Powerful amplifier on a chip. Low frequency amplifier (LF) on the TDA7250 chip
Making a good power amplifier has always been one of the difficult stages when designing audio equipment. Sound quality, softness of bass and clear sound of mid and high frequencies, detail of musical instruments - all these are empty words without a high-quality low-frequency power amplifier.
Preface
Of the variety of homemade low-frequency amplifiers on transistors and integrated circuits that I made, the circuit on the driver chip performed best of all. TDA7250 + KT825, KT827.
In this article I will tell 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 was selected for the Phoenix-P400 amplifier:
- Power approximately 100W per channel at 4 Ohm load;
- Power supply: bipolar 2 x 35V (up to 40V);
- Low input impedance;
- Small dimensions;
- High reliability;
- Speed of production;
- High sound quality;
- Low noise level;
- Low cost.
This is not a simple combination of requirements. First I tried the option based on the TDA7293 chip, but it turned out that this was not what I needed, and here’s why...
Over all this time, I had the opportunity to assemble and test different ULF circuits - transistor ones from books and publications of Radio magazine, on various microcircuits...
I would like to say my word about the TDA7293 / TDA7294, because a lot has been written about it on the Internet, and more than once I have seen that the opinion of one person contradicts the opinion of another. Having assembled several clones of an amplifier using these microcircuits, I made some conclusions for myself.
The microcircuits are really quite good, although a lot depends on the successful layout of the printed circuit board (especially the ground lines), good nutrition and quality of strapping elements.
What immediately pleased me about it was the fairly large power delivered to the load. As for a single-chip integrated amplifier, the low-frequency output power is very good, I also want to note the very low level noise in no signal mode. It is important to take care of good active cooling of the microcircuit, since the chip operates in “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 were left working! I burned one out 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 I turned it on again for the 3rd time, although before that it worked normally and no anomalies were observed... Maybe I was just unlucky.
And now, the main reason why I did not want to use modules based on TDA7293 in my project is the “metallic” sound that is noticeable to my ears, there is no softness and richness in it, the mid frequencies are a little dull.
I concluded that this chip is perfect for subwoofers or low-frequency amplifiers that will drone in the trunk of a car or at discos!
I will not touch on the topic of single-chip power amplifiers further; we need something more reliable and of high quality so that it is not so expensive in terms of experiments and errors. Assembling 4 channels of an amplifier using transistors is a good option, but rather cumbersome in execution, and it can also be difficult to set up.
So what should you use to assemble if not transistors or integrated circuits? - on both, skillfully combining them! We will assemble a power amplifier using a TDA7250 driver chip with powerful composite Darlington transistors at the output.
LF power amplifier circuit based on TDA7250 chip
Chip TDA7250 in a DIP-20 package 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 or even exceed 100 W 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 produced by this microcircuit “came to life” in combination with transistors KT825, KT827. Very small details began to be heard in the compositions, the instruments sounded rich and “light”.
You can burn this chip in several ways:
- Reversing the polarity of power lines;
- Exceeding the maximum permissible supply voltage ±45V;
- Input overload;
- High static voltage.
Rice. 1. TDA7250 microcircuit in a DIP-20 package, appearance.
Datasheet for the TDA7250 chip - (135 KB).
Just in case, I purchased 4 microcircuits at once, each of which has 2 amplification channels. The microcircuits were purchased from an online store at a price of approximately $2 per piece. At the market they wanted more than $5 for such a chip!
The scheme according to which my version was assembled does not differ much from the one shown in the datasheet:
Rice. 2. Circuit of a stereo low-frequency amplifier based on the TDA7250 microcircuit and transistors KT825, KT827.
For this UMZCH circuit, a homemade bipolar power supply of +/- 36V was assembled, with capacitances of 20,000 μF in each arm (+Vs and -Vs).
Power Amplifier Parts
I’ll tell you more about the features of the amplifier parts. List of radio components for circuit assembly:
| Name | Quantity, pcs | Note |
| TDA7250 | 1 | |
| KT825 | 2 | |
| KT827 | 2 | |
| 1.5 kOhm | 2 | |
| 390 Ohm | 4 | |
| 33 Ohm | 4 | power 0.5W |
| 0.15 ohm | 4 | power 5W |
| 22 kOhm | 3 | |
| 560 Ohm | 2 | |
| 100 kOhm | 3 | |
| 12 ohm | 2 | power 1W |
| 10 ohm | 2 | power 0.5W |
| 2.7 kOhm | 2 | |
| 100 Ohm | 1 | |
| 10 kOhm | 1 | |
| 100 µF | 4 | electrolytic |
| 2.2 µF | 2 | mica or film |
| 2.2 µF | 1 | electrolytic |
| 2.2 nF | 2 | |
| 1 µF | 2 | mica or film |
| 22 µF | 2 | electrolytic |
| 100 pF | 2 | |
| 100 nF | 2 | |
| 150 pF | 8 | |
| 4.7 µF | 2 | electrolytic |
| 0.1 µF | 2 | mica or film |
| 30 pf | 2 |
The inductor coils 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 coils 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 remaining electrolytes - for a voltage of 25V or more. 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 were used.
