Low frequency amplifiers on microcircuits etc. Subwoofer amplifier based on TDA7294 (bridge circuit)

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. Maximum nameplate power 100 W, but this is with non-linear 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 overdrive. 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

At 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 didn’t 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 smooth start. This circuit is very suitable for novice electronics engineers because of its prostate.

Frame.

The case was purchased.

I was one of the first to assemble an amplifier based on the TDA7294 according to the circuit proposed by the manufacturer.

At the same time, I was not very happy with the quality of sound reproduction, especially in the high frequencies. On the Internet, my attention was drawn to the LINCOR article posted on the website datagor.ru. The author's rave reviews about the sound of the UMZCH on the TDA7294, