Amplifier circuits based on 7294 chips. A simple powerful stereo amplifier on a single TDA7297 chip. Scheme. Protective functions of the TDA7294 chip

The article provides a project to create an amplifier on a single chip TDA7297 a simple powerful 2 x 15 W stereo amplifier powered by 12 volts. It has a minimum of parts and is very compact, just like the .

Building an amplifier on the TDA7297 chip does not require a lot of body kit. The electronic circuit is built according to the scheme proposed by the manufacturer from the datasheet with minor modifications. In particular, the refinement of the typical TDA7297 amplifier circuit is to add a volume control using a 10 kΩ double logarithmic potentiometer.

Specifications TDA7297

• Mounting type: Through hole
• Output power: 15W
• Output signal: Differentiated
• Supply voltage range TDA7297: 6.5 ... 18V
• Power Source: Unipolar
• Maximum Potential Gain: 32dB
• Maximum power dissipation: 33W
• Product: Class AB
• Operating supply voltage: 9V, 12V, 15V
• Working temperature range: 0…+ 70C
• Speaker impedance: 8 ohm
• Total harmonic distortion + noise: 0.1%
• Output type: 2 stereo channels
• Enclosure Type: Multiwatt-15
• Consumption current: 2A

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TDA7297 - wiring diagram from datasheet

This diagram from the datasheet shows how easy it is to connect the TDA7297.

TDA7297 - power amplifier circuit

Below is a diagram of an amplifier on the TDA7297, which you can assemble with your own hands. The TDA7297 amplifier is an output bridge chip and, therefore, the connected speakers must be equipped with electrolytic capacitors.

The output bridge configuration is simple - two identical amplifiers for each channel, operating in antiphase. Each output pin is connected to one speaker pole. This control of the output voltage allows you to get high power with a very low supply voltage. According to the declared parameters of the TDA7297 chip, this circuit can operate at a voltage of 6.5 volts to 18 volts. In this version, a voltage of 12V was used.

A resistive divider consisting of two 47 kΩ resistors and an electrolytic capacitor of 10 microfarads at 25 volts serve to eliminate distortion when the power is turned on. Two 2.2 microfarad capacitors - polyester or ceramic.

Updated: 04/27/2016

An excellent amplifier for the home can be assembled on the TDA7294 chip. If you are not strong in electronics, then such an amplifier is ideal, it does not require fine tuning and debugging like a transistor amplifier and is easy to build, unlike a tube amplifier.

The TDA7294 chip has been produced for over 20 years and still has not lost its relevance, and is still in demand among radio amateurs. For a beginner radio amateur, this article will be a good help for getting to know integrated audio frequency amplifiers.

In this article I will try to describe in detail the amplifier device on the TDA7294. I will focus on a stereo amplifier assembled according to the usual scheme (1 microcircuit per channel) and briefly talk about the bridge circuit (2 microcircuits per channel).

Chip TDA7294 and its features

TDA7294 is the brainchild of SGS-THOMSON Microelectronics, this microcircuit is an AB class low frequency amplifier, and is built on field effect transistors.

Of the advantages of TDA7294, the following can be noted:

• output power, with distortion 0.3–0.8%:
  • 70 W into 4 ohm load, typical circuit;
  • 120 W into 8 ohm load, bridged;
• mute function (Mute) and standby function (Stand-By);
• low noise level, low distortion, frequency range 20–20000 Hz, wide operating voltage range - ±10–40 V.

Specifications

Pin assignment

Note. The microcircuit housing is connected to the power supply minus (pins 8 and 15). Don't forget to insulate the heatsink from the amplifier case, or isolate the chip from the heatsink by installing it through a thermal pad.

I also want to note that in my circuit (as well as in the datasheet) there is no separation of input and output "lands". Therefore, in the description and on the diagram, the definitions of “common”, “ground”, “case”, GND should be taken as concepts of the same sense.

Differences in hulls

The TDA7294 chip is available in two types - V (vertical) and HS (horizontal). TDA7294V, having a classic vertical design of the case, was the first to leave the assembly line and to this day is the most common and affordable.

Protection complex

The TDA7294 chip has a number of protections:

• protection against power surges;
• protection of the output stage against short circuit or overload;
• thermal protection. When the microcircuit is heated to 145 °C, the mute mode is activated, and at 150 °C, the standby mode (Stand-By) is activated;
• protection of microcircuit outputs from electrostatic discharges.

Power amplifier on TDA7294

A minimum of parts in the harness, a simple printed circuit board, patience and obviously good parts will allow you to easily assemble an inexpensive UMZCH on the TDA7294 with clear sound and good power for home use.

You can connect this amplifier directly to the line output of your computer's sound card. the nominal input voltage of the amplifier is 700 mV. And the nominal voltage level of the line output of the sound card is regulated within 0.7–2 V.

