Amplifier for tda 7293 bridge circuit. Universal power amplifier on tda7293. Description of the pins of the TDA7294 chip

Continuous experiments and searches for new circuit solutions have made it possible to create a very versatile high-quality power amplifier based on the already "bored" TDA7293 chip. Unlike all other circuit implementations, this version of the amplifier allows you to use both non-inverting and inverting switching. In addition, a regulator has been introduced into the amplifier, which allows you to smoothly switch from a typical operating mode to a voltage-controlled current source (ITUN) mode, i.e. match the amplifier with the speaker system as much as possible and get a completely new, better sound.
A wide range of supply voltages makes it possible to build an amplifier with a power of 20 to 100 W, and at powers up to 50 W, the TDA7294 chip has a coff. non-linear distortion does not exceed 0.05%, which makes it possible to attribute the amplifier based on these ICs to the Hi-Fi category. The schematic diagram is shown in Figure 1.

Picture 1.

Schematic diagram of the switching on of the power amplifier for m / s TDA7293 TDA7294 drawing of the printed circuit board direct connection inverse connection ITUN current source controlled by voltage characteristics of the amplifier on the microcircuit TDA7293 TDA7294 description UMZCH TDA7293.pdf TDA7294.pdf

As can be seen from the characteristics, the amplifiers on the TDA7294 TDA7293 are very versatile and can be successfully used in any power amplifiers where good UMZCH characteristics are required.
Switching options are shown in Figures 2...7. Pay attention to the position of the trimmer slider and the presence or absence of a jumper on the right side of the board (just below the middle).

Figure 2 is a typical non-inverting power amplifier connection.

Figure 3 - typical inverting connection of a power amplifier

Figure 4 - non-inverting switching with the possibility of a smooth transition from the typical mode
work in ITUN mode

Figure 5 - inverting inclusion TDA 7293 with the possibility of a smooth transition from
typical operating mode to ITUN mode

The practical use of the ITUN mode is obvious - it is a voltage-controlled current source. In other words, the dynamic head takes part in the formation of amplifier feedback, which significantly increases the sound quality. Using the amplifier on the TDA7293 in YITUN mode, it turns out to significantly outweigh the PRICE-QUALITY ratio in favor of quality. However, this system is not devoid of shortcomings - the ITUN mode is designed to work with wideband dynamic heads. If the speaker contains two bands, and the woofer does not have a choke in the filter, then the ITUN works more or less correctly. But when working on three-way acoustics TDA7293, you should not switch to ITUN mode - the influence of a large number of capacitors and inductances installed in the speakers greatly complicates the correct assessment of the current actually flowing through the speaker and, as a result, strong signal distortions appear.
However, no one forbids switching this power amplifier to combo mode - when operating in a typical mode, the rotation of the tuning resistor adds an effect on the OOS of the voltage drop across the current-measuring resistor, achieving optimal sound and matching of the TDA7293 and the speaker system.

Figure 6 - bridge circuit for switching on two power amplifiers

Figure 7 - parallel connection of two power amplifiers (only for UM7293)

Figure 8 - appearance of the power amplifier on the chip TDA7293 (TDA7294)

It only remains to add that there are some well-wishers who claim that TDA 7294 chips in the bridge give 200 watts into 4 ohms or that the TDA7294 can work in parallel. Such information has nothing to do with the TDA7294 chip., since such powers (200W) will simply disable the microcircuit due to thermal breakdown, since the crystal simply does not have time to give off heat even to the flange of the microcircuit. Well, it is certainly possible to confuse the TDA7294 with the TDA7293, but it is absolutely not necessary, since although they are in the same technological row, they have VERY strong differences. If anyone has any doubts about what was written, then you are welcome to get acquainted with the datasheet for both microcircuits and make a correction for the results of numerous experiments.
Figure 8 shows the appearance of the amplifier on TDA7293 and TDA7294 chips, and below is a link to a video on how to assemble this universal power amplifier on your own.

PS Endless battles over which of the microcircuits is better (TDA7294 or LM3886) have not yet ended in anything, there are no comrades for taste and color ...

Details on how much power a power supply is needed for a power amplifier can be viewed in the video below. The STONECOLD amplifier is taken as an example, however, this measurement gives an understanding that the power of the mains transformer can be less than the power of the amplifier by about 30%.

