- January 13th, 2014
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For a recent class building project, I chose to take a shot at building my very own theremin. Such an instrument has always captivated my imagination and I hoped that by being able to build one cheaply that I would make a powerful gestural tool to use as a voltage control for other analog gear I want to build. I purchased the PAIA Theremax kit (minus the case) and began the process of assembling it.
Having built a Bleep Labs Thingamagoop LED earlier this year, this new project seemed daunting with much more parts and complexity than I had encountered before. My first endeavor would be to take inventory of all the parts to make sure they were correct. After checking for all the individual parts listed, it turned out the only thing I missing was a single 47k ohm resistor. I emailed PAIA about this and they immediately sent me the missing part.
Starting with the bare PC board, or PCB, I began by cutting small lengths of bare wire for jumper points designated by the directions. After soldering them in place, I moved on to the resistors.
There were more resistors than any other component in the kit, so this required quite a bit of back and forth between installing them and soldering them in place. After installing so many resistors, the back of the PCB gets cluttered and hard to solder, so I would install about 5-10 resistors at a time, solder them, clip the leads, and move on to the next batch of resistors.
I then installed the four oscillator coils, each of which had 7 pins to solder in.
Next came the capacitors!
The types of capacitors used were both ceramic and electrolytic, the latter of which were polarized and needed careful consideration in the direction of their leads as indicated by the board.
Next for the circuit came the diodes, which were also polarized and came in Zener, Germanium, and Silicon. I then installed the LM339 Quad Comparator and 748 OpAmp along with twelve 2N4124 NPN transistors. I was now ready to begin the wiring.
I had found an old wooden magazine rack at Goodwill for cheap that I could modify to fit the theremin assembly. Knowing someone who works at a photography studio in a nearby warehouse, I made use of their tool closet to disassemble and modify the furniture into a case.
This required quite a bit of prying, sawing, drilling, cutting, sanding, and wood-gluing…
But by the end at least I had a fairly authentic looking housing for the instrument!
At this point, I began to install the hardware jacks, various potentiometers, and SPDT switch into the metal faceplate that was then screwed into a wood panel I had cut a hole for it to fit into. I also drilled holes on each side of the case for the antennae soon to be installed.
Wiring up the theremin was a painstaking process, particularly when it came to working with connections to the lugs on the pots and jacks that I had pre-tinned beforehand. Cutting lengths of wire measured as specified in instructions, I also had to strip and tin them prior to connecting.
Luckily, the PCB and instructions were very well labeled, so there was no confusion as to how the wires should be connected. Extra resistors between some of the pots and two LEDs for Power and Gate that also utilize current limiting resistors were installed behind the face plate.
Soldering a main ground connection to a lug and screwing bolts onto the circuit to hold it in place, all I needed to do was solder the insulated wire to the antennae, the volume requiring a 1000uH choke coil added in between the wire and antennae. Having worked on this all night, I was excited to see if it would work.
Indeed the LED lit up, so I plugged it in to check the audio. At first there was no sound, so I looked in the instructions and realized there was a whole calibration process to get it going properly.
I then used a tiny screwdriver to twist the coils in the oscillators until they began creating sound. This was exciting as it turned out my project had been a success!
In terms of sound quality, it does still seem to have a bit of high frequency leakage from the oscillators which is somewhat negligible compared to the main signal. I noticed the Moog Etherwave Plus theremin has a cleaner tone in this regard, with different oscillators from the Theremax. The Etherwave’s waveform control alters the harmonics, which sound like either a square or PWM oscillator at the extremes, and the Brightness control adds a filter that the Theremax lacks.
The Theremax does have more CV outputs than the Etherwave, with additional Mute and Velocity CV. However, the Theremax does not have a headphone output jack, as does the Etherwave. As well, the Theremax does not produce a pitch when you touch the pitch antenna, as opposed to the Etherwave which jumps to a solitary frequency. This can be a neat effect but is still not very practical, so not much of an issue either way.
The theremin I built works well with plenty of control voltage routing along with a gate to send out to external equipment. I’m glad that I built it and look forward to using it in my home studio, especially after building some more modular analog equipment to connect to it!