Bridge umzch on tda 7294. Low frequency amplifier (ULF) on the TDA7250 microcircuit. View of the finished amplifier in a wooden case with a transparent plexiglass top cover

We present to your attention a 100W class H stereo ULF, which is easy to assemble even for novice radio amateurs. TDA7294 integrated circuit in a monolithic Multiwatt15 case. It has a wide range of +/- 40V supply voltages and can provide high output power into 4 and 8 Ohm loads.

There is built-in protection against short-circuit in the load and protection against overheating (upon reaching 145 degrees).

There is also a Mute function, which is used to eliminate clicks when turning on and stand-by mode. The range of reproducible frequencies is 20-20000Hz. Total harmonic distortion is not more than 0.1%.

Please note that the microcircuit case is connected to -Vcc, so it should not be installed in a metal case without insulation. Otherwise, a short circuit to ground will occur. Do not forget to apply thermal paste before screwing the microcircuit to the heatsink.

Below is a schematic diagram of a power amplifier based on the TDA7294 microcircuit.

The photo shows only one of the amplifier channels.

The figures show the printed circuit board and the location of the parts on it.

The photos show the assembly sequence of the boards.

Notes:

The TDA7294 IC is not compatible with 1% tolerance resistors.
About 1000uF filter capacitors: If you are using speakers larger than 10 inches (25.4cm) in diameter, increase the capacitance to 2200uF.
Choice of 47uF capacitor: I recommend using 47uF 50V from Elna SilmicII and 47uF 50V from Nichicon MUSE KZ.

The amplifier, the assembly of which we will describe today, despite its relative simplicity, provides fairly high parameters. Of course, "microcircuit" devices have a number of limitations, therefore, "loose" amplifiers can provide higher performance. At the same time, the scheme we have chosen has a number of advantages:

• it's pretty simple;
• is cheaper;
• practically does not need adjustment;
• gathers quickly (literally over the evening);
• surpasses many amplifiers of the 70s – 80s in quality, and it is quite enough for most applications (and modern systems up to $ 300 can yield to it);
• this version of the amplifier is universal (suitable for both beginners and experienced radio amateurs).

In any case, a poorly made and incorrectly tuned "loose" amplifier will sound worse than a microcircuit one. And our task is to make a very good device. It should be noted that the sound of the described amplifier is very good (if it is made correctly and properly powered). There is information that some company produced Hi-End amplifiers on the TDA7294 microcircuit. Believe me, our version will be no worse!

• See characteristics - what devices can be created on its basis

The main parameters of the Hi-Fi amplifier on the TDA7294 chip

Immediately, we note that the microcircuit worked steadily on an active load of 2-24 Ohms, on an active resistance of 4 Ohms, with a capacitive load of +/- 15 μF, as well as with an inductive load of +/- 1.5 mH. Moreover, on capacitive and inductive loads, distortions remained small. It should be said that the amount of distortion is highly dependent on the power source (especially on a capacitive load).

Directly with the measurement results you can find in the table below:

Parameter	Meaning	Measurement conditions
Pout.max, W (long-term sinusoidal)	36	Supply voltage + - 22V, Rн = 4 Ohm
Frequency range at the level of -3 dB	9 Hz-50 kHz	Rн = 8 Ohm, Uout = 4 V
Kg,% (RMAA 5.5 program)	0,008	Rn = 8 Ohm, Pout = 16 W, f = 1 kHz
Sensitivity, V	0,5	Pout.max = 50 W, Rn = 4 Ohm, Uip = +/- 27 V

Hi-Fi amplifier on the TDA7294 chip: circuit and its description

Detailed diagram of the Hi-Fi amplifier on the TDA7294 chip

The circuit of this amplifier is practically a repetition of the switching circuit offered by the manufacturer. And this is no coincidence - who knows better how to turn it on. And for sure there will be no surprises due to non-standard switching or operating mode.

Immediately, we note that you will not get any 80 watts (and even more so 100 watts) from it. Really 40-60, but it will be honest long-term watts. In a short-term pulse, you can get much more, but this will already be the PMRO power, by the way, also honest (80-120 W). In "Chinese" watts, this will be several thousand. If anyone is interested - five thousand. It all depends on the power source.

