The Theremin Project : Part 2

(continued from part 1)

I picked this up again a few days later and carried on soldering the transistor coils, diodes, voltage regulator etc. onto the circuitboard. I also had to use a few small bits of wire to connect the potentiometer (the knob) and connectors for the two antennas. Finally I got it looking like this.


And I was ready to start tackling the case! This part was a bit of a nuisance, since there were some things that had to be soldered from the outside of the case (like the power switch) and other things like the RCA jack had to be soldered on the inside... anyhow, I had to do some planning here to get some of the external components connected up properly. Then I screwed in the two antennas with the cable I set up earlier and I was ready to test!


With the case open, I connected the power adapter and flipped the switch. Nothing exploded, which made me feel a little better. The instructions then go on to say something like "make sure there is a nominal +5.6-5.8V current between the transistor coil and pin 8 of IC2" or something like that, so I connect up the voltmeter: +0.7V. Not good. After a while I decided to take the circuitboard out of the case and double-check all my solder joints for anything obvious. When I tried to pull the circuitboard out of the case, I accidentally touched the voltage regulator which was really hot and painful. When I flipped the circuitboard over, there was a small bit of runaway solder connecting two of the pins on the voltage regulator causing the whole thing to short circuit. I broke out a file and cleaned the joints up a little bit until they were no longer touching, then I tried again and got my +5.7V. Awesomeness! In retrospect I'm glad it was something that simple and not a defective diode or something.

After adjusting the tranistor coils a little, I started getting some eerie tones coming out. I spent a little bit more time trying to tune it properly, which is a bit tricky, but I think I got it to more or less a good range for playing now. This is what the final product looks like. Anyhow, I like to think I learned a fair bit about (very) basic electronics out of this. I have a pretty decent understanding of what the parts do (in general) and I've become fairly adept at soldering. But enough about that; more importantly it's really fun to play and sounds awesome. Here's a little sample of the theremin, put through some fairly heavy echo and reverb effects for extra coolness.

ThereminDemo.mp3

I can't wait to bust this out at a gig now!