|
Arabic
Bengali
Chinese
English
French
German
Hebrew
Hindi
Italian
Japanese
Korean
Malay
Polish
Portuguese
Spanish
Turkish
Ukrainian
Vietnamese|
ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Car radios. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Audio equipment The article brought to your attention continues the series of publications under the general title "Sound in the car", opened by our regular author A. Shikhatov in the second issue of the "Radio" magazine. In this cycle, it is planned to consider the main features and specifics of radio receiving paths and tape drive mechanisms of modern car radios, their amplifying-switching units, control units and acoustic systems. Much attention will be paid to the problems of optimal selection of components, placement of equipment in a car, technological methods of standard and original installation of acoustic systems, and achieving high-quality sound of the complex. The articles will be useful to those who are interested in high-quality sound reproduction, like to do everything with their own hands, and are engaged in the repair, maintenance and adjustment of car radio equipment. The schedule of their publications can be found on our website on the Internet. The author of the articles A. Shikhatov is known as one of the active participants in the popular Autosound conference on the auto.ru website. A graduate of MATI, he chose sound engineering as his hobby. And now he is developing his own designs, enthusiastically working on improving the sound reproduction technique in his car, he was a participant in the first car audio competitions held in 1998 in Moscow. LITTLE HISTORY Now it is difficult to establish who first came up with the idea to combine a car receiver with a tape recorder. Even with a network of radio broadcasting stations, it is impossible to satisfy the musical tastes of all listeners, and attempts to use a tape recorder in a car have been made for a long time. The practical implementation of this idea became possible with the advent of various versions of the tape recorder, which make it easier for the driver and listeners to manipulate the tape recorder. Competing with each other in the home audio market, the compact cassette, proposed by Philips in 1964, and the so-called EL cassette, a little larger, continued to fight in the car radio market. The EL cassette used a standard 6,25 mm wide magnetic tape for sound recording (as in reel-to-reel tape recorders), its movement speed was also “reel-to-reel” - 9,53 cm / s. Despite the higher technical parameters, over time, this standard was completely defeated - for the mass consumer, the small dimensions of the compact cassette outweighed its shortcomings, so by the mid-70s, EL cassettes were completely out of use. This was facilitated by the rapid improvement in the quality of magnetic tapes, heads, and the cassette recorders themselves. The cartridge-cassette, which appeared a little later, owes its birth equally to the car and the quadraphony that was fashionable at that time (the car, thanks to a certain location of the listeners relative to the speaker system, contributed to attempts to introduce quadraphonic sound reproduction). In the cartridge cassette, which was intended primarily for the distribution of ready-made quadraphonic (four-track) phonograms, a wide magnetic tape was also used, but this was not the feature of the cassette. The tape roll was endless - the tape was pulled from the middle of the roll and wound around it from the outside, and no rewind was provided. This quality was presented at that moment as an additional safety factor - the driver no longer needs to be distracted from driving. By the way, in some countries the driver is forbidden to operate the radio while driving, which to a large extent contributed to the emergence of remote controls mounted on the steering wheel. Unfortunately, the design of the cartridge-cassette was not entirely successful. Despite the short length of the tape (25 meters), it often got tangled, and the introduction of graphite lubricant did not help either. Therefore, by the end of the 70s, the production of equipment with a cartridge cassette was discontinued. In the USSR, car radios appeared in the early 70s. Initially, these were copies brought from abroad, designed mainly for the use of compact cassettes, but along with foreign cars, we sometimes got devices of other types. The first domestic automobile compact cassette player (not yet a radio tape recorder) "Electron-501" appeared in 1976 and immediately became the "hit of the season". Its design was not very original, but it turned out to be surprisingly reliable, and the model itself became a rare long-liver and underwent several upgrades. In the late 80s - early 90s. it was even sold as a self-assembly kit. The main functions and design solutions of most car radios are approximately the same, and the circuitry is quite traditional. But the layout of the devices went through several stages. The original layout of the front panel, inherited from the car radio (two handles at the edges, a scale in the center), was dictated by the design of the regular seat in the car and held back the developers for quite a long time. Placing additional controls on a small panel is not at all easy, so coaxial regulators are widely used. Usually, the left controls adjusted the volume, balance and treble tone, and the right controls tuned the receiver and switched the receiver ranges. There was practically no room left for other governing bodies. In the very first radio tape recorders, the cassette was installed in the cassette receiver with the tape forward (a similar arrangement has been preserved in domestic-made devices to this day), but very soon there were CVLs into which the cassette was inserted with the narrow side, which made it possible to place additional controls on the saved space. However, the design remained outwardly symmetrical, and the mounting of the radio in the car was still carried out using nuts on the axes of the regulators. Ultimately, manufacturers of cars and car radios developed a certain standard that determines the installation dimensions of the radio and connecting dimensions. This made it possible to introduce unified ISO connectors for connecting the radio to the vehicle's on-board network, which are used by all European manufacturers. The next step was the rejection of the symmetry of the front panel, which improved ergonomics. Initially, radio tape recorders were installed permanently in a car, but the increasing theft forced manufacturers to pay attention to improving the safety of equipment. This is how removable models of radio tape recorders appeared, which the owner could take with him when leaving the car. This theft prevention method is still the most effective, but also the most inconvenient. The introduction of microprocessor control of radio tape recorders made it possible to apply access authorization (coding), which is usually used in devices of a fairly high price category. In order to turn on the radio, you need to install a special card with a code in it or enter a code combination from the keyboard. Unfortunately, there is a master key for every lock, and deciphering the code of a stolen radio is a matter of technology. Therefore, after the transition from analog regulators of the AF path to digital, removable front panels have become widespread, on which all the radio controls are concentrated, however, as practice shows, this method is not a panacea. In addition to historical design features, car radios are characterized by regional features associated with local standards. First of all, this applies to the radio. For models oriented to Western Europe, in addition to the VHF 88-108 MHz band, the presence of long and medium wave bands is mandatory, and in many models there are also short wave bands of 41 and 49 m, on which local broadcasting is carried out in a number of countries. In models for Eastern Europe, the presence of LW and MW ranges is also mandatory, but short-wave ranges are practically not found, and the VHF range either has boundaries of 65,8-74 MHz, or is divided into two sub-bands. The US and Asia Pacific models do not have a LW band, and the Asia Pacific models use the 76-90 MHz VHF band. Since the USA has its own frequency grid for broadcasting, models for the US market may not be suitable for use in other countries, and vice versa. (In the USA, the frequency grid step in the medium wave range is 10 kHz, in the VHF band - 50, in Europe - 9 and 25 kHz, respectively, and switching the frequency grid is not provided for in all receiver frequency synthesizers). Especially for the CIS countries and Eastern Europe, Sony produces radio models not only with an extended VHF range, but also with a two-standard stereo decoder "Stereo Plus", designed for stereo signals with both pilot tone and polar modulation. Finally, there are features that can only be explained by tradition. So, for European and Asian models, the cassette is installed with the narrow side forward, with the tape to the right. For most domestic and a number of US-made models - the wide side forward. In addition, in the US, the passion for big cars has spread to radios, so many devices for the US market are 105 mm high. In the 70s and 80s, block car radios were popular there, which in miniature repeated home radio complexes - a deck, an equalizer, a tuner, an amplifier. However, it is impossible to explain the absence of stereo decoders in domestic car radios even by traditions, although according to the results of a survey conducted by the Radio magazine more than ten years ago, it was the stereo reception of radio broadcasts that was recognized as the most important function of the receiver. RADIO RECEIVING TRACT Since radio tape recorders are direct descendants of car radios, it is appropriate to start a story about their circuitry with a radio receiving path. The radio receiver part of car radios is characterized by the use of already proven solutions and some conservatism. So, the use of conventional variable capacitors (KPI) with an air dielectric in the first car receivers led to signal modulation due to the vibration of the plates, so they began to use a block of variable inductance coils for tuning - a ferrovariometer, which continued to be used even after KPI with solid dielectric, free from the indicated drawback. Ferrovariometers were used up to the widespread use of specialized microcircuits for frequency synthesizers. As an example, consider the medium-wave path of the radio "Road Star" model of the late 80s, made entirely on discrete elements (Fig. 1). Although the circuit now looks somewhat archaic, it is built on the time-tested principles of traditional circuitry. The adjustment is made with a ferrovariometer. The input circuit is formed by the L2C1 circuit and the L1 inductor, which attenuates interference through the mirror channel. From the coupling coil L3, the signal enters the first stage on the transistor VT1 - resonant UHF. To simplify the pairing of circuits and reduce the risk of self-excitation in the high-frequency portion of the range, the quality factor of the L4C4 circuit is reduced by resistor R3. The cascade on the transistor VT2 is a frequency converter with a combined local oscillator. From the L5C7 IF circuit, through the L6 coupling coil, the signal is fed to the resonant IF made on the VT3 transistor. Amplifier load - bandpass filter L11C11C12L13C14. The signal from the first circuit is fed to the AGC detector, made on a silicon diode VD1. The AGC voltage is supplied to the bases of the UHF and UHF transistors, reducing their gain with strong signals. From the second circuit, the signal is fed to the signal detector, made on a silicon diode VD2. A small voltage is applied to the diode through resistors R13R14, which increases the sensitivity of the detector.
