Amplifier based on TDA 7293 and field-effect transistors. Bitter experience of buying TDA7293 microcircuits. Chips TDA7294 and TDA7293

POWER AMPLIFIER ON TDA7293.
With the most intimate details!

http://detalinadom. *****/stats/UMZTDA7293.htm

The TDA7293 microcircuit is a logical continuation of the TDA7294, and despite the fact that the pinout is almost the same, it has some differences that distinguish it favorably from its predecessor. First of all, the supply voltage has been increased and now it can reach ±50V, protection against overheating of the crystal and short circuit in the load has been introduced, and the possibility of parallel connection of several microcircuits has been implemented, which allows the output power to be varied within a wide range. THD at 50W does not exceed 0.1% in the range of 20...15000Hz (typical value 0.05%). Supply voltage ±12…±50V, output stage current at peak reaches 10A. All this data was taken from the data book. However!!! The endless upgrades of stationary power amplifiers have revealed some very interesting issues...

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Figure 2

Figure 3 shows a parallel connection diagram, here the upper microcircuit operates in the “master” mode, and the lower one in the “slave” mode. In this option, the output stages are unloaded, nonlinear distortions are noticeably reduced, and it is possible to increase the output power by n times, where n is the number of microcircuits used. However, it should be taken into account that at the moment of switching on, voltage surges may form at the outputs of the microcircuits, and since the protection systems have not yet reached operating mode, the entire line of microcircuits connected in parallel may fail. To avoid this trouble, it is strongly recommended to introduce a timer into the circuit that connects, using relay contacts, the output of the microcircuits no earlier than 2...3 seconds from the moment power is supplied to the microcircuits. Although the manufacturer stubbornly remains silent on this topic and many have already fallen for the “bait” of unlimited capacity. However, tests of single versions of amplifiers on the TDA7293 show stable operation, but it was necessary to switch the single variants to the “slave” mode and connect to the “master”...
When turned on - not necessarily the first time - the microcircuit was simply torn to the very heat-dissipating flange, and the entire paralleled line. And this happened with the TDA7293 more than once, so we can talk about a pattern, and if you don’t have extra money to repeat our experiments, then install a timer and relay.
As for parallel connection, the datasheet is absolutely right - yes, indeed the TDA7293 can operate in this mode even when using 12 TDA7293 microcircuits, included in 6 pieces. in parallel and when these lines are connected to a bridge circuit, it is theoretically possible to obtain up to 600W of output power into a 4-ohm load. In reality, 3 microcircuits were tested in the bridge arm; with a power supply of ±35 V, about 260 W were obtained into a 4 Ohm load.

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Parameter

Meaning

Output power when switched on once

Rн - 4 Ohm Uip - ±30V
Rн - 8 Ohm Uip - ±45V

80W (110W max)
110W (140W max)

Output power when connected in parallel

Rн - 4 Ohm Uip - ±27V
Rн - 8 Ohm Uip - ±40V

110W
125W

Output voltage slew rate

Frequency range at 3dB ripple

C1 not less than 1.5 µF

Distortions

at a power of 5 W, a load of 8 Ohms and a frequency of 1 kHz
from 0.1 to 50 W from 01/01/010 Hz no more

Supply voltage

Current consumption in STBY mode

Quiescent current of the final stage

Threshold voltage for input and output stage blocking devices

"Enabled"
"Turned off"

1.5 V
+3.5 V

Thermal resistance crystal-case, deg.

And finally, tests were carried out on some more features of the TDA7293, but of Chinese (or maybe not Chinese... In short, this secret is shrouded in darkness) production:
The short circuit protection system worked the first time - there was a dry pop and the microcircuit took on a completely different appearance:

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The markings on these wonderful microcircuits were made with a laser, but the font of the inscription was slightly different, and while the amplifier was working, its performance was practically no different from the normally marked TDA7293 in all switching modes. By the way, these microcircuits have already practically replaced the old samples, so some suppliers have seriously increased the price for “rarities”. We are already selling “new” microcircuits and have not yet identified any complaints, since we strongly warn everyone that the “new” TDA7293 (as well as the TDA7294 - also already “new”) should not be tested for survivability, and in normal operation modes they behave very well They even feel good...

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As for the TDA7293 markings given below, these microcircuits are not even worth buying, since they are not useful for anything except for making key fobs, since they do not even consume current...

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The values ​​are not marked as in the typical connection diagram.

TDA7293.pdf TDA7294.pdf TDA7295.pdf Power amplifier based on TDA7293 on a simple high-quality chip

Finally, it remains to add that the TDA7293 can be used with floating power, the circuit diagram is shown in Figure 4. This option allows you to develop up to 200 W at 4 Ohms with typical distortion.

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Figure 5

And finally, how can you attach the TDA7293 chip to the radiator. You can use insulating washers that will prevent the heat sink flange of the microcircuit with the radiator from shortening - after all, it has a “MINUS” supply voltage, or you can use “tails” from our KT818 type transistors. The “tail” must be placed between strips of fiberglass from which the foil has been removed, having previously lubricated them with well-mixed epoxy glue. If you don’t want to wait a long time for the glue to polymerize, then you can use a piece of cotton wool soaked in ANY “SUPER GLUE” - after 15 minutes. it will already be completely hardened.
As soon as the glue hardens, file the edges, drill holes in the bracket strip and in the radiator, and it is better to cut an M3 thread in the radiator. Coat the mica with thermal paste on both sides! Well, you can see how it will look in Figure 6.