DID NOT FIND WHAT YOU WERE LOOKING FOR? GOOGLED:

In this FAQ, we will try to consider all issues related to the recently popular VLF TDA7293 / 7294 chip. The information is taken from the forum topic of the same name soldering iron. I gathered all the information together and designed it, for which many thanks to him. Microcircuit parameters, switching circuit, printed circuit board, all this. The datasheet of the TDA7293 and TDA7294 microcircuits is available.

1) Power supply
Oddly enough, but for many problems begin already here. The two most common mistakes are:
- Single supply
- Orientation to the voltage of the secondary winding of the transformer (effective value).

Here is the power supply diagram:

What do we see here?

1.1 Transformer- should 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 must 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). Mix it up, nothing will work. When both windings are connected, we check the voltage at points 1 and 2. If there is a voltage equal to the sum of the voltages of both windings, then you connected everything correctly. The connection point of the two windings will be "common" (ground, body, 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 indicates: +/-27 is recommended for a 4Ω load. The mistake is that people often take a transformer with two windings 27V, DO NOT DO THIS!!! When you buy a transformer, they write on it 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 amplitude value which is 1.41 (root of 2) times the effective value. Therefore, in order for the microcircuit to have a voltage of 27V, then the transformer windings must be 20V (27 / 1.41 \u003d 19.14 Since transformers do not make such a voltage, we take the nearest one: 20V). I think the point is clear.
Now about the power: in order for the TDA to give out its 70W, it needs a transformer with a power of at least 106W (the efficiency of the microcircuit is 66%), preferably more. For example, for a stereo amplifier on the TDA7294, a 250W transformer is very well suited

1.2 Rectifier bridge- As a rule, there are no questions here, but still. I personally prefer to install rectifier bridges, because. no need to mess around with 4 diodes, it's more convenient. The bridge must have the following characteristics: reverse voltage 100V, forward current 20A. We put such a bridge and do not worry that one "beautiful" day it will burn. Such a bridge is enough for two microcircuits and the capacitance of the capacitors in the PSU is 60 "000uF (when the capacitors are charged, a very high current passes through the bridge)

1.3 Capacitors- As you can see, 2 types of capacitors are used in the power supply circuit: polar (electrolytic) and non-polar (film). Non-polar (C2, C3) are necessary to suppress RF interference. According to the capacitance, set what will happen: from 0.33 microfarads to 4 microfarads. It is advisable to install our K73-17, pretty good capacitors. Polar (C4-C7) are necessary to suppress voltage ripple, and besides, they give up their energy at amplifier load peaks (when the transformer cannot provide the required current). In terms of capacity, people are still arguing how much is still needed. I realized from experience that for one microcircuit, 10,000 microfarads per shoulder 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 \u003d 28.2), the capacitors can be set to 35V. Same thing with the non-polar ones. Looks like I didn't miss anything...
As a result, we got a power supply unit containing 3 terminals: "+", "-" and "common" With the power supply unit finished, 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 signal ground
5 - The output is not used, you can safely break it off (the main thing is not to confuse !!!)

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


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

2.1.2 Description of the pins of the TDA7293 chip
1 - Signal ground
2 - Inverted input of the microcircuit (in the standard scheme, the OS is connected here)
3 - Non-inverse input of the microcircuit, we supply an audio signal here, through the isolation capacitor C1
4 - Also signal ground
5 - Clipmeter, in principle, an absolutely unnecessary function
6 - Boost (Bootstrap)
7 - "+" power
8 - "-" supply
9 - Output St-By. Designed to transfer the microcircuit to standby mode (that is, roughly speaking, the amplifying part of the microcircuit is turned off 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 - Capacitor POS (C5) is connected here when the supply voltage exceeds +/-40V
13 - "+" power
14 - Chip output
15 - "-" power

2.2 Difference between TDA7293 and TDA7294 chips
Such questions come up all the time, so here are the main differences of the TDA7293:
- The possibility of parallel connection (complete garbage, you need a powerful amplifier - collect on transistors and you will be happy)
- Increased power (a couple of tens of watts)
- Increased supply voltage (otherwise the previous paragraph 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 from myself that all TDA7293s have increased buggy - they burn 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)
- When the supply voltage is >40V, it is only necessary to change the location of the POS capacitor. It must be between the 12th and 6th paws of the microcircuit, otherwise glitches in the form of excitement, etc. are possible.