Structural diagram of the amplifier

The diagram shows a variant of a stereo amplifier. The structure of the amplifier in a bridge circuit is similar - there are also two boards with TDA7294.

• A0. Power Supply
• A1. Control unit for Mute and Stand-By modes
• A2. UMZCH (left channel)
• A3. UMZCH (right channel)

Pay attention to block connections. Improper wiring inside the amplifier can cause additional noise. To minimize noise as much as possible, follow a few rules:

1. Power to each amplifier board must be supplied with a separate harness.
2. Power wires must be twisted into a pigtail (bundle). This will compensate for the magnetic fields created by the current flowing through the conductors. We take three wires (“+”, “-”, “Common”) and weave a pigtail out of them with a slight tightness.
3. Avoid ground loops. This is such a situation when a common conductor, connecting the blocks, forms a closed circuit (loop). The connection of the common wire must go in series from the input connectors to the volume control, from it to the UMZCH board and further to the output connectors. It is advisable to use connectors isolated from the body. And for the input circuits also shielded wires in isolation.

Parts list for PSU TDA7294:

When purchasing a transformer, note that the effective value of the voltage is written on it - U D, and by measuring with a voltmeter you will also see the effective value. At the output after the rectifier bridge, the capacitors are charged to the amplitude voltage - U A. The amplitude and effective voltages are related by the following relationship:

U A \u003d 1.41 × U D

According to the characteristics of TDA7294 for a load with a resistance of 4 ohms, the optimal supply voltage is ± 27 volts (U A). The output power at this voltage will be 70 watts. This is the optimal power for TDA7294 - the level of distortion will be 0.3-0.8%. There is no point in increasing power to increase power. the level of distortion grows like an avalanche (see graph).

We calculate the required voltage of each secondary winding of the transformer:

U D \u003d 27 ÷ 1.41 ≈ 19 V

I have a transformer with two secondary windings, with a voltage of 20 volts on each winding. Therefore, in the diagram, I designated the power terminals as ± 28 V.

To obtain 70 W per channel, taking into account the efficiency of the microcircuit 66%, we consider the power of the transformer:

P = 70 ÷ 0.66 ≈ 106 VA

Accordingly, for two TDA7294, this is 212 VA. The nearest standard transformer, with a margin, will be 250 VA.

Here it is appropriate to state that the power of the transformer is calculated for a pure sinusoidal signal, corrections are possible for a real musical sound. So, Igor Rogov claims that for a 50 W amplifier, a 60 VA transformer will be enough.

The high-voltage part of the PSU (before the transformer) is assembled on a 35 × 20 mm printed circuit board, it can also be surface mounted:

The low-voltage part (A0 according to the block diagram) is assembled on a 115 × 45 mm printed circuit board:

All amplifier boards are available in one.

This power supply for TDA7294 is designed for two microcircuits. For more chips, you will have to replace the diode bridge and increase the capacitance of the capacitors, which will entail a change in the dimensions of the board.

Control unit for Mute and Stand-By modes

The TDA7294 chip has a standby mode (Stand-By) and a mute mode (Mute). These functions are controlled through pins 9 and 10, respectively. The modes will be enabled as long as there is no voltage on these pins or it is less than +1.5 V. To “wake up” the microcircuit, it is enough to apply a voltage of more than +3.5 V to pins 9 and 10.

To simultaneously control all UMZCH boards (especially important for bridge circuits) and save radio components, it makes sense to assemble a separate control unit (A1 according to the block diagram):

Parts list for control box:

• Diode (VD1). 1N4001 or equivalent.
• Capacitors (C1, C2). Polar electrolytic, domestic K50-35 or imported, 47uF 25V.
• Resistors (R1-R4). Ordinary underpowered.

The printed circuit board of the block has dimensions of 35 × 32 mm:

The task of the control unit is to ensure silent switching on and off of the amplifier due to the Stand-By and Mute modes.

The principle of operation is the following. When the amplifier is turned on, along with the capacitors of the power supply, the capacitor C2 of the control unit is also charged. As soon as it is charged, the Stand-By mode will turn off. Capacitor C1 takes a little longer to charge, so the Mute mode will turn off in the second turn.

When the amplifier is disconnected from the network, the capacitor C1 is first discharged through the VD1 diode and turns on the Mute mode. Then the capacitor C2 is discharged and sets the Stand-By mode. The microcircuit becomes silent when the power supply capacitors have a charge of about 12 volts, so no clicks or other sounds are heard.

Amplifier on TDA7294 in the usual way

The microcircuit switching circuit is non-inverting, the concept corresponds to the original one from the datasheet, only the component values ​​have been changed to improve the sound characteristics.

