Monoblock car amplifier on a TDA7294 chip. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Automotive power amplifiers

 Comments on the article

foreword

I think every music lover motorist will want to have a high-quality audio system in his car. Consider the situation of reproduction of low frequencies, hmm, one thought - without a subwoofer anywhere! And if almost everyone can assemble a sub with a desire (for example, on the well-known 75GDN or on any (any) other low-frequency head), then things are much more difficult with an amplifier. A high-quality, powerful enough amplifier that can drive a subwoofer is quite expensive (quite dubious devices cost at least $80). Therefore, I will try to help in creating a sufficiently high-quality and powerful automobile monoblock.

The amplifier contains 4 blocks - a power amplifier, a voltage converter, a signal processing unit, as well as a switching and rectifier unit. Now about each of them in more detail.

Amplifier

Based on the article by A. Chivilch "Increasing the power of an amplifier on a microcircuit TDA7294"from RADIO magazine No. 11 in 2005, since the amplifier was tested by me more than once and was noted for quite high reliability, high output power, high-quality bass. The amplifier circuit is shown below. It differs from the original only by replacing the output transistors with better imported ones.

I will not delve into the principle of operation of the circuit, you can read about this in more detail in the original article. I will only tell you the fundamental patterns of drawing up a diagram. It is assembled on a board with dimensions of 125x70mm. All non-electrolytic capacitors, except for C2, are film capacitors with an input capacitance of 1 μF, 2.2 μF can be used. Resistors 0.25W, although 0.125W is enough. The output transistors are bent and pressed against the board so that their cases are parallel to the board and their heat-removing part is smeared with thermal paste and pressed to the radiator through a dielectric film. That is, the transistor cases are isolated from one another and from the radiator. The inductor L1 is frameless, wound with a wire with a diameter of 1 mm in two layers and contains 25 turns, an inner diameter of 5 mm. The fuses have been moved to the rectifier board.

Voltage transformer

Most often, it is precisely through the complexity of this block that most beginner radio amateurs refuse to assemble amplifiers from two polarized power supplies into cars. Indeed, this block is the heaviest part of this amplifier, although not everything is as complicated as it seems, so I will try to tell you about this block in more detail. And so, the converter circuit is shown below.

(click to enlarge)

The heart of the converter is a pulse generator built on the TL494 chip. The generation frequency can be changed by varying the value of the resistor R3. If you wish, you can roll the datasheet and learn more about the operation of the microcircuit. The muscles of the power supply are naturally field-effect transistors IRFZ44N. All resistors (except R4, R9, R10) are 0,25W, you can even 0,125W. R9, R10 - 2W, R4 - even 1W is possible (I generally have 0,5W). Diode VD1 at the input is set to protect against reverse polarity, I excluded it. The L1 inductor in my case is wound on a ferite ring with a diameter of about 2 cm from a computer power supply. It contains 10 turns of double wire 0,8mm in diameter distributed throughout the ring. This inductor can also be wound on a ferite rod with a diameter of 8-10mm and a length of 2-3cm.

Probably the most difficult thing in the converter is the correct manufacture of the transformer, since the performance of the unit as a whole strongly depends on it. My trance is wound on a 2000NM grade ferrite ring with dimensions 40 * 25 * 11. First, I rounded off all the edges with a file, both external and internal, and wrapped it with linen electrical tape. The primary winding is wound with a bundle which consists of 5 cores 0,7 mm thick and contains 2 * 6 turns, that is, 12. It is wound like this: we take one core and wind it with 6 turns evenly distributed around the ring, then we wind the next one close to the first one and so on 5 lived. At the conclusions, the cores are twisted. Then, on the wire-free part of the ring, we begin to wind the second half of the primary winding in the same way. We get two equivalent windings. After that, we again carefully wrap the ring with electrical tape and wind the secondary winding. I wound it with a 1,5mm wire 2 * 18 turns in the same way as the primary. Ready trance again wrapped with electrical tape. Here with the trance and completed! Unfortunately, I did not take pictures of the manufacturing process.

Construction photo below. In the photo, resistors R9, R10 1W, then replaced with imported 2W.

Signal processing unit

Since the amplifier is for a subwoofer, the signal that goes to it must first be processed, cutting out only the low-frequency components of the audio signal. The device diagram is shown below.

