A theremin is a musical instrument that is played without touching it. In practice, the magnetic fields generated by an antenna are exploited by modifying them with the hands. This instrument is best known as a special effects generator in science fiction films, rather than in the musical field, despite its inventor having toured the United States performing in concerts playing classic pieces and even original compositions of ethereal music. It has been used in Beach Boys, Led Zeppelin and Pixies songs; you can build a theremin using radio frequency oscillators and other items readily available at electronics stores. While you need to have a good basic knowledge of electronics and wiring, you can learn how to make a basic circuit and build a theremin yourself.
Steps
Part 1 of 3: Design
Step 1. Know the essentials that make up a theremin
It is a box with two antennas, one of which controls the tone of the instrument and the other the volume. The antennas create electromagnetic fields that are "played" by manipulating them with the hands. Coils of tightly wound electrical wire act as oscillators, producing signals that go to the antennas. While it may sound like scary magic, magnetic fields are actually created by a rather simple circuit. To make a theremin, you need the following components, most of which are available at electronics stores:
- Reference oscillator for the tone.
- Tone control oscillator.
- Mixer.
- Volume control oscillator.
- Volume resonance circuit and voltage controlled amplifier.
- Audio amplifier.
- 12 volt electric generator.
Step 2. Develop the essential skills for building a theremin
Building this instrument from scratch is not a project for “Sunday planners” with a passion for weird sounds. If you want to build one easily and cheaply, buy a kit and, following the instruction manual, assemble it. If you want to build one entirely with your own hands, then there are a lot of things you need to know. First, you need to be able to read a simple wiring diagram. Here are the basic knowledge essential to your project:
- You must be able to read an electronic diagram.
- You must know how to tin the electrical components.
- You must be able to connect a potentiometer.
- You have to be able to build an electrical circuit.
- If you want to mount a theremin, there are many kits with a wide range of models and prices; some are simple to assemble, others are more complex. This is an easier solution than creating from scratch and individually designing all the electronic boards and circuits you will need. Unless you have good experience in creating electronic circuits, it will be very difficult - if not impossible - to make a theremin without a kit.
Step 3. Begin by creating the circuit housing structure
Find or build a box large enough to hold all of the internal circuitry. A professional theremin, one that can be played comfortably, should be large enough to stand in front of you while keeping your arms outstretched as much as your shoulders (approximately 60cm for most adults).
The cover should be fixed with hinges so that it can be opened to assemble the components and make the necessary modifications. There are kits for this purpose, and they can be an excellent solution for the case, even if you later want to customize the circuits
Step 4. Install the antennas
That monopole for the tone must be fixed at the top of the box, in a vertical position. The ring instead, which controls the volume, must be mounted on the side of the box. This second antenna is a bit more difficult to find, but you should be able to buy it in very specialized electronics stores.
While you may believe that the most important thing to start with is the circuits, know that it is much easier to build the housing before thinking about the wiring, so that you can be sure that each element is in the right and comfortable place to "play".. The process is similar to building an electric guitar: you have to assemble the body before thinking about the cables and pickups; after all you are making a musical instrument, not a radio
Part 2 of 3: Wiring
Step 1. Plug in the tone control
The tone of the theremin is managed by creating a circuit between the variable oscillator and the reference oscillator that you can find in electronics stores as single pieces. Both should be set to the same frequency, theoretically in the middle of the low frequency wave band.
- The tone reference oscillator should operate at around 172 kHz and used in conjunction with a 10k potentiometer. The signal created by this oscillator should be routed into the mixer through a shielded cable. The variable pitch oscillator should also be adjusted to 172 kHz and will be affected by the parasitic capacitance of the reference unit.
- Potentiometers need to be connected to the circuit to create a more linear relationship between hand movement and pitch change. Without them, it would be almost impossible to control the tone of the instrument, as it would change abnormally with respect to the microscopic movements of your body.
Step 2. Connect the variable oscillator to the tone antenna
Always use a shielded cable and wire the elements that make up the tone control to the antenna, once you have finished making them. When you play the theremin, your hands alter the antenna's capacity by changing the frequency of the variable oscillator. In practice, you send a signal to the antenna that can be manipulated.
Step 3. Connect the variable oscillator to the volume antenna
This too should be set in the low frequency wave band and operate at a level close to 441 kHz. You must install a 10k trimmer that allows the operator to "tune" the theremin correctly.
- Connect the output of this variable oscillator to the volume resonance circuit. This must be direct current, which changes according to the signal sent by the variable oscillator.
- If adjusted correctly, the oscillator frequency will correspond to that of the volume resonance circuit when the operator approaches the antenna with his hand, gradually interrupting the signal. In other words, the closer the hand is to the antenna, the lower the sound volume.
Step 4. Insert the output signal of each oscillator into the mixer
The purpose of the mixer is to compare the variable oscillator frequency with the reference one. The output should be an audio signal between 20 Hz and 20 kHz. Assembling the mixer is the simplest step in the whole process. When fed with two slightly different frequencies from the two oscillators, the mixer produces an output signal with a complex waveform, giving it the classic slightly ghostly sound typical of science fiction films.
The output signal contains two distinct frequencies which need a low pass filter used to extract the output signal and increase the audible frequency range. A low pass filter consists of two 0.0047uF capacitors and a 1k resistor
Step 5. Route the signal from the mixer to the amplifier
Route the mixer and volume resonant circuit output signals to a voltage controlled amplifier. The electrical voltage of the volume resonance circuit changes the amplitude of the audio signal coming from the mixer, increasing the sound and controlling the volume of the instrument.
Part 3 of 3: Final Phase
Step 1. Install the speaker
It sends the output signal of the voltage controlled amplifier to an audio amplifier and then to the speaker to amplify the sound created by the magnetic fields modified by you. In practice, you can use the internal components or the amplifier of a guitar connected to the theremin via a jack installed at the base of the box.
Step 2. Power the theremin with 12 volt alternating current
For this you will need a transformer that generates a 12 volt current to drive this type of theremin. You can build one that reduces the normal voltage of the house current, or you can buy a cable with a built-in transformer.
Be very careful if you are not very experienced with electricity. The amount of energy flowing through the circuits is quite large, and a mistake could cause a fire or injury. Review your electronics knowledge as described at the beginning of this tutorial before connecting the theremin to an electrical power source
Step 3. Adjust the components of the theremin with an oscilloscope
If you've taken the time to build a theremin from scratch, it's critically important to tune it accurately and make sure you've made a prototype that can be played. Each element should be built, tested and tuned so that the final step is a simple process of assembling the various pieces and adjustments.
To test and tune the various modules, connect the theremin to an oscilloscope via the jacks, to be able to see the sound waves you create as you manipulate the magnetic fields. Adjust the modules accordingly if the sound waves are out of tune
Step 4. Join a community of enthusiasts
It's essential to start with a very detailed electronic schematic and brush up on the skills needed to wire a circuit if you want to build a theremin entirely yourself. On the internet you can find thousands of patterns, tips and tricks for this project. You can do some simple research online and you will find many forums and sites dedicated to this tool.