Resistances R20-R23, as well as R.L. can be installed with a power of 0.5W. Resistors Rx - power of at least 1W. All other resistances in the circuit can be set to a power of 0.25W.
It is better to select pairs of transistors KT827 + KT825 with the closest parameters, for example:
- KT827A(Uke=100V, h21E>750, Pk=125W) + KT825G(Uke=70V, h21E>750, Pk=125W);
- KT827B(Uke=80V, h21E>750, Pk=125W) + KT825B(Uke=60V, h21E>750, Pk=160W);
- KT827V(Uke=60V, h21E>750, Pk=125W) + KT825B(Uke=60V, h21E>750, Pk=160W);
- KT827V(Uke=60V, h21E>750, Pk=125W) + KT825G(Uke=70V, h21E>750, Pk=125W).
Depending on the letter at the end of the marking for KT827 transistors, only the voltages Uke and Ube change, 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 a high gain contain two transistors, a couple of resistances and a diode inside, so a regular test 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. Transistor testing circuit P-N-P structures and N-P-N for operability in key mode.
In each of the circuits, when the button is pressed, the LED should light up. Power can be taken from +5V to +12V.
Rice. 5. An example of testing the performance of the KT825 transistor, P-N-P structure.
Each pair of output transistors must be installed on radiators, since already at an average ULF output power their heating will be quite noticeable.
The datasheet for the TDA7250 chip shows the recommended pairs of transistors and the power that can be extracted using them in this amplifier:
| At 4 ohm load | ||||
| ULF power | 30 W | +50 W | +90 W | +130 W |
| Transistors | BDW93, BDW94A |
BDW93, BDW94B |
BDV64, BDV65B |
MJ11013, MJ11014 |
| Housings | TO-220 | TO-220 | SOT-93 | TO-204 (TO-3) |
| At 8 ohm load | ||||
| ULF power | 15 W | +30 W | +50 W | +70 W |
| Transistors | BDX53 BDX54A |
BDX53 BDX54B |
BDW93, BDW94B |
TIP142, TIP147 |
| Housings | TO-220 | TO-220 | TO-220 | TO-247 |
Mounting transistors KT825, KT827 (TO-3 housing)
Particular attention should be paid to the installation of output transistors. A collector is connected to the housing of transistors KT827, KT825, so if the housings of two transistors in one channel are accidentally or intentionally shorted, you will get a short circuit in the power supply!
Rice. 6. Transistors KT827 and KT825 are prepared for installation on radiators.
If the transistors are planned to be mounted on one common radiator, then their cases must be insulated from the radiator through mica gaskets, having previously coated them on both sides with thermal paste 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 to install isolated transistors on radiators, I will give a simple drawing that shows everything in detail:
Rice. 8. Insulated mounting of transistors KT825 and KT827 on radiators.
Printed circuit board
Now I'll tell you about the printed circuit board. It will not be difficult to separate it, since the circuit is almost completely symmetrical for each channel. You need to try to distance the input and output circuits from each other as much as possible - this will prevent self-excitation, a lot of interference, and protect 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, you need to tin them well with solder and rosin (or flux), do not ignore this step - it is very important!
I laid out the tracks for the printed circuit board manually, on a sheet of checkered paper using a simple pencil. This is what I have been doing since the times when one could only dream about SprintLayout and LUT technology. Here is a scanned stencil of the printed circuit board design for the ULF:
Rice. 9. Printed circuit board of the amplifier and the location of the components on it (click to open full size).
Capacitors C21, C3, C20, C4 are not on the hand-drawn board, they are needed to filter the power supply voltage, I installed them in the power supply itself.
UPD: Thank you Alexandru 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 the printed circuit board from Alexander in *.lay(Sprint Layout) format - (71 KB).
UPD. Here are 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 greater the thickness of the conductors, the less current loss and interference in the power amplification circuit.
The result was 4 amplification channels on two small scarves:
Rice. 11. Photo ready-made boards UMZCH for four channels of power amplification.
Setting up the amplifier
A correctly assembled circuit made from serviceable parts begins to work immediately. Before connecting the structure to the power source, you need to carefully inspect the printed circuit board for any short circuits, and also remove excess rosin using a piece of cotton wool soaked in a solvent.
I recommend connecting speaker systems to the circuit when you first turn it on and during experiments using resistors with a resistance of 300-400 Ohms; this will save the speakers from damage if something goes wrong.
It is advisable to connect a volume control to the input - one dual variable resistor or two separately. Before turning on the UMZCH, we put the switch of the resistor(s) in the left extreme position, as in the diagram (minimum volume), then by connecting the signal source to the UMZCH and applying power to the circuit, you can smoothly increase the volume, observing how the assembled amplifier behaves.