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ATTENTION!!! If there is a constant voltage at the output of the signal source, you need to place a capacitor at the input!

When listening, you can try turning on the Mute mode.

Two-way amplifier with second-order filters (12dB/Octave). If you use a standard connection circuit, then a two-way amplifier can be made without using additional elements.

Selection table for separating filter elements

The TDA7293 chip is the logical completion of the TDA7294 assembly, and despite the fact that the pinout is almost the same, there are a number of improvements compared to its predecessor. First of all, it should be noted that the voltage has been increased to ±50V, protection against overheating of the crystal and short circuit in the ULF load has been added, and the possibility of parallel connection of several microcircuits has been implemented to increase the output power. THD at 50W is not higher than 0.1% in the range of 20…15000Hz. Supply voltage ±12…±50V, output stage current at peak reaches 10A.

There are several known modifications of this design. Only one output stage is used here, which is made on the complementary pair 2SC5200 + 2SA1943, widely used among radio amateurs. Therefore, the circuit is capable of outputting up to 120 watts of sound power. The microassembly hardly heats up, but the transistors of the output stage heat up very much, since they operate in AB mode, therefore, they must be placed on a radiator.

If you decide to assemble this ULF design for wideband acoustics, then I do not recommend using this circuit option. The coefficient of nonlinear distortion at the output is quite high, so this ULF is more suitable for powering a subwoofer. When using the TDA7293 with the maximum permitted supply voltage, the amplifier power will increase to 140 watts, but the chip will already begin to heat up.

The proposed ULF has a very low nonlinear distortion coefficient and noise floor. The assembled structure has small dimensions.

Coil L1 is frameless, three-layer, made by hand and contains ten turns of PEV-1.0 wire in each layer. Winding must be carried out on a 12 mm mandrel. Approximate inductance: 5 µH. For a list and ratings of radio components, as well as a drawing of the printed circuit board, see the archive above.

The circuit from the radio magazine was developed on the basis of a ULF that has been repeated many times by radio amateurs and has proven itself. The R1C1 chain forms a low-frequency input filter necessary to suppress high-frequency interference. Input capacitance C2 sets the lower limit of the amplified frequency range. With the nominal value shown in the figure, this frequency is about 7 Hz. To improve operation at frequencies above 5-7 kHz, the oxide capacitors located in the signal path are shunted with film capacitors: these are C4, C5 in the negative feedback circuit and C8, C9 as a voltage booster. Also, film capacitors C10 and C12 are required in the power supply. Circuits R12C6 and R8R9C3VD1 carry out the correct sequence of alternating Stand-By and Mute modes when the supply voltage is applied and turned off, in order to eliminate annoying clicking in the speakers. The R14C7 circuit is necessary for stable operation of the circuit under a real load.

The combined OOS circuit for voltage and current is formed by resistors R3, R4, R6, R7, R10, R11, R15. Of these, resistances R4 and R11 set the OOC, resistor R15 is a current sensor, and the remaining resistances set the depth of the OOC, and the option of both the OOC supply circuit according to Figure 4a and according to the figure is possible. 4b (see archive for detailed description). The option for switching on the OOST circuit is set by a jumper between points 1, 2, 3.

Resistance R2 is necessary to separate the common wire of the input and output circuits. Pin 5 of the TDA7293 is the output of the signal clipping sensor and is used to connect the corresponding indicator or electronic gain control.

The amplifier is assembled on a printed circuit board; a drawing made in the Sprint Layout program is available in the general archive. The design uses resistors with a nominal power of 0.125 W, in addition to resistance R15 - 5 W, it must be mounted on a printed circuit board (PCB) with a small gap to improve cooling. The same applies to resistances R10 and R14. Particular attention must be paid to resistance R2. Its value should be in the range of 1-5 Ohms, and before mounting it on the PCB, it is recommended to check it with a multimeter. If there is no suitable resistance, it can be replaced with a regular jumper. All other resistors, except those included in the negative feedback circuits, can have a small resistance variation of up to 20%.

Diode VD1 should be used with a maximum reverse voltage of at least 50 V. The author took a 1N4007 diode. The microassembly must be installed on a heat sink with an area of ​​at least 500 cm2 using thermal paste. It should be taken into account that the TDA7293 case is connected to the negative power bus. Therefore, it is necessary to take an insulating gasket, or isolate the heat sink from the body of the structure.

The amplifier is powered by a bipolar power supply, a circuit diagram of which is included in the archive.

Supply voltage 1 -10…-40V; Supply voltage 2 +10…+40V; Output current 4A, quiescent 60mA; P out 140 W; R in 100 kOhm; Gain 30dB; Frequency band 20-20000Hz; Load resistance 8 ohms.

In this FAQ we will try to consider all issues related to the recently popular ULF microcircuit TDA7293/7294. The information was taken from the forum topic of the same name on the Soldering Iron website. I collected all the information together and compiled it, for which I thank him very much. Microcircuit parameters, switching circuit, printed circuit board, all this. Datasheet of TDA7293 and TDA7294 microcircuits is available.

1) Power supply
Oddly enough, for many people the problems begin here. The two most common mistakes:
- Unipolar power supply
- Focus on the voltage of the secondary winding of the transformer (rms value).

Here is the power supply diagram:

What do we see here?

1.1 Transformer- must have TWO SECONDARY WINDINGS. Or one secondary winding with a tap from the midpoint (very rare). So, if you have a transformer with two secondary windings, then they need to be connected as shown in the diagram. Those. the beginning of one winding with the end of another (the beginning of the winding is indicated by a black dot, this is shown in the diagram). Get it wrong and nothing will work. When both windings are connected, we check the voltage at points 1 and 2. If the voltage there is equal to the sum of the voltages of both windings, then you have connected everything correctly. The connection point of the two windings will be the “common” (ground, case, GND, call it what you want). This is the first common mistake, as we see: there should be two windings, not one.
Now the second error: The datasheet (technical description of the microcircuit) for the TDA7294 microcircuit states: +/-27 power is recommended for a 4 Ohm load. The mistake is that people often take a transformer with two 27V windings, THIS CAN'T BE DONE!!! When you buy a transformer, it says effective value, and the voltmeter also shows you the effective value. After the voltage is rectified, it charges the capacitors. And they are already charging before amplitude value which is 1.41 (root of 2) times greater than the current value. Therefore, in order for the microcircuit to have a voltage of 27V, the transformer windings must be 20V (27 / 1.41 = 19.14 Since transformers are not made for such voltage, we will take the nearest one: 20V). I think the point is clear.
Now about the power: in order for the TDA to deliver its 70W, it needs a transformer with a power of at least 106W (the efficiency of the microcircuit is 66%), preferably more. For example, a 250W transformer is very suitable for a stereo amplifier on the TDA7294

1.2 Rectifier bridge- As a rule, questions do not arise here, but still. I personally prefer to install rectifier bridges, because... no need to bother with 4 diodes, it’s more convenient. The bridge must have the following characteristics: reverse voltage 100V, forward current 20A. We put up such a bridge and don’t worry that one “fine” day it will burn down. This bridge is enough for two microcircuits and the capacitor capacity in the power supply is 60"000 μF (when the capacitors are charged, a very high current passes through the bridge)

1.3 Capacitors- As you can see, the power supply circuit uses 2 types of capacitors: polar (electrolytic) and non-polar (film). Non-polar (C2, C3) are necessary to suppress RF interference. By capacity, set what will happen: from 0.33 µF to 4 µF. It is advisable to install our K73-17, which are pretty good capacitors. Polar (C4-C7) are necessary to suppress voltage ripple, and besides, they give up their energy during amplifier load peaks (when the transformer cannot provide the required current). Regarding capacity, people still argue about how much is needed. I learned from experience that for one microcircuit, 10,000 uF per arm is enough. Capacitor voltage: choose yourself, depending on the power supply. If you have a 20V transformer, then the rectified voltage will be 28.2V (20 x 1.41 = 28.2), capacitors can be set to 35V. It's the same with non-polar ones. It seems like I didn't miss anything...
As a result, we got a power supply containing 3 terminals: “+”, “-” and “common”. We’re done with the power supply, let’s move on to the microcircuit.

2) Chips TDA7294 and TDA7293

2.1.1 Description of the pins of the TDA7294 chip
1 - Signal ground


4 - Also a signal ground
5 - The pin is not used, you can safely break it off (the main thing is not to mix it up!!!)

7 - "+" power supply
8 - "-" power supply


11 - Not used
12 - Not used
13 - "+" power supply
14 - Chip output
15 - "-" power supply

2.1.2 Description of the pins of the TDA7293 chip
1 - Signal ground
2 - Inverse input of the microcircuit (in the standard circuit the OS is connected here)
3 - Non-inverted input of the microcircuit, we supply an audio signal here through the isolation capacitor C1
4 - Also a signal ground
5 - Clippmeter, basically an absolutely unnecessary function
6 - Voltage boost (Bootstrap)
7 - "+" power supply
8 - "-" power supply
9 - Conclusion St-By. Designed to put the microcircuit into standby mode (that is, roughly speaking, the amplifying part of the microcircuit is disconnected from the power supply)
10 - Mute output. Designed to attenuate the input signal (roughly speaking, the input of the microcircuit is turned off)
11 - Input of the final amplification stage (used when cascading TDA7293 microcircuits)
12 - The capacitor POS (C5) is connected here when the supply voltage exceeds +/-40V
13 - "+" power supply
14 - Chip output
15 - "-" power supply

2.2 Difference between TDA7293 and TDA7294 chips
Such questions come up all the time, so here are the main differences between the TDA7293:
- Possibility of parallel connection (complete garbage, you need a powerful amplifier - assemble it with transistors and you will be happy)
- Increased power (by a couple of tens of watts)
- Increased supply voltage (otherwise the previous point would not be relevant)
- They also seem to say that it is all made on field-effect transistors (what’s the point?)
That seems to be all the differences, I’ll just add that all TDA7293 have increased glitches - they light up too often.

Another common question: Is it possible to replace TDA7294 with TDA7293?
Answer: Yes, but:
- At supply voltage<40В заменять можно спокойно (конденсатор ПОС между 14ой и 6ой лапами как был, так и остается)
- With a supply voltage >40V, it is only necessary to change the location of the PIC capacitor. It must be between the 12th and 6th legs of the microcircuit, otherwise glitches in the form of excitement, etc. are possible.