Most radio tape recorders have completely separate AM and FM paths, which is caused by the desire to simplify switching and improve quality. They are performed, as a rule, on microcircuits, and in models of a higher class, microcircuits of a lesser degree of integration are used. This is explained by the fact that when several functional units are combined on one chip, their mutual influence increases, which inevitably leads to a deterioration in the parameters. In especially high-quality paths, cascades on discrete transistors are used. The combination of AM and FM paths in one chip (partial or complete) is found only in simple models with analog tuning. An example is the diagram of the radio receiving path of the UNISEF radio tape recorder, manufactured in 1995 (Fig. 2). The radio receiving path of almost all cheap Asian-made car radios with analog tuning is made according to the same or similar scheme. The AM, FM and stereo decoder paths are made on a single CXA1238 chip from Sony, which is included according to a typical circuit.
The restructuring of the receiver is carried out by a quad block of capacitors of variable capacitance. Range switching is internal at pin 15, the only control is switch SA1. The signals of the CB range are selected by the input circuit L1C2L5CP2.1 and are fed to the input of the AM path (pin 19). The L7C6CP2.2 local oscillator circuit is completely connected to the microcircuit. The broadband input circuit of the VHF range is formed by the L2C3C1 circuit, then the signal after the resonant UHF (load - L3C5CP1.1 circuit) is fed to the frequency converter. Broadband IF - common for both paths, its selectivity is determined by piezoceramic filters ZF1 and ZF2. The ZF3 resonator is part of the PLL FM detector. The stereo decoder, in addition to the main function, performs the functions of a linear amplifier in the AM path. Trimmer resistor RP1 sets the mode of operation of the stereo decoder (subcarrier frequency - 38 kHz, synchronized by the pilot tone). Capacitors C21, C22 together with resistors R10, R11 form pre-distortion compensation circuits. Since in modern equipment the AM path has become additional, and the FM path is the main one, the main attention is paid to its design. The structure of this path is as follows: resonant UHF (possible AGC or discrete gain control), frequency converter, IF piezo filter, broadband IF, frequency detector, stereo decoder. The number of adjustable circuits is from two to four, depending on the requirements for the selectivity of the receiver. UHF and frequency converter are usually made on the same chip (for example, TA7358AP or KA22495), less often - on discrete elements (in high-end models). The IF and the stereo decoder are also separate microcircuits, although there are also combined ones that combine these two nodes. As an example, consider the path of the IF FM and the stereo decoder of the "Road Star" car radio, manufactured in 1993 (Fig. 3). From the output of the frequency converter, the IF signal with a frequency of 10,7 MHz is fed to the first aperiodic cascade of the IF. Its task is to match the converter with the ZF1 piezoceramic filter and compensate for losses in it. The signal is then sent to the broadband IF. The phase-shifting circuit L1C3, tuned to the IF, is part of the frequency detector. After detection, the complex stereo signal is fed to the stereo decoder. The setting of its operating mode is carried out by the resistor R7. Capacitors C11, C12 together with signal switch elements (not shown in the diagram) form pre-distortion compensation circuits.
The structure of the input stages of the FM path - a resonant UHF and a frequency converter with a separate local oscillator - is also traditional. In older models, the VHF unit is made on discrete bipolar transistors and is a single design with a ferrovariometer. Currently, tuning of circuits with varicaps is widely used, and only in radio receiving paths with frequency synthesizers (in a PLL loop). In domestic car receivers, multi-turn resistors are often used for tuning. Tuning with capacitors is now used only in cheap models made with a combined AM-FM path on microcircuits. Since with such a construction in the VHF path there is only one tunable circuit at the URF output, the selectivity over the image channel is low. In large cities, where there are many VHF stations, and their power is limited, the high sensitivity of the receiver with insufficient selectivity only worsens the reception quality. Bipolar transistor input stages create significant crosstalk under these conditions. To obtain high selectivity and sensitivity in high-quality VHF paths, two-stage URF and an additional tunable bandpass filter were used. For the same purpose, field-effect transistors have been increasingly used in VHF paths of medium and high classes in recent years. Due to their high input impedance, a high quality factor of the circuits is maintained and the signal level is increased, and a small throughput capacitance contributes to high gain, which makes it possible to get by with just one cascade of URF. The mixer of the frequency converter, both in integral and discrete versions, is performed exclusively on a bipolar transistor according to a common emitter circuit. In this regard, the FM path of domestic car radios, built using a balanced mixer on the K174PS1 chip, is much more perfect. The RF signal and the local oscillator signal in the considered mixers are fed into the base circuit, and the IF signal with a frequency of 10,7 MHz is separated into the collector circuit by a single circuit. Adjacent channel selectivity is completely determined by the piezoceramic filter in the IF path. The local oscillator of the VHF path on discrete elements is usually performed according to the capacitive three-point scheme. In integrated frequency converters, local oscillators are used on two transistors, the local oscillator circuit is connected to them only by two points. In radio receiving paths with analog tuning, a non-switchable APCG is necessarily used using a varicap in the local oscillator circuit, which is controlled from the output of a frequency detector. In radio receiving paths with digital tuning, the frequency synthesizer is responsible for the frequency stability of the local oscillator, while there is no need for special tuning elements. An integral part of almost all modern VHF units is a buffer stage for supplying a local oscillator signal to a frequency synthesizer or a digital scale, which is increasingly used in devices with analog tuning instead of the traditional scale. To ensure the stability of the local oscillator frequency, the coupling of the buffer stage to the local oscillator circuit is minimal, sometimes through the mounting capacitance. The URF and local oscillator coils are usually frameless, wound with copper enameled wire 0,6 ... 1 mm with a coil diameter of 4 ... 6 mm. The conjugation of the contours is carried out by bending the extreme turns, after adjusting the turns of the coil, they are fixed with paraffin or compound. As an example, consider the VHF unit of the Yamaha YX-9500 car radio, manufactured in 1996 (Fig. 4). It contains several interesting technical solutions that are typical for equipment from other manufacturers.