Rice. 12. Schematic representation of connecting variable resistors as volume controls for ULF.
Variable resistors can be used with any resistance from 47 KOhm to 200 KOhm. When using two variable resistors, it is desirable that their resistances be the same.
So, let's check the performance of the amplifier at low volume. If everything is fine with the circuit, then the fuses on 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 connecting an ammeter or multimeter in current measurement mode (10-20A) to the collector gap of each transistor. The amplifier inputs must be connected to common ground (complete absence of input signal), and speakers must be connected to the amplifier outputs.
Rice. 13. Circuit diagram for connecting an ammeter to measure the quiescent current of the output transistors of an audio power amplifier.
The quiescent current of the transistors in my UMZCH using KT825+KT827 is approximately 100mA (0.1A).
Power fuses can also be replaced with powerful incandescent lamps. If one of the amplifier channels 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 speaker systems, about the case and front panel...
The TDA7294 microcircuit is an integrated low-frequency amplifier, which is very popular among electronics engineers, both beginners and professionals. The network is full of different reviews about this chip. I decided to build an amplifier on it. I took the diagram from the datasheet.
This “micruha” feeds on a bipolar diet. For beginners, I will explain that it is not enough to have a “plus” and a “minus”.
You need a source with a positive terminal, a negative terminal and a common one. For example, relative to the common wire there should be plus 30 Volts, and in the other arm minus 30 Volts.
The amplifier on the TDA7294 is quite powerful. The maximum rated power is 100 W, but this is with nonlinear distortion of 10% and at maximum voltage (depending on load resistance). You can reliably shoot at 70W. Thus, on my birthday, I listened to two parallel-connected “Radio Engineering S30” speakers on one TDA 7294 channel. The entire evening and half of the night, the speakers sounded, sometimes putting them into overload. But the amplifier withstood it calmly, although it sometimes overheated (due to poor cooling).
Main characteristicsTDA7294
Supply voltage +-10V…+-40V
Peak output current up to 10A
Operating temperature of the crystal up to 150 degrees Celsius
Output power at d=0.5%:
At +-35V and R=8Ohm 70W
At +-31V and R=6Ohm 70W
At +-27V and R=4Ohm 70W
With d=10% and increased voltage (see), you can achieve 100W, but it will be a dirty 100W.
Amplifier circuit for TDA7294
The diagram shown is taken from the passport, all denominations are preserved. With proper installation and correctly selected element values, the amplifier starts the first time and does not require any settings.
Amplifier elements
The values of all elements are indicated in the diagram. Resistor power 0.25 W.
The “microphone” itself should be installed on the radiator. If the radiator is in contact with other metal elements of the case, or the case itself is the radiator, then it is necessary to install a dielectric gasket between the radiator and the TDA7294 case.
The gasket can be silicone or mica.
The radiator area should be at least 500 sq.cm, the larger the better.
Initially, I assembled two channels of the amplifier, since the power supply allowed, but I did not choose the right housing and both channels simply did not fit into the housing in terms of dimensions. I tried to make the PCB smaller, but it didn't work.
After fully assembling the amplifier, I realized that the case was not enough to cool one channel of the amplifier. My case was a radiator. In short, I rolled out the lip into two channels.
When listening to my device at full volume, the crystal began to overheat, but I lowered the volume level and continued testing. As a result, I listened to music at a moderate volume until midnight, periodically causing the amplifier to overheat. The TDA7294 amplifier turned out to be very reliable.
ModeSTAND- BY TDA7294
If 3.5V or more is applied to the 9th leg, the microcircuit exits sleep mode; if less than 1.5V is applied, it will enter sleep mode.
In order to wake the device from sleep mode, you need to connect the 9th leg through a 22 kOhm resistor to the positive terminal (bipolar power source).
And if the 9th leg is connected through the same resistor to the GND terminal (bipolar power source), then the device will enter sleep mode.
The printed circuit board located under the article is routed so that leg 9 is connected via a 22 kOhm resistor to the positive terminal of the power supply. Consequently, when the power source is turned on, the amplifier immediately begins to operate in sleep mode.
ModeMUTE TDA7294
If 3.5V or more is applied to the 10th leg of the TDA7294, the device will exit the muting mode. If you apply less than 1.5V, the device will enter muting mode.
In practice, this is done like this: through a 10 kOhm resistor, connect the 10 leg of the microcircuit to the plus of a bipolar power source. The amplifier will “sing”, that is, it will not be muted. On the printed circuit board attached to the article, this is done using a track. When power is applied to the amplifier, it immediately begins to sing, without any jumpers or toggle switches.
If we connect the TDA7294 leg through a 10 kOhm resistor 10 to the GND pin of the power supply, then our “amplifier” will enter mute mode.
Power supply.
The voltage source for the device was an assembled one, which showed itself very well. When listening to one channel, the keys are warm. Schottky diodes are also warm, although there are no radiators installed on them. IIP without protection and soft start.