Parts list:

1. Capacitors:
   • C1. Film, 0.33-1 uF.
   • C2, C3. Electrolytic, 100-470uF 50V.
   • C4, C5. Film, 0.68 uF 63 V.
   • C6, C7. Electrolytic, 1000uF 50V.
2. Resistors:
   • R1. Variable dual with linear characteristic.
   • R2-R4. Ordinary underpowered.

Resistor R1 is dual because stereo amplifier. Resistance not more than 50 kOhm with a linear, not a logarithmic characteristic for smooth volume control.

The R2C1 circuit is a high-pass filter (HPF), suppresses frequencies below 7 Hz, not passing them to the input of the amplifier. Resistors R2 and R4 must be equal to ensure stable operation of the amplifier.

Resistors R3 and R4 organize a negative feedback circuit (NFB) and set the gain:

Ku = R4 ÷ R3 = 22 ÷ 0.68 ≈ 32 dB

According to the datasheet, the gain should be in the range of 24-40 dB. If less, then the microcircuit will be self-excited, if more, distortion will increase.

Capacitor C2 is involved in the OOS circuit, it is better to take it with a larger capacitance in order to reduce its effect on low frequencies. Capacitor C3 provides an increase in the supply voltage of the output stages of the microcircuit - "voltage boost". Capacitors C4, C5 eliminate interference introduced by wires, and C6, C7 supplement the capacitance of the power supply filter. All capacitors of the amplifier, except for C1, must be with a voltage margin, so we take 50 V.

The printed circuit board of the amplifier is single-sided, rather compact - 55 × 70 mm. During its development, the goal was to breed the "earth" with a star, provide versatility and at the same time maintain minimal dimensions. I think this is one of the smallest boards for TDA7294. This board is designed for the installation of one chip. For the stereo version, respectively, you will need two boards. They can be installed side by side or one above the other like mine. I'll talk more about versatility a little later.

The radiator, as you can see, is indicated on one board, and the second, similar one, is attached to it from above. Photos will be a little further.

Amplifier on TDA7294 in a bridge circuit

A bridge circuit is a pairing of two conventional amplifiers with some amendments. Such a circuit solution is designed to connect acoustics with a resistance of not 4, but 8 ohms! Acoustics is connected between amplifier outputs.

There are only two differences from the usual scheme:

• the input capacitor C1 of the second amplifier is connected to ground;
• added feedback resistor (R5).

The printed circuit board is also a combination of amplifiers in the usual way. The board size is 110×70 mm.

Universal board for TDA7294

As you have already noticed, the above boards are essentially the same. The next PCB option fully confirms the versatility. On this board, you can assemble a 2x70W stereo amplifier (conventional circuit) or a 1x120W mono amplifier (bridged). The board size is 110×70 mm.

Note. To use this board in a bridge version, you must install the resistor R5, and install the jumper S1 in a horizontal position. In the figure, these elements are shown by dotted lines.

For a conventional circuit, resistor R5 is not needed, and the jumper must be installed in a vertical position.

Assembly and adjustment

Assembling the amplifier will not cause any particular difficulties. As such, the amplifier does not require adjustment and will work immediately, provided that everything is assembled correctly and the microcircuit is not defective.

Before first use:

1. Make sure the radio components are installed correctly.
2. Check the correct connection of the power wires, do not forget that on my amplifier board the "ground" is not in the center between plus and minus, but on the edge.
3. Make sure the chips are isolated from the heatsink, if not, then check that the heatsink is not in contact with ground.
4. Apply power to each amplifier in turn, so there is a chance not to burn all the TDA7294 at once.

First power on:

1. We do not connect the load (acoustics).
2. We close the inputs of the amplifiers to the "ground" (close X1 with X2 on the amplifier board).
3. We serve food. If everything is fine with the fuses in the PSU and nothing smoked, then the launch was a success.
4. With a multimeter, we check the absence of direct and alternating voltage at the output of the amplifier. A slight constant voltage is allowed, not more than ± 0.05 volts.
5. We turn off the power and check the microcircuit case for heating. Be careful, the capacitors in the PSU are discharged for a long time.
6. Through a variable resistor (R1 according to the diagram), we give a sound signal. We turn on the amplifier. The sound should appear with a slight delay, and immediately disappear when turned off, this characterizes the operation of the control unit (A1).

Conclusion

I hope this article will help you build a high-quality amplifier on the TDA7294. Finally, I present a few photos during the assembly process, do not pay attention to the quality of the board, the old textolite was unevenly etched. As a result of the assembly, some edits were made, so the boards in the .lay file are slightly different from the boards in the photographs.