Here's how it looks in the datasheet for the TDA7293 chip:

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

2.3 Supply voltage
There are such extreme people, they feed the TDA7294 from 45V, then they are surprised: why is it burning? 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 !!!”, the answer is simple: “Turn it up to the maximum volume and mark the time with a stopwatch”

If you have a load of 4 ohms, 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 a short circuit of the output for a minute, and nothing burned out, I don’t know how things are with this with fellow extreme sportsmen, 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 won’t get anywhere from distortion. listen to this rattle is impossible!

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

As we can see, with an output power of 70W, we have distortion in the region of 0.3-0.8% - this is quite acceptable and is not noticeable by ear. At 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 distortions. It turns out that by increasing the supply voltage, you increase the output power of the microcircuit, but what's the point? All the same, after 70W it is not possible to listen !!! So take note, there are no pluses here.

2.4.1 Switching schemes - original (usual)

Here is the schematic (taken from the datasheet):

C1- It is better to put a film capacitor K73-17, the capacitance is from 0.33uF and higher (the larger the capacitance, the less the low frequency is weakened, i.e. everyone's favorite bass).
C2- It is better to put 220uF 50V - again, the bass will get better
C3, C4- 22uF 50V - determine the turn-on time of the microcircuit (the larger the capacitance, the longer the turn-on time)
C5- here it is, the POS capacitor (I wrote how to connect it in paragraph 2.1 (at the very end). It is also better to take 220uF 50V (guess it 3 times ... the bass will be better)
C7, C9- Film, any rating: 0.33uF and higher for a voltage of 50V and higher
C6, C8- You can not put it, we already have capacitors in the PSU

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

The diagram has incomprehensible terminals VM and VSTBY - they must be connected to the POSITIVE supply, otherwise nothing will work.

2.4.2. Switching schemes - bridge

The diagram is also taken from the datasheet:

In fact, this circuit consists of 2 simple amplifiers, with the only difference being that the column (load) is connected between the amplifier outputs. There are a couple more nuances, about them a little later. Such a circuit can be used when you have a load of 8 ohms (optimal supply of chips +/-25V) or 16 ohms (optimal supply of +/-33V). For a load of 4 Ohm, it is pointless to make a bridge circuit, 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 more than 5V, then the microcircuit will work.

2.4.3 Switching schemes - powering the microcircuit
My advice to you: do not suffer from garbage, you need more power - do it on transistors
Perhaps later I will write how the help is done.

2.5 A few words about the Mute and Stand-By functions
- Mute - At its core, this feature of the chip allows you to disable the input. When the voltage at the Mute pin (10th leg of the microcircuit) is from 0V to 2.3V, the input signal is attenuated by 80dB. If the voltage on the 10th leg is more than 3.5V, there is no weakening
- Stand-By - Switching the amplifier to standby mode. This function turns off the power to the output stages of the microcircuit. When the voltage at the 9th output 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? Essentially nothing, do as you please. I personally chose the first option (separate control)
The outputs of both circuits must be connected either to the "+" power supply (in this case, the microcircuit is on, there is sound), or to the "common" (the microcircuit is turned off, there is no sound).

3) PCB
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, on it you can assemble both a simple circuit and a bridge circuit. A program is required to view.
Let's go over the board and see what applies 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 collect either 4 channels, or 2 bridge channels, or 2 simple channels and one bridge. Universal in one word.
Pay attention to the 22k resistor circled in red square, it must be soldered if you plan to make a bridge circuit, it is also necessary to solder the input capacitor as shown in the wiring (cross and arrow). The radiator can be bought at the Chip and Dip store, such a 10x30cm is sold there, the board was made just for it.
3.2 Mute/St-By board- It just so happened that for these functions I made a separate board. Connect everything according to the diagram. Mute (St-By) Switch is a switch (tumbler), the wiring shows which contacts to close in order for the microcircuit to work.

Connect the signal wires from the Mute/St-By board on 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 the bridge, electrolytic capacitors, connect the wires, DO NOT confuse the polarity !!!

I hope the assembly will not cause difficulties. The circuit board has been tested and everything works. With proper assembly, the amplifier starts immediately.