And do not forget that for a stereo amplifier you need a twice as powerful power supply unit (when calculating according to the proposed program, everything is taken into account automatically).

Important!!! There must be at least a fuse in the primary winding of the transformer! Remember that high voltages are life-threatening and a short circuit can cause fire! And one more thing: the fuse cannot be included in the "ground" circuit!

The circuit also works from a pulsed source, but here high requirements are imposed on the source itself: small ripples, the ability to deliver current up to 10 amperes without problems, strong "drawdowns" and generation disruptions. Remember that high-frequency ripples are suppressed by the microcircuit much worse, so the level of distortion can increase by 10-100 times, although everything is "apparently" all right there. A good switching power supply suitable for Hi-Fi audio is complex and expensive, so making an “old-fashioned” analog power supply will often be easier and cheaper.

Printed circuit board and amplifier assembly on the TDA7294 microcircuit

The printed circuit board is one-sided and measures 65x70 mm:

The board is wired to meet all the wiring requirements for high-quality amplifiers. The entrance is divorced as far as possible from the exit, and is enclosed in a "screen" from the divided land - input and output. The supply paths provide the maximum efficiency of the filtering capacitors (while the length of the leads of the capacitors C10 and C12 should be minimal). In this experimental board, we installed terminal blocks for connecting input, output and power. A place for them is provided (the capacitor C10 may interfere a little), but for stationary structures it is better to solder all these wires, because this is more reliable.

In addition to low resistance, wide tracks have the advantage that they are more difficult to peel off when overheated. Yes, and when manufacturing by the "laser-ironing" method, if a 1x1 mm square is not "printed" anywhere, then it is not scary. All the same, the conductor will not break. In addition, a wide conductor holds heavy parts better (while a thin conductor can simply peel off the board).

There is only one jumper on the board. It lies under the pins of the microcircuit, so you need to mount it first, and leave enough space under the pins so that it does not close.

During the installation, the following important components were used:

• 0.12 W resistors (except for R9);
• capacitors C9, C10, C12 K73-17 63V;
• capacitors C4 K10-47v 6.8 uF 25V.

We consider the use of expensive "audiophile" parts to be economically unjustified, and cheap "ceramic" elements will give the worst sound (although they can be used, just remember that some of them can withstand voltage no more than 16 Volts and cannot be used as C7).

Any modern electrolytes will do. The polarity of the connection of all electrolytic capacitors and the diode is marked on the board. A diode is any low-power rectifier that can withstand a reverse voltage of at least 50 Volts (for example, 1N4001-1N4007). It is better not to use high frequency diodes.

In the corners of the board there is a place for the holes of the M3 fixing screws. You can fix the board only for the microcircuit case, but it's still safer to grab it with screws.

The microcircuit must be installed on a radiator with an area of ​​at least 350 cm2. More is better. In principle, thermal protection is built into it, but it is better not to tempt fate. Even if active cooling is assumed, the radiator should still be quite massive: with pulsed heat release, which is typical for music, heat is more efficiently taken away by the heat capacity of the radiator (that is, a large cold piece of iron) than by dissipation into the environment.

The metal case of the microcircuit is connected to the "minus" of the power supply. Hence, there are two ways to install it on a radiator:

1. Through an insulating gasket. In this case, the radiator can be electrically connected to the housing.
2. Directly, while the radiator is necessarily electrically isolated from the case.

The first option is recommended if you are going to drop metal objects (paper clips, coins, screwdrivers) into the case so that there is no short circuit. In this case, the gasket should be as thin as possible, and the radiator should be larger.

The second option provides better cooling, but requires care (for example, you cannot dismantle the microcircuit when the power is on).

In both cases, you need to use a heat-conducting paste, and in the 1st version it should be applied both between the microcircuit case and the gasket, and between the gasket and the radiator.

The printed circuit board in Sprint-Layout 4.0 format, the diagram in pdf format and the location of the parts on the board in gif format can be found in the archive below:

Debugging the Hi-Fi amplifier on the TDA7294 chip

As practice shows, 90% of all problems with the equipment are its "unsettled". That is, having soldered the next circuit, and failing to establish it, the radio amateur puts an end to it, and publicly declares the circuit bad. Therefore, commissioning is the most important (and often the most difficult) stage in creating an electronic device.