The signal from the antenna through the coupling capacitor C1 is fed to the input circuit L1C2C3VD1. The restructuring of the block in frequency is carried out by changing the control voltage on the varicaps VD1-VD3. The resonant URC is made on a double-gate field-effect transistor VT1. The peculiarity of the cascade is that the input signal is applied to the second gate, and the first gate is used to control the gain. Transistor VT2 is a key that changes the bias on the first gate VT1 (and hence the gain) on command from the control microprocessor. To obtain optimal matching and stable operation over the entire frequency range, the load is switched on - the L3VD2 circuit - through the L2 coupling coil. At the mixer input, the L4C8 rejector circuit is turned on, tuned to an intermediate frequency. It reduces the likelihood of overloading the mixer with signals close to the intermediate frequency. The amplified input signal and the local oscillator signal are fed to the base of the mixer transistor VT3. The IF signal with a frequency of 10,7 MHz is selected in the collector circuit and fed to the IF through the coupling coil L6. The local oscillator is assembled on a VT4 transistor according to the traditional capacitive three-point circuit. The L7VD3 local oscillator circuit, in order to obtain the highest possible quality factor, is weakly connected both to the local oscillator transistor and to the buffer stage on the VT5 transistor. The design of the IF path and the stereo decoder is similar to that already considered - a matching stage on a transistor, two piezo filters, a booster on the LA1140 chip and a stereo decoder on the LA3375 chip. Loop coils are wound with copper enameled wire with a diameter of 0,8 mm, a coil diameter of 5 mm and have the following data: L1 - 6,5 turns, L2 - 2,5 turns, L3 - 6,5 turns, L7 - 5,5 turns. Filter coils: L4 - standard inductor with an inductance of 0,68 μH; L5, L6 - standard 10,7 MHz IF filter (capacitor C "is included in the filter design). Path sensitivity - 2,5 μV, adjacent channel selectivity - 45 dB. The considered construction of the radio receiving path is typical mainly for the equipment of European manufacturers. In modern mass models of Japanese-made car radios, combined radio receiving paths of the second generation, made on a single chip, are increasingly being used. For example, Sanyo manufactures the LA1883M chip in a 64-pin package that works in conjunction with a control microprocessor. Similar paths are used in their radio tape recorders by Sony, Kenwood, Pioneer. Let's finish the story about the AM and FM radio receiving paths by considering frequency synthesizers, without which a modern car radio or car radio is already unthinkable. The widespread use of frequency synthesizers since the mid-80s has completely changed the idea of a car receiver. In addition to the high stability of the tuning frequency even in the absence of a useful signal, there are such functions as automatic tuning, scanning of fixed tunings, tuning in stations with the best signal quality, tuning memory, etc. Attempts to introduce additional functions in the control of the radio receiver have been made before, but their technical solutions have not received distribution. More or less successfully, only automatic tuning in the VHF band was implemented. Charging the capacitor in the integrator changed its output voltage applied to the varicaps to tune the receiver in the frequency range. Scanning was terminated by a signal from the noiseless tuning system, which controlled the level of the useful signal in the IF passband, and the integrator was switched to the storage mode. The station was held by the AFC system. The setting was saved until the receiver was turned off or a command was received for further rebuilding. Attempts to introduce analog tuning memory were unsuccessful, as were attempts to use such systems in the AM bands. Frequency synthesizers of modern receivers are made according to the PLL circuit (in English terminology PLL - Phase Locked Loop). The principles of building such systems are known: the local oscillator signal after frequency division is compared in frequency and phase with the reference signal, the frequency of which is equal to the frequency grid step in the selected range. The resulting error signal changes the local oscillator frequency so that it becomes equal to the reference frequency multiplied by the division factor. The speed of the first generation integrated synthesizers was insufficient, therefore, in the VHF band, they were used in conjunction with an external frequency divider. The feature set was extremely limited. Synthesizers of the second generation are already made completely in one chip. They include a control microprocessor and settings memory cells. Typically, 5-6 memory cells are used in each of the AM bands and from 10 to 30 or more in the VHF band. Cells in the VHF range are usually divided into groups for ease of use. To indicate the tuning frequency in the first generation synthesizers, LED indicators were used, then they switched to the use of liquid crystal screens (LCD display) with backlighting and cathodoluminescent indicators (in expensive models). Changing the frequency grid (European or American standard) was previously performed by external jumpers or switches on the radio board, in new models this operation is carried out from the keyboard purely by software. In addition to controlling the actual tuning frequency of the receiver, the microprocessor of the frequency synthesizer also performs a number of service functions. The algorithm of work and the name of the functions for different manufacturers are quite different. The usual set of functions is as follows: switching ranges (band), manual tuning (manual tuning) with the possibility of memorizing (memory), automatic tuning and storing all available stations (auto tuning, auto memory store - AMS) or stations with a maximum signal level (best stations memory, BSM), automatic tuning to the next frequency station (seek), scanning memory cells forward (scan up) or backward (scan down) with listening for 5-10 s. In addition, the last tuning on each of the bands is automatically remembered (in receivers with analog tuning, this feature was taken for granted). The functions of the microprocessor also include keyboard scanning, indication of the range, tuning frequency, memory cell numbers, receiver or tape recorder operating modes, the set of which can be quite different from model to model, even among the products of the same company. With the spread of digital controls (volume, balance, timbre) in the audio path, their control was also entrusted to the synthesizer microprocessor. Tape drives with logical control and a number of external devices are also serviced by this microprocessor, which gives reason to classify such control systems as third generation. Radio data transmission systems (RDS) that have appeared in recent years use the same display and microprocessor to display information. Traffic reports for drivers, weather forecast, financial news and other information that can be stored in memory are transmitted. Data decoding is still performed by a separate device, but it can be assumed that its functions will also soon be transferred to the main microprocessor. Unfortunately, in Russia this system is still at the first stage of development. The automatic tuning algorithm for modern radio receiving paths is approximately the same and differs only in details. Tuning, for example, is first performed in the local reception mode (Local) with reduced sensitivity of the receiving path, and only then in the long-distance reception mode (DX). Some modern receivers can search for stations broadcasting certain programs (sports, news, music of certain genres). Unfortunately, domestic radio stations do not yet transmit identification signals, and the musical vinaigrette on the air does not contribute to the use of this function. The processor tunes the receiver in range until it receives a stop signal from it. It is generated by the coincidence of two conditions - the capture of the frequency and the achievement of a given level of the IF signal. In the VHF band, this is usually done using the silent tuning system signal available on most microcircuits. Further, depending on the selected algorithm, other conditions are analyzed. For example, in the VHF band, in addition to the signal level, you can control the presence and level of the pilot tone. Then, with a weak signal, the stereo decoder is forced into mono mode. If the station satisfies the set conditions, its frequency is stored in the processor's memory. As an example, consider the frequency synthesizer and control microprocessor UPD1719G-014 of the 9500 Yamaha YX-1996 radio (Fig. 5). This microcircuit is now somewhat outdated, but using its example it is easy to disassemble the construction of a simple frequency synthesizer and its interaction with the radio receiving path.