This is what it looks like in the datasheet for the TDA7293 chip:

As can be seen from the diagram, the capacitor is connected either between the 6th and 14th legs (supply voltage<40В) либо между 6ой и 12ой лапами (напряжение питания >40V)

2.3 Supply voltage
There are such extreme people who power the TDA7294 from 45V, then they wonder: what’s on fire? It lights up because the microcircuit is working at its limit. Now here they will tell me: “I have +/-50V and everything works, don’t drive it!!!”, the answer is simple: “Turn it up to maximum volume and time it with a stopwatch”

If you have a 4 Ohm load, then the optimal power supply will be +/- 27V (20V transformer windings)
If you have an 8 Ohm load, then the optimal power supply will be +/- 35V (25V transformer windings)
With such a supply voltage, the microcircuit will work for a long time and without glitches (I withstood an output short-circuit for a minute, and nothing burned out; I don’t know how things are with fellow extreme sports enthusiasts, they are silent)
And one more thing: if you still decide to make the supply voltage higher than the norm, then do not forget: you still can’t escape distortion. More than 70W (supply voltage +/-27V) is useless from the microcircuit, because It is impossible to listen to this grinding noise!!!

Here is a graph of distortion (THD) versus output power (Pout):

As we can see, with an output power of 70W, the distortion is around 0.3-0.8% - this is quite acceptable and not noticeable by ear. With a power of 85W, the distortion is already 10%, this is already wheezing and grinding, in general it is impossible to listen to sound with such distortion. It turns out that by increasing the supply voltage, you increase the output power of the microcircuit, but what’s the point? It’s still impossible to listen after 70W!!! So take note, there are no advantages here.

2.4.1 Connection circuits - original (conventional)

Here is the diagram (taken from the datasheet):

C1- It is better to install a film capacitor K73-17, a capacitance of 0.33 µF and higher (the larger the capacitance, the less the low frequency is attenuated, i.e. everyone’s favorite bass).
C2- It’s better to set 220uF 50V - again, the bass will be better
C3, C4- 22uF 50V - determine the turn-on time of the microcircuit (the larger the capacitance, the longer the turn-on duration)
C5- here it is, the PIC capacitor (I wrote how to connect it in paragraph 2.1 (at the very end). It’s also better to take 220 μF 50V (guess 3 times... the bass will be better)
S7, S9- Film, any rating: 0.33 µF and higher for voltage 50V and higher
C6, C8- You don’t have to install it, we already have capacitors in the power supply

R2, R3- Determine the gain. By default it is 32 (R3 / R2), it is better not to change
R4, R5- Essentially the same function as C3, C4

There are strange terminals VM and VSTBY on the diagram - they need to be connected to the power Plus, otherwise nothing will work.

2.4.2. Switching circuits - bridge

The diagram is also taken from the datasheet:

In essence, this circuit consists of 2 simple amplifiers, the only difference being that the speaker (load) is connected between the amplifier outputs. There are a couple more nuances, more on them later. This circuit can be used when you have a load of 8 Ohm (Optimal power supply for microcircuits +/-25V) or 16 Ohm (Optimal power supply +/-33V). For a 4 Ohm load, making a bridge circuit is pointless; the microcircuits will not withstand the current - I think the result is known.
As I said above, the bridge circuit is assembled from 2 conventional amplifiers. In this case, the input of the second amplifier is connected to ground. I also ask you to pay attention to the resistor that is connected between the 14th “leg” of the first microcircuit (in the diagram: above) and the 2nd “leg” of the second microcircuit (in the diagram: below). This is a feedback resistor; if it is not connected, the amplifier will not work.
The Mute (10th “leg”) and Stand-By (9th “leg”) chains have also been changed here. It doesn't matter, do what you like. The main thing is that the voltage on the Mute and St-By paws is greater than 5V, then the microcircuit will work.

2.4.3 Switching circuits - microcircuit enhancement
My advice to you: don’t suffer with bullshit, you need more power - use transistors
Perhaps later I’ll write how the enhancement is done.

2.5 A few words about the Mute and Stand-By functions
- Mute - At its core, this function of the chip allows you to turn off the input. When the voltage at the Mute pin (10th pin of the microcircuit) is from 0V to 2.3V, the input signal is attenuated by 80dB. When the voltage on the 10th leg is more than 3.5V, attenuation does not occur
- Stand-By - Transfers the amplifier to standby mode. This function turns off the power to the output stages of the microcircuit. When the voltage at the 9th pin of the microcircuit is more than 3 volts, the output stages operate in their normal mode.

There are two ways to manage these functions:

What is the difference? Basically nothing, do what you feel comfortable with. I personally chose the first option (separate control)
The terminals of both circuits must be connected either to the “+” power supply (in this case, the microcircuit is turned on, there is sound), or to “common” (the microcircuit is turned off, there is no sound).

3) Printed circuit board
Here is a printed circuit board for TDA7294 (TDA7293 can also be installed, provided that the supply voltage does not exceed 40V) in Sprint-Layout format: .