The circuit of this SMPS is criticized by many, but it is very easy to assemble. It works reliably without soft start. This circuit is very suitable for novice electronics engineers because of its prostate.
Frame.
The case was purchased.
Amplifiers whose main purpose is to amplify the signal by power are called power amplifiers. As a rule, such amplifiers drive a low-impedance load, such as a loudspeaker.
3-18 V (nominal - 6 V). The maximum current consumption is 1.5 A with a quiescent current of 7 mA (at 6 V) and 12 mA (at 18 V). Voltage gain 36.5 dB. at -1 dB 20 Hz - 300 kHz. Rated output power at 10% THD
temporarily turn off the sound. You can double the output power of the TDA7233D when you turn them on according to the circuit shown in Fig. 31.42. C7 prevents self-excitation of the device in the area
high frequencies. R3 is selected until an equal amplitude of the output signals is obtained at the outputs of the microcircuits.
Rice. 31.43. KR174UNZ 7
KR174UN31 is intended for use as output low-power household electronic devices.
When the supply voltage changes from
2.1 to 6.6 V with an average current consumption of 7 mA (without input signal), the voltage gain of the microcircuit varies from 18 to 24 dB.
The coefficient of nonlinear distortion at an output power of up to 100 mW is no more than 0.015%, the output noise voltage does not exceed 100 μV. The input of the microcircuit is 35-50 kOhm. load - not lower than 8 ohms. Operating frequency range - 20 Hz - 30 kHz, limit - 10 Hz - 100 kHz. The maximum input signal voltage is up to 0.25-0.5 V.
In this article I will tell you about such a chip as TDA1514A
Introduction
Let me start with something sad... At the moment, production of the microcircuit has been discontinued... But this does not mean that it is now “worth its weight in gold”, no. You can get it in almost any radio store or radio market for 100 - 500 rubles. Agree, a little expensive, but the price is absolutely fair! By the way, on global Internet sites such as these they are much cheaper...
The microcircuit is characterized by a low level of distortion and a wide range of reproduced frequencies, so it is better to use it on full-range speakers. People who have assembled amplifiers on this chip praise it for high quality sound. This is one of the few microcircuits that truly “sounds well.” The sound quality is in no way inferior to the currently popular TDA7293/94. However, if errors are made in the assembly, high-quality work is not guaranteed.
Brief description and advantages
This chip is a single-channel Hi-Fi amplifier of class AB, the power of which is 50W. The chip has built-in SOAR protection, thermal protection (overheating protection) and a "Mute" mode.
The advantages include the absence of clicks when turning on and off, the presence of protection, low harmonic and intermodulation distortion, low thermal resistance, and more. There is practically nothing to highlight among the shortcomings, except failure when the voltage “runs” (the power supply must be more or less stable) and the relatively high price
Briefly about appearance
The chip is available in a SIP package with 9 long legs. The pitch of the legs is 2.54mm. On the front side there are inscriptions and a logo, and on the back there is a heat sink - it is connected to the 4th leg, and the 4th leg is the “-” power supply. There are 2 eyelets on the sides for attaching the radiator.
The original or a fake?
Many people ask this question, I will try to answer you.
So. The microcircuit must be carefully made, the legs must be smooth, minor deformation is allowed, since it is unknown how they were handled in a warehouse or store
The inscription... It can be made either with white paint or with a regular laser, the two chips above are for comparison (both are original). If the inscription is painted, there should ALWAYS be a vertical stripe on the chip, separated by an eyelet. Don't be confused by the "TAIWAN" inscription - it's okay, the sound quality of such copies is no worse than those without this inscription. By the way, almost half of the radio components are made in Taiwan and neighboring countries. This inscription is not found on all microcircuits.
I also advise you to pay attention to the second line. If it contains only numbers (there should be 5 of them) - these are “old” production microcircuits. The inscription on them is wider, and the heat sink may also have a different shape. If the inscription on the microcircuit is applied with a laser and the second line contains only 5 digits, there should be a vertical stripe on the microcircuit
The logo on the microcircuit must be present and only “PHILIPS”! As far as I know, production ceased long before NXP was founded, and this is 2006. If you come across this microcircuit with the NXP logo, there is one of two things - they started producing the microcircuit again or it is a typical “leftist”
It is also necessary to have depressions in the shape of circles, as in the photo. If they are not there, it is a fake.
Perhaps there are still ways to identify the “leftist”, but you shouldn’t stress over this issue so much. There are only a few cases of marriage.
Technical characteristics of the microcircuit
* Input impedance and gain are adjusted by external elements
Below is a table of approximate output powers depending on power supply and load resistance
| Supply voltage | Load resistance | ||
| 4 ohm | 8 ohm | ||
| 10W | 6W | ||
| +-16.5V |
28W |
12W | |
| 48W | 28W | ||
| 58W | 32W | ||
| 69W | 40W | ||
Schematic diagram
The diagram is taken from the datasheet (May 1992)
It's too bulky... I had to redraw it:
The circuit differs slightly from that provided by the manufacturer, all the characteristics given above are exactly for THIS circuit. There are several differences and they are all aimed at improving the sound - first of all, filter capacitors were installed, the “voltage boost” was removed (more on that a little later) and the value of resistor R6 was changed.
