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Home | Technical | Hardware | Theremins

Theremins

Leon Theremin

The Story of the Theremin

The Theremin is the invention of the Russian scientist Leon Theremin (an Anglicanisation of Lev Sergeivitch Termen and was first built in Russia in 1920 but never actually gained audience until around 1928. The peculiar sound of the Theremin is perhaps best known as a source for sound effects in movies (such as"The Day the Earth Stood Still" but has also been used in more serious compositions. The fact that there is no physical contact between the player and the instrument makes the Theremin somewhat unique and has given it an almost magical quality in the public's perception. The eerie sounds that it produces have no doubt helped add to this impression.

Leo Theremin first began working on the ideas that led to the Theremin when he was 21. As a student he began experimenting with vacuum tubes and first produced a pitch only version. Apparently he was thinking more of burglar alarms than music at this point and showed his invention (which he called an Ether Phone, Aetherphon, Thereminvox and later known Theremin) to several scientists and engineers.

During the next few years he continued to develop the Theremin and added a volume antenna. He even staged a few early performances playing pieces by popular composers such as Rachmaninoff and Tchaikovsky. The first piece written specifically for the Theremin was "A Symphonic Mystery" written by A.F Paschtschenko. This was premiered in May, 1924 with Proffesor Theremin on Theremin accompanied by the Leningrad Orchestra. A later piece "First Airphonic Suite" written by Joseph Schillinger in 1929 was particularity influential in promoting the Theremin.

In 1927 Leon Theremin embarked on a European tour playing concert halls in London, Rome, Paris and Berlin. As this was the first electronic instrument and a fairly remarkable one it was received with considerable enthusiasm.

Robert Moog writes...

"At the Paris opera , police were called to keep order among the crowds that thronged Theremins concert- demonstration. For the first time in history, standing room was sold in the boxes"

When Theremin arrived in New York at the end of 1927 he was already a celebrity amongst the upper classes and staged a performance for invitation only at which composers such as Rachmaninoff, Toscanini and others attended. He aimed to create a theremin orchestra and in pursuit of this he trained four musicians at a Manhattan residence, building new instruments for them. Theremin , his four performers and The Royal Philharmonic Orchestra Of New York played on the night of August 27 1928.

An observer noted:

"I couldn't believe it , When I first heard of this instrument I pictured a sharp scratchy noise , The evening was haunting and When The Theremins formed a chord The sound was better than all the orchestras of the world together"

In 1929 the RCA Victor Company placed a simple Tube Theremin on the market , as well as a combined Theremin and Electric Gramophone , with records providing the accompaniment to melodies to be played by the Theremin operator and instruction records for finding scales, with arpeggio passages to imitate .

The theremin was not a commercial success, however, and after making 200 or so theremins , RCA discontinued the line. Despite this the instrument has retained something of a cult status and has survived 70 years of technical evolution: a transistorised version of the Theremin is still available today from Robert Moog's society (Big Briar).

Leon Theremin died in Moscow in November 1993 at the age of 97.

The Principle of the Theremin

The technical principle behind the theremin is a phenomenon known asheterodyning: when you mix two signals with two slightly different frequencies the resulting signal has a frequency equal to the difference of the two frequencies. This technical trick was used because the oscillators made with vacuum tubes were high frequency oscillators (and human ears are not able to hear these frequencies). So heterodyning allows the creation of low frequency oscillators from the mixture of two high frequency oscillators.

The great idea of Leon Theremin consists in using a reference high frequency oscillator and a variable high frequency oscillator: the resulting low frequency varies as the variable high frequency oscillator varies. The variation of the variable oscillator is due to the position of the Theremin player body between two antennae. This original electronic controller allows new kinds of expression. As an example: a dance platform called the Terpsitone designed by Theremin in the early 1930's was used by dancers to generate Theremin music.

Analogue Theremins

The first Theremin circuits were analogue, employing electronic vacuum tube oscillators. Vacuum tube electronics was already a fast developing field by 1920, driven primarily because of its possible applications in radio. With the advent of the transistor, however, present day oscillators can be made considerably more stable than early designs. An early design originally developed by Colpitts uses four oscillators, arranged in two pairs. Each pair forms a beat-frequency oscillator, the outputs of which are modulated by the capacitance near each antenna that is caused by the player's hand. This allows control over both the volume and pitch of the sound.

Digital Theremins

A digital theremin uses CMOS oscillators and logic gates to produce two DC levels. One DC level is affected by the proximity of the player's hands to the pitch antenna, and the other varies similarly when the volume antenna is approached. This design of circuit is advantageous because it pretty much depends on the imagination of the constructor as to what he/she wants to do with these DC levels.

