Three way amplifier. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Transistor power amplifiers

 Comments on the article

Splitting the signal into strips in the pre-amplification path is an effective way to improve the quality of sound reproduction. This makes it possible to reduce intermodulation distortion, to obtain a linear amplitude-frequency characteristic in terms of sound pressure by relatively simple means, to simplify the design of power amplifiers, since each of them operates in a narrow frequency band.

The main parameters:

• Rated frequency range (with uneven frequency response not more than ±3 dB), Hz 20.......200 000
• Section frequencies, Hz.......400 and 4000
• Rated output power, W, channels: LF and MF at a load with a resistance of 8 Ohm.......14
• HF on a load with a resistance of 16 ohms ....... 5
• Harmonic coefficient, %, at an output power of 4 W, at a frequency, Hz: 100.......0,4
• 1000......0,7
• 10 000......0,4
• 20 000......0,5
• Relative level of noise and background, dB, LF channel.......-90
• MF and HF.......-80
• Crosstalk attenuation between channels, dB, at frequency, Hz 1000.......70
• 20 000......50

Each channel of the device (amplifier - stereo) consists of a block of crossover filters with adjustable transmission coefficients separately in the low-frequency (LF), mid-frequency (MF) and high-frequency GHF) signal bands and a three-band power amplifier.

The filter block contains a signal level switch (S1), a volume control (R2), two amplifying stages (VI, V2) with high (C2R3C3R4C4R5) and low (R7C6R8C7R9C8) filters turned on at the input, and two emitter followers (V3, V4) also with filters of high (C16R18C17R19C18R20) and low (R17C11R14C12R15C13) frequencies at the input.

The cutoff frequencies of the first two filters are 400 Hz, the second ones are 4000 Hz. Thus, from the engine of the variable resistor R12, components with a frequency below 400 Hz enter the input of the corresponding bandpass amplifier, from the engine of the resistor R24 ​​- with a frequency of 400 to 4000 Hz, and from the engine of the resistor R23 - with a frequency above 4000 Hz.

Each of the bandpass power amplifiers (Fig. 1) is made on one op-amp and two complementary pairs of transistors.

Ris.1

The circuits of the amplifiers of the MF and LF bands of the signal are almost identical and differ only in that the latter is covered by a positive feedback circuit (PIC) for current. The signal of this connection is taken from the trimmer resistor R10 and fed through the resistor R9 to the non-inverting input of the op-amp A3. The output stages of the amplifiers of the midrange and low-frequency bands operate in mode B, the amplifier of the high-frequency band - in mode AB.

Fig.2-4

A schematic diagram of a bipolar amplifier power supply is shown in the following figure.

With switch S2, the electronic protection threshold can be set equal to 1 or 3 A. Voltages + 18 and -18 V are used to power the amplifiers of the mid and low bands, as well as the output stage of the high band amplifier, +12 and -12 V are used to power the op-amp AJ of this amplifier The filter block is powered by a low-power voltage regulator on the V8 transistor.

In addition to those indicated in the diagram, in the amplifiers of the midrange and bass, you can use the OU K140UD6A, KN0UD6B, K140UD8A, K140UD8B, K553UD1 Complementary pairs of transistors KT502B, KT503B can be replaced by pairs KT502G, KT503G; KT502V, KT503V, and also (in the RF amplifier) ​​a pair of KT361E, KT315E transistors. The static current transfer coefficients of the replacement transistors must be at least 40. To obtain small non-linear distortions, a pair of transistors of the output stages is recommended to be selected according to the coefficient h21e with a deviation of no more than ± 10% (V7, V8 and V13, V14) and ± 20% (all others) .

Transistors V13-V18 (Fig. 2) must be installed on ribbed heat sinks with an effective area of ​​300...400 cm2, transistors V15 and V22 (Fig. 3) - on heat sinks with approximately twice the area.

The transformer T1 of the power supply is wound on a twisted toroidal magnetic circuit with an outer diameter of 115, an inner diameter of 60 and a height of 40 mm. Winding I contains 880 turns of PEL wire - 0,6 with a tap from the 510th turn, winding II - 2 X 70 turns of PEL wire - 1,5. The inductor L1 is wound on a magnetic core made of Sh10 plates (the thickness of the set is 10 mm). Its winding contains about 1000 turns of PEL wire - 0,17.