The clock frequency of the microprocessor is 4,5 MHz, stabilized by a quartz resonator. Most of the inputs and outputs of the microcircuit are occupied by servicing the liquid crystal display and the keyboard, 16 buttons of which are combined into an incomplete matrix 6 (4. When switching to the cassette playback mode, the supply and control voltages are removed from the radio receiving path, the keyboard scanning stops and only the direction of tape movement is indicated. Depending on the tuning range selected from the keyboard, a set of signals at pins 12 and 13, through switches on bipolar transistors (not shown in the diagram), supplies power to the corresponding stages of the receiver. The local oscillator signal of the AM path is fed to pin 5, the FM path - to pin 6. The width-modulated signal for controlling the frequency of the local oscillators from pin 3 is fed to an integrator made on transistors VT4, VT5. The tuning voltage for varicaps is taken from capacitor C1. This microprocessor does not automatically switch the sensitivity of the receiving path and stereo mode, the "Local" / "DX" and "Mono-Stereo" (only for VHF) modes are switched manually. The corresponding signals are generated at pins 10 and 18. In the process of searching for stations or switching fixed settings, the microprocessor outputs a mute signal at pin 14, which controls the keys at the UMZCH input (not shown in the diagram). At pin 63, stop signals are active for the FM path (from the silent tuning system) and the AM path. Additionally, an intermediate frequency is supplied from the AM path (pin 16). Pin 64 receives a signal from the stereo decoder's pilot tone detector to indicate stereo reception. Several sources are used to power the microprocessor. Firstly, this is a 3,6 V voltage regulator on a VD20 zener diode, from which the microprocessor itself is powered in operating mode. To power the memory cells, a stabilized voltage source of 5 V was used, made on the basis of a 78L05 micropower voltage regulator. Power is constantly supplied to it from the car battery through the VD18 diode. When removing the main battery, you can connect a galvanic battery with a voltage of 9 ... 15 V through the VD19R13 circuit. Finally, in the event of a complete shutdown of power sources (removable radio), an ionistor C8 with a capacity of 0,22 F is provided. The energy stored by it is enough to power the memory cells for 4-5 days. In the process of evolution of car radios and cassette players, the tape drive mechanism (LPM) has undergone the greatest changes. As mentioned in the first part of the article, there are two options for installing the cassette - "tape forward" and "tape sideways". The first of them turned out to be not the most successful for reasons of front panel layout and was used for a short time only in LPM with tape rewinding in both directions. Their share in the total output was small. Most of the older models used to load the cassette "tape sideways" and calculated only on playback and fast forward. The radio tape recorders with auto-reverse that appeared at the turn of the 80s were already built on the basis of CVL with the cassette loading "tape sideways". In the first models of car radios and cassette players, the receiving container was motionless, and the tape transport units, when loading the cassette, fell onto it from above (Electron-501) or rose from below (AM-302, Zvezda, Eola). The advantages of such systems are the stable position of the heads relative to the cassette and the convenience of cleaning their working surface with the cassette door open. However, depending on the selected loading scheme, the installation or removal of the cassette required the application of significant efforts to charge the springs and overcome the weight of the LPM. Therefore, at present, it is mainly used to load a cassette into a fixed LPM using a movable container - a cassette receiver. In mechanisms with a single receiving unit, swinging containers are used. The cassette in this case rotates in the receiving window, descending onto the capstan and the receiving unit. Part of the cassette protrudes from the cassette window. In LPM with auto-reverse, a complete installation of the cassette is necessary, therefore, an elevator loading mechanism is used there. When installing the cassette, it first moves parallel to the plane of the CVL, and then lowers. Such a mechanism can be with a manual drive (in inexpensive models) or with an electric drive for loading. The latter is now becoming more widespread, since it completely eliminates the possibility of incorrect installation of the cassette. The loading process is controlled by the microprocessor: if the installation is not completed within the allotted time or the current consumed by the loading motor has increased, the LPM returns to its original state. LPM of most car radios are built according to a single-engine kinematic scheme with an indirect drive of the drive shaft with a rubber belt of square or flat section. There are known cases of using two- and three-motor CVLs in high-end radio tape recorders, including those with direct drive. From the whole variety of LPM car radios, there are mainly two groups that are widespread - the simplest ones, which provide only a working stroke and rewind the tape forward, and auto-reverse mechanisms that allow the tape to be rewound in both directions. An exception to this rule are some domestic models of car radios and models of the highest class. In the simplest LSM, in addition to the drive shaft assembly with a pressure roller, there is only a receiving assembly in which the required winding force is provided by a friction clutch. Rotation to the receiving unit is transmitted from the flywheel by a square belt or a gear. For fast forwarding, the pressure roller is retracted from the capstan. The rewinding speed is not high, the complete rewinding of the C-90 cassette usually takes 4-6 minutes. The mechanical control of such a LPM is carried out with one button. It is usually located on the side of the cassette window. When the cassette is inserted into the LPM, the playback mode is activated, when the button is pressed partially, the rewind mode is fixed (turned off by pressing again). The ejection of the cassette and the transfer of the LPM to the "Stop" mode is carried out after the button is fully pressed. Due to the lack of a feeding unit and a brake, when switching modes, loops and steps may form in the tape roll. Since the tape tension is maintained solely by the cassette mechanism, when using low-quality cassettes, the detonation coefficient can increase to unacceptable values. The typical value of the detonation coefficient for such CVLs is about 0,2%. The carriage with the playback head can be swivel or sliding, its design provides a stable position of the HV relative to the tape. For the same purpose, a guide is used, which is inserted into the small window of the cassette (next to the GV). It limits the movement of the tape in height and to some extent stabilizes its tension. Most LPMs of this type are equipped with a hitchhiking, as a rule, when it is triggered, the radio receiving path is turned on. In the simplest case, the autostop sensor is a spring-loaded lever in contact with the tape. At the end of the tape in the cassette, its tension increases, the lever moves and opens the motor power circuit. Such a system works only in the working stroke mode. In more modern LSMs, a mechanical rotation sensor of the receiving unit is used, which turns off the engine not only at the end of the tape in the cassette, but also when it stops for any reason during the working stroke or rewinding. The pinch roller does not move away from the capstan at the time of autostop operation, which can cause deformation of the roller and an increase in the detonation coefficient. You must remember this and do not leave the cassette in the radio turned off. The simplicity of such LPM is the key to their highest reliability. They are able to last more than 10 years. Due to the fact that part of the cassette remains outside, it is possible to remove the jammed tape without disassembling the radio and tape recorder, which cannot be said about systems with lift loading. The lack of rewind for those who listen to the cassette from beginning to end is not a disadvantage, so devices with such a CVL are still in demand. However, they are completed, as a rule, with cheap GW with a relatively large gap, so the reproducible frequency band is usually small - 100 ... 