The amplifier was made for a good friend, he came up with and implemented such an original case. Photos of the stereo amplifier on the TDA7294 assembly:

On a note: All printed circuit boards are collected in one file. To switch between "seals" click on the tabs as shown in the figure.

list of files

The addition of the TDA7294 chip with powerful complementary transistors controlled from its output stage increases the nominal output power of the UMZCH to 100 W with a load of 4 ohms. In addition to domestic transistors, more powerful imported ones can be recommended for this purpose. The use by the author in the design of a low-noise fan - a "cooler" from a computer processor made it possible to reduce the size of heat sinks and an amplifier.

UMZCH on the TDA7294 chip has gained well-deserved popularity among radio amateurs. At a minimum cost, you can assemble a high-quality UMZCH.

The amplifier version based on the TDA7294 chip turns out to be more reliable when operating on a real load, but its main technical characteristics remain the same: the non-linear distortion factor, which is small for an output power of 5 W, increases to 0.5% at a power of more than 50 W. At a load of 4 ohms, it is not possible to achieve an output power of more than 80 watts. The bridge circuit for switching on the microcircuit recommended by the manufacturer does not provide for the possibility of working with a load with a resistance of 4 ohms.

The version of the amplifier shown here, its circuit is shown in Fig. 1, solves the problem of increasing the output power and reducing the coefficient of non-linear distortion at an output power of more than 50 W compared to a typical microcircuit switching circuit. To reduce the load on the output stage of the microcircuit, an additional push-pull follower is built-in on powerful bipolar transistors that operate in mode B. There are no ladder-type distortions in the output stage because the output of the microcircuit is also connected to the load through a low-resistance resistor, and the OOS voltage is removed from emitter circuit of additional transistors. Resistor R7 provides fast discharge of the capacitance of the emitter junctions of the output stage transistors.

Main technical characteristics:

Input impedance: 22 kOhm

Input voltage: 0.8V

Rated output power: 100W/4 ohm

Frequency response: 20 - 20000 Hz

The disadvantage of the proposed UMZCH, in comparison with the variant according to the typical circuit for switching on the microcircuit, can be attributed to a steeper increase in non-linear distortion at an output power close to the maximum. In a typical circuit, the output signal clipping has a "softer" character.

A simplified block diagram of the TDA7294 shown in fig. 1 allows us to make the following assumption. Resistive current sensors are included in the circuits of the output transistors of the microcircuit, therefore, when the output signal voltage is close to the supply voltage (when the current through the powerful transistors of the microcircuit is maximum), the protection unit begins to smoothly limit the current in the load, the field effect transistors of the output stage probably also contribute to a softer restriction. Additional transistors of this UMZCH are not covered by such a tracking circuit, and a "hard" limitation of the output signal occurs, which is noticeable by ear.

A decrease in capacitance C6, C7 in comparison with that indicated in the circuit leads to unstable operation of the UMZCH at high power, but an increase in capacitance can lead to failure of transistors VT1, VT2, since when the load is shorted, the microcircuit protection unit does not always provide reliable protection for additional transistors until the fuses FU1, FU2 blow. The amplifier is powered by an unstabilized power supply from a 220 V network.

Not all parts purchased from radio markets are of high quality. There are microcircuits that are prone to self-excitation. In the described embodiment, the self-excitation of some microcircuits has to be eliminated by selecting the capacitor C6 as well.

In the UMZCH, according to the scheme proposed here, even with a small self-excitation, distortions of the "step" type occur. If it is not possible to replace the "unsuccessful" microcircuit, the effect can be eliminated by soldering a capacitor with a capacity of 0.047-0.15 microfarads in parallel with the resistor R7. Self-excitation is also eliminated by reducing the depth of the OOS (increasing the resistance of the resistor R3), while increasing the sensitivity of the amplifier.

Parts in the amplifier used:

1. MLT resistors
2. capacitors C1 - K73-17, KM-6; C2 - KT-1, KM-5; C8 - K73-17; SZ-S7 - K50-35 or imported.
3. inductor L1 - 25 turns of wire PEV-2 with a diameter of 1 mm - wound on a frame with a diameter of 5 mm in two layers.

Two channels of the amplifier are assembled on a printed circuit board made of one-sided foil fiberglass 2 mm thick; its drawing with the arrangement of elements is shown in Fig. 2 (the contour of the fans is conditionally transparent).

There is no place on the printed circuit board for blocking capacitors C9, C10. The use of transistors, which differ significantly in the base current transfer coefficient, practically does not affect the reliability and sound quality.

The absence of a quiescent current allows using a fan ("cooler") from the "Pentium" processor to cool the heat sinks of both channels of the amplifier. The board and fans must be installed so that warm air flows do not heat other parts of the amplifier.

Powerful transistors are mounted parallel to the plane of the printed circuit board by the metal surface of the heat sink to the cooler. On the flat side of the cooler, it is necessary to drill through holes with a diameter of 2.5 mm, coinciding with the holes in the printed circuit board, then cut the M3 thread. Through the holes in the board, the fan is pressed with screws to the transistors. On them it is necessary to put thin mica gaskets and lubricate with heat-conducting paste.