(click to enlarge)

Since there is only one subwoofer, it must reproduce the low-frequency components from both stereo channels, therefore there is an adder at the input that sums the signals of both channels into one single one. After that, the signal is filtered, frequencies lower than 16Hz and higher than 300Hz are cut off. Then there is an adjustment filter that cuts the signal from 35Hz to 150Hz. And at the output, a smooth phase control for better matching of the subwoofer with acoustics and a volume control. All parts are mounted on a board measuring 80x55mm. Resistors 0,125W, capacitors are mostly ceramic, a few film ones in signal circuits.

Switching and rectifier unit

The unit consists of two separate parts, a switching unit, and a rectifier unit, which includes filter capacitors to power the power amplifier and a voltage regulator to power the signal processing unit.

In the rectifier unit, everything is simple. The voltage from the converter enters the filter capacitors, is smoothed and goes to the power amplifier, as well as to the voltage stabilizer. The transistors lower the voltage to + -26V, after which the rolls stabilize it to 15. I did not observe the heating of transistors or the roll, therefore I did not put it on the radiator.

The switching unit works as follows: when a 12V voltage (power lines) is applied to the terminals (power lines), the red LED lights up, no voltage is supplied to the voltage converter, the amplifier does not use energy. When +12V is applied to the REM terminal from an external source (from a car radio or a lock), the relay is activated, turning off the red diode, while voltage is applied to the converter and the green LED lights up, the amplifier is ready for operation.

12V relay, which can withstand a current of 30A at the key terminals, 0,125W resistors.

Hull and construction

The case has dimensions 270x200x70. The base is made of laminated MDF 8mm thick, the side walls are made of chipboard 16, they are sheathed with carpet. Front and rear panels - aluminum plates 3mm thick. On the front panel there are 3 holes through which you can turn the volume, phase and cutoff frequency controls with a screwdriver, as well as two LEDs. On the rear panel are all connectors, inputs, output and clamps for supplying voltage and the REM terminal, all of them, except for the input, are well isolated from the plate. The top cover is a plastic grill, in my opinion from the Accord speaker system. All boards are attached to the bottom panel of the case, except for the signal processing unit, in which variable resistors are additionally fixed to an aluminum plate. The TDA7294 chip and the transistors from the voltage converter are mounted on one L-shaped heatsink, which is attached to the side panel. Transistors and microcircuit are isolated from the heatsink. There is also a small cooler in the case. At first it was not planned to install it, but then I installed it anyway. As it turned out, it was enough to drive air in the case, even after two hours of operation, the radiators were barely warm (however, this is in winter).

You can download printed circuit boards in LAY format here

Author: Alexander Korchinsky, Sashakorch [dog] mail.ru; Publication: cxem.net

See other articles Section Automotive 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 Don't scratch your dog's belly 17.04.2018 Veterinarians say that if a dog lies on its back, this is really a sign of special trust in a person. But at the same time, this is not an "invitation" to touch the belly of an animal. A professor at the University of Edinburgh spoke about the behavior of dogs: if an animal trusts a person, it can lie on its back. But do not take this as an invitation to touch the dog's stomach - this is a violation of the animal's personal space. Dogs allow a person to scratch their stomach, not because it gives them pleasure, but because they know that this procedure pleases a person. The veterinarian drew attention to another common mistake dog owners make - they scold their pets when they start barking at new guests or strangers. The raised and angry tone of the owner's voice tells the dog that the person is alarmed, so the animal perceives the guest as an even greater threat and barks louder. It’s better to either not respond to barking, or gently calm the dog and somehow distract it.

Other interesting news:

▪ The efficiency of the split laser beam is increased

▪ Today's old people are smarter than before

▪ Holographic display for mobile devices

▪ Wind turbines underwater

▪ On January 4, the Earth will get as close as possible to the Sun.

News feed of science and technology, new electronics

Interesting materials of the Free Technical Library:

▪ section of the site Winged words, phraseological units. Selection of articles

▪ article Careful topping up of water in the aquarium. Tips for the home master

▪ article Which animals cannot recognize their usual food away from their trees? Detailed answer

▪ article Common eagle. Legends, cultivation, methods of application

▪ article Bidirectional frequency scanning in a VHF radio receiver based on the TDA7088T chip. Encyclopedia of radio electronics and electrical engineering

▪ article Experience with a dry stick. physical experiment

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