The board is drawn from the side of the tracks, i.e. when printing you need to mirror (for)
I made the printed circuit board universal; you can assemble both a simple circuit and a bridge circuit on it. A program is required to view it.
Let's go over the board and figure out what's what:

3.1 Main board(at the very top) - contains 4 simple circuits with the ability to combine them into bridges. Those. On this board you can assemble either 4 channels, or 2 bridge channels, or 2 simple channels and one bridge. Universal in a word.
Pay attention to the 22k resistor circled in a red square; it must be soldered if you plan to make a bridge circuit; you also need to solder the input capacitor as shown in the wiring (a cross and an arrow). You can buy a radiator at the Chip and Dip store, they sell a 10x30cm one, the board was made just for it.
3.2 Mute/St-By board- It just so happened that I made a separate board for these functions. Connect everything according to the diagram. Mute (St-By) Switch is a switch (toggle switch), the wiring shows which contacts to close in order for the microcircuit to work.

Connect the signal wires from the Mute/St-By board to the main board as follows:

Connect the power wires (+V and GND) to the power supply.
Capacitors can be supplied 22uF 50V (not 5 pieces in a row, but one piece. The number of capacitors depends on the number of microcircuits controlled by this board)
3.3 PSU boards. Everything is simple here, we solder in the bridge, electrolytic capacitors, connect the wires, DO NOT CONFUSE THE POLARITY!!!

I hope the assembly will not cause any difficulties. The printed circuit board has been checked and everything works. When assembled correctly, the amplifier starts up immediately.

4) The amplifier did not work the first time
Well, it happens. We disconnect the amplifier from the network and begin to look for an error in the installation; as a rule, in 80% of cases the error is due to incorrect installation. If nothing is found, then turn the amplifier back on, take a voltmeter and check the voltage:
- Let's start with the supply voltage: on the 7th and 13th legs there should be a "+" supply; On the 8th and 15th paws there should be “-” nutrition. The voltages must be the same value (at least the spread should be no more than 0.5V).
- On the 9th and 10th legs there should be a voltage greater than 5V. If the voltage is less, then you made a mistake in the Mute/St-By board (the polarity was reversed, the toggle switch was installed incorrectly)
- When the input is shorted to ground, the output of the amplifier should be 0V. If the voltage there is more than 1V, then there is something wrong with the microcircuit (possibly a defect or a left-handed microcircuit)
If all points are in order, then the microcircuit should work. Check the volume level of the sound source. When I first assembled this amplifier, I turned it on... there was no sound... after 2 seconds everything started playing, do you know why? The moment the amplifier was turned on occurred during a pause between tracks, this is how it happens.

Other tips from the forum:

Strengthening. The TDA7293/94 is quite suitable for connecting several cases in parallel, although there is one nuance - the outputs must be connected 3...5 seconds after the supply voltage is applied, otherwise new m/s may be required.

(C) Mikhail aka ~D"Evil~ St. Petersburg, 2006

List of radioelements

In this FAQ we will try to consider all issues related to the recently popular ULF microcircuit TDA7293/7294. Information taken from the forum topic of the same name on the Soldering Iron website, forum.cxem.net/index.php?showtopic=8669. All the information was put together and designed by ~D"Evil~, for which many thanks to him. Microcircuit parameters, switching circuit, printed circuit board, all this.

Here is the power supply diagram

(click to enlarge)

1.1 Transformer- must have two secondary windings. Or one secondary winding with a tap from the midpoint (very rare). So, if you have a transformer with two secondary windings, then they need to be connected as shown in the diagram. Those. the beginning of one winding with the end of another (the beginning of the winding is indicated by a black dot, this is shown in the diagram). Get it wrong and nothing will work. When both windings are connected, we check the voltage at points 1 and 2. If the voltage there is equal to the sum of the voltages of both windings, then you have connected everything correctly. The connection point of the two windings will be the “common” (ground, case, GND, call it what you want). This is the first common mistake, as we see: there should be two windings, not one.

Now the second error: The datasheet (technical description of the microcircuit) for the TDA7294 microcircuit states: +/-27 power is recommended for a 4 Ohm load.

The mistake is that people often take a transformer with two 27V windings, this cannot be done!!!

When you buy a transformer, it says effective value, and the voltmeter also shows you the effective value. After the voltage is rectified, it charges the capacitors. And they are already charging before amplitude value which is 1.41 (root of 2) times greater than the current value. Therefore, in order for the microcircuit to have a voltage of 27V, the transformer windings must be 20V (27 / 1.41 = 19.14 Since transformers are not made for such voltage, we will take the nearest one: 20V). I think the point is clear.
Now about the power: in order for the TDA to deliver its 70W, it needs a transformer with a power of at least 106W (the efficiency of the microcircuit is 66%), preferably more. For example, a 250W transformer is very suitable for a stereo amplifier on the TDA7294

1.2 Rectifier bridge

Here, as a rule, questions do not arise, but still. I personally prefer to install rectifier bridges, because... no need to bother with 4 diodes, it’s more convenient. The bridge must have the following characteristics: reverse voltage 100V, forward current 20A. We put up such a bridge and don’t worry that one “fine” day it will burn down. This bridge is enough for two microcircuits and the capacitor capacity in the power supply is 60"000 μF (when the capacitors are charged, a very high current passes through the bridge)

1.3 Capacitors

As you can see, the power supply circuit uses 2 types of capacitors: polar (electrolytic) and non-polar (film). Non-polar (C2, C3) are necessary to suppress RF interference. By capacity, set what will happen: from 0.33 µF to 4 µF. It is advisable to install our K73-17, which are pretty good capacitors. Polar (C4-C7) are necessary to suppress voltage ripple, and besides, they give up their energy during amplifier load peaks (when the transformer cannot provide the required current). Regarding capacity, people still argue about how much is needed. I learned from experience that for one microcircuit, 10,000 uF per arm is enough. Capacitor voltage: choose yourself, depending on the power supply. If you have a 20V transformer, then the rectified voltage will be 28.2V (20 x 1.41 = 28.2), capacitors can be set to 35V. It's the same with non-polar ones. It seems like I didn't miss anything...