Under the screw heads on the side of the tracks, place washers with a diameter of 10-12 mm or a small metal plate to firmly press the transistors to the heat sink surface. Between the printed circuit board and the transistors, put thin cardboard 0.5-0.8 mm thick, it will ensure uniform pressing of the transistors to the fan plane, since their thickness is not always the same, even for those made in the same production batch.

Chip DA1 is located on an additional heat sink with an effective surface area of ​​at least 50 cm 2 .

It is advisable to "strengthen" the tracks on the printed circuit board, through which the supply voltage is supplied to the output transistors, by soldering a tinned copper wire with a diameter of about 1 mm along them.

An amplifier assembled from serviceable parts does not require adjustment and can be repeated even by novice radio amateurs. Operation for two years showed its high reliability.

With new wiring, as well as fastening the microcircuit and transistors on the same radiator.

In this article I will tell you about such a chip as TDA1514A

Introduction

I'll start a little sad... At the moment, the production of the microcircuit has been discontinued... But this does not mean that it is now "worth its weight in gold", no. In almost any radio store or on the radio market, it can be obtained at a price of 100 - 500 rubles. Agree, a bit pricey, but the price is absolutely fair! By the way, on the world's Internet sites, such as they are much cheaper ...

The microcircuit has a low level of distortion and a wide range of reproducible frequencies, so it is better to use it on full-range speakers. People who assembled amplifiers on this chip praise it for its high sound quality. This is one of the few microcircuits that really "sounds good". In terms of sound quality, it is almost as good as the now popular TDA7293/94. However, if errors are made in the assembly, quality work is not guaranteed.

Brief description and advantages

This chip is a single-channel Hi-Fi class AB amplifier with a power of 50W. Built-in SOAR protection, thermal protection (protection against overheating) and "Mute" mode

The advantages include the absence of clicks when turning on and off, the presence of protection, low harmonic and intermodulation distortion, low thermal resistance, and more. Of the shortcomings, there is practically nothing to single out, except for a failure with a "running" voltage (the power supply must be more or less stable) and a relatively high price

Briefly about the appearance

The chip is available in a SIP package with 9 long legs. The pitch of the legs is 2.54mm. There are inscriptions and a logo on the front side, and a heat sink on the back - it is connected to a 4-leg, and 4-leg is a "-" power supply. On the sides there are 2 eyelets for mounting the radiator.

The original or a fake?

Many people ask this question, I will try to answer you.

So. The microcircuit must be carefully made, the legs must be smooth, slight deformation is allowed, since it is not known how they were treated in a warehouse or in a store

The inscription... It can be done either with white paint or with an ordinary laser, two microcircuits are higher for comparison (both are original). In the event that the inscription is applied with paint, the chip must ALWAYS have a vertical strip separated by an eyelet. Don't let the inscription "TAIWAN" confuse you - it's okay, the sound quality of such specimens is just as good as those without this inscription. By the way, almost half of the radio components are made in Taiwan and neighboring countries. This inscription is not on all microcircuits.

I also advise you to pay attention to the second line. If it contains only numbers (there should be 5 of them), these are chips of the "old" production. The inscription on them is wider, and the heat sink can also have a different shape. If the inscription on the chip is laser printed and the second line contains only 5 digits, the chip must have a vertical stripe

The logo on the chip must be present, and only "PHILIPS"! As far as I know, production ceased long before the founding of NXP, and this is 2006. If you come across this microcircuit with the NXP logo, then one of two things - the microcircuit has started to be produced again or a typical "leftist"

It is also necessary to have depressions in the form of circles, as in the photo. If they don't, it's fake.

Perhaps there are other ways to identify the "leftist", but you should not strain so hard on this issue. There are only a few cases of marriage.

Specifications of the microcircuit

* Input impedance and gain adjustable by external elements

Below is a table of approximate output powers depending on the power supply and load resistance

circuit diagram

Schematic taken from datasheet (May 1992)

It's too bulky... I had to redraw it:

The scheme is slightly different from that provided by the manufacturer, all the characteristics given above are exactly for THIS scheme. There are several differences, and all of them are aimed at improving the sound - first of all, filter capacitances are installed, the "voltage boost" is removed (about it a little later) and the value of the resistor R6 is changed.

Now in more detail about each component. C1 - input isolating capacitor. Passes through itself only the alternating voltage of the signal. It also affects the frequency response - the smaller the capacitance, the smaller the bass and, accordingly, the larger the capacitance, the greater the bass. I would not recommend setting more than 4.7uF, since the manufacturer has provided for everything - with a capacitance of this capacitor equal to 1uF, the amplifier reproduces the declared frequencies. Use a film capacitor, in extreme cases, an electrolytic one (non-polar is desirable), but not a ceramic one! R1 reduces the input impedance, and together with C2 forms an input noise filter.