8000 Hz. The sensitivity of such heads is relatively low, therefore, the noise level in the playback channel can be noticeable (when the engine is off). Replacing the playback head with a more advanced one will greatly improve playback quality. LPM with auto-reverse are performed practically according to two or three kinematic schemes and differ slightly. In such mechanisms, there are two drive shafts rotating in different directions, and two pressure rollers, alternately brought to the tape by the reverse mechanism. In most LPMs, the rotation from the engine is transmitted to the flywheels by a long belt, the return branch of which passes through the bypass roller. The flywheels are equipped with a ring gear, rewinding is switched on by introducing parasitic gears between the sub-cassette assemblies and the flywheels of the drive shafts. The reverse mechanism is driven from the main engine by a short belt. When one of the cassette units stops, the rocker mechanism moves the pressure rollers, which leads to a change in the direction of the tape movement. In inexpensive models, mechanical control of the LPM is used. Usually, on the left side of the cassette window there is a cassette ejection button, and on the right side there are buttons for rewinding, pressing them simultaneously changes the direction of the tape. The inclusion of the LPM in the playback mode occurs when the cassette is installed, and the HV block on the carriage is inserted into the cassette by a spring. In more expensive LPMs, control is carried out by low-power electromagnets and a cam mechanism driven by the drive shaft flywheel. Such LSMs allow you to leave the cassette in the tape recorder, since in the "Stop" mode the pressure rollers are removed from the drive shafts. Until the early 90s, autoreverse LPMs used exclusively a fixed four-channel head unit, switching was carried out either by a small-sized mechanical switch (on a LPM) or by an electronic switch as part of a reproduction amplifier (UV). Then the technological spread of the parameters of the heads in the block (mutual skew and displacement of the gaps) led to the fact that the head could only be adjusted for playback in the forward direction, and the frequency band in the reverse mode was much narrower. For heads of average quality, the typical values of the frequency response are 50...12000 Hz in the forward direction and 100...8000 Hz in the reverse mode. Often, the frequency band in the reverse mode was not normalized at all. Now, the improved technology for the production of HVs makes it possible to obtain four-channel head blocks with similar parameters. Therefore, in modern radio tape recorders, reproduction in both directions is of the same quality: the frequency band is usually 14 kHz in mass models, and in expensive models it reaches 16 ... 18 kHz. In the early 90s, CVLs with two-channel GVs moved up by the reverse mechanism when played in the opposite direction became widespread. The head block assembly allows adjusting their position in height and azimuth separately for each direction of tape movement. However, gaps and backlashes in this mechanism lead to instability of the GW position during operation; therefore, such CVLs are currently used only in inexpensive models. A significant part of the components of modern LPMs is made of plastic, so there is a risk of warping when installing radio tape recorders in domestic cars near the stove. In cheap LPMs, even the flywheel of the input shaft can be plastic, and to increase the moment of inertia, a stamped steel washer is pressed onto it. Chassis, cassette and carriage are usually stamped from thin sheet steel. Additional functions provided by the tape recorder depend on its class. So, in simple and inexpensive devices, there is no blocking of the amplifier during rewinding, and therefore interference and noise can penetrate. In radio tape recorders of a higher level, such blocking is mandatory, some of them also have a built-in search system for the first pause in the playback track. In some models with electronic logic control, programming of the playback order is possible. In modern car radios, HC is performed exclusively on specialized microcircuits, usually included according to a typical scheme. Most often, simple devices use microcircuits BA328, BA329, BA3302 (Rohm), KA1222, KA2221, KA21222 (Samsung), LA3160, LA3161 (Sanyo), TA7375P (Toshiba). These microcircuits are close in their characteristics and switching schemes. The signal level at their output is usually 30...50 mV. In modern domestic devices, the K157UL1 microcircuit is usually used, the parameters of which, with a supply voltage reduced to 5 ... 6 V and a sufficiently high (150 ... 200 mV) output voltage, noticeably deteriorate. As an example, consider the playback amplifier on the LA3161 chip (Fig. 6). The switching scheme practically does not differ from the typical one. The SA1 switch selects the appropriate heads of the BG1 block, depending on the direction of the tape. In models with a "floating" HW unit, there is no such switch. High-frequency correction is performed by capacitor C1 (C2), which forms a resonant circuit with the inductance of the head. The standard frequency response of the playback channel is formed by the frequency-dependent OOS C5R1C7R2R3 (C6R7C9R5R6) circuit. The supply voltage is supplied to the SW when the LPM is turned on, the constant component of the output voltage is used to control the signal switch. Such a scheme, with minor variations, is used in Pioneer (KEH2430, KE2800), Yamaha (YX9500, YM95000) radios and the like.
A more advanced path with a BA3413 chip is shown in fig. 7. An electronic switch is built into the microcircuit, switching the heads of the HV block, and two electronic keys that change the playback time constants for tapes with different working layers. A feature of the circuit is the presence of a "virtual ground" (pin 4, capacitor C5) and the absence of input isolating capacitors. The purpose of the remaining parts is similar to those previously considered. Such a UV was used, in particular, in some models of Sony car radios. Switching the frequency response correction for different types of tape is done either manually from the front panel of the radio, or automatically - from the sensor on the chassis of the LPM, which reacts to the window in the rear wall of the cassette.
Many car radios previously used DNR (Dynamic Noise Reduction) based on a dedicated LM1894 chip. The principle of its operation is the dynamic filtering of signals by a controlled low-pass filter, the cutoff frequency of which varies within 1,5 ... 25 kHz. To control the filter, the stereo channels are summed over a frequency band above 6 kHz. In the absence or low level of high-frequency components, its frequency band is limited and the noise is hardly noticeable. With an increase in the level of high-frequency signals, the bandwidth expands and the noise is well masked. In car radios, a simplified scheme for switching on microcircuits is usually used (Fig. 8). Capacitors C5, C6 are part of the tunable low-pass filter, the variable resistor R2 is used to adjust the response threshold. If there are no elements R2 and C9 in the circuit, capacitor C10 is connected between pins 5 and 6. In some models, such a noise suppressor was used in the common signal amplification path, in this case, instead of capacitor C8, a pilot tone notch filter at a frequency of 19 kHz was installed, provided for in a typical circuit inclusions. Without this filter, the penetration of the pilot tone into the control circuit of the squelch blocks its operation.
In modern car radios, Dolby-B (in mass models) and Dolby-C noise reduction systems are increasingly being used. Expanders are made either on separate specialized microcircuits, or are part of combined UV microcircuits. Their nomenclature is quite diverse, an example is the TEA0675 chip (Philips). It includes a head switch, a switchable equalization playback amplifier, a pause detector for the search (programming) system, mute keys, and Dolby-B noise reduction. Similar microcircuits are produced by other manufacturers. AUTO PATH The AF path of a car radio is exactly what often determines its class in consumer assessment. Differences in the structure and parameters of the radio receiving paths and decks are hardly understood by anyone, especially since they are practically absent in models of the same family. Service functions are also mostly standard. The main thing that distinguishes radio tape recorders is the construction of the AF tract. Since there are at least two signal sources in the radio (tuner and tape deck), the AF path begins with the signal switch. In the cheapest devices, it is explicitly absent - the outputs of both signal sources are combined on a resistive mixer or on the volume control, and one of them is activated only by turning on its power. Since the output stages of signal sources with power off have a sufficiently high output impedance, their mutual influence is excluded. However, this is possible only at low signal levels - several tens of millivolts, otherwise the nonlinear distortions of the path will increase sharply. In more advanced paths, diode switches are used. As an example, consider the circuit used in Pioneer radio recorders of the KEH23xx, KE28xx series (Fig. 9).
