A simple audio frequency amplifier on a K548UN1A chip. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Transistor power amplifiers

 Comments on the article

The stereo power amplifier offered to the attention of readers was designed for a car cassette player, but, of course, it can also be used in portable equipment with a supply voltage of 9 ... 13 V.

The amplifier contains a minimum of parts, is easy to manufacture and set up, is economical, is not afraid of a short circuit in the load, and can operate at elevated ambient temperatures. In addition to adjusting the volume, it provides for adjusting the stereo balance and timbre of the sound at higher frequencies. The main technical characteristics of the amplifier are as follows:

Schematic diagram one of the power amplifier channels (the second one is identical to it) is shown in fig. one.

(click to enlarge)

As can be seen from the diagram, each channel contains only two stages. The first of them is made on one of the halves of the A1 dual integrated amplifier (in brackets are the pin numbers of another amplifier of the microcircuit), the second is a push-pull emitter follower. - on a complementary pair of transistors V1, V2. The amplifier is covered by OOS for direct (divider R5R4) and alternating (R5R3C2) voltages. To control the tone, a serial circuit R5C6.1R6 connected in parallel with the resistor R7 is used, which deepens the OOS at the higher frequencies of the nominal range. amplifiers without attenuation. As the slider moves up (also according to the scheme), the depth of the feedback at higher frequencies increases and the components of these frequencies are weakened.

The volume is controlled by a double variable resistor R1, the stereo balance is controlled by a resistor R2.

The output stage of the amplifiers (V1, V2) operates without an initial bias voltage at the bases of the transistors, i.e. in mode B. The absence of a quiescent current solves the problem of thermal stabilization of the transistor mode, which is important for automotive radio equipment and, in addition, allows you to reduce the size of the heat sink. and hence the device as a whole. The distortions of the "step" type signal waveform inherent in mode B are practically not noticeable by ear due to the large gain margin and the speed of the amplifier of the K.548UN1A microcircuit.

From overload during a short circuit in the load, the output transistors are protected by an output current limiting device built into the K548UN1A microcircuit. The maximum value of this current, as you know, is 12 mA, so the collector currents of transistors V1, V2 cannot exceed the maximum allowable.

The L1C3C4 filter protects the amplifier from interference from the ignition system when powered from the car's on-board network; in all other cases, when another source is used for power, it can be completely excluded.

All parts of the stereo amplifier, except for the variable resistors R1, R2 and R6, are mounted on a printed circuit board (Fig. 2) made of foil fiberglass 1,5 mm thick.

Fig. 2

The transistors of the output stages V1, V2, V1', V2' and the female part of connector X1 (SG-5) are mounted on a heat sink bracket (Fig. 3) made of AMts-11 sheet duralumin alloy 2 mm thick. Transistors V2 and V2' are fixed on it directly, and V1 and V1' - through mica gaskets 0,03 mm thick. The bracket is connected to the printed circuit board with three screws МЗХ6 with nuts МЗ.

The amplifier uses fixed resistors MLT-0.125 (MLT-0.25), variable resistors SPZ-12, group B - (R1, R6) and SP3-12a group A (R2). capacitors K50-12 (C1, C2). K50-6 (C4, C5) and KM-6 (C3) Transistors V1, V2 must be selected according to the static current transfer coefficient h21e, which at a collector current of 0.8 A must be at least 90. Choke 1,1 is wound (until the frame is filled) wire PEV-1 0,5. The core Ш6X6 from the output transformer of the pocket receiver is used as a magnetic circuit. When assembling the inductor in the magnetic circuit, it is necessary to provide a non-magnetic gap of 0,1 ... 0,2 mm. On the printed circuit board, the inductor is fixed together with the capacitor C5.