Now in more detail about each component. C1 is the input coupling capacitor. It passes through only the alternating voltage signal. It also affects the frequency response - the smaller the capacitance, the smaller the bass and, accordingly, the larger the capacitance, the greater the bass. I would not recommend setting it to more than 4.7 µF, since the manufacturer has provided for everything - with the capacitance of this capacitor equal to 1 µF, the amplifier reproduces the declared frequencies. Use a film capacitor, at least an electrolytic one (non-polar is desirable), but not a ceramic one! R1 reduces the input resistance, and together with C2 forms a filter against input noise.
As with any operational amplifier, the gain can be set here. This is done using R2 and R7. At these ratings, the gain is 30 dB (may deviate slightly). C4 affects the activation of SOAR and Mute protection, R5 affects the smooth charging and discharging of the capacitor, and therefore there are no clicks when the amplifier is turned on and off. C5 and R6 form the so-called Zobel chain. Its task is to prevent the amplifier from self-excitation, as well as to stabilize the frequency response. C6-C10 suppress power supply ripples and protect against voltage sags.
The resistors in this circuit can be taken with any power, for example I use the standard 0.25W. Capacitors for a voltage of at least 35V, except for C10 - I use 100V in my circuit, although 63V should be enough. All components must be checked for serviceability before soldering!
Amplifier circuit with "voltage boost"
This option The diagrams are taken from the datasheet. It differs from the above-described scheme in the presence of elements C3, R3 and R4.
This option will allow you to get up to 4W more than stated (at ±23V). But with this inclusion, distortion may increase slightly. Resistors R3 and R4 should be used at 0.25W. I couldn’t handle it at 0.125W. Capacitor C3 - 35V and above.
This circuit requires the use of two microcircuits. One gives a positive signal at the output, the other a negative one. With this connection, you can remove more than 100W into 8 ohms.
According to those gathered, this scheme absolutely functional and I even have a more detailed plate of approximate output powers. It's below:
And if you experiment, for example, at ±23V you connect a 4 ohm load, you can get up to 200W! Provided that the radiators do not heat up too much, the 150W microcircuit will be easily pulled into the bridge.
This design is good to use in subwoofers.
Operation with external output transistors
The microcircuit is essentially a powerful operational amplifier and it can be further powered by adding a pair of complementary transistors to the output. This option has not yet been tested, but it is theoretically possible. You can also power up the bridge circuit of the amplifier by attaching a pair of complementary transistors to the output of each microcircuit
Operation with unipolar power supply
At the very beginning of the datasheet, I found lines that say that the microcircuit also works with single-supply power. Where is the diagram then? Alas, it’s not in the datasheet, I couldn’t find it on the Internet... I don’t know, maybe such a circuit exists somewhere, but I haven’t seen one... The only thing I can recommend is TDA1512 or TDA1520. The sound is excellent, but they are powered from a single-polar supply, and the output capacitor can slightly spoil the picture. Finding them is quite problematic; they were produced a very long time ago and were discontinued a long time ago. The inscriptions on them can be of various shapes; there is no need to check them for “fake” - there have been no cases of refusal.
Both microcircuits are Hi-Fi amplifiers of class AB. Power is about 20W at +33V into a 4 ohm load. I won’t give the diagrams (the topic is still about the TDA1514A). You can download printed circuit boards for them at the end of the article.
Nutrition
For stable operation of the microcircuit, you need a power source with a voltage from ±8 to ±30V with a current of at least 1.5A. Power must be supplied with thick wires, the input wires should be kept as far away from the output wires and the power source as possible.
You can power it with an ordinary simple power supply, which includes a mains transformer, a diode bridge, filter tanks and, if desired, chokes. To obtain ±24V, you need a transformer with two 18V secondary windings with a current of more than 1.5A for one microcircuit.
You can use switching power supplies, for example the simplest one, on IR2153. Here is his diagram:
This UPS is made using a half-bridge circuit, frequency 47 kHz (set using R4 and C4). Diodes VD3-VD6 ultrafast or Schottky
It is possible to use this amplifier in a car using a boost converter. On the same IR2153, here is the diagram:
The converter is made according to the Push-Pull scheme. Frequency 47kHz. Rectifier diodes need ultrafast or Schottky ones. Transformer calculations can also be performed in ExcellentIT. The chokes in both schemes will be “recommended” by ExcellentIT itself. You need to count them in the Drossel program. The author of the program is the same -
I would like to say a few words about the IR2153 - the power supplies and converters are quite good, but the microcircuit does not provide for stabilization of the output voltage and therefore it will change depending on the supply voltage, and it will also sag.