As with any op amp, you can set the gain here. This is done with R2 and R7. At these values, the gain is 30dB (may vary slightly). C4 affects the activation of the SOAR and Mute protection, R5 affects the smooth charging and discharging of the capacitor, and therefore there are no clicks when the amplifier is turned on and off. C5 and R6 form the so-called Zobel chain. Its task is to prevent the self-excitation of the amplifier, as well as to stabilize the frequency response. C6-C10 suppress power supply ripples, protect against voltage drops.
Resistors in this circuit can be taken with any power, for example, I use the standard 0.25W. Capacitors for a voltage of at least 35V, except for C10 - I use 100V in my circuit, although 63V should be enough. All components before soldering must be checked for serviceability!

Amplifier circuit with "voltage boost"

This version of the circuit is taken from the datasheet. It differs from the above scheme by the presence of elements C3, R3 and R4.
This option will allow you to get up to 4W more than stated (at ± 23V). But with this inclusion, distortion may slightly increase. Resistors R3 and R4 should be used at 0.25W. I couldn't stand it at 0.125W. Capacitor C3 - 35V and above.

This circuit requires the use of two microcircuits. One gives a positive signal at the output, the other - a negative one. With this inclusion, you can remove more than 100W at 8 ohms.

According to those who gathered, this circuit is absolutely efficient and I even have a more detailed plate of approximate output powers. She is below:

And if you experiment, for example, at ± 23V connect a load of 4 ohms, you can get up to 200W! Provided that the radiators do not get very hot, 150W will be easily pulled into the bridge of the microcircuit.

This design is good to use in subwoofers.

Work in external output transistors

The microcircuit is, in fact, a powerful operational amplifier and it can be further powered by hanging a pair of complementary transistors on the output. This option has not yet been tested, but theoretically it is possible. You can also power up the bridge circuit of the amplifier by hanging a pair of complementary transistors on the output of each microcircuit

Operation with single supply

At the very beginning of the datasheet, I found lines that say that the microcircuit also works with unipolar power. Where is the diagram then? Alas, I don’t have it in the datasheet, I didn’t find it on the Internet ... I don’t know, maybe such a scheme exists somewhere, but I haven’t seen one ... The only thing I can advise is TDA1512 or TDA1520. The sound is excellent, but they are powered by a unipolar power supply, and the output capacitor can slightly spoil the picture. Finding them is quite problematic, they were produced a very long time ago and were long out of production. The inscriptions on them can be of various shapes, it is not worth checking them for "fake" - there were no cases of refusal.

Both chips are Hi-Fi class AB amplifiers. Power is about 20W at + 33V into a load of 4 ohms. I will not give diagrams (the topic is still about TDA1514A). You can download printed circuit boards for them at the end of the article.

Nutrition

For stable operation of the microcircuit, a power supply with a voltage of ±8 to ±30V with a current of at least 1.5A is required. Power should be supplied with thick wires, the input wires should be removed as far as possible from the output wires and the power source
You can power it with an ordinary simple power supply, which includes a mains transformer, a diode bridge, filter capacitances and, if desired, chokes. To obtain ± 24V, a transformer is required with two secondary windings of 18V each with a current of more than 1.5A for one microcircuit.

You can use switching power supplies, for example, the simplest one, on the IR2153. Here is his diagram:

This UPS is half-bridge, frequency 47kHz (set using R4 and C4). Diodes VD3-VD6 ultrafast or Schottky

It is possible to use this amplifier in a car using a boost converter. On the same IR2153, here is the schematic:

The converter is made according to the Push-Pull scheme. Frequency 47kHz. Rectifier diodes need ultra-fast or Schottky. The transformer calculation can also be done in ExcellentIT. Chokes in both circuits will be "advised" by ExcellentIT itself. You need to count them in the Drossel program. The author of the program is the same -

I want to say a few words about the IR2153 - power supplies and converters are pretty good, but the microcircuit does not provide stabilization of the output voltage and therefore it will change depending on the supply voltage, and it will sag.

It is not necessary to use IR2153 and switching power supplies in general. You can do it easier - as in the "old days", an ordinary transformer with a diode bridge and huge power capacities. This is what his scheme looks like:

C1 and C4 at least 4700uF, for a voltage of at least 35V. C2 and C3 - ceramics or film.

Printed circuit boards

Right now I have the following board collection:
a) the main one - it can be seen in the photo below.
b) slightly modified first (main). All tracks have been increased in width, the power tracks are much wider, the elements have been slightly moved.
c) bridge circuit. The board is not drawn very well, but it works
d) the first version of the software - the first trial version, there is not enough Zobel chain, but as it was assembled, it works. There is even a photo (below)
e) printed circuit board fromXandR_man - found on the forum site "Soldering iron". What can I say ... Strictly the scheme from the datasheet. Moreover, I have seen kits based on this seal with my own eyes!
In addition, you can draw the board yourself if you are not satisfied with the provided ones.