A properly assembled amplifier does not need to be adjusted. But, since no one can guarantee that all parts are absolutely functional, you need to be careful when you turn it on for the first time.

The first turn on is carried out without load and with the input signal disconnected (it is better to short-circuit the input with a jumper altogether). It would be nice to include fuses of about 1A in the power circuit (both in the "plus" and in the "minus" between the power supply and the amplifier itself). For a short time (about 0.5 seconds) we apply the supply voltage and make sure that the current consumed from the source is small (the fuses do not burn out). Convenient if the source has LED indicators. When disconnected from the network, the LEDs continue to burn for at least 20 seconds: the filter capacitors are discharged for a long time by a small quiescent current of the microcircuit.

If the current consumed by the microcircuit is large (more than 300 mA), then there can be many reasons:

• Short circuit in installation;
• poor contact in the "earth" wire from the source;
• "plus" and "minus" are confused;
• the microcircuit pins touch the jumper;
• defective microcircuit;
• capacitors C11, C13 are incorrectly soldered;
• the capacitors C10-C13 are faulty.

After making sure that everything is in order with the quiescent current, boldly turn on the power and measure the constant voltage at the output. Its value should not exceed +/- 0.05 V. A high voltage indicates problems with C3 (less often with C4) or with a microcircuit. There were cases when the "inter-ground" resistor was either poorly soldered, or instead of 3 ohms had a resistance of 3 kOhm. In this case, the output was a constant of 10–20 volts. By connecting an AC voltmeter to the output, we make sure that the AC voltage at the output is zero (this is best done with a closed input or simply with an unconnected input cable, otherwise there will be noise at the output).

The presence of an alternating voltage at the output indicates problems with the microcircuit or circuits C7R9, C3R3R4, R10. Unfortunately, often ordinary testers cannot measure the high-frequency voltage that appears during self-excitation (up to 100 kHz), so it is best to use an oscilloscope here.

If everything is in order here, we connect the load, once again check for the absence of excitation already with the load, and that's it - you can listen!

But it’s better to do one more test. The fact is that the most disgusting type of amplifier excitation is "ringing" (when excitation appears only in the presence of a signal, and at a certain amplitude). The main problem is that it is difficult to detect it without an oscilloscope and a sound generator (and it is not easy to eliminate it), and the sound deteriorates enormously due to huge intermodulation distortions. This is usually perceived by ear as a "heavy" sound, that is, without any additional overtones (since the frequency is very high), so the listener does not even know that his amplifier is being excited. He just listens and decides that the microcircuit is "bad" and "does not sound". With the correct assembly of the amplifier and a normal power supply, this should not be the case.

Graphical representation of the "ringing" of the amplifier

However, sometimes such distortions occur, and the C7R9 chain is exactly what fights with them. But in a normal microcircuit, everything is fine even in the absence of C7R9. We came across copies of a microcircuit with a ringing. In them, the problem was solved by the introduction of the C7R9 circuit (which is why we use it, even though it is not in the datasheet). If such muck takes place even in the presence of C7R9, then you can try to eliminate it by "playing" with the resistance (it can be reduced to 3 ohms), but we would not recommend using such a microcircuit. This is definitely some kind of marriage, and who knows what else will come out in it.

As we noted above, "ringing" can be seen only on an oscilloscope, and not all radio amateurs have this equipment. Although if you want to be good at electronics, try to get hold of such devices or at least use them somewhere. To always get high-quality sound, it is imperative to be checked on devices. Remember, "ringing" is the most insidious thing that can spoil the sound in a thousand ways.

You can view another method of assembling a Hi-Fi amplifier on a TDA7294 chip in the video below:

One of the first I assembled an amplifier on the TDA7294 according to the scheme proposed by the manufacturer.

At the same time, the quality of sound reproduction, especially in the high-frequency range, did not suit me very much. On the Internet, my attention was attracted by the LINCOR article posted on the datagor.ru website. The author's enthusiastic reviews about the sound of the UMZCH on the TDA7294, assembled according to the circuit of a voltage-controlled current source (ITUN), intrigued me. As a result, the UMZCH was assembled by me according to the following scheme.

