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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Electric guitar from the usual. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Musician Talking about various electric musical instruments, it is impossible not to recall the most popular and indispensable in modern orchestras and rock bands. Of course, this is an electric guitar. The history of the conventional acoustic guitar spans many centuries. No doubt - the instrument is very musical and small in size. Only bad luck - the guitar sounds too quiet. And if at home, in a circle of friends or by a tourist campfire, the volume of her "voice" is enough, then what can be said, for example, about a musician's performance in a large concert hall? At best, the sound of his guitar will be heard by the audience only from the rows closest to the stage. Craftsmen who make musical instruments have repeatedly tried to increase the volume of the guitar: they made a resonating box with a double bottom, increased its size, attached bells (similar to those that were on old gramophones). However, all these tricks gave only insignificant results. Only in the early twenties of our century did they come up with an effective way to increase the volume of the guitar sound. With the help of a special sensor - a pickup, the sounds emitted by the instrument were converted into an electrical signal, amplified, and with the help of an electro-acoustic system they again turned it into the same sound, but now many times louder. At first, musicians used a wide variety of pickups. For example, the simplest of them is a regular microphone. It was placed inside a resonating box and connected to a low-frequency amplifier with the help of an electrical cord. They also made pickups based on piezoelectric elements. In such designs, a piezoelectric element was attached to the soundboard and converted into an electrical signal mechanical vibrations caused by resonance with the sound vibrations of the strings. Other ways to electrify an acoustic guitar were also devised. However, they were all very imperfect. The fact is that pickups that perceive sound vibrations are sensitive not only to useful signals, but also to extraneous noise. It was enough to accidentally touch the body of the instrument, and in the "speakers" a squeak or crackle is heard, reinforced many times over. The best results were obtained when they tried to equip the guitar with an electromagnetic pickup (abbreviated as EMPS). Such a device creates a magnetic field around the strings, which reacts to their vibrations. At the same time, this pickup is insensitive to soundboard vibrations and extraneous noise.
How does an electromagnetic pickup work, what is the principle of its operation? Suppose we have a permanent magnet in the form of an elongated cylinder, and a wire is wound on top of it, the ends of which are connected to the input of the amplifier (Fig. 1). Now let's place this structure under one of the metal strings of the guitar. The string must be made of a magnetic material, such as steel.
As is known, a permanent magnet creates a magnetic field around itself (Fig. 1 conventionally shows the distribution of its lines of force). As long as the string is stationary and is located strictly opposite the magnet, the whole system is in a state of "balance", and there is no signal at the output of the pickup. And now we hit the string, and it oscillates. What will happen in this case? Vibrations of the string will lead to deformations of the magnetic field of the pickup. Following the movement of the string, for example, to the right or left, synchronously with it in different directions, the field lines of force will also be "stretched". This happens due to the magnetic properties of the string - it seems to take the lines of force behind it. In this case, the magnetic flux penetrating the winding changes continuously. Those of you who remember a school physics course will immediately realize that a variable magnetic flux causes an electromotive force to appear in the coil. As a result, the input of the amplifier receives an electrical signal with a frequency equal to the frequency of the string vibrations. As they decay, the amplitude of the output signal also decreases. The same will happen if the string vibrates up and down. It is necessary to note one more feature of the electromagnetic pickup. Since it does not perceive the vibrations of the resonating body of the guitar, the "clean" sound of the strings, transmitted to the amplifier without the participation of acoustics, acquires a kind of "electronic" tone. We have described how an electromagnetic pickup works for a single string. Now let's imagine that we installed such coils with magnets under each of the six guitar strings, connected the leads of the coils in series, and connected the free ends to a powerful amplifier. And what - we got a real electric guitar with an electromagnetic pickup. By the way, the design of the EMZS, which we talked about, is not the only one. Sometimes they make only one pickup, common to all strings. To do this, take a flat elongated magnet, and wind the inductor over its ends. Over time, the electric guitar has lost much of what it originally looked like to its acoustic predecessor. Firstly, the musicians abandoned the resonating box - after all, now it was not needed. The electric guitar has become much thinner, and in addition, it has lost its socket - a hole in the center of the body. Then, trying to give the new instrument more originality, they began to change the shape of the neck, body, and their color. Pickups, various mechanical clamps, vibrators, volume and tone controls appeared on the guitar deck. So the guitar got its new "electric" appearance. All modern electric guitars have electromagnetic pickups, but the instruments themselves have become diverse. There are ordinary six-strings, and with twelve strings - such an instrument allows you to get a "juicy" sound rich in harmonics. There are electric guitars with a short neck - you can extract sounds of a very high tonality from them. There are even electric guitars with two necks at once - one of them has six strings, and the other has twelve. Finally, it is impossible not to say about such an instrument as the bass guitar. It has only four strings, but they are much thicker than a regular guitar. Such an instrument, like a double bass, produces sounds of the lowest tonality. The "electronic" sound of a modern guitar is not only the result of the absence of acoustic coloring in it. A unique originality is given to the sound by a variety of electronic prefixes for guitars. For example, the “wow effect” gives the instrument an iridescent, smoothly vibrating sound, and the “leslie” system creates the impression that the sound is being carried by a gust of wind, then approaching again. There are other electronic systems: fuzz box, distortion, booster, vibrato - the list goes on. Modern electric guitars are quite complex devices. Even the simplest of them is not so easy to make at home - just the mechanical work to make the body and neck is worth it! But you can electrify an ordinary acoustic guitar without much difficulty. How? Let's talk about this in more detail. A schematic diagram of an electromagnetic pickup for an acoustic guitar is shown in Figure 2. As you can see, it consists of six pickups L1-L6 connected in series (one for each string), which are inductors with permanent magnets as cores. The pickup is connected to the input of the amplifier using a shielded wire with an XP1 plug at the end.