It is not necessary to use IR2153 or switching power supplies in general. You can do it simpler - like in the old days, a regular transformer with a diode bridge and huge power supply capacities. This is what its diagram looks like:
C1 and C4 at least 4700 µF, for a voltage of at least 35V. C2 and C3 - ceramics or film.
Printed circuit boards
Now I have the following collection of boards:
a) the main one - it can be seen in the photo below.
b) slightly modified first (main). All tracks have been increased in width, the power ones are much wider, the elements have been slightly moved.
c) bridge circuit. The board is not very well drawn, but it is functional
d) the first version of the PP is the first trial version, there is not enough Zobel chain, but I assembled it this way and it works. There is even a photo (below)
d) printed circuit board fromXandR_man - found it on the forum of the Soldering Iron site. What can I say... Strictly a diagram from the datasheet. Moreover, I saw with my own eyes sets based on this signet!
In addition, you can draw the board yourself if you are not satisfied with the ones provided.
Soldering
After you have made the board and checked all the parts for serviceability, you can start soldering.
Tin the entire board, and tin the power traces with as thick a layer of solder as possible
All jumpers are soldered in first (their thickness should be as large as possible in the power sections), and then all components increase in size. The microcircuit is soldered last. I advise you not to cut the legs, but solder them as they are. You can then bend it to make it easier to fit on the radiator.
The microcircuit is protected from static electricity, so you can solder with the soldering iron turned on, even while sitting in woolen clothes.
However, it is necessary to solder so that the chip does not overheat. For reliability, you can attach it to the radiator by one eye during soldering. You can do it in two, there won’t be any difference, as long as the crystal inside doesn’t overheat.
Setup and first launch
After all the elements and wires are soldered, a “test run” is necessary. Screw the microcircuit onto the radiator and connect the input wire to ground. You can connect future speakers as a load, but in general, to prevent them from “flying out” in a split second due to defects or installation errors, use a powerful resistor as a load. If it crashes, you know that you made a mistake, or you got a defect (the microcircuit is meant). Fortunately, such cases almost never happen, unlike TDA7293 and others, of which you can get a bunch of them from one batch in a store and, as it turns out later, they are all defective.
However, I want to make a small note. Keep your wires as short as possible. It happened that I just lengthened the output wires and began to hear a hum in the speakers, similar to a “constant”. Moreover, when the amplifier was turned on, due to the “constant” mode, the speaker produced a hum that disappeared after 1-2 seconds. Now I have wires coming out of the board, a maximum of 25 cm and going straight to the speaker - the amplifier turns on silently and works without problems! Also pay attention to the input wires - use a shielded wire; it shouldn’t be long either. Follow simple requirements and you will succeed!
If nothing happened to the resistor, turn off the power, attach the input wires to the signal source, connect your speakers and apply power. You can hear a slight hum in the speakers - this indicates that the amplifier is working! Give a signal and enjoy the sound (if everything is perfectly assembled). If it “grunts” or “farts” - look at the food, at the correctness of assembly, because, as has been discovered in practice, there are no such “nasty” specimens that, with proper assembly and excellent nutrition, worked crookedly...
What the finished amplifier looks like
Here is a series of photographs taken in December 2012. The boards are just after soldering. Then I assembled it to make sure the microcircuits were working.
But my first amplifier, only the board has survived to this day, all the parts went to other circuits, and the microcircuit itself failed due to alternating voltage coming into contact with it
Below are the latest photos:
Unfortunately, my UPS is at the manufacturing stage, and I previously powered the microcircuit from two identical batteries and a small transformer with a diode bridge and small power supply capacities, in the end it was±25V. Two such chips with four columns from music center“Sharp” played in such a way that even the objects on the tables “danced to the music”, the windows rang, and the power was felt quite well in the body. I can’t remove this now, but there is a ±16V power supply, from it you can get up to 20W at 4 ohms... Here is a video for you as proof that the amplifier is absolutely working!
Acknowledgments
I express my deep gratitude to the users of the “Soldering Iron” site forum, and specifically, a huge thank you to the user for some help, and I also thank many others (sorry for not calling you by nickname) for their honest feedback, which pushed me to build this amplifier. Without all of you, this article might not have been written.
Completion
The microcircuit has a number of advantages, first of all, excellent sound. Many microcircuits of this class may even be inferior in sound quality, but this depends on the quality of the assembly. Bad assembly - bad sound. Approach assembly electronic circuits seriously. I strongly do not recommend soldering this amplifier by surface mounting - this can only worsen the sound, or lead to self-excitation, and subsequently complete failure.
I collected almost all the information that I checked myself and could ask other people who assembled this amplifier. It's a pity that I don't have an oscilloscope - without it, my statements about sound quality mean nothing... But I will continue to say that it sounds just great! Those who collected this amplifier will understand me!
If you have any questions, write to me on the forum of the Soldering Iron site. to discuss amplifiers on this chip, you can ask there.
I hope the article was useful to you. Good luck to you! Regards, Yuri.