As a result, we got a power supply containing 3 terminals: “+”, “-” and “common”. We’re done with the power supply, let’s move on to the microcircuit.

2) Chips TDA7294 and TDA7293

2.1.1 Description of the pins of the TDA7294 chip

1 - Signal ground

4 - Also a signal ground
5 - The pin is not used, you can safely break it off (the main thing is not to mix it up!!!)
7 - "+" power supply
8 - "-" power supply

11 - Not used
12 - Not used
13 - "+" power supply
14 - Chip output
15 - "-" power supply

2.1.2 Description of the pins of the TDA7293 chip

1 - Signal ground
2 - Inverse input of the microcircuit (in the standard circuit the OS is connected here)
3 - Non-inverted input of the microcircuit, we supply an audio signal here through the isolation capacitor C1
4 - Also a signal ground
5 - Clippmeter, basically an absolutely unnecessary function
6 - Voltage boost (Bootstrap)
7 - "+" power supply
8 - "-" power supply
9 - Conclusion St-By. Designed to put the microcircuit into standby mode (that is, roughly speaking, the amplifying part of the microcircuit is disconnected from the power supply)
10 - Mute output. Designed to attenuate the input signal (roughly speaking, the input of the microcircuit is turned off)
11 - Input of the final amplification stage (used when cascading TDA7293 microcircuits)
12 - The capacitor POS (C5) is connected here when the supply voltage exceeds +/-40V
13 - "+" power supply
14 - Chip output
15 - "-" power supply

2.2 Difference between TDA7293 and TDA7294 chips
Such questions come up all the time, so here are the main differences between the TDA7293:
- Possibility of parallel connection (complete garbage, you need a powerful amplifier - assemble it with transistors and you will be happy)
- Increased power (by a couple of tens of watts)
- Increased supply voltage (otherwise the previous point would not be relevant)
- They also seem to say that it is all made on field-effect transistors (what’s the point?)
That seems to be all the differences, I’ll just add that all TDA7293 have increased glitches - they light up too often.

Another common question: Is it possible to replace TDA7294 with TDA7293?

Answer: Yes, but:
- At supply voltage<40В заменять можно спокойно (конденсатор ПОС между 14ой и 6ой лапами как был, так и остается)
- With a supply voltage >40V, it is only necessary to change the location of the PIC capacitor. It must be between the 12th and 6th legs of the microcircuit, otherwise glitches in the form of excitement, etc. are possible.

This is what it looks like in the datasheet for the TDA7293 chip:

As can be seen from the diagram, the capacitor is connected either between the 6th and 14th legs (supply voltage<40В) либо между 6-ой и 12-ой лапами (напряжение питания >40V)

There are such extreme people who power the TDA7294 from 45V, then they wonder: what’s on fire? It lights up because the microcircuit is working at its limit. Now here they will tell me: “I have +/-50V and everything works, don’t drive it!!!”, the answer is simple: “Turn it up to maximum volume and time it with a stopwatch”

If you have a 4 Ohm load, then the optimal power supply will be +/- 27V (20V transformer windings)
If you have an 8 Ohm load, then the optimal power supply will be +/- 35V (25V transformer windings)
With such a supply voltage, the microcircuit will work for a long time and without glitches (I withstood an output short-circuit for a minute, and nothing burned out; I don’t know how things are with fellow extreme sports enthusiasts, they are silent)
And one more thing: if you still decide to make the supply voltage higher than the norm, then do not forget: you still can’t escape distortion. More than 70W (supply voltage +/-27V) is useless from the microcircuit, because It is impossible to listen to this grinding noise!!!

Here is a graph of distortion (THD) versus output power (Pout)

As we can see, with an output power of 70W, the distortion is around 0.3-0.8% - this is quite acceptable and not noticeable by ear. With a power of 85W, the distortion is already 10%, this is already wheezing and grinding, in general it is impossible to listen to sound with such distortion. It turns out that by increasing the supply voltage, you increase the output power of the microcircuit, but what’s the point? It’s still impossible to listen after 70W!!! So take note, there are no advantages here.

2.4.1 Connection circuits - original (conventional)

Here is the diagram (taken from the datasheet)

C1- It is better to install a film capacitor K73-17, a capacitance of 0.33 µF and higher (the larger the capacitance, the less the low frequency is attenuated, i.e. everyone’s favorite bass).
C2- It’s better to set 220uF 50V - again, the bass will be better
C3, C4- 22uF 50V - determine the turn-on time of the microcircuit (the larger the capacitance, the longer the turn-on duration)
C5- here it is, the PIC capacitor (I wrote how to connect it in paragraph 2.1 (at the very end). It’s also better to take 220 μF 50V (guess 3 times... the bass will be better)
S7, S9- Film, any rating: 0.33 µF and higher for voltage 50V and higher
C6, C8- You don’t have to install it, we already have capacitors in the power supply

R2, R3- Determine the gain. By default it is 32 (R3 / R2), it is better not to change
R4, R5- Essentially the same function as C3, C4

There are strange terminals VM and VSTBY on the diagram - they need to be connected to the power Plus, otherwise nothing will work.