4) The amplifier did not work the first time
Well, it happens. We disconnect the amplifier from the network and start looking for an error in the installation, as a rule, in 80% of cases the error is in the wrong installation. If nothing is found, then turn on the amplifier again, 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 a "-" supply. The voltages must be the same value (at least the spread should be no more than 0.5V).
- On the 9th and 10th paws there should be a voltage of more than 5V. If the voltage is less, then you made a mistake in the Mute / St-By board (they mixed up the polarity, the toggle switch was set wrong)
- With the input shorted to ground, the output of the amplifier should be 0V. If the voltage there is more than 1V, then there is already something with the microcircuit (possibly a marriage or a left microcircuit)
If all the points are in order, then the microcircuit must work. Check the volume level of the sound source. When I just assembled this amplifier, I turn it on ... there is no sound ... after 2 seconds everything started to play, do you know why? The moment the amplifier was turned on fell on a pause between tracks, that's how it happens.

Other tips from the forum:

Helping. TDA7293 / 94 is quite sharpened 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 radio elements

And better both at once!
From search history

The last integrated circuit, tested with its pens, was on a clone - K174UN14.
He was capricious, all the time in a hurry to break into excitement, the quality of his work could not be compared with Radio Engineering, and reliability could not be compared with - oh, the horror of Vega-122, which is still legendary, and those who dismantled it in order to replace output transistors are still jumping up at night in a cold sweat.
I understand that in those days I did it wrong, and the board was not the same, and the layout. And there was no datasheet with an appnote for it, in general it didn’t work for me. And then I was not up to them.

He gave the radio equipment to a friend, as usual, to “use it” irrevocably, Vega, after another unsuccessful repair, he put it on a non-ferrous metal, and the surviving Amphiton entertained his neighbors in the country on weekends. The MP3 format was entering our lives, and computer audio was pushing cassettes and reels out of our homes. And I began to master the lamps, with a delay of many years. While I was collecting bit by bit the pieces of iron left from color-markers and half-dead lamps in the trash, progress in microelectronics for audio equipment rushed past me.

Stupid foreigners have long understood that repairing an amplifier in the Vega-122 style is not only unprofitable, but also absurd, and they chose the path of modular design. The guys from the Sanyo office were the first with their products "all on a chip" of the STK series, others did not lag behind them.
Marketers waved flags with incomprehensible inscriptions THD, THD + N, fantastic 0.00000% and hundreds of watts of power unrealistic for home use.
And all this on a piece of silicon smaller than a matchbox. Do not forget about protection against overheating, overload and fool. Communities of lovers of old technology and new technology appeared on the network, periodically fighting each other for their ideals that only they understood.
And only that, for the sake of which all this happened, remained eternal - this is music.

But I will not discuss any directions in technology here, but I want to talk about my first experience with integrated amplifiers after such a long break.

We will talk about the two leaders in today's popularity among household integrated amplifiers - and.
Only the lazy or the one who has never had a computer has heard of them, and progress has stopped at P214.
But it is one thing to hear, and another thing to feel with your hands and listen with your own ears.!

It was a bit unexpected and I didn't know where to start for quite some time. Too many questions immediately arose - power, cooling, protection, housing. It's been so long since I've done anything like this that I just lost my skills and gave away parts. In general, I was a little unprepared.
But I decided, by all means, to launch both pairs, compare them, and, if necessary, leave one working option or abandon them altogether in favor of lamps.

I must say right away that both types of microcircuits are monophonic, so two cases are required for a stereo amplifier. The task was also such - the most simple scheme. Ruffles and chips can be tolerated up to a certain limit, but when an op-amp is added to the circuit, with a native gain of more than a hundred dB, I consider this op-amp to be overkill.

It remains to think about which inclusion to choose. Here, as always, opinions were divided, so I decided - I use what is simpler and requires a minimum of strapping, because this is a microcircuit, and everything you need is already inside.

LM3886. High-Performance 68W Audio Power Amplifier w/Mute

My circuit on LM3886

TDA7293. 120V - 100W DMOS AUDIO AMPLIFIER WITH MUTE/ST-BY

My circuit on TDA7293

Maybe someone recognized the radiators in the photo? It was the amp Oda-102. Small such, from a block stereo complex.
Once I got it for nothing without speakers, I even used a transceiver from a tape recorder in one of the DACs, but the tuner, pre and power were lying around idle.
From there, the power trance was taken. I don’t need kilowatts of power, I’m no longer at the age to measure length and thickness with my neighbors, so if there are 20 watts, then I’ll have enough through the roof, and my neighbor will also have it.