The scheme works as follows. The signal from the IN input goes through the pass capacitor C1 to the low-impedance feedback arm R1 R3, which, together with the capacitor C2, forms a low-pass filter that prevents the penetration of pickups and high-frequency noise into the sound path. Together with the resistor R4, the input circuit creates the first OOS segment, which Ku is 2.34. Further, if it were not for the current sensor R7, the gain of the second circuit would be set by the ratio R5 / R6 and would be equal to 45.5. The final Ku would be about 100. However, there is still a current sensor in the circuit, and its signal, summing up with the voltage drop across R6, creates a partial OOS for the current. At our circuit ratings Ku=15.5.

Amplifier characteristics when operating on a 4 Ohm load:

- Operating frequency range (Hz) - 20-20000;

- Supply voltage (V) - ± 30;

- Rated input voltage (V) - 0.6;

- Rated output power (W) - 73;

- Input impedance (kOhm) - 9.4;

- THD at 60W, no more (%) - 0.01.

The printed circuit board has a 12V parametric regulator for powering service circuits 9 and 10 of TDA7294, shown in the figure.

In the "Play!" Position, the amplifier is in the unlocked state and is ready for operation every second. In the "Mute" position, the input and output stages of the microcircuit are blocked, and its consumption is reduced to the minimum standby currents. Capacities C11 C12 are doubled compared to the standard capacity to provide a longer delay when turning on and prevent a click in the speaker even with prolonged charging of the power supply capacitors.

Amplifier parts

All resistors, except for R7 and R8, are carbon or metal-film resistors for 0.125–0.25W, such as C1-4, C2-23 or MLT-0.25. Resistor R7 is a 5W wire wound resistor. White ceramic SQP resistors are recommended. R8 - Zobel circuit resistor, carbon, wire or metal film for 2W.

C1 - film, of the highest available quality, lavsan or polypropylene. K73-17 at 63V will give a satisfactory result. C2 - ceramic disc or any other type, for example K10-17B. C3 - electrolyte of the highest available quality for a voltage of at least 35 V, C4 C7, C8, C9 - film type K73-17 for 63 V. C5 C6 - electrolytic for a voltage of at least 50 V. C11 C12 - any electrolytic for a voltage of at least 25 B. D1 - any 12 ... 15 V zener diode with a power of at least 0.5 W. Instead of the TDA7294 chip, you can use the TDA7296 ... 7293. In the case of using TDA7296, TDA7295, TDA7293, you must bite off or bend and do not solder the 5th leg of the microcircuit.

Both amplifier output terminals are "hot", neither of them is grounded. the speaker system is also a feedback link. The speaker is switched on between and.

Below is a board layout with element and wire side views created using Sprint-Layout_6.0.

Full ULF 2x70 Watts on TDA7294.

When assembling an amplifier on microcircuits, the TDA7294 is not a bad choice. Well, however, we will not dwell on the technical characteristics, you can see them in the PDF file TDA7294_datasheet, located in the folder for downloading the material for assembling this ULF. As you already understood from the title of the article, this is a full amplifier circuit, which contains a power supply, pre-amplification stages with a three-band tone control, implemented on two common 4558 operational amplifiers, two channels of power stages, as well as a protection node. The schematic diagram is shown below:

With a supply voltage of ± 35 volts into an 8 ohm load, you will get 70 watts of power.

The PCB sources are as follows:

Printed circuit board LAY6 format:

Arrangement of elements on the amplifier board:

Photo view of LAY board format:

The board has a J5 connector for connecting a temperature sensor (Bimetal Thermostat), it is designated B60-70. In normal mode, its contacts are open, when heated to 60 ° C, the contacts close, the relay disconnects the load. In principle, it is possible to use thermo-sensors with normally closed contacts, designed to operate at 60 ... 70 ° C, only it must be turned on in the gap between the emitter of the Q6 transistor and the common wire, while the J5 connector is not used. If you are not going to use this function, leave J5 connector empty.

Operational amplifiers are installed in sockets. Relay for operation voltage of 12 Volts with two groups of switching contacts, contacts must withstand 5 Amperes.