2.4.2. Switching circuits - bridge

The diagram is also taken from the datasheet

In essence, this circuit consists of 2 simple amplifiers, the only difference being that the speaker (load) is connected between the amplifier outputs. There are a couple more nuances, more on them later. This circuit can be used when you have a load of 8 Ohms (Optimal power supply for microcircuits +/-25V) or 16 Ohms (Optimal power supply +/-33V). For a 4 Ohm load, making a bridge circuit is pointless; the microcircuits will not withstand the current - I think the result is known.

As I said above, the bridge circuit is assembled from 2 conventional amplifiers. In this case, the input of the second amplifier is connected to ground. I also ask you to pay attention to the resistor that is connected between the 14th “leg” of the first microcircuit (in the diagram: above) and the 2nd “leg” of the second microcircuit (in the diagram: below). This is a feedback resistor; if it is not connected, the amplifier will not work.

2.4.3 Switching circuits - microcircuit enhancement

My advice to you: don’t suffer with bullshit, you need more power - use transistors
Perhaps later I’ll write how the enhancement is done.

2.5 A few words about the Mute and Stand-By functions

Mute - At its core, this function of the chip allows you to mute the input. When the voltage at the Mute pin (10th pin of the microcircuit) is from 0V to 2.3V, the input signal is attenuated by 80 dB. When the voltage on the 10th leg is more than 3.5V, attenuation does not occur
- Stand-By - Transfers the amplifier to standby mode. This function turns off the power to the output stages of the microcircuit. When the voltage at the 9th pin of the microcircuit is more than 3 volts, the output stages operate in their normal mode.

There are two ways to manage these functions:

What is the difference? Basically nothing, do what you feel comfortable with. I personally chose the first option (separate control).

The terminals of both circuits must be connected either to the “+” power supply (in this case, the microcircuit is turned on, there is sound), or to “common” (the microcircuit is turned off, there is no sound).

3) Printed circuit board

Here is a printed circuit board for TDA7294 (TDA7293 can also be installed, provided that the supply voltage does not exceed 40V) in Sprint-Layout format: download.

The board is drawn from the side of the tracks, i.e. When printing, you need to mirror (for the laser-iron method of producing printed circuit boards)

I made the printed circuit board universal; you can assemble both a simple circuit and a bridge circuit on it. Sprint Layout 4.0 is required to view.

Let's go over the board and figure out what belongs to what.

3.1 Main board(at the very top) - contains 4 simple circuits with the ability to combine them into bridges. Those. On this board you can assemble either 4 channels, or 2 bridge channels, or 2 simple channels and one bridge. Universal in a word.

Pay attention to the 22k resistor circled in a red square; it must be soldered if you plan to make a bridge circuit; you also need to solder the input capacitor as shown in the wiring (a cross and an arrow). You can buy a radiator at the Chip and Dip store, they sell a 10x30cm one, the board was made just for it.

3.2 Mute/St-By board

It just so happened that I made a separate board for these functions. Connect everything according to the diagram. Mute (St-By) Switch is a switch (toggle switch), the wiring shows which contacts to close in order for the microcircuit to work.

If nothing is found, then turn the amplifier back on, take a voltmeter and check the voltage:

Let's start with the supply voltage: on the 7th and 13th legs there should be a "+" supply; On the 8th and 15th paws there should be “-” nutrition. The voltages must be the same value (at least the spread should be no more than 0.5V).
- On the 9th and 10th legs there should be a voltage greater than 5V. If the voltage is less, then you made a mistake in the Mute/St-By board (the polarity was reversed, the toggle switch was installed incorrectly)
- When the input is shorted to ground, the output of the amplifier should be 0V. If the voltage there is more than 1V, then there is something wrong with the microcircuit (possibly a defect or a left-handed microcircuit)

If all points are in order, then the microcircuit should work. Check the volume level of the sound source. When I first assembled this amplifier, I turned it on... there was no sound... after 2 seconds everything started playing, do you know why? The moment the amplifier was turned on occurred during a pause between tracks, this is how it happens.
useful

Those who create home audio or assemble amplifiers themselves have probably come across a description of the ST TDA7293 microcircuits. If you haven’t seen it, be sure to look for it and read it. Using these fairly simple chips you can build a very high-end amplifier.
I build such an amplifier into a wall niche, install hidden wiring and built-in acoustics. This allows you to avoid unnecessary wires in the room, speakers in the corners and the installation of a mandatory shelf or bedside table under the TV.
Initially I but, unfortunately, its design and circuitry turned out to be poor. All amplifier channels were driven by long wires, and the board layout was terrible. Trying to somehow correct this Chinese craft, many modifications were made. During one of them, I mixed up the plus and minus of the power supply, and all the TDA7293 microcircuits burned out with pops resembling firecrackers.
After that, I changed the approach to modularity and used a proven scheme and ordered printed circuit boards for it, wired independently, to the dimensions I needed. Of course, I also ordered parts along with the boards, including TDA7293 chips.


