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HISTORY OF TECHNOLOGY, TECHNOLOGY, OBJECTS AROUND US
Record player. History of invention and production
Directory / The history of technology, technology, objects around us A tape recorder is an electromechanical device designed both for recording (converting acoustic vibrations into electromagnetic ones and fixing them on a medium) and for playing back signals previously recorded on magnetic media. Materials with magnetic properties are used as a carrier: magnetic tape, wire, cuff, disk, magnetic drum, etc.
The progenitor of the tape recorder - the telegraph - was invented by the Danish physicist Valdemar Poulsen. In 1898, Poulsen created a device that uses the phenomenon of residual magnetization and converts sound waves into magnetic pulses that are recorded on a thin steel wire. At the input of the telegraph phone, a sound source was connected - a microphone. The current from it was fed to an electromagnet of a special form. The magnetic field created by the electromagnet magnetized the steel wire, which moved past the magnet at a certain speed. In time with the transmitted sound, the current taken from the microphone increased or decreased, and, consequently, the intensity of the magnetic field created by the recording magnet increased or decreased. To reproduce the phonogram, the wire was passed past the playback magnet. In the process of movement, the lines of force of the magnetic field of the phonogram crossed the turns of the coil, in which, due to the law of electromagnetic induction, an electric current arose corresponding to the sounds recorded on the wire. These weak electrical impulses were converted into sound waves in the phone. They were listened to without an amplifier using headphones. The sound quality was very poor and the telegraph was not widely used.
It took thirty years for Poulsen's remarkable invention to gain recognition. This was facilitated primarily by the appearance of electronic tubes and the development of amplifier circuits based on them, as well as the improvement of the sound carrier itself. The wire tended to quickly self-demagnetize. To compensate for this unpleasant property, it was necessary to increase the speed of its movement, which at first reached several meters per second. Even a small phonogram required a huge amount of wire. Although its thickness did not exceed 0 mm, the recording coils took up a lot of space and were very heavy. The thin wire was torn, tangled, twisted during movement. They tried to replace it with a steel tape. The breaks stopped, but the volume and weight of the sound carrier increased several times more. To spin the coil with such a tape, a powerful electric motor was required. The running gears were very bulky. During this period, magnetic recording gave unpromising results.
Commercial success came to the tape recorder only after the invention of a new sound carrier. The German inventor Pfeimer developed a technology for applying a layer of powdered iron on a paper tape: the new sound carrier was well magnetized and demagnetized, it could be cut and glued. Subsequently, the paper tape was replaced by a plastic one - from cellulose acetate, which is more durable, elastic and non-flammable. A ferromagnetic powder (iron oxides) preliminarily mixed with a binder (for example, nitro lacquer) was sprayed onto the tape. For the first time such a tape began to be produced in 1935 by the German company AEG. The tape recorder revolutionized magnetic sound recording. It was light, compact, retained magnetization well, which made it possible to reduce the speed of the sound carrier by several tens of times. On such a film, it was possible to record a much longer work than on wire.
Recording on tape took place in the same way as on wire. From all that has been said, it can be seen that the most important elements of a tape recorder were recording and reproducing electromagnets, which are called magnetic heads. Both heads were magnetic cores surrounded by coils. The core had a gap filled with special bronze foil. The current passing through the winding of the recording head formed a magnetic field that passed through the magnetic core and exited its working gap into the surrounding space.
When this field was constant, it uniformly magnetized the entire tape passing through it. When an electric current passed through the winding of the head, which arose as a result of the sound effect on the microphone, the magnetic field in the gap of the head changed depending on the strength of the microphone current, that is, in accordance with the strength of the sound vibrations. At the same time, the tape acquired a different magnetization and turned into a phonogram. Its various sections turned out to be differently magnetized, both in strength and in direction. The magnetic lines of force of these individual sections, closing in space, formed an external magnetic field. When playing a magnetic phonogram, the tape moved past the reproducing head at the same speed as during recording and excited an electric current in its windings, which changed in accordance with the strength of the magnetic field of the tape. Then the current that arose in the winding and amplified, came to the speaker. For repeated use of the same tape, there was an erasing head powered by a special lamp generator with high-frequency currents. The current generated by this generator was passed through the windings of the erasing head. While the tape passed through the field created by this head, it repeatedly remagnetized and, as a result, left it in a demagnetized state. After erasing, the magnetic tape fell into the field of the recording head. Here, each element of the tape was subjected to double action of the magnetic field, which was formed, on the one hand, by the current of the recording signal, and, on the other hand, by the additional bias current coming into the recording head from the high-frequency generator. This additional supply of high frequency current is called magnetization. It is necessary to combat the distortions that various parts of the tape recorder had on the sensitive magnetic tape - primarily lamps and transformers. During operation, a sufficiently strong magnetic field was created around them, which also magnetized the tape.
For a long time, this undesirable magnetization (manifested during listening in the form of noise, crackling and hum) greatly reduced the quality of phonograms. Only after they learned how to mix a high-frequency bias current to the signal current, the quality of the magnetic phonogram increased so much that it began to compete with mechanical sound recording - gramophone records. The tape recorder had two reels - feed and receive. To move the tape, a mechanism consisting of an electric motor, a drive shaft, a pressure roller and other parts served. Usually the tape recorder had a device for fast rewinding the tape from reel to reel in both directions. Since the early 1950s, designers have made efforts to simplify the handling of magnetic tape. The proposed solutions generally boiled down to two options: either two coils with tape were combined in one cassette, or one core with a roll of tape glued into a ring was placed in the cassette. In 1950, New York's Mohawk Business Machines Company released their Midget Recorder, billing it as "the world's first pocket tape recorder." The ring tape for him was placed in a metal cassette. Tefi cassettes appeared on the consumer market (Germany, 1955, with a ring tape, for the Tefifon tape recorder), Dictet (USA, 1957, for a portable voice recorder), Saba (Germany, 1958, for the Sabamobil tape recorder), RCA Sound Tape Cartridge (USA, 1958 ), Fidelipac (with ring tape, USA, 1959). None of these early systems gained wide acceptance.
Truly mass cassette recorders appeared in the early 1960s. In 1963 Philips released the compact cassette. For several decades, it became the main format for tape cassettes throughout the world.
In 1964, a consortium of American firms introduced the Stereo 8 cassette with an endless roll of tape and 8-track recording. They were popular in the US until the early 1980s. Other competing systems, such as Grundig's DC International (1965), Sony's Elcaset, Olympus's microcassette, either failed to compete with the compact cassette or occupied rather narrow niches of special applications (for example, microcassette - in miniature voice recorders and telephones). answering machines). The most popular type of cassette tape recorder was the radio - a combination of a tape recorder and a radio receiver with the possibility of battery power. They were produced in all sorts of formats, from pocket-sized microcassettes to large and powerful stereo systems ("boomboxes" and "ghettoblasters"). The first cassette recorder was produced by Philips in 1966.
In 1979, Sony released the first miniature cassette player, the Walkman TPS-L2.
Author: Ryzhov K.V.
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