Fuse PCB LAY6 format:

Photo view of LAY fuse board format:

The protection unit power connector is located on the board just above the J5 connector. Just jumper two wires between this connector and the main power connector as shown in the picture below:

External connections:

Additional Information:

4Ohm - 2x18V 50Hz
8Ohm - 2x24V 50Hz

When powered by 2x18V 50Hz:

Resistors R1, R2 - 1 kOhm 2W
RES resistor - 150 Ohm 2W

When powered by 2x24V 50Hz:

Resistors R1, R2 - 1.5 kOhm 2W
RES resistor - 300 Ohm 2W

The JRC4558 operational amplifier can be replaced with the NE5532 or TL072.

We draw your attention, from the side of the printed circuit board conductors between the contacts of the relay coil, a LL4148 diode in SMD version is installed, you can solder the usual 1N4148.

There is a GND point near the volume control on the board, it is intended for grounding the housings of all controllers. This piece of bare copper wire is clearly visible in the main picture of the news.

List of elements for repeating the amplifier circuit on the TDA7293 (TDA7294):

Electrolytic capacitors:

10000mF / 50V - 2 pcs.
100mF / 50-63V - 9 pcs.
22mF - 5 pcs.
10mF - 6 pcs.
47mF - 2 pcs.
2,2mF - 2 pcs.

Film capacitors:

1 mF - 8 pcs.
100n - 8 pcs.
6n8 - 2 pcs.
4n7 - 2 pcs.
22n - 2 pcs.
47n - 2 pcs.
100pF - 2 pcs.
47pF - 4 pcs.

0.25W resistors:

220R - 1 pc.
680R - 2 pcs.
1K - 6 pcs.
1K5 - 2 pcs.
3K9 - 4 pcs.
10K - 10 pcs.
20K - 2 pcs.
22K - 8 pcs.
30K - 2 pcs.
47K - 4 pcs.
220K - 3 pcs.

0.5W resistors:

2W resistors:

RES - 300R - 2 pcs.
100R - 2 pcs.

Diodes:

Zener diodes 12V 1W - 2 pcs.
1n4148 - 1 pc.
LL4148 - 1 pc.
1n4007 - 3 pcs.
Bridge 8 ... 10A - 1 pc.

Variable resistors:

A50K - 1 pc.
B50K - 3 pcs.

Microcircuits:

NE5532 - 2 pcs.
TDA7293 (TDA7294) - 2 pcs.

Connectors:

3x - 1 pc.
2x - 2 pcs.

Relay - 1 pc.

Transistors:

BC547 - 5 pcs.
LM7812 - 1 pc.

Download the schematic diagram of the amplifier for TDA7294, TDA7294_datasheet, printed circuit boards of the LAY6 format, you can in one file from our website. Archive size - 4 Mb.

There are quite a few varieties of budget amplifiers, and this is one of them. The circuit is very simple and contains only one microcircuit, several resistors and capacitors. The characteristics of the amplifier are quite serious at such a small cost. The output power reaches 100W at maximum power. The absolutely clean output is 70 watts.

Amplifier characteristics

More detailed characteristics of the amplifier on the TDA7294:

• The power supply is bipolar with a midpoint from 12 to 40 V.
• F out. - 20-20000 Hz
• P out. Max. (supply + - 40V, Rn = 8 Ohm) - 100 W.
• P out. Max. (supply + - 35V, Rn = 4 Ohm) - 100 W.
• To harm. (Pout. = 0.7 Р max.) - 0.1%.
• Uin - 700 mV.

The TDA7294 chip is cheap and costs a penny, I bought it -.

These amplifiers work well in pairs, so do two of these and you have a simple stereo amplifier. More detailed characteristics of the amplifier and switching circuits can be found in.
It is advisable to choose a power supply for the amplifier one and a half times more powerful, so take into account.

Amplifier circuit board

Drawing of the arrangement of elements:

Download to board in lay format:

(Downloads: 1377)

When printing, set the scale to 70%.

Ready amplifier

The microcircuit must be installed on a radiator, preferably with a fan, since it will be smaller in size. It is not at all necessary to make a printed circuit board. You can take a breadboard with a large number of holes and assemble the amplifier in about 30 minutes.
I advise you to build such a simple amplifier that has proven itself very well.

Power Supply

The power supply is completed according to the classical scheme with a 150 W transformer. I recommend taking a ring-core transformer, since it is more powerful, smaller and emits a minimum of line noise and electromagnetic background of alternating voltage. Filtering capacitors of each leg 10000 uF.

Collect your amplifier and see you soon!