Wilco Botermans, the professional thereminist from The Netherlands, shares his knowledge on theremin amplification, grounding, weird sounds, and other common technical issues.
Amplification
The theremin is an electronic musical instrument, and it needs to be plugged into an amplifier to be heard. This sounds simple enough, but there are a few things to consider when choosing the correct amplification method.
Output level
In sound amplification there are 3 different levels of output. Mic(rophone) level, Instrument level and Line level. A theremin has a Line level output. The signal level of a microphone is very low, and an instrument, like an electric guitar, has a slightly higher level. A line output has a much higher signal level. Each level needs a dedicated amplifier. If you plug in an electric guitar into an amplifier that expects a line level signal, the volume on the amplifier needs to be set very high for the sound to become audible/usable. I you would plug a line level instrument, like a keyboard or theremin, into a guitar amplifier, which expects a low signal level, the sound will be distorted, even if you keep the volume on the amplifier low.
The safest way to go is using a keyboard amplifier. These are dedicated amplifiers for instruments that have a line level output like a keyboard, synthesizer, drumcomputer, etc. Examples of keyboard amps are the Roland KC series, Behringer KXD series and Behringer B207MP3 and the Laney AH series. Many of these keyboard amps are also called multi-purpose amps, with inputs for guitar, keyboards, mp3 players (to play along with pre-recorded music, and even a microphone input. The Laney I just mentioned has so called ‘Hi-Z’ input, which indicates that a line level instrument can be safely plugged in, others may have that as well.
These are just a few examples of many amplifiers that are suitable for the theremin.
Most guitar amplifiers are unsuitable for use with the theremin, but there are exceptions. It is usually safe to try a theremin on a guitar amplifier. Their inputs should be guarded for input levels that are too high. If you wish to try, at your own risk of course, turn down all volume and gain knobs before plugging in, then plug in the theremin, switch it on, and lastly switch on the amplifier. Carefully raise the volume and gain on the amplifier and monitor the sound quality of the theremin. If you hear any distortion of the sound it is best to unplug and switch off. (Unless that is the sound you are aiming for. 😉
Another option to amplify a theremin is with the use of a mixing desk. A mixing desk usually has multiple inputs for microphones, instruments, keyboards, etc, where the required level can be adjusted right at the input. In a typical setup, a mixing desk will be connected to 2 monitor speakers, and you can plug in as many instruments and microphones as the desk allows. As a traveling thereminist, a setup with a mixing desk usually is less practical, but it can work fine when using at home or in a studio. If you only need to plug in an mp3 or other device for playing backing tracks, a multi purpose amp might be your best choice.
When you are just starting out and don’t have a reason yet to spend much on more professional (expensive) amplification, a decent computer speaker or active monitor speaker can to the job just fine. They often come in pairs (for use with a mixing desk in a stereo setup, but you can plug into one directly as well.
Lastly, do get a good cable to connect your theremin to your amplifier. It doesn’t have to be expensive, but should be reliable. Theremins usually have a mono-jack, 1/4” output, and most amps and mixing desks have a mono-jack, 1/4” input. There are exceptions, some active computer speakers have an RCA input. Jack-RCA cables are also widely available.
Weird sounds
So after all that, Can anything go wrong? Well it shouldn’t, but it could. This can happen because the theremin is a very sensitive piece of electronics, that can in some cases be disturbed via both external influence and internal fluctuations.
A theremin is played by altering the electric capacitance around its two antennas. Conductive objects or materials with high moisture content (like the human body) moving within this field will change the capacitance, resulting in a change in sound. Dry insulators, such as plastic or glass, have a negligible effect. Any conductive object or body with sufficient mass and moisture moving near the antennas will affect the sound. Also, before being played, many theremins first need to get used to their environment, as also temperature, humidity and air pressure influence the electric capacitance. Therefore, each time you switch on a theremin, you have to tune it to optimise the playing field for that moment. Lastly, other electromagnetic fields can influence a theremin. When you place two theremins near each others, their electromagnetic field may merge in unexpected ways, which can immediately be heard. Other electronic devices that emit electromagnetic fields may also produce an electromagnetic field that causes fluctuations in the theremin’s sound.
Internally, the theremin can also sound ‘dirty’ because of issues with the mains, where the theremin is plugged into for its power. A theremin needs to be electronically grounded, and receive a clean and steady AC current. Grounding is typically done automatically when you connect your theremin to an amplifier using a jack-jack cable. The theremin itself may not have a grounded plug, but an amplifier usually does. If the connection to ground is unreliable, or even absent, because the power socket you are plugged into has no ground connection, chances are you will hear this in the sound.
Additionally the current of AC voltage on the mains usually alternates in a clean sine wave at 50 or 60 Hz. Some electronic devices can disturb the cleanliness of this sine wave. For instance, some light dimmers cut off the top and bottom of the sine wave, flattening the sine wave (turn it more into a square wave), to reduce the output of light. Like with a bad grounding, this can cause dirt on the power of the theremin as well. Similarly neon lights, an old refrigerator or a cheap telephone charger can have an effect on the sound quality of the theremin.
So if your theremin sound weird, while your amplification is clean, check if there are light dimmers turned on only partially, unplug phone chargers, turn of the lights and wait for the fridge to switch off. Unplug all other devices that use the same power group in your house. If this solves the sound problem, plug everything back in one by one, and keep checking if the sound of the theremin changes. Sometimes an electronic device develops a problem where it may work itself, while still causing dirt in either the ether the mains or the grounding. (I once had it with a new wifi router. The sound of the theremin was unusable. A replacement router of the same type did not cause a problem.)
Additionally, old buildings sometimes have old wiring with unknown faults. Try plugging your theremin and amplifier into a different mains group in your house. For instance the kitchen, where all sockets usually are well grounded. Or check the meter closet. There is often a socket that has its own dedicated power group.