Soldering

After you have made the board and checked all the details for serviceability, you can start soldering.
Tin the entire board, and tin the power tracks with as thick a layer of solder as possible
All jumpers are soldered first (their thickness should be as large as possible in the power sections), and then all components increase in size. the last chip is soldered. I advise you not to cut the legs, but to solder it as it is. You can then bend it for ease of landing on the radiator.

The microcircuit is protected from static electricity, so you can solder with the included soldering iron, sitting even in woolen clothes.

However, it is necessary to solder so that the microcircuit does not overheat. For reliability, you can attach one eye to the radiator during soldering. It is possible for two, there will be no difference, if only the crystal inside does not overheat.

Setup and first start

After all the elements and wires are soldered, a "test run" is necessary. Screw the chip onto the heatsink, short the input wire to ground. As a load, you can connect future speakers, but in general, so that they do not "fly out" in a split second in case of marriage or installation errors, use a powerful resistor as a load. If it crashes, know that you made a mistake, or you got a marriage (the microcircuit means). Fortunately, such cases almost never occur, unlike the TDA7293 and others, which you can pick up a bunch from one batch in the store and, as it turns out later, they are all marriages.

However, I want to make a small remark. Keep your wires as short as possible. It was such that I just extended the output wires and began to hear a hum in the speakers that looked like a "permanent". Moreover, when the amplifier was turned on, due to the "permanence" the speaker gave out a hum, which disappeared after 1-2 seconds. Now I have wires coming out of the board, a maximum of 25 cm and go straight to the speaker - the amplifier turns on silently and works without problems! Also pay attention to the input wires - put a shielded wire, you should not make it long either. Follow the simple requirements and you will succeed!

If nothing happened to the resistor, turn off the power, attach the input wires to the signal source, plug in your speakers and apply power. You can hear a small background in the speakers - this indicates that the amplifier is working! Give a signal and enjoy the sound (if everything is perfectly assembled). If it "grunts", "farts" - look at the food, at the correctness of the assembly, because as revealed in practice - there are no such "nasty" specimens that, with proper assembly and excellent nutrition, worked crookedly ...

What does the finished amplifier look like?

Here is a series of photos taken in December 2012. Boards just after soldering. Then I collected to make sure that the microcircuits were working.

But my first amplifier, only the board survived to this day, all the details went to other circuits, and the microcircuit itself failed due to an alternating voltage on it

Below are recent photos:

Unfortunately, my UPS is at the manufacturing stage, and I powered the microcircuit earlier from two identical batteries and a small transformer with a diode bridge and small power capacities, in the end it was±25V. Two such microcircuits with four speakers from the Sharp music center played so that even the objects on the tables "danced to the music", the windows rang, and the body felt good power. I can’t remove it now, but there is a ±16V power supply, from it you can get up to 20W at 4 ohms ... Here is a video for you as proof that the amplifier is absolutely working!

Thanks

I express my deep gratitude to the users of the Soldering Iron site forum, and specifically, many thanks to the user for some help, I also thank you, and many others (sorry for not calling you by nickname) for honest reviews that prompted me to assemble this amplifier. Without all of you, this article could not have been written.

Completion

The microcircuit has a number of advantages, excellent sound in the first place. Many microcircuits of this class may even be inferior in sound quality, but this depends on the quality of the assembly. Bad build means bad sound. Get serious about assembling electronic circuits. I strongly do not recommend soldering this amplifier by surface mounting - this can only worsen the sound, or lead to self-excitation, and subsequently a complete failure.

I collected almost all the information that I checked myself and could ask other people who collected this amplifier. It is a pity that I do not have an oscilloscope - without it, my statements about sound quality mean nothing ... But I will continue to say that it sounds just fine! Those who assembled this amplifier will understand me!

If you have any questions, write to me on the forum site "Soldering Iron". to discuss amplifiers on this chip, you can ask there.

I hope the article was useful to you. Good luck to you! Regards, Yuri.

List of radio elements

Pretty simple. Even a person who is not very strong in electrical engineering can repeat it. ULF on this chip will be ideal for use as part of a speaker system for a home computer, TV, cinema. Its advantage is that fine tuning and tuning is not required, as is the case with transistor amplifiers. And what can we say about the difference from lamp structures - the dimensions are much smaller.

No high voltage is required to power the anode circuits. Of course, there is heating, as in lamp designs. Therefore, if you plan to use the amplifier for a long time, it is best to install, in addition to an aluminum radiator, at least a small fan for forced airflow. Without it, on the TDA7294 microassembly, the amplifier circuit will work, but there is a high probability of switching to temperature protection.

