A theremin is a musical instrument that is played without touching it. The antenna generates electromagnetic fields, which are manipulated with the hands and thus sound is created. While the inventor toured the US playing classical pieces with this ethereal-sounding creation, the instrument is better known for its use as a special effect in science fiction movies than for music. The Beach Boys, Led Zeppelin and the Pixies used it wonderfully in their songs. You can do this with radio frequency oscillators and other items readily available at electronic parts stores. While it is necessary that you have a good handling of wiring and basic electronics, you can learn the basic fundamentals of circuit wiring and thus assemble it on your own.
Steps
Part 1 of 3: Plan your project
Step 1. Learn about the essential components of the theremin
A theremin is basically a box with two antennas, one of which controls the tone of the instrument and the other the volume. These antennas create electromagnetic fields, which are manipulated with the hands to "make them ring." The tight wire coils act as oscillators, which produce signals that feed the antennas. While it may seem like ghostly magic, the relatively direct circuits create the fields. A theremin involves the following components, most of which you should be able to buy at an electronics supply store:
- Reference oscillator and pitch
- Control oscillator and tone
- Mixer
- Control and volume oscillator
- Voltage controlled amplifier and volume and resonant circuitry
- Audio amplifier
- 12 volt power supply
Step 2. Develop the essential skills to make a theremin
Making a theremin from scratch is not a project for someone who loves weekends and spooky sounds. If you want to make one easily and cheaply, buy a set of pieces, follow the instructions, and put it together. If you want to make the connections on your own, there are many things you need to learn first in order for you to do so. Even if you want to put together a theremin, you probably need to understand how to read a basic outline. For you to make a theremin, you need to know how to:
- Read electronic diagrams
- Weld
- Wire a potentiometer
- Make a circuit
- If you want to put together a theremin, parts kits are available in a variety of different price ranges, some of which are relatively easy to put together and some of which are more complex. It's a bit easier than starting from scratch and getting all the boards and circuits you'll need individually. Unless you are an experienced circuit maker, it will be difficult but not impossible for you to make your own theremin without a set of parts.
Step 3. Start with the theremin housing
Find or make a box large enough for the internal circuits of the theremin to fit. A professional theremin, the kind that can be played comfortably, should be large enough for you to stand in front, with your arms about 24 inches (61 cm) apart. for most adults.
The top should rotate so that you can install the components and make adjustments when necessary. Parts kits are available for this purpose, which can be a good idea for you to get to the basic shell shape, even if you still want to customize the circuits
Step 4. Install the antennas
A monopole antenna for tone needs to be attached to the top of the box and a similar antenna for tone needs to be installed vertically. The loop antenna used to control the volume is attached to the side of the box. This antenna is sometimes a bit more difficult to find, but it should be available at specialist electronics stores.
While it may seem like it's more important to connect the circuits first, it's a lot easier to get the case out before you start worrying about the circuits to make sure everything is precisely spaced and comfortable to play. You must start the case before wiring the pickups in the same way that you would do the body of a guitar. You are going to make an instrument, not a radio
Part 2 of 3: Wire the theremin
Step 1. Connect the tone control
The pitch of a theremin is controlled by a circuit between a variable oscillator and a reference oscillator, both of which must be available from specialist electronics stores as individual units. You should set each one to the same frequency, ideally in the middle of the low frequency radio range.
- The reference and pitch oscillator should operate at nearly 172 kHz, in conjunction with a 10 k potentiometer. The signal that this oscillator creates must feed the mixer with a shielded cable. The variable pitch oscillator must also operate at nearly 172 kHz and must be affected by the parasitic capacitance of the reference unit.
- The potentiometers need to be connected to the circuit so that they establish the relationship of the movement of the hand with the change in the more linear tone. Without them, the instrument's pitch will be nearly impossible to control and will change wildly with just a microscopic movement of the hand.
Step 2. Connect the variable oscillator to the field antenna
When you're done, connect the tone control component circuit with a shielded wire to the antenna. By touching the theremin, the hand will change the capacitance of the antenna and thus the frequency of the variable oscillator will change. Essentially, you will send the signal to the antenna to manipulate it manually.
Step 3. Connect a variable oscillator to the volume antenna
It must also be in the low frequency radio range and must be carefully tuned, thus operating somewhere around 441 kHz. This signal will be directly influenced by the volume antenna and will be manipulated by hand. A 10k trim pot needs to be installed for the operator to adjust the theremin properly.
- Sends the output of the variable oscillator to a volume resonant circuit. The output will be a direct current voltage that will vary according to the output of the variable oscillator.
- If set correctly, the oscillator frequency will match the volume resonance circuit setting as the operator's hand approaches the antenna, thus gradually cutting off the signal. In other words, the closer your hand is to the antenna, the quieter the sound.
Step 4. Feed the output of each oscillator to a mixer
The purpose of the mixer is to compare the frequency of the variable oscillator with the reference frequency. The output will be an audio signal between 20 Hz and 20 kHz. Assembling the mixer is the simplest step in the process. The mixer will feed two slightly different frequencies from the oscillators and produce a complex wave output, giving you the distinctive trill associated with the sci-fi sound of the theremin.
The output actually contains two different frequencies, both of which require a low-pass filter, that is, two 0.0047uF capacitors and a 1k resistor, both of which are used to pull the output and boost it over an audible range
Step 5. Route the mixer signal to an amplifier
Orients the mixer outputs and volume resonant circuitry to a voltage controlled amplifier. The voltage of the volume resonant circuit changes the amplitude of the audio signal from the mixer, thus helping to drive the sound and control the volume of the instrument.
Part 3 of 3: Finish the theremin
Step 1. Install a speaker
It sends the output of the voltage-controlled amplifier to an audio amplifier, and then a speaker will amplify the sound created by the electromagnetic fields as you manipulate them. On a tone, you can use the internal components or a guitar amp that you connect to the theremin with a jack installed on the back of the case.
Step 2. Power the theremin with 12 volt alternating current
You will need a power converter that runs at nearly 12 volts to power a basic theremin with this assembly. You can either make a step-down transformer that will convert the internal normal voltage or purchase a power cord with a built-in converter.
Be very careful if you are not an experienced electrician. There is quite a lot of voltage going through these circuits and it can cause fire or injury due to errors. Improve the skills mentioned at the beginning of this article before you try to connect the circuits and apply them to power
Step 3. Tune the components with an oscilloscope
If you're going to take the time to make a theremin from scratch, it's important that you fine-tune it and make sure you get a prototype that sounds. You need to make each module, test it and adjust it so that the final assembly is a simple process of connecting everything and making some final adjustments.
In order to test and adjust the modules, connect the theremin to the input jacks of an oscilloscope and you can see the sound waves that you will create as you manipulate it. Adjust the modules accordingly if the sound waves are bad
Step 4. Explore the theremin community
If you are going to undertake a project to make a theremin yourself, it is important that you work from a detailed schematic and improve the necessary circuit wiring skills. There are quite a few schemes, tips, and tricks for making a theremin online. You can learn more about how to make theremins with the ThereminWorld community.