Realizing that there was a high risk of running into a fake, I looked for the distinctive features of genuine ST microcircuits.
It turns out that to verify authenticity, it is enough to measure the resistance between the metal eye (positive wire) and pins 5, 10 and 11 (negative wire of the tester). For genuine microcircuits, the resistance should be about 3 megohms. In the opposite polarity of the tester, the measured resistance should be infinite.

Be careful not to fall for fakes! Always open a dispute and never withdraw it in exchange for a promise to send you something else in return. This is the only way to protect yourself from losing money. No one will compensate you for your lost time. Therefore, I hope what is stated here will help you.

UPD for questions in the comments:
All 28 (twenty-eight) microcircuits ordered on E-bay and Aliexpress (that is, 100% of the number ordered) turned out to be counterfeit and completely non-functional. They did not make calls using the specified method, did not work (or warmed up, but did not work) in the test board. I checked everything 10 times.

E-bay and Aliexpress returned money for all open disputes. As proof, I published photographs of measurements with a resistance tester between the 5th or 11th pin and the metal eye. For the very first order (I took two pieces to try) on Ebay, I did not receive money, because I did not know how to check the authenticity, and missed the time to open a dispute.

Chinese sellers have very funny answers in disputes. Here is an example of the seller’s “argumentation” in the last dispute I won on Aliexpress:
Hi!Sir
The goods are in transit!
You can wait for time!
You cancel the dispute!
I can extend the receipt time for you!Add 15 days！
Thank you!
You can cancel the dispute!Thank you very much!
Of course, there is no need to answer this, much less swear. It is necessary to calmly remind the essence of the complaint and ask whether there is anything to answer on the merits.

Another very interesting point: Have you noticed that in the description of goods (in particular microcircuits and other equipment) there is a field: “Brand name” (manufacturer’s name). If not, please note that sellers NEVER indicate the original brand. For example, instead of ST or ST Microelectronics, CazenOveyi is indicated. According to Aliexpress rules, this is enough to accuse the seller of counterfeiting. After all, you receive a chip with the ST logo, but you ordered CazenOveyi :)
And also, if the seller erases or blurs the manufacturer’s logo in the photo, expect a fake. Brazen or cunning, but wait...

I have not yet found (did not receive) original ST TDA7293 microcircuits on Ebay and Aliexpress. Perhaps they exist, I’ll give an example: After the second order and dispute, I wrote a detailed review to the seller on E-bay with photos of the tests. Of course, he didn’t like this, but he honestly admitted that he doesn’t understand the authenticity of microcircuits, but simply sells them. He promised to send me new ones to replace them so that I would withdraw the review. But he deceived me and didn’t send anything.
The most interesting thing is that after this the lot with TDA7293 for two dollars was removed from sale, and after some time the same lot with TDA7293 appeared, but for seven dollars. Apparently, this is how much the real ones cost to purchase them, or the seller decided to insure himself with a protective price.

Chip and Dip is really a way out, but since I ordered a lot of things from the package on Ebay and Aliexpress, I didn’t pay attention to the store “nearby”. If two of the ordered batches are fake while on the way, then I’ll go shopping at Chip and Dip.
To be fair, it should be noted that some items from local sellers are taken from China, but cost two prices.

P.S. I apologize for the quality of the photos, but there is no equipment for macro photography. I tried my best: I waited for the sun, laid out the microcircuits on white paper (so that there would be no problems with balance) and spent a long time selecting an angle and choosing from the received photos.

P.P.S. For those who are interested, I took the information about checking authenticity by dialing. Of course, only a test board can give a 100% guarantee. In my case, the test results with the tester and on the board coincided completely.

P.P.P.S The verified diagram is taken. And this is what the boards on which the microcircuits were tested look like:


Unfortunately, no errors were found in the boards. Of course, I checked everything with an oscilloscope. And even with a test radiator (to avoid pops and smoke). Resistor R6 was soldered off to ensure unmute. The track from the 12th leg of the TDA7293 is cut to allow testing of the TDA7294 (jumper on the back of the board).

If anything, 10 more such boards have been assembled:


Waiting in the wings (genuine TDA7293) :)

Regarding “fakes” or “replicas”. Let’s say that replicas (that is, fully or partially functional copies) of original ST TDA7293 microcircuits are produced in China. You can't set up microchip production in a garage. It must be a large factory with multi-million dollar equipment and large staff. Most chip manufacturing equipment is not manufactured in China. It (the equipment) is supplied by well-known companies under well-known contract conditions. Of course, the obligation not to print crystals in violation of copyright is one of the points of delivery of such equipment. You, as an individual, will not be sold machines for printing money. And states buy them.
But suppose there is chaos in China. And the Chinese, having bought (or copied) American or European production lines, began to print whatever they wanted. And they called it “replicas.” But since these microcircuits are printed at the factory, why would they then erase the names from the cases and engrave new ones? Therefore, the existence of “replicas” is possible, but I don’t really believe in such a story. She's not logical. Imagine yourself in the shoes of a factory owner: you have service contracts for many, many millions, and you, at the risk of termination of contracts and loss of money, will churn out (even hundreds of thousands) microcircuits for one dollar. A very risky and dangerous business. It's easier to print money. Fakes can also be called “replicas”. :))

Therefore, everything in sawn casings must be called by its proper name: fake or counterfeit. In Aliexpress terminology this is “counterfeit”.

Good luck and attention!