For fastening, a getinax or textolite (2,5 ... 28 mm thick) bar with a hole in the middle and an M1x2 stud with two nuts are used. With variable resistors R6, R1 and R0,1, the board is connected with a shielded wire. Setting up an amplifier, as already mentioned, is not difficult. By applying a sinusoidal signal with a frequency of 1 kHz and a voltage of 3 V to the inputs (the volume control R1 is in the maximum gain position, the stereo balance control is in the middle position), by selecting the resistor R0,3 in one of the channels, the same voltages are achieved on the load equivalents connected to the X4 connector instead of the speakers . Then increase the voltage of the test signal to 4 V and use an oscilloscope to control the shape of the signals at the outputs of both channels. Symmetrical limitation of half-waves of the signal is achieved by selecting resistors R1 and R2'. In the absence of an oscilloscope, by selecting these resistors, a voltage equal to half the supply voltage is set on the emitters of transistors VXNUMX, VXNUMX. On this, the adjustment of the amplifier can be considered complete.

The amplifier uses fixed resistors MLT-0.125 (MLT-0.25), variable resistors SPZ-12, group B - (R1, R6) and SP3-12a group A (R2). capacitors K50-12 (C1, C2). K50-6 (C4, C5) and KM-6 (C3) Transistors V1, V2 must be selected according to the static current transfer coefficient h21e, which at a collector current of 0.8 A must be at least 90. Choke 1,1 is wound (until the frame is filled) wire PEV-1 0,5. The core Ш6X6 from the output transformer of the pocket receiver is used as a magnetic circuit. When assembling the inductor in the magnetic circuit, it is necessary to provide a non-magnetic gap of 0,1 ... 0,2 mm. On the printed circuit board, the inductor is fixed together with the capacitor C5. For fastening, a getinax or textolite (2,5 ... 28 mm thick) bar with a hole in the middle and an M1x2 stud with two nuts are used. With variable resistors R6, RXNUMX and RXNUMX, the board is connected with a shielded wire.

Establishment amplifier, as already mentioned, is easy. By applying a sinusoidal signal with a frequency of 1 kHz and a voltage of 0,1 V to the inputs (the volume control R1 is in the maximum gain position, the stereo balance control is in the middle position), by selecting the resistor R3 in one of the channels, the same voltages are achieved on the load equivalents connected to the X1 connector instead of the speakers . Then increase the voltage of the test signal to 0,3 V and use an oscilloscope to control the shape of the signals at the outputs of both channels. Symmetrical limitation of half-waves of the signal is achieved by selecting resistors R4 and R4'. In the absence of an oscilloscope, by selecting these resistors, a voltage equal to half the supply voltage is set on the emitters of transistors V1, V2. On this, the adjustment of the amplifier can be considered complete.

Author: I. Borovik; Publication: radiokot.ru

See other articles Section Transistor power amplifiers.

Read and write useful comments on this article.

<< Back

Latest news of science and technology, new electronics:

Machine for thinning flowers in gardens 02.05.2024

In modern agriculture, technological progress is developing aimed at increasing the efficiency of plant care processes. The innovative Florix flower thinning machine was presented in Italy, designed to optimize the harvesting stage. This tool is equipped with mobile arms, allowing it to be easily adapted to the needs of the garden. The operator can adjust the speed of the thin wires by controlling them from the tractor cab using a joystick. This approach significantly increases the efficiency of the flower thinning process, providing the possibility of individual adjustment to the specific conditions of the garden, as well as the variety and type of fruit grown in it. After testing the Florix machine for two years on various types of fruit, the results were very encouraging. Farmers such as Filiberto Montanari, who has used a Florix machine for several years, have reported a significant reduction in the time and labor required to thin flowers. ... >>