The signal from the radio receiving path with a level of about 100 mV is normalized using dividers R1VD1R3, R2VD2R4 and is fed to the input of an amplifier made on a VT1 transistor according to a common emitter circuit (only one amplifier channel is shown in the diagram). Diode keys VD1, VD2 are opened by the constant component of the signal (separating capacitors are absent at the output of the radio receiving path). Chains R1C1, R2C2 simultaneously perform signal correction and additional filtering of pilot tone residuals. The signal from the SW with a level of about 50 mV passes to the input of the amplifier on VT1 through the diode switches VD3, VD4. The opening voltage is supplied to them through resistors R5, R6 from the R7C3 circuit when the LPM is turned on. At the output of the SW there are isolation capacitors C4 and C5. A signal with a level of about 200 mV from the amplifier output comes to a passive two-band tone control according to the Baksandal scheme. Then, depending on the level of complexity of the radio, the signal through the volume and balance controls comes to the UMZCH input either directly or through a linear amplifier with a gain of 20 dB, made on a dual op-amp (mounted on an additional board). The latter circumstance is due to the fact that UMZCH microcircuits with a sensitivity of 50 mV are used in radio recorders of the "younger" series, and 500 mV in the "older" series, which have higher parameters. To avoid distortion, the signal voltage in the diode switches should not exceed 100 mV. In more advanced paths, signal switching is performed by field-effect transistor keys. Often, CD4052 digital microcircuits (analogous to K561KP1) are used for this purpose. The permissible signal level in this case increases to 1 V. A similar solution was used in the "Supra", "Philips", etc. radio receivers. 3,5 mm (with open contacts), in more complex switching of the signal from the external input is carried out by electronic switches. Volume and tone controls are used both traditional, with variable resistors, and electronic. The latter are currently practically replacing variable resistors, since in mass production the cost of electronic regulators is much lower. Two-band regulators, as a rule, are passive, while the magnitude of the rise in the frequency response is limited to 6 ... 8 dB in order to avoid overloading the UMZCH. Volume controls usually provide simple loudness compensation (one-tap variable resistor), but the amount of correction at low volume is chosen somewhat more than in "home" equipment. It should be noted that the volume control range for automotive equipment, taking into account the noise in the cabin without soundproofing measures, is no more than 35 ... 40 dB, so the initial section of the volume control remains unclaimed. As an example of a passive adjustment unit, we present the circuit used in the "Philips-410" radio tape recorder (Fig. 10). It is quite simple and does not require further explanation.
In the AF path of some radio tape recorders, instead of tone controls, a three- or five-band graphic equalizer is used. Such designs cannot be considered successful, since their capabilities are clearly insufficient for correcting acoustic defects inherent in car interiors, while the reliability of small-sized slide regulators leaves much to be desired. Electronic equalizers have incomparably greater possibilities. They are based on microchips with control over the I2C bus (for example, TEA6360 from Philips). The switching unit for signal sources and adjustments with such equalizers is now also assembled on microcircuits with control over the I2C bus (TDA7312 manufactured by SGS-Thomson, TDA8425, TEA6320, TEA6321, TEA6330 manufactured by Philips and other similar microcircuits). In addition to the volume and tone controls, the UZCH radio tape recorder provides other functions and adjustments. Almost all modern models of radio tape recorders have a four-channel sound path - two front (front) stereo channels and two rear (rear). This is not a quad system, as some users think, and the front and rear signals are the same except for level. Since the amplifiers built into the radio are not able to provide high power, most modern models have line outputs for connecting external UMZCH. Simple models have only one pair of line outputs (usually labeled rear), while more complex models have two pairs (front and rear). High-end radios also have a separate line output for the low-frequency (subwoofer) channel, the signal level on which does not depend on the distribution of levels between the front and rear channels. The sum (mono) signal level at this output is independently adjustable. In some models, it is possible to change the cutoff frequency of the low-pass filter. All line outputs are equipped with buffer stages, usually on an op-amp. With a signal level at the linear output of about 0,5 V, they are turned on by repeaters, and for a higher signal level - by amplifiers. In connection with the tightening of requirements for the level of interference in the audio system (mainly due to interference from the vehicle's on-board network), there has recently been a tendency to increase the signal level at the linear outputs to 4 and even 8 V, and differential outputs have been introduced in the most advanced systems. Increasing the signal level to such values requires the use of an increased supply voltage for buffer stages, therefore, such systems have a built-in voltage converter. To adjust the distribution of the signal between the front and rear channels, use a special control - fader (Fader). Its regulation characteristic is such (Fig. 11) that when the regulator is moved from the extreme position to the middle position, the signal level of the input channel decreases slightly, and the output channel, on the contrary, grows rapidly. After passing the middle position, the picture reverses.
In the radio, performing the function of the main unit of the audio system, there is a power amplifier. Some high-end devices are designed for use with an external power amplifier and built-in radio tape recorders. UMZCH was made on discrete elements, but since the mid-70s, microcircuits have been widely used - first hybrid, and then integrated. Currently, power amplifiers are performed exclusively on ICs. Almost all UMZCH (except for models with an output power of up to 4 ... 5 W) are now performed using a bridge circuit. Almost all modern devices with built-in amplifiers, except for the cheapest ones, can work on two acoustic systems - front (front) and rear (rear). Built-in amplifiers have two or four channels, and in the latter case, their power may be different. The acoustic systems of the first car radios "for the sake of simplicity" were mounted on the rear shelf of the cabin, so the four-channel devices "by inertia" had a powerful amplifier (2x20 ... 25 W) for the rear channels and a low-power (2x5 ... 7 W) for the front ones. At present, the channels are equivalent in terms of power, although there are still models made "in the old fashioned way" (for example, several recent models manufactured by LG Electronics Corporation). In two-channel amplifiers, the distribution of the signal between the front and rear speakers is carried out at the output of the amplifier, which leads to power losses in the mechanical regulator (powerful variable resistor or switch). Such a solution only makes sense when using a bridged power amplifier - otherwise the power of the amplifier will be too small. This design was born at the dawn of car audio and is almost never found in modern models. As an example, let's consider the regulators used in Pioneer radio recorders of the KEH23xx, KE28xx series, as well as in devices from other manufacturers (Fig. 12 shows one channel in a simplified way).
The variable resistor-switch is designed in such a way that in its middle position the engine is closed with the extreme conclusions. When moving the slider from the middle position, one of the sections is introduced into the loudspeaker circuit. The resistance of the section is about 180 Ohm, which allows you to reduce the signal level on it to almost zero. The radio amplifier can be used in two versions - two-channel (in this case, the output power reaches 25 W per channel) and four-channel (11 W per channel). The regulator itself has a fairly massive design with cooling fins. In radio tape recorders with a four-channel amplifier, there is no problem of power loss, here adjustments are made at the input of power amplifiers (usually by an electronic regulator, less often by a variable resistor). Consider the scheme of such a node (Fig. 13), used, for example, in radio "Sony 1253" and the like.