For tests, two identical PSUs were made, more precisely, 2 boards of rectifiers and filter capacities, as well as a universal connector for connecting two different power trances, one from Oda, the second from the Behringer active speaker.

Launch and compare amplifiers

But the sound surprised me. No seriously. I once abandoned solid-state amps in favor of tubes precisely because of their sound.
Apparently, progress has nevertheless corrected this unfortunate omission.
I will not give here the characteristics, frequency response, Kg, and so on - this is all full on the net and written in the datasheet.
When comparing, I relied on my perception. I must say right away that if you do not approach from the position of phallometry, then they are the same in everything and, under equal conditions, are almost indistinguishable.

Which of them did I like more?
And here I will return to the abbreviation DMOS. The fact is that it is a pure bipolar, but in my opinion it is more interesting - it has an output stage on field-effect transistors! And these guys, in terms of their properties, will be closer to the lamps, which is probably why the sound of the field workers impressed me more.
But this is an amateur.
In my opinion, it sounds clean, almost sterile, but it's kind of softer, not so tiring for the ear - again, all this is extremely subjective.

I decided for now to make the finished design on .
And I'll start with the body! To be continued.

Files

Good! The freebie is over. If you want files and useful articles - help me!

Making a good power amplifier has always been one of the hardest parts of audio design. Sound quality, bass softness and clear mid and high frequencies, musical instrument detail - all these are empty words without a quality low-frequency power amplifier.

Foreword

Of the variety of homemade low-frequency amplifiers on transistors and integrated circuits that I made, the circuit on the driver chip showed itself best of all TDA7250 + KT825, KT827.

In this article, I will show you how to make an amplifier amplifier circuit that is perfect for use in homemade audio equipment.

Amplifier parameters, a few words about TDA7293

The main criteria by which the ULF circuit for the Phoenix-P400 amplifier was selected:

• Power is approximately 100W per channel at a load of 4 ohms;
• Power supply: bipolar 2 x 35V (up to 40V);
• Small input impedance;
• Small dimensions;
• High reliability;
• Manufacturing speed;
• High sound quality;
• Low noise level;
• Small cost.

Not a simple combination of requirements. At first I tried the option based on the TDA7293 chip, but it turned out that this is not what I need, and here's why ...

For all the time I had a chance to collect and test different ULF circuits - transistor ones from books and publications of the Radio magazine, on various microcircuits ...

I want to say my word about TDA7293 / TDA7294, because a lot has been written about it on the Internet, and I have met more than once that the opinion of one person contradicts the opinion of another. Having collected several clones of the amplifier on these microcircuits, I made some conclusions for myself.

The microcircuits are really good, although a lot depends on the successful layout of the printed circuit board (especially the ground lines), good power supply and the quality of the strapping elements.

What immediately pleased me in it was the rather large power delivered to the load. As for a single-chip integrated bass amplifier, the output power is very good, I also want to note the very low noise level in the no signal mode. It is important to take care of good active cooling of the chip, since the chip operates in the "boiler" mode.

What I didn’t like about the 7293 amplifier was the low reliability of the microcircuit: out of several purchased microcircuits, at various points of sale, only two remained working! I burned one by overloading the input, 2 burned out immediately when turned on (it seems like a factory defect), another one burned out for some reason when it was turned on again for the 3rd time, although before that it worked fine and no anomalies were observed ... Maybe just bad luck.

And now, the main reason why I did not want to use modules on the TDA7293 in my project is the "metallized" sound that is noticeable to my hearing, it does not hear softness and saturation, the mids are a little dull.

I concluded for myself that this chip is perfect for subwoofers or bass amplifiers that will hum in the trunk of a car or at discos!

I will not touch on the topic of single-chip power amplifiers further, I need something more reliable and of high quality, so that it is not so expensive with experiments and mistakes. Collecting 4 channels of an amplifier on transistors is a good option, but rather cumbersome in execution, and it can also be difficult to set up.

So what to assemble on if not on transistors and not on integrated circuits? - and on both, skillfully combining them! We will assemble a power amplifier on a TDA7250 driver chip with powerful composite Darlington transistors at the output.

