Baars by installing an air wound inductor, but I have not yet fully understood how an inductor coil, placed between the pitch "wand" and the pitch detection electronics can achieve this. Max Baars gives recommendations about the number of Henrys required for various "wand" sizes but I don't understand how he derived these. I use the word "wand" because my reading tells me that it is not an aerial. Also wand sounds more poetic, as befits a musical instrument. Is there a better term?
