A WAVE OF THE HAND

A WAVE OF THE HANDNot long ago, musical instruments even pop bands — be it saxophone, violin, accordion, piano, double bass and even a drum — gave his listeners a natural, “natural” sound. Today music has become different — is now in Vogue “electronic” sound.

The fantasy that the creators of the show various musical technology, it seems limitless. The instruments and amplifying equipment, loudspeakers, device for synthesizing the sound effects — all to the limit “stuffed” with electronics. Today musicians have little than to be surprised — after all, they are armed there are the creation of engineers, which generate thousands of a variety of shades of sound: strings, woodwinds, keyboards.
 
Modern electronic musical instrument (abbreviated EMP) is a very complex device. Not even every experienced radio engineer is able to make it at home. And then what to say about those who are only making their first steps in the development of electronics?
 
One solution is to start collecting until only the simplest AMY. A few of those designs we want to tell you.
Do you think when the story of electronic music? Many probably think in the late 50’s-early 60-ies, when the light appeared and elektroorgana electric guitar and vocal-instrumental ensembles began to emerge like mushrooms after rain. But it all happened much earlier.
 
The honor of being the Creator of electronic music belongs to the Soviet scientist, engineer, physicist L. S. Termen. He invented the world’s first AMY. Experimenting with the device for measuring the dielectric constant of gases, he discovered the influence of the hands on the electric field distribution. This phenomenon was the basis of the first musical instrument called “waves of ether”. In 1921, the inventor presented his “child” at the VIII all-Russian electrotechnical Congress. Contemporaries of L. S. theremin appreciated his device. “The invention of the musical instrument opens up great prospects… By electric excitation can you get such sound, such tone, which still did not know music…” — so wrote the newspaper “Pravda” in 1927.
 
Over time, the first electric musical instrument became known as the theremin — a combination consisting of the names of inventor of the theremin and the words “wok” — the distorted voice, which means “voice.”
 
So, what is a theremin? The principle of this instrument is based on the change of the electric field created around AMY from the movements of the human body. Changing the position of the body or parts of it, e.g., owner, contractor thereby affects the spatial pattern of the field. AMY takes these influences and transforms them into sound signals, the tone of which depends on the manipulation of a person becomes higher or lower in time with his movements.
 
To understand how spatial movement of the hand can be turned into sound, let us examine the device of the theremin. Its functional scheme is shown in figure 1. The tool consists of two high-frequency generators, one of which is connected W antenna, mixer, amplifier of audio frequency and dynamic head VA.
 
Fig. 1. Functional diagram of the theremin.
Fig. 1. Functional diagram of the theremin.
 
While the worker is at a sufficient distance from the antenna, the RF generators produce signals of the same frequency which are fed to the mixer. Suppose that the frequencies of the two generators in the initial state is equal to 90 kHz. What will happen when mixing two signals? To understand this, it is necessary to note one feature of the mixer is allocated to the output oscillations with a frequency equal to the frequency difference of the input signals. And since in the initial state, the frequency of both generators is equal, therefore, the signal at the output of the mixer there is no sound in dynamic head no.
 
Fig. 2. Concept AMY.
Fig. 2. Concept AMY.
 
But the contractor put his hand to the antenna. What happens now? The human body is like a capacitor, included between the antenna and the electrical circuits in the upper scheme generator, that is, the capacity of the body artist begins to affect the operation of this generator. As a result of changes in frequency of oscillations produced by them. Suppose it was equal to 91 kHz. Now if you mixed signals there are so-called beating — oscillations with a frequency equal to the frequency difference of both generators. In our case, this difference will be 1 kHz. A signal with such frequency and will emit at its output the mixer. Then will be the gain and dynamic head you will hear a sound.
Continuously changing the distance between the palm of the hand and the antenna, the contractor thereby continuously – variable capacitive parameters castorocauda upper circuit on the oscillator circuit. This changes the frequency of the beating, and the tool extracted sounds of different pitch. If the result of manipulation by the performer, the frequency of oscillations at the output of the first RF generator varies, say, from 90 to 100 kHz, the musical range of theremin will lie in the interval from 0 to 10 000 Hz.
 
So, the performance of music on the theremin is to move one or both hands near the antenna of the instrument. To get a more smooth change of the pitch, the palm, monr keep stationary, and all actions produce only the fingers. In any case, in order to see such a musical instrument and master the technique it required good training and of course hearing.
 
Over 70 years of creative activities of L. S. theremin created lots of different versions of their AMY, and not less original. For example, one of his creations — terpsitone — electronic musical instrument, made in the form of a flat platform. Getting on it and making various movements, as if in a bizarre dance, the musician may execute at such an exotic instrument any product.
 