Low-frequency power amplifier circuit on the TDA7250 chip

Chip TDA7250 in a DIP-20 package, this is a reliable stereo driver for Darlington transistors (high-gain composite transistors), on the basis of which you can build a high-quality two-channel stereo UMZCH.

The output power of such an amplifier can reach and even exceed 100W per channel with a load resistance of 4 ohms, it depends on the type of transistors used and the supply voltage of the circuit.

After assembling a copy of such an amplifier and the first tests, I was pleasantly surprised by the sound quality, power and how the music published by this microcircuit came to life in the company with KT825, KT827 transistors. In the compositions, very small details began to be heard, the instruments sounded rich and "easy".

You can burn this chip in several ways:

• Reversal of power lines;
• Exceeding the level of the maximum allowable supply voltage ± 45V;
• Input overload;
• High static voltage.

Rice. 1. Chip TDA7250 in a DIP-20 package, appearance.

Datasheet (datasheet) for the TDA7250 chip - (135 KB).

Just in case, I immediately purchased 4 microcircuits, each of which is 2 amplification channels. Microcircuits were bought in an online store at a price of about $ 2 per piece. At the market for such a microcircuit, they already wanted more than $ 5!

The scheme according to which my version was assembled is not much different from the one given in the datasheet:

Rice. 2. Low-frequency stereo amplifier circuit based on the TDA7250 chip and KT825, KT827 transistors.

For this UMZCH circuit, a self-made bipolar power supply for +/- 36V was assembled, with capacities of 20,000 microfarads in each arm (+ Vs and -Vs).

Power Amplifier Parts

I'll tell you more about the features of the parts of the amplifier. The list of radio components for assembling the circuit:

The inductors at the output of the UMZCH are wound on a frame with a diameter of 10 mm and contain 40 turns of enameled copper wire with a diameter of 0.8-1 mm in two layers (20 turns per layer). To prevent the turns from falling apart, they can be fastened with fusible silicone or glue.

Capacitors C22, C23, C4, C3, C1, C2 must be designed for a voltage of 63V, the rest of the electrolytes - for a voltage of 25V. Input capacitors C6 and C5 are non-polar, film or mica.

Resistors R16-R19 must be designed for a power of at least 5Watt. In my case, miniature cement resistors are used.

Resistances R20-R23, as well as RL can be set with a power of 0.5W. Resistors Rx - with a power of at least 1W. All other resistances in the circuit can be set with a power of 0.25W or more.

It is better to select pairs of transistors KT827 + KT825 with the closest parameters, for example:

1. KT827A(Uke=100V, h21E>750, Pk=125W) + KT825G(Uke=70V, h21E>750, Pk=125W);
2. KT827B(Uke=80V, h21E>750, Pk=125W) + KT825B(Uke=60V, h21E>750, Pk=160W);
3. KT827V(Uke=60V, h21E>750, Pk=125W) + KT825B(Uke=60V, h21E>750, Pk=160W);
4. KT827V(Uke=60V, h21E>750, Pk=125W) + KT825G(Uke=70V, h21E>750, Pk=125W).

Depending on the letter at the end of the marking, only the voltages Uke and Ube change for KT827 transistors, while the rest of the parameters are identical. But KT825 transistors with different letter suffixes already differ in many parameters.

Rice. 3. Pinout of powerful transistors KT825, KT827 and TIP142, TIP147.

It is advisable to check the transistors used in the amplifier circuit for serviceability. Darlington transistors KT825, KT827, TIP142, TIP147 and others with high gain contain two transistors inside, a couple of resistances and a diode, so the usual continuity with a multimeter may not be enough here.

To test each of the transistors, you can assemble a simple circuit with an LED:

Rice. 4. Scheme for checking transistors of the P-N-P and N-P-N structure for operability in the key mode.

In each of the schemes, when the button is pressed, the LED should light up. Power can be taken from + 5V to + 12V.

Rice. 5. An example of checking the performance of the KT825 transistor, P-N-P structure.

Each of the pairs of output transistors must be installed on radiators, since already at the average ULF output power, their heating will be quite noticeable.

The datasheet on the TDA7250 chip provides the recommended pairs of transistors and the power that can be extracted using them in this amplifier:

Mounting transistors KT825, KT827 (TO-3 package)

Particular attention should be paid to the installation of output transistors. A collector is connected to the case of transistors KT827, KT825, therefore if the cases of two transistors in one channel are accidentally or intentionally closed, then a power short circuit will result!