List of radioelements
| Designation | Type | Denomination | Quantity | Note | Shop | My notepad | |
|---|---|---|---|---|---|---|---|
| Chip | TDA1514A | 1 | To notepad | ||||
| C1 | Capacitor | 1 µF | 1 | To notepad | |||
| C2 | Capacitor | 220 pF | 1 | To notepad | |||
| C4 | 3.3uF | 1 | To notepad | ||||
| C5 | Capacitor | 22 nF | 1 | To notepad | |||
| C6, C8 | Electrolytic capacitor | 1000uF | 2 | To notepad | |||
| S7, S9 | Capacitor | 470 nF | 2 | To notepad | |||
| C10 | Electrolytic capacitor | 100uF | 1 | 100V | To notepad | ||
| R1 | Resistor | 20 kOhm | 1 | To notepad | |||
| R2 | Resistor | 680 Ohm | 1 | To notepad | |||
| R5 | Resistor | 470 kOhm | 1 | To notepad | |||
| R6 | Resistor | 10 ohm | 1 | Selected during setup | To notepad | ||
| R7 | Resistor | 22 kOhm | 1 | To notepad | |||
| Circuit with voltage boost | |||||||
| Chip | TDA1514A | 1 | To notepad | ||||
| C1 | Capacitor | 1 µF | 1 | To notepad | |||
| C2 | Capacitor | 220 pF | 1 | To notepad | |||
| C3 | Electrolytic capacitor | 220uF | 1 | From 35V and above | To notepad | ||
| C4 | Electrolytic capacitor | 3.3uF | 1 | To notepad | |||
| C5 | Capacitor | 22 nF | 1 | To notepad | |||
| C6, C8 | Electrolytic capacitor | 1000uF | 2 | To notepad | |||
| S7, S9 | Capacitor | 470 nF | 2 | To notepad | |||
| C10 | Electrolytic capacitor | 100uF | 1 | 100V | To notepad | ||
| R1 | Resistor | 20 kOhm | 1 | To notepad | |||
| R2 | Resistor | 680 Ohm | 1 | To notepad | |||
| R3 | Resistor | 47 Ohm | 1 | Selected during setup | To notepad | ||
| R4 | Resistor | 82 Ohm | 1 | Selected during setup | To notepad | ||
| R5 | Resistor | 470 kOhm | 1 | To notepad | |||
| R6 | Resistor | 10 ohm | 1 | Selected during setup | To notepad | ||
| R7 | Resistor | 22 kOhm | 1 | To notepad | |||
| Bridge connection | |||||||
| Chip | TDA1514A | 2 | To notepad | ||||
| C1 | Capacitor | 1 µF | 1 | To notepad | |||
| C2 | Capacitor | 220 pF | 1 | To notepad | |||
| C4 | Electrolytic capacitor | 3.3uF | 1 | To notepad | |||
| C5, C14, C16 | Capacitor | 22 nF | 3 | To notepad | |||
| C6, C8 | Electrolytic capacitor | 1000uF | 2 | To notepad | |||
| S7, S9 | Capacitor | 470 nF | 2 | To notepad | |||
| C13, C15 | Electrolytic capacitor | 3.3uF | 2 | To notepad | |||
| R1, R7 | Resistor | 20 kOhm | 2 | To notepad | |||
| R2, R8 | Resistor | 680 Ohm | 2 | To notepad | |||
| R5, R9 | Resistor | 470 kOhm | 2 | To notepad | |||
| R6, R10 | Resistor | 10 ohm | 2 | Selected during setup | To notepad | ||
| R11 | Resistor | 1.3 kOhm | 1 | To notepad | |||
| R12, R13 | Resistor | 22 kOhm | 2 | To notepad | |||
| Impulse power block | |||||||
| IC1 | Power Driver and MOSFET | IR2153 | 1 | To notepad | |||
| VT1, VT2 | MOSFET transistor | IRF740 | 2 | To notepad | |||
| VD1, VD2 | Rectifier diode | SF18 | 2 | To notepad | |||
| VD3-VD6 | Diode | Any Schottky | 4 | Ultrafast diodes or Schottky | To notepad | ||
| VDS1 | Diode bridge | 1 | Diode bridge for the required current | To notepad | |||
| C1, C2 | Electrolytic capacitor | 680uF | 2 | 200V | To notepad | ||
| C3 | Capacitor | 10 nF | 1 | 400V | To notepad | ||
| C4 | Capacitor | 1000 pF | 1 | To notepad | |||
| C5 | Electrolytic capacitor | 100uF | 1 | To notepad | |||
| C6 | Capacitor | 470 nF | 1 | To notepad | |||
| C7 | Capacitor | 1 nF | 1 | ||||
Quite simple, even a person who is not very strong in electrical engineering can repeat it. The ULF on this chip will be ideal for use as part of an acoustic system for home computer, TV, cinema. Its advantage is that it does not require fine adjustment and tuning, as is the case with transistor amplifiers. And what can we say about the difference from lamp designs - the dimensions are much smaller.