A basic instrument would have the DC levels controlling a voltage-controlled oscillator (VCO) and voltage-controlled amplifier (VCA). However, such a DC level could also control a voltage-controlled filter (VCF). There are numerous designs of such voltage-controlled circuit elements.

A Tube-Type Theremin Construction Project (Unknown Author).

When RCA introduced their version of Lev Termen's invention they said it was as easy to play as humming. While the sound that can be produced by the Theremin may at times sound like singing or like a violin, the fact that you don't touch it to play it removes the tactile feedback normally found in the playing of a musical instrument. The musician stands motionless except the slight movement of the hands, closer to the pitch antenna and the notes glide up scale, further away and lower tones are produced. The closer the hand is to the volume antenna, the louder the sound. (this is the reverse of the original instrument, but I find it more intuitive to play this way.) Of the many Theremins that I have built the ones based on tubes sound the best and have the most sensitivity to the players' hand positions. The design presented here is the culmination of many years of experimentation.

The Theremin works on the principle that if you add two radio frequency signals together in a nonlinear amplifier the resulting output will be the sum and the difference of the input frequencies. In the Theremin we want the pitch antenna to control one frequency and the other one to be fixed. As the performers' hand adds capacitance to the tuned circuit controlling the variable frequency, the difference between the two becomes greater, resulting in an audible tone.

The same "detuning" principle controls the volume. The pitch antenna is connected to a parallel resonant circuit that forms a Hartly oscillator operating at about 7OOkHz. I chose the operating frequency to be high enough so that the half a pico-farad that the hand represents would provide a sufficiently large change in frequency and so alignment could be done using a AM radio.

The fixed-frequency is provided by the Hartly oscillator around Va. The 150pf variable capacitor is mounted on the front panel and is the pitch control. It is adjusted so that when the performer is furthest away there is no audible tone but as the hand is brought forward the pitch rises.

Another design criterion was that the Theremin be capable of playing very low notes. There is a tendency for the oscillators to lock onto one another when their frequencies are close. This causes the lowest note to be the one right before lock, usually a few hundred hertz. By using separate tubes for the two oscillators and by preventing any coupling between them the unit can produce tones down to tens of hertz. The RF signals are added and subtracted in the mixer tube V2b. By changing the value of the lk resistor in the cathode line, the tube can be operated in a more nonlinear manner which along with the 10k resistor in the cathodes of V3 can alter the sound of the Theremin dramatically. The sum of the RF signals is not wanted and can cause background noises so it is bypassed to ground by the lonf cap in V3a's grid. V3a and b are used as a voltage controlled amplifier in which the audio is applied to the grid of V3a and the control voltage to the grid of V3b. V4a is an oscillator just like the pitch ones except that the operating frequency is different. If the frequencies were close there would be hetrodyning (sum and differencing) between these stages resulting in extra notes that would not follow the pitch antenna. The output of the volume oscillator is connected to a parallel resonant circuit that shunts the RF signal to ground when the oscillator frequency is above or below the circuits centre frequency. When the two frequencies match, maximum voltage is presented to the voltage doubler consisting of the two diodes. As a result the grid of V3b is less negative and maximum output is achieved at the plate of V3a. The 150pf capacitor that controls the volume oscillator is mounted on the front panel and is adjusted for minimum volume when the performer is furthest away.

As can be seen the circuit is Class-A, single- ended-triode throughout. The power supply is a straightforward, zener shunt-regulated type and any combination of components resulting in a regulated supply of approximately 250 volts DC would work as well. As far as construction notes are concerned; keep the wires short, I used point-to-point wiring in my unit, and place the pitch and volume oscillators as far away from one another as possible. The volume antenna on my unit is a piece of PC board material about 8" by 4" mounted parallel to the floor and on the left-hand side of the Theremin. The pitch antenna is mounted vertically and is a telescoping antenna from a portable radio. My Theremin was designed around inexpensive coils available from Antique Electronics (PC-70-OS $3.00) and the other parts should be available in a well-stocked junk box. Silver Mica or NPO caps in the tuned circuit are a nice addition to keep the unit from drifting to much, but the player compensates for the drift anyway.