Rice. 6. Transistors KT827 and KT825 are prepared for mounting on radiators.

If the transistors are planned to be mounted on one common radiator, then their cases must be isolated from the radiator through mica gaskets, having previously smeared them with thermal paste on both sides to improve heat transfer.

Rice. 7. Radiators that I used for transistors KT827 and KT825.

In order not to describe for a long time how it is possible to perform an isolated mounting of transistors on radiators, I will give a simple drawing on which everything is shown in detail:

Rice. 8. Isolated fastening of transistors KT825 and KT827 to radiators.

Printed circuit board

Now let's talk about the printed circuit board. It will not be difficult to separate it, since the circuit is almost completely symmetrical for each channel. It is necessary to try to move the input and output circuits as far as possible from each other - this will prevent self-excitation, a lot of interference, and save you from unnecessary problems.

Fiberglass can be taken with a thickness of 1 to 2 millimeters, in principle, the board does not need special strength. After etching, the tracks need to be well tinned with solder with rosin (or flux), do not ignore this step - this is very important!

I did the layout of the tracks for the printed circuit board manually, on a sheet of paper in a box using a simple pencil. I have been doing this since the days when SprintLayout and LUT technology could only be dreamed of. Here is a scanned stencil of a PCB design for ULF:

Rice. 9. The circuit board of the amplifier and the location of the components on it (click - open in full size).

Capacitors C21, C3, C20, C4 are not on the hand-drawn board, they are needed to filter the voltage by supply, I installed them in the power supply itself.

UPD: Thanks Alexander for PCB layout in Sprint Layout!

Rice. 10. Printed circuit board for UMZCH on the TDA7250 chip.

In one of my articles, I told how to make this printed circuit board using the LUT method.

Download printed circuit board from Alexander in *.lay(Sprint Layout) format - (71 KB).

UPD. I give here other printed circuit boards mentioned in the comments to the publication:

As for the connecting wires for power supply and at the output of the UMZCH circuit, they should be as short as possible and with a cross section of at least 1.5 mm. In this case, the shorter the length and the greater the thickness of the conductors, the less current losses and interference in the power amplification circuit.

The result is 4 amplification channels on two small scarves:

Rice. 11. Photo of finished UMZCH boards for four power amplification channels.

Setting up the amplifier

Correctly assembled and from serviceable parts, the circuit starts working immediately. Before connecting the structure to the power source, you need to carefully inspect the printed circuit board for short circuits, and also remove excess rosin with a piece of cotton wool soaked in solvent.

I recommend connecting speakers to the circuit when you first turn on and during experiments through resistors with a resistance of 300-400 Ohms, this will save the speakers from damage in case something goes wrong.

It is desirable to connect a volume control to the input - one dual variable resistor or two separately. Before turning on the UMZCH, we set the slider of the resistor (s) to the left extreme position, as in the diagram (minimum volume), then by connecting the signal source to the UMZCH and supplying power to the circuit, you can gradually increase the volume, observing how the assembled amplifier behaves.

Rice. 12. Schematic representation of the connection of variable resistors as volume controls for ULF.

Variable resistors can be used with any resistance from 47 KΩ to 200 KΩ. In the case of using two variable resistors, it is desirable that their resistances be the same.

So, we check the performance of the amplifier at a low volume. If everything is fine with the circuit, then the fuses along the power lines can be replaced with more powerful ones (2-3 Amperes), additional protection during operation of the UMZCH will not hurt.

The quiescent current of the output transistors can be measured by including an ammeter or multimeter in the current measurement mode (10-20A) in the collector gap of each of the transistors. Amplifier inputs must be connected to common ground (complete absence of input signal), speaker systems should be connected to amplifier outputs.

Rice. 13. Ammeter switching circuit for measuring the quiescent current of the output transistors of the sound power amplifier.

The quiescent current of transistors in my UMZCH using KT825 + KT827 is approximately 100mA (0.1A).

Power fuses can also be replaced with powerful incandescent lamps. If any of the channels of the amplifier behaves inappropriately (hum, noise, overheating of transistors), then it is possible that the problem lies in the long conductors going to the transistors, try reducing the length of these conductors.

In conclusion

That's all for now, in the following articles I'll tell you how to make a power supply for an amplifier, output power indicators, protection circuits for speakers, about the case and the front panel...