The sensor (Fig. 3) consists of a cylindrical frame with an inner diameter of 2 mm and a height of 15 mm, a cheek diameter of 10 mm (made of cardboard or thick paper), on which the winding is wound in heaps with PEV or PEL wire 0,075-0,1 until the frame is filled . A permanent magnet with a diameter of 2 mm and a length of about 18 mm is inserted inside the frame. Any ready-made one, for example, from the letters of the magnetic alphabet, is suitable as it. Each of the sensors is glued to the base - a board 1-2 mm thick cut from fiberglass. For greater strength, fix the magnet in a hole previously made in the board.
The assembled pickup design is shown in Fig. 4. The distance between the center lines of the pickups must be equal to the spacing between the strings (indicated by the letter d). The dimensions of the base board are 6-7dx20mm. Drill four holes with a diameter of 2,5 mm along the edges of the base. Connect the outputs of the sensors according to the circuit diagram, and solder a shielded cord to the free ends of the pickup, for example, from household radio equipment.
If the gap between the guitar strings at the location of the pickup is less than 10 mm, then the sensors can be placed on the base in a "staggered" manner. The pickup housing, made up of a base and a cover, is made from a sheet of duralumin about 1 mm thick (Fig. 5). Its dimensions depend on the dimensions of the pickup, so we do not indicate the exact data. Eight holes are made in the base: two for attaching the top cover have an internal M2 thread, two for fixing on the guitar body and four for mounting the board with sensors. The top cover, in addition to two mounting holes with a diameter of 2,5-3 mm, has one more for a connecting cord. In addition, a window approximately 5,5x10 mm in size is cut out in the upper part of the lid; it is closed with a dielectric lining, for example, from thin colored or matte plexiglass. The hole is necessary so that the metal case does not shield the magnetic field concentrating around the sensors. It is desirable to paste over the top cover of the pickup with a film "under the tree".
Collect EMZS in the following order. After mounting the pickups and soldering the connecting cord to them, install the pickup on the base of the body and secure with four countersunk screws and nuts. It is desirable to connect the shielding braid of the cord to a metal base - in this case, the case will act as a screen that protects the pickup from interference. Then, thread the connecting cord through the hole in the top cover specially designed for it and install it on the base of the case so that both side lobes with holes for attaching the cover are inside. Fix the cover with two screws, solder the plug to the free end of the connecting cord to connect the electric guitar to the amplifier. Now it remains to fix the pickup on the resonating box of the guitar - it is best to install it in the outlet hole. From a piece of rubber 8-10 mm thick, make two clamps 10 mm wide each (you can use ordinary pencil erasers). The length of the latches depends on the diameter of the socket and the size of the pickup body. Their profile is shown in Figure 6.
With the help of two screws with nuts, the clamps are attached to the pickup. Due to the elasticity of the rubber, the entire structure is effortlessly installed in the socket of the guitar body. In addition, the latches act as shock absorbers, preventing the soundboard bounce that is unpleasant to the ear, which occurs due to resonance phenomena. When assembling an electric guitar, remember that it will sound louder the closer you place the pickup to the strings. However, do not overdo it, otherwise the strings will touch his body. Pay attention to the location of the EMZS sensors. Their center lines should be located strictly opposite the strings - the sound quality of the instrument depends on this. And of course, be careful and diligent to make the pickup small and fit freely in the guitar socket. After assembly, the electric guitar can be connected to the amplifier. If you do not have one, use the amplifier of the player, tape recorder, radio Author: V. Yantsev
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