No high voltage is required to power the anode circuits. Of course, there is heating, as in lamp designs. Therefore, if you plan to use the amplifier for a long time, it is best to install, in addition to an aluminum radiator, at least a small fan for forced airflow. Without it, the amplifier circuit on the TDA7294 microassembly will work, but there is a high probability of it going into temperature protection.
Why TDA7294?
This chip has been very popular for more than 20 years. It has won the trust of radio amateurs, since it has very high characteristics, the amplifiers based on it are simple, and anyone, even a novice radio amateur, can repeat the design. The amplifier on the TDA7294 chip (the circuit is shown in the article) can be either monophonic or stereophonic. The internal structure of the microcircuit consists of an Amplifier audio frequency, built on this chip, belongs to class AB.
Advantages of the microcircuit
Advantages of using a microcircuit for:
1. Very high power output. About 70 W if the load has a resistance of 4 ohms. In this case, the usual circuit for connecting the microcircuit is used.
2. About 120 W at 8 ohms (bridged).
3. Very low level of extraneous noise, distortion is insignificant, reproduced frequencies lie in the range that is completely perceivable by the human ear - from 20 Hz to 20 kHz.
4. The microcircuit can be powered from a DC voltage source of 10-40 V. But there is a small drawback - it is necessary to use a bipolar power source.
It is worth paying attention to one feature - the distortion coefficient does not exceed 1%. On the TDA7294 microassembly, the power amplifier circuit is so simple that it’s even surprising how it allows you to get such high-quality sound.
Purpose of the microcircuit pins
And now in more detail about what conclusions the TDA7294 has. The first leg is the “signal ground”, connected to the common wire of the entire structure. Pins “2” and “3” are inverting and non-inverting inputs, respectively. The "4" pin is also the "signal ground" connected to the common wire. The fifth leg is not used in audio amplifiers. “6” leg is a volt add-on; an electrolytic capacitor is connected to it. “7” and “8” pins are plus and minus power supply for the input stages, respectively. Leg “9” – standby mode, used in the control unit.
Similarly: “10” leg - muting mode, also used when designing an amplifier. “11” and “12” pins are not used in the design of audio amplifiers. The output signal is taken from the “14” pin and supplied to the speaker system. “13” and “15” pins of the microcircuit are “+” and “-” for connecting the power to the output stage. On the TDA7294 chip, the circuit is no different from those proposed in the article, it is supplemented only by the circuit that is connected to the input.
Features of microassembly
When designing an audio amplifier, you need to pay attention to one feature - the minus power supply, and these are the legs “15” and “8”, electrically connected to the microcircuit body. Therefore, it is necessary to isolate it from the radiator, which will be used in the amplifier in any case. For this purpose it is necessary to use a special thermal pad. If you are using a bridge amplifier circuit on the TDA7294, pay attention to the housing design. It can be vertical or horizontal type. The most common version is designated TDA7294V.
Protective functions of the TDA7294 chip
The microcircuit provides several types of protection, in particular, against supply voltage drop. If the supply voltage suddenly changes, the microcircuit will go into protection mode, therefore, there will be no electrical damage. The output stage also has overload protection and short circuit. If the device body heats up to a temperature of 145 degrees, the sound turns off. When 150 degrees is reached, it switches to standby mode. All pins of the TDA7294 chip are protected from electrostatics.
Amplifier
Simple, accessible to everyone, and most importantly - cheap. In just a few hours you can assemble a very good audio amplifier. Moreover, you will spend most of the time etching the board. The structure of the entire amplifier consists of power and control units, as well as 2 ULF channels. Try to use as few wires as possible in the amplifier design. Follow simple recommendations:
1. A prerequisite is to connect the power source with wires to each ultrasonic circuit board.
2. Tie the power wires into a bundle. With this you can slightly compensate for the magnetic field that is created electric shock. To do this, you need to take all three power wires - “common”, “minus” and “plus”, and with a little tension weave them into one braid.
3. Under no circumstances use so-called “earth loops” in the design. This is the case when the common wire connecting all the blocks of the structure is closed into a loop. The ground wire must be connected in series, starting from the input terminals further to the ultrasonic circuit board, and ending at the output connectors. It is extremely important to connect the input circuits using shielded and insulated wires.
Control unit for standby and mute modes
This chip also has muting. Functions must be controlled using pins “9” and “10”. The mode is turned on if there is no voltage on these legs of the microcircuit, or it is less than one and a half volts. To enable the mode, it is necessary to apply a voltage to the legs of the microcircuit, the value of which exceeds 3.5 V. In order for the amplifier boards to be controlled simultaneously, which is important for bridge-type circuits, one control unit is assembled for all stages.
When the amplifier is turned on, all the capacitors in the power supply are charged. There is also one capacitor in the control unit that stores charge. When the maximum possible charge is accumulated, the standby mode is turned off. The second capacitor used in the control unit is responsible for the operation of the muting mode. It charges a little later, so the mute mode turns off second.