Advanced Infrared Microscope 02.05.2024

Microscopes play an important role in scientific research, allowing scientists to delve into structures and processes invisible to the eye. However, various microscopy methods have their limitations, and among them was the limitation of resolution when using the infrared range. But the latest achievements of Japanese researchers from the University of Tokyo open up new prospects for studying the microworld. Scientists from the University of Tokyo have unveiled a new microscope that will revolutionize the capabilities of infrared microscopy. This advanced instrument allows you to see the internal structures of living bacteria with amazing clarity on the nanometer scale. Typically, mid-infrared microscopes are limited by low resolution, but the latest development from Japanese researchers overcomes these limitations. According to scientists, the developed microscope allows creating images with a resolution of up to 120 nanometers, which is 30 times higher than the resolution of traditional microscopes. ... >>

Air trap for insects 01.05.2024

Agriculture is one of the key sectors of the economy, and pest control is an integral part of this process. A team of scientists from the Indian Council of Agricultural Research-Central Potato Research Institute (ICAR-CPRI), Shimla, has come up with an innovative solution to this problem - a wind-powered insect air trap. This device addresses the shortcomings of traditional pest control methods by providing real-time insect population data. The trap is powered entirely by wind energy, making it an environmentally friendly solution that requires no power. Its unique design allows monitoring of both harmful and beneficial insects, providing a complete overview of the population in any agricultural area. “By assessing target pests at the right time, we can take necessary measures to control both pests and diseases,” says Kapil ... >>

Random news from the Archive Cigarettes and alcohol lead to dementia 13.07.2013 In people who smoke and drink a lot, dementia occurs much faster, according to a study by psychiatrists at University College London (UK). Many people know about the dangers of smoking and alcohol, about the dangerous diseases that bad habits cause. However, people do not always think that by smoking another cigarette or drinking another glass, they bring themselves closer to dementia or, simply speaking, dementia. Researchers have shown that smokers who also abuse alcohol develop dementia 36% faster than those who do not smoke and drink moderately. Prior to this, researchers have already noted that smoking and alcohol separately contribute to the development of dementia. However, for the first time, psychiatrists drew attention to the combination of these factors, and found that the effect is really detrimental. The research team evaluated 6473 adults (4635 men and 1838 women) aged 45 to 69 over a 10-year period. All participants were asked questions about their drinking habits and smoking frequency. Next, the researchers assessed cognitive functions - the ability to reason, solve simple mathematical problems, memory, speech development, etc. Similar cognitive tests were conducted three times during the ten-year study. It turned out that in smokers who abuse alcohol, cognitive decline occurred 36% faster than in non-smokers and moderate drinkers. Simply put, their brains wore out faster. We can say that in ten years of research, the brains of heavy drinkers smokers were "worn out" as if 12 years had passed. Scientists hope that the results of their study will make people think. The influence of alcohol and smoking is detrimental not only to the lungs and liver, but also to the brain. The combination of smoking and alcohol accelerates the development of dementia, and it is unlikely that anyone at a relatively young age of 60 wants to forget where they put the keys or the name of their grandson, just because in their young and mature years they could not refuse themselves in an extra glass and a cigarette.

Other interesting news:

▪ Smart watch Amazfit Bip 5

▪ Mobile chip Wi-Gig

▪ Rules for testing robotic vehicles

▪ Seagate is the first to equip an external hard drive with a 4G LTE modem

▪ Solar panels from cheap raw materials

News feed of science and technology, new electronics

Interesting materials of the Free Technical Library:

▪ Telephony site section. Article selection

▪ article GPS navigation system. History of invention and production

▪ article How fast do trees grow? Detailed answer

▪ article Electrician for the repair of electrical equipment. Job description

▪ Antenna article. Theory. Directory

▪ article Measurements of electrical quantities. Frequency measurement. Encyclopedia of radio electronics and electrical engineering

Leave your comment on this article:

All languages ​​of this page

Arabic	Hebrew	Polish
Bengali	Hindi	Portuguese
Chinese	Italian	Spanish
English	Japanese	Turkish
French	Korean	Ukrainian
German	Malay	Vietnamese

Home page | Library | Articles | Website map | Site Reviews

www.diagram.com.ua
2000-2024