Alignment of the unit is most easily done with an oscilloscope or a frequency counter or both, but the 7OOkHz range was chosen so that an AM radio could be used to align the Theremin. Start by removing Vl and V4, this will leave V2 as the only operating oscillator. Adjust the pitch capacitor on the front panel to the halfway position, tune the radio to about 7OOkHz and bring it near L2. Tune the radio and the pitch capacitor until a hiss is heard that can be moved along the radio dial with the pitch cap. Plug Vl in and repeat the above procedure using the slug in Ll and the radio dial. When you get both hisses on the radio adjust the slugs in Ll and L2 so that they occur at the same place on the radio dial. When they are close, a squeal will be heard on the radio and if you can't wait, you can start playing the instrument right now. Replace V4 and connect the Theremin to an amplifier line input. The squeal on the radio should now be coming out of the amp. Adjust the volume capacitor on the front panel to the halfway position and alternately adjust L3 and L4 until a point can be found where minimum volume occurs.

There are a few areas to explore now that you have a working model. First how about a second fixed-pitch oscillator for a second note say a fifth up. Second you might try wiring another parallel resonant circuit in series with the pitch and volume antenna wires to increase the sensitivity even further. All of the Theremin articles I have read caution the would-be Thereminist to practice for quite a while before attempting the "premier performance" and after hearing Clara Rockmore (The Art of the Theremin, Delos CD) I totally agree. I use the instrument with a bunch of synthesizers and stick to more experimental kinds of music. Some really great, although non-traditional, Theremin sounds can be obtained by running the output through signal processors such as frequency dividers, Echo, and distortion units. Rave On.

Clara Rockmore

Clara Rockmore (Reisenberg), was born in Russia, the youngest of three musically gifted sisters. She was a true child prodigy, with absolute pitch and an uncanny sense of music. At the age of two, she could pick out on the piano or sing any melody she heard. Her career as a violinist began when her uncle gave her a quarter-size violin for her fourth birthday. At the age of 5 she was admitted as an exceptional student to the Imperial Conservatory of Music in St. Petersburg (now Leningrad). She was the youngest student ever to have received this honour. Later she became one of Professor Leopold Auer's most promising pupils and, at the age of nine, received permission from the Russian government to leave her native land in order to concertize.

Clara and her sister Nadia (a well-known concert pianist in her own right) embarked on an extensive tour of Europe and their recital circuit led them to New York City, where Clara met Leon Theremin for the first time and became aware of the musical potential of his invention. Apparently her bowing arm was becoming ill and so the theremin had an added appeal. She spent several years collaborating with Theremin during which time he developed the theremin into a sensitive, wide-range musical instrument. Clara subsequently embarked on a performance career that encompassed well over a hundred concerts, including appearances with major symphony orchestras, and set the definitive standard for theremin performance technique.

Playing the Theremin

(Comments on the performances of Clara Rockmore, one of the most celebrated theremin players)

To play the theremin, the performer stands in front of the instrument, a little left of centre. The feet are spread slightly to keep the body as motionless as possible. To determine the pitch of the instrument's tone, the player varies the distance between her right hand and the pitch antenna. When the instrument is properly tuned, the pitch goes from lower than two octaves below middle C when the player's right hand is back at her shoulder, to approximately 2 1/2 octaves above middle C when the player's hand barely touches the pitch antenna.To determine the loudness of the instrument's tone, the player varies the distance between her left hand and the middle of the volume antenna. Maximum loudness occurs when the hand is removed from the antenna; complete silence occurs when the hand is an inch or so from the loop.

The two antennas actually respond to all body movements. Therefore, it is necessary for the player to exert firm control over her body and head motions as well as her hand motions. The ability to stand motionless is absolutely essential. Concert-goers have remarked on Ms. Clara Rockmore's controlled stance. One reviewer even wrote:

"Miss Rockmore's seance-like management of this slightly supernatural instrument is quite amazing. Of course, the purpose of remaining still is not theatrical or hypnotic at all, but strictly musical."

The thereminist must move her hands with incredible precision as well as speed if she wishes to play distinct notes with coherent intonation. Ms. Rockmore actually uses fingering patterns to play the most rapid passages. No other theremin player has ever mastered this difficult and intricate technique for playing rapid successions of precise pitches - "aerial fingering" as one reviewer termed it.

The theremin performer plays without the benefit of any tactile reference whatever. Unlike the violinist, who is in constant contact with the instrument's fingerboard, (...) the thereminist feels no shape or force as she moves from one pitch to another. She is constantly moving her hands, listening to the resulting pitch changes, then "trimming" the precise position of her hands to home in on the desired pitch and volume.

The process is one of continuous aural feedback. For this reason, placement of the theremin loudspeaker is extremely important. Ms. Rockmore uses a large open-backed speaker which she places behind and slightly above her head, pointing out toward her audience. With such an arrangement, she is able to hear the effect of her hand motions soon enough so that her audience is rarely, if ever, aware of the aural feedback corrections that she intuitively applies.


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