Interestingly, on the basis of the theremin was created and such “non-musical” devices, such as security devices for industrial buildings, warehouses, safes. Such a device was even guarding one of the halls of the Leningrad Hermitage. Developed by L. S. Termen electronic “watchman”, as it AMY, reacted to the change of the pattern of the electric field near the protected object and in case of unusual filed alarm.
 
But back to the musical abilities of the theremin. With the principles laid down in this tool, we have already met. Now it’s time to proceed to their practical implementation.
 
The theremin, which we offer, is assembled with just two logic chips, easy to establish and does not require hard to find parts. Of course, such a device far from a professional tool, but nevertheless, collecting it, you have to practice to get acquainted with the design, principle of operation and equipment performance of music on the theremin.
 
The first generator is assembled on the logical elements 2I-NOT DD1.1 and DD1.2 chips of DD1 (Fig. 2) and the second on the elements DD2.1 and DD2.2 IC DD2. Inverters DD1.3 and DD2.3 perform the role of decoupling devices for preventing mutual influence of the oscillators on each other. As a mixer used logic element DD2.4. Low-frequency amplifier assembled on the transistor VT1 by the scheme of the electronic key. Resistor R6 limits the base current of the transistor, and R7 is used to adjust the volume of the dynamic head of BA1. Capacitors C4—C6 and resistors R4, R5 form a low-pass filter, which excludes the mutual influence of the oscillators on each other through a supply chain. The device is powered by battery GB1 voltage of 9 V.
 
Both high-frequency generator assembled according to the schemes of asymmetrical multivibrators, with which you are already familiar (see “M-K”, 1990, № 1, “Six projects a single IMS”). Resistors R1, R3 and the capacitor C2 form customizados circuit of the first generator, a, R2 and C3— the same circuit of the second oscillator. Trimmer resistor R1 is necessary to “align” operating frequencies of both generators. Antenna WA1 is connected to the tool through the isolation capacitor C1.
 
Elements of the theremin are placed on a circuit Board with a size of 50X30 mm, made of foil Micarta or fiberglass with a thickness of 1-2 mm (Fig. 3).
 
Fig. 3. Circuit Board tool with the layout of the elements.
Fig. 3. Circuit Board tool with the layout of the elements.
 
For the musical instrument will fit the following details. Transistor — КТ602АМ (BM) or КТ815, КТ817, КТ819 with any alphabetic index. Electrolytic capacitors C4—C6 of the brand K53, and the rest — ceramic compact, for example, KM5, КМ6. Fixed resistors — VS, MLT, OMLT, C2-23, C2-33 with a power of 0.125 W, trimmer — CP3-1B, JS4-1B, AC — type, SPO-0,25, SPO-0,5, JS1, JS2. Dynamic head — 0.5 GDS-2 or any other power 0.1—0.5 W with coil resistance of 4-8 Ohms. Toggle switch — small, brand VSD, MT1, МТД1. The battery “Corundum” or six-disc battery voltage of 1.5 V (for example, STS-30).
 
Details of the theremin housed in a metal enclosure of a suitable size. If this is not found, you can use any plastic box, pre-paste over it from within a foil. The metal body or foil is necessary to electrically connect a common wire feeding tool. The antenna is a copper or aluminum rod Ø 2-4 mm and a length of 25-40 mm is installed on the front panel of the case in a rubber or plastic insulator (Fig. 4). In addition, on the front panel are the on / off toggle switch power supply, variable resistor R7, is provided with a decorative handle, and dynamic head; diffuser “dynamics” is covered with a thin colored cloth. On the side wall of the shell — hole under the engine trimmer R1. Wiring connections are made of thin stranded wires in isolation.
 
Fig. 4. The appearance of the theremin.
Fig. 4. The appearance of the theremin.

At the correct installation and serviceable details the tool starts working immediately after power on. Setting it down in a zero beat frequency generators. If after power-up sound sound drivers not then need to setup disappears. If the sound appeared, rotating engine trimmer, until his disappearance. After that, the theremin is ready for operation.
 
It may happen that the sound of AMY will be unstable. In this case, perform the melody with one hand producing manipulations near the antenna, and the second touching metal parts of the housing. If you used a plastic box, covered the inside with foil, on the front panel, you must install a special metal plate about the size of 20X20 mm connecting the common wire power supply.
 
…The theremin was the world’s first musical instrument. Over the past decade created a lot of new AMY, what is easy to see, looking, for example, to equip a modern rock band. The electronic organ, electric guitar, electroman, electronic drum set is a list of musical instruments with the prefix “electro”, you can continue. Some of them we will tell in the next releases.
 
E. APRELEV

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