Why TDA7294?

This chip has been very popular for over 20 years. It has won the trust of radio amateurs, since it has very high characteristics, amplifiers based on it are simple, anyone, even a beginner radio amateur, can repeat the design. The amplifier on the TDA7294 chip (the diagram is given in the article) can be either monophonic or stereophonic. The internal device of the microcircuit consists of an audio frequency amplifier built on this microcircuit belongs to class AB.

Advantages of the microcircuit

Benefits of using a microchip for:

1. Very high output power. About 70 W if the load has a resistance of 4 ohms. In this case, the usual scheme for switching on the microcircuit is used.

2. Approximately 120W into 8 ohms (bridged).

3. A very low level of extraneous noise, insignificant distortion, reproducible frequencies lie in the range that is completely perceived by the human ear - from 20 Hz to 20 kHz.

4. The microcircuit can be powered from a constant voltage source of 10-40 V. But there is a small drawback - you must use a bipolar power supply.

It is worth paying attention to one feature - the distortion factor does not exceed 1%. On the TDA7294 microassembly, the power amplifier circuit is so simple that it is even surprising how it allows you to get such high-quality sound.

The purpose of the pins of the microcircuit

And now in more detail about what conclusions the TDA7294 has. The first leg is the “signal ground”, it is connected to the common wire of the entire structure. Conclusions "2" and "3" - inverting and non-inverting inputs, respectively. The "4" pin is also a "signal ground" connected to ground. The fifth leg is not used in audio frequency amplifiers. The "6" leg is a volt additive, an electrolytic capacitor is connected to it. "7" and "8" conclusions - plus and minus the power supply of the input stages, respectively. Leg "9" - standby mode, used in the control unit.

Similarly: "10" leg - mute mode, also used when designing an amplifier. "11" and "12" conclusions are not used in the design of audio frequency amplifiers. From the "14" output, the output signal is taken and fed to the speaker system. "13" and "15" pins of the microcircuit are "+" and "-" for connecting the power supply of the output stage. On the TDA7294 chip, the circuit is no different from those proposed in the article, it is only supplemented by which it is connected to the input.

Features of microassembly

When designing an audio frequency amplifier, you need to pay attention to one feature - the power minus, and these are the legs "15" and "8", electrically connected to the microcircuit case. Therefore, it is necessary to isolate it from the heat sink, which in any case will be used in the amplifier. For this purpose it is necessary to use a special thermal pad. If you use a bridge amplifier circuit on the TDA7294, pay attention to the version of the case. It can be vertical or horizontal type. The most common is the version designated as TDA7294V.

Protective functions of the TDA7294 chip

The microcircuit provides several types of protection, in particular, against a drop in the supply voltage. If the supply voltage suddenly changes, the microcircuit will go into protection mode, therefore, there will be no electrical damage. The output stage is also protected against overloads and short circuits. If the body of the device heats up to a temperature of 145 degrees, the sound is turned off. When it reaches 150 degrees, it goes into standby mode. All pins of the TDA7294 chip are protected from electrostatics.

Amplifier

Simple, accessible to everyone, and most importantly - cheap. In just a few hours, you can assemble a very good audio frequency amplifier. And most of the time you will spend on etching the board. The structure of the entire amplifier consists of power and control units, as well as 2 ULF channels. Try to use as few wires as possible in the design of the amplifier. Follow these simple guidelines:

1. A prerequisite is the connection of a power source by wires to each UZCH board.

2. Bundle the power wires. With this, it will be possible to slightly compensate for the magnetic field that is created by the electric current. To do this, you need to take all three supply wires - “common”, “minus” and “plus”, with a slight tension weave them into one pigtail.

3. In no case do not use the so-called "earth loops" in the construction. This is the case when a common wire connecting all blocks of the structure closes in a loop. The ground wire must be connected in series, starting from the input further to the UZCH board, and must end at the output connectors. It is extremely important to connect the input circuits with shielded wires in isolation.

Standby and mute control unit

This chip also has muting. It is necessary to control the functions using the conclusions "9" and "10". The mode is turned on if there is no voltage on these legs of the microcircuit, or it is less than one and a half volts. To enable the mode, it is necessary to apply a voltage to the microcircuit legs, the value of which exceeds 3.5 V. In order for the amplifier boards to be controlled simultaneously, which is important for bridge-type circuits, one control unit is assembled for all cascades.

When the amplifier turns on, all the capacitors in the power supply are charged. In the control unit, one capacitor also accumulates a charge. When the maximum possible charge is accumulated, the standby mode is turned off. The second capacitor used in the control unit is responsible for the operation of the mute mode. It charges a little later, so the mute mode is disabled second.