Loudspeakers are made in the form of phase inverters. Cases (external dimensions 320 X 240 X 500 mm) are made of chipboard 20 mm thick. The woofer is mounted on the front panel from the inside, all the rest are outside. The hole for the bass head is located on the vertical axis of symmetry of the panel at a distance of 130 mm from the bottom wall, the holes for the midrange and high-frequency heads are symmetrical about this axis (each pair is on the same level) at a distance of 310 and 420 mm, respectively, from the same wall and 130 and 165 mm from one another. The midrange heads are isolated from the rest of the body volume by a cap in the form of a half-cylinder with a diameter of 130 mm made of 0,5 mm thick duralumin. The semi-bases of the hood are made of 15 mm thick foam plastic sheet. The hole for the phase inverter tunnel (thin-walled - 1,5 mm - cardboard tube with an inner diameter of 45 and a length of 150 mm) is located in the upper part of the front panel between the HF heads. The tuning frequency of the phase inverter is 30 Hz. All connections in the housing are sealed with plasticine. The walls, except for the front, are lined with a compacted (30 mm thick) layer of cotton wool pressed against them with a plastic mesh. Microporous rubber is laid between the front wall and the body.

The filter block is set up first. By setting the sliders of resistors R2, R12, R24 and R23 (Fig. 1) to the upper (according to the diagram) position, an alternating voltage of 200 mV with a frequency of 200, 2 and 000 Hz is applied to the input and the voltages at the unit outputs are measured. If these voltages are less than 10 mV, transistors VI and V000 are replaced by others with a greater slope.

The establishment of power amplifiers is carried out at a protection current of 1 A. The quiescent current of transistors V13, V14 (about 100 mA) is set by selecting the resistor R14, the minimum constant voltage at the output (permissible value ± 0,1 ... 0,2 V) - by selecting resistor R3*. The absence of a constant voltage at the outputs of the amplifiers of the midrange and HF bands is achieved by building resistors R11 and R12.

After that, a voltage of 100 mV with a frequency of 200 Hz is applied to the input of the filter unit and, by selecting resistor R7 *, a voltage of 10,5 V is set on the load equivalent of the low-frequency amplifier. Similarly, at frequencies of 2 and 10 kHz, by selecting resistors R2 * and R4 *, they are set on the load equivalent of the midrange amplifier voltage is 10,5 V, and on the equivalent load of the RF amplifier - 9V. Lastly, the depth of the POS is selected. By connecting the speakers and setting the engines of the resistors R12 and R23, R24 (Fig. 1) to the lower (according to the diagram) position, a musical signal with a predominance of bass sounds is fed to the input. Gradually moving the slider of the resistor R12 upwards, the most pleasant sounding of the lower sound frequencies is achieved.

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 New BMW bulbs won't need to be replaced 21.04.2014 The BMW Group is going to equip its vehicles with Organic Light Emitting Diode (OLED) optics, which have many advantages over the currently common LED elements. The technology being tested by the German automaker is referred to as Organic Light. Unlike conventional LEDs, which use semiconductor chips in their construction, OLEDs use organic polymers that have the properties of semiconductors. The light is generated in thin semiconductor layers, the total thickness of which is only 40 nm, which is 150 times thinner than a human hair. The thickness of the entire OLED component does not exceed 1,5 mm. According to BMW, Organic Light technology is characterized by high brightness and low consumption, which will allow it to be used for interior lighting and for outdoor lighting. Initially, OLED lighting is planned to be implemented in the taillights, while LEDs will remain in the turn signals and brake lights. In the future, the automaker hopes to completely switch to organic light, which, according to the developers, will not require replacement during the entire period of operation of the car. OLED elements can take almost any shape, they do not require the installation of lenses and reflectors, which opens up great opportunities for designers and marks a new approach in automotive design. In addition, OLEDs are lighter in weight, consume less energy and emit less harmful emissions than other light sources used in the automotive market, so OLED components can be widely used in hybrid and electric vehicles. BMW plans to start serial production of cars with organic light-emitting diodes in the next three years. In the meantime, the German company is preparing to bring to market the first production car with laser headlights. This is a hybrid sports car BMW i8, which is scheduled for release in autumn 2014. As for OLED technology, other automotive companies are also testing it. In July 2013, it became known about the creation of the world's first three-dimensional automotive optics, which uses organic light emitting diodes. Developed by Philips and Audi. The novelty allows you to create complex "drawings" of lighting and change their transparency.

Other interesting news:

▪ Electrical Brain Stimulation Improves Cognitive Ability

▪ Anker Soundcore Space Q45 and Space A40 Wireless Headphones

▪ Iiyama ProLite B4UHSU 2888K Monitor

▪ Graphene will improve HDD

▪ Drug test

News feed of science and technology, new electronics

Interesting materials of the Free Technical Library:

▪ section of the site Palindromes. Article selection

▪ article by William Saroyan. Famous aphorisms

▪ article What is ringworm? Detailed answer

▪ article Instruction on labor protection for an operator on automatic and semi-automatic lines, engaged in facing the shields. Standard instruction on labor protection

▪ article The principle of operation of the metal detector. Encyclopedia of radio electronics and electrical engineering

▪ UHF Antenna article. 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