The fader itself (R1 - R5) in this case is nothing more than a panoramic control invented back in the 50s, distributing the signal of one source between two amplifying channels. Such an amplifier can also be used as a two- or four-channel. With two-channel switching on, the inputs of the amplifiers are closed to each other, the amplifier becomes a bridge amplifier with a maximum output power of 2x25 W. The fader has virtually no effect on the gain. With a four-channel connection, each of the channels operates independently, and the oxide capacitor C1 forms a "virtual ground". The output power of the radio in this case is 4x12 watts. A similar construction is now used only in the cheapest models of radio tape recorders. In modern devices, each of the four amplifying channels is made according to a bridge circuit, and the fader is part of the audio path controller microcircuit. When using a modern radio in a two-channel configuration, the two remaining channels are simply left unconnected. Connecting the outputs of the channels to increase the power is unacceptable! As power amplifiers in car radios, ICs TDA2003, TDA2004 (single-channel), TDA1719, TDA1521 (two-channel), TA8210, TA8221, TDA1554, TDA1556 (two-channel bridge) are used. The latest models of radio tape recorders use four-channel UMZCH bridges, made on the TDA7384 chip. Bridge amplifiers are used in car radios for a reason. The maximum output power can be realized when the signal voltage swing becomes equal to the supply voltage. In practice, this is impossible, since the saturation voltage of the transistors does not allow the output signal to be brought up to the supply voltage. The easiest way to increase output power is to reduce the load resistance. However, this method has disadvantages:
At one time, high-end radio tape recorders used hybrid power amplifiers of the STK series, designed to operate with a load of 2, 1 and even 0,5 ohms. Their potential capabilities could only be realized when working in conjunction with special low-resistance heads, so such amplifiers were not widely used. It turned out to be more convenient to turn on two amplifiers in a bridge circuit (when one of them inverts the phase). The loudspeaker is connected directly to their outputs without coupling capacitors, which to a certain extent improves the sound quality. The output voltage at the load turns out to be twice as high, therefore, at the same supply voltage and load, the output power of the amplifier in the bridge circuit is theoretically 4 times greater than that of a single channel (in practice, it is slightly lower, since the maximum output power decreases with increasing load current). voltage). According to this scheme, power amplifiers of almost all modern models, except for the cheapest ones, are made. Along with the advantage - greater output power - bridge amplifiers also have disadvantages. First of all, it is about 1,2 ... 1,7 times higher harmonic coefficient compared to the original amplifiers and twice the damping coefficient. It would seem that the harmonic coefficient should not change, but in practice the increase is due to the difference in the characteristics of real (even made on the same chip) amplifiers. Damping deterioration is explained by the fact that the output impedances of the amplifiers add up. In addition, since the load is connected to outputs without coupling capacitors, its wires are under constant voltage relative to ground, so an accidental short circuit of the load to ground can lead to amplifier failure. Modern integrated UMZCHs have built-in protection systems against such troubles, but the chips of the old series were not reliable enough. But there is a class of amplifiers literally born for cars. These are UMZCH, in which the output stage operates in H mode (with a variable supply voltage). The impetus for the development of such amplifiers was the fact that the real sound signal has a pulsed character and the average power is much lower than the maximum. The device is based on a conventional bridge-connected amplifier, and the "zest" is in doubling the supply voltage using a large storage capacitor, which is recharged from the main power source. At power peaks, this capacitor is connected in series with the main source. The power supply to the output stage of the amplifier is doubled for a fraction of a second, allowing it to cope with the transmission of signal peaks and almost quadruple the maximum power. An example of an amplifier of this class is UMZCH on a TDA1560Q chip suitable for this mode of operation. It develops an output power of 40 W into an 8 ohm load at a supply voltage of 14,4 V. Unfortunately, the manufacturers of such equipment, reporting this, are silent about a significant drawback. The maximum power of the amplifiers in H mode depends on the capacitance of the storage capacitors and the frequency of the signal. The smaller their capacitance, the smaller the "increase" of power at low frequencies, that is, just where it is most needed. From those shown in Fig. 14 graphs clearly show the dependence of the maximum output power on the capacitance of storage capacitors.
It is quite obvious that it is difficult to hide a battery of capacitors of an impressive capacity (2x10 uF for each of the four channels!) inside a standard case, therefore the power of 000x4 W declared by the manufacturers of radio tape recorders is provided only at medium and higher frequencies. An example of a class H amplifier is the TDA1560Q chip, which develops an output power of 40 W at a load of 8 ohms at a supply voltage of 14,4 V. A typical diagram of its inclusion is shown in fig. 15. The microcircuit has the functions of controlling the modes (off, standby, mute mode, work in B mode, work in H mode). Buffer capacitors with a capacity of 2200 uF provide almost doubling the supply voltage in H mode. 14 graphs clearly show the dependence of the maximum power on the capacitance of storage capacitors. CONTROLS AND LAYOUT The layout of the car radio units is determined primarily by the layout of the LPM and controls. The dimensions of the radio tape recorder are limited to a width of 178 and a depth of 150 mm. The height of a standard radio is 50 mm, but recently there are more and more devices with a height of 76 and 102 mm (one and a half and double height, respectively). It is for this size that the installation places in many American and Japanese cars are designed. Unfortunately, it is not easy to install such devices in domestic cars, although they have a number of advantages. The increased dimensions of the case allow to reduce the density of installation and more rationally arrange the nodes. Cooling of the UMZCH is facilitated, and the power can be significantly increased. On the enlarged front panel, all controls are easily placed, the number of which in a modern radio tape recorder can be more than twenty. Recently, combined devices (radio tape recorder and CD player) have been placed in such cases.
In standard-sized radios, controls sometimes perform several functions. Combined (coaxial) volume, tone, balance controls appeared several decades ago and have long become "classics". Rarely used mechanical controls can be hidden so as not to clutter up the front panel. So, Blaupunkt uses variable resistors with a retractable axis for tone controls, the knobs of which, when inoperative, are flush with the front panel. With the spread of electronic regulators in the AF tract, electronic-logical control of the CVL and a new element base, a number of layout problems have disappeared. It became possible to place the regulators of the AF tract in close proximity to the UMZCH, to move the LPM to the side wall of the case. The simplified layout of the removable panel has reduced its dimensions. For example, the first radio tape recorders with removable front panels were equipped with LPM drive pushers, which increased the thickness of the removed panel to 30 mm, while the modern removable panel has a thickness of no more than 15 mm. Removable front panels are connected to the control microprocessor with a multi-pin connector, which is a weak point in the design. Even gold-plated contacts do not always ensure uninterrupted operation - in winter, when the interior warms up, they fog up, which leads to false positives. Therefore, some manufacturers use an optical channel to communicate with the microprocessor, and only power circuits are connected through the connector (for example, a number of LG Electronics models). The controls of modern radio tape recorders are made on the basis of low-speed buttons or graphite-coated rubber pushers. Depending on the operating modes, the same group of buttons performs several functions. So, the fixed settings buttons can control the change of discs in the changer, the modes of operation of the LPM. The volume control through the menu allows you to make other sound adjustments - bass and treble tone, front and rear level balance (fader), sound processor settings, etc. Exiting the sound adjustment menu is automatic, after a few seconds. The menu system is widely used to call rarely used functions (setting the clock, the initial volume level when the radio is turned on, the depth of loudness, the color of the display backlight, the choice of the radio frequency grid). Most manufacturers use buttons or keys of various sizes and shapes as controls, grouped by function, but there are other types of controls. So, Sony uses a rotating wheel for basic adjustments - an encoder, supplemented in the latest models with a coaxial lever for switching receiver settings or CD changer tracks. In Clarion radios, a miniature joystick in the form of a swinging pyramid or hemisphere is used for the same purpose. For remote control, you can also use a remote joystick mounted on the steering wheel, or an infrared remote control. CLASSIFICATION OF RADIO In the field of view of anyone who wants to purchase new equipment, there may be car radios of various levels of complexity, so it makes sense to classify them again in order to make it easier to choose when buying and evaluate the possibilities of their self-repair and modernization. The classification of modern radio tape recorders is carried out according to functional saturation and technical characteristics, therefore, in the same price category there may be devices that are very different in capabilities. The given division is very conditional, since some signs may also be found in other groups. A family of radio tape recorders from one manufacturer is formed on the basis of a base board, while in simplified models, some of the components on the board are missing. For a radio amateur of average qualification, even without a circuit diagram, it is easy to find connection points and enter the necessary functions. The installation of modern radio tape recorders is quite dense, surface-mounted elements are widely used, but the nodes of interest are usually either mounted on sub-boards or connected to the rest of the nodes with wire jumpers, so there are no difficulties in repair and modernization. In practice, during the operation of all models, only the UMZCH fails (if the power and load are connected incorrectly) and the electric motor (wear of bearings, commutator, brushes). Before the wear of the variable resistors and the capstan shaft assembly, the car radio rarely survives. The main maintenance is periodic cleaning of the working surfaces of the heads, capstan and pressure roller. Modern LPM do not require lubrication during the entire service life. The first group is the simplest car radios. Currently, it is represented by domestic models and cheap devices manufactured in Southeast Asia. The receiver of such radio tape recorders has an analog setting, the scale can be analog, digital-to-analog or digital. LPM has mechanical control and is usually designed only for playback and fast forward, less often it has auto reverse and rewind in both directions. Switching between the operating modes of the receiver is carried out by mechanical switches with fixation, as a rule, by push-buttons. Adjustments in the AF channels are made by variable resistors, the path itself is two-channel, the output power of the UMZCH is insignificant (3-5 W). Tone control, as a rule, is carried out only on the treble "to blockage". In some models, there is a 3-5-band equalizer or tone registers (modes "classic", "rock", "pop", etc.). These models are available in both fixed and fully removable versions. Technical characteristics are at the lower limit of requirements for normal sound reproduction, operational conveniences are practically absent. It is impossible to improve the characteristics of the tuner without a radical alteration; without significant modernization costs, only the playback path and ultrasonic frequency can be subjected. If a car enthusiast prefers tape recordings to radio broadcasts, this choice justifies the cost savings when buying. The second group consists of entry-level radios. The receiver already has a digital setting and a preset memory. In most models, the LPM has a mechanical control and is usually equipped with an auto-reverse, much less often the LPM provides only playback and fast forward. Adjustments in the AF path, as a rule, are made by variable resistors, but there is also a combined control (electronic volume control, the rest of the adjustments are conventional). UMZCH, as a rule, is designed to work in two-channel bridge and four-channel versions, the output power is 2x (20 ... 25) and 4x (5 ... 7) W, respectively. Available in both fixed and fully removable versions. The technical characteristics of both the tape recorder part and the radio receiving path are quite high, but from the operational conveniences there is only automatic tuning and memory of fixed settings. Work with different types of tape is usually not provided, there are no noise reduction systems. Many models have a line-in jack on the front panel for connecting a portable CD player via a cable (with a 3,5 mm plug). Line outputs, as a rule, are not provided. Simple improvements, available even to a novice radio amateur, can significantly improve the performance of radio tape recorders of this class and bring them closer in their capabilities to the devices of the next group. Typical representatives of this class are "Sony XR-1253", "Sony XR-1853", "LG TCC-672X". The third group, the most numerous, is represented by radio tape recorders of the middle class. They are equipped with LPM exclusively with auto-reverse, in the vast majority of models it has electronic-logical control. The radio tape recorders of this group are usually produced in the version with a removable front panel, the non-removable version is less common. All adjustments in the AF path are electronic, UMZCH is a four-channel bridge with an output power of 4x (20 ... 35 W). Other technical characteristics are the same as in entry-level models, but the operational conveniences are significantly expanded (mute, turn on the radio while rewinding the tape, auto-search by pauses, clock, display backlight color switching, spectrum analyzer, RDS, etc.) . Unlike simplified radios, these require manual or automatic switching of the tape type, and almost all models have Dolby B noise reduction, and sometimes Dolby C. In many models, as a rule, there is an input on the front panel, one or two pairs of line outputs (front and rear) for further system expansion. Such a radio tape recorder, without any modifications, is capable of arranging a rather demanding music lover. Typical representatives are "Sony XR-C850RDS", "Sony XR653SP", "Philips RC429 RDS". The fourth group consists of radio tape recorders - control centers. In terms of their technical characteristics and functionality, they practically do not differ from the radio tape recorders of the third group (output power can be increased to 40 ... 45 W per channel), but they can control a CD or MD changer of a compatible family. The line input for such radios is located on the rear panel and is activated only if there is a changer in the system, a number of models have an additional line output of the low-frequency channel (subwoofer). Communication protocols with the head unit and connectors from different manufacturers are incompatible, but in some cases the problem can be circumvented using a pairing device. It makes sense to purchase such a radio tape recorder only if in the future it is planned to purchase a changer from the same company. In addition to the changer, it is also possible to control other components from the same manufacturer (for example, an external sound processor). Many models in this group have a built-in sound processor that allows you to compensate for time delays in the crossover and the difference in signal propagation time from different groups of speakers, as well as to simulate the acoustic characteristics of certain rooms. Typical representatives are "Pioneer KEH-P7600R", "Kenwood KRC-758RE", "Clarion ARX7470". The fifth group, which is very small, includes radios without UMZCH. Their technical characteristics are generally similar to the fourth group, but the functional richness is even higher (CD-text systems, user menu when controlling the changer, etc.). The radio tape recorder of this group is already becoming the core of a high-quality audio system with a changer, a sound processor, and several amplifiers. Their release, however, is almost discontinued, since a digital signal source should act as the core of a high-level car audio system. With the spread of digital sources and signal processing devices, it became possible to install components in any convenient place in the car. This layout allows you to place the main signal source - CD changer in the trunk next to the amplifier and avoid the problems associated with long signal wires. Alpine releases the CRA-1656 system controller, in which signal sources are switched and all sound adjustments are carried out, in this case only the system control panel remains on the dashboard. In this case, the radio receiver or radio tape recorder becomes an additional signal source and is connected to high-level inputs. But the compact cassette as a sound carrier abroad is already dying off, giving up its positions to compact and mini-discs. In our country, it will retain its popularity for another five to ten years. The production of car radios is gradually declining, and the race for the technical characteristics of the tape section has stopped a long time ago. Therefore, the appearance of automotive equipment with CD and MD players is a regularity. In addition to the already mentioned changers, which have quite impressive dimensions, built-in devices appeared in the dimensions of a standard radio. In addition to the single-disc models produced by many manufacturers, Alpine offered a three-disc cassette-loading CD receiver "3DE-7886R", JVC a three-disc "KD-GT5R", and Nakamichi a six-disc slot-loading "MB-100". JVC recently released a combo machine "KD-MX3000R" that works with both CD and MD (the reader automatically recognizes the media type). The CD, with all its advantages, has only one drawback - the inability to independently compose phonograms. Recordable and rewritable discs, as a rule, are not perceived by automotive equipment. Therefore, an excellent alternative to both a tape recorder and a CD is a minidisc developed by Sony. Its sound quality is slightly inferior to a CD, but its dimensions are much smaller, and the guaranteed number of re-recordings is up to a million. Car equipment for a mini-disk is produced, in addition to Sony, by other manufacturers. Author: A. Shikhatov, Moscow
Machine for thinning flowers in gardens
02.05.2024 Advanced Infrared Microscope
02.05.2024 Air trap for insects
01.05.2024
▪ Wide-gap semiconductors for automobiles ▪ Olive oil as a pain reliever ▪ By analyzing user actions, the phone works longer
▪ section of the website Basics of First Medical Aid (BFA). Selection of articles ▪ Article Internal Medicine. Crib ▪ article Agrochemist. Job description ▪ article Homemade iron. Encyclopedia of radio electronics and electrical engineering ▪ article Inseparable friends. Focus Secret
Comments on the article: Sergey Please help me with the sony xrm510 radio tape recorder in the place of the lpm which I don’t have in it, I have a desire to mount an MPXNUMX player board in the place of the lpm I can’t find the line input on the Internet a lot of tips related to the tuner, but for me it’s stupid to find the emulator circuit I can’t find the cassette mode without the lpm it doesn’t turn on because there are a lot of sensors on it and how to bypass this system I don’t have enough mind, kindly tell me how to be with respect self-taught master
Home page | Library | Articles | Website map | Site Reviews
www.diagram.com.ua |
See other articles Section 
Latest news of science and technology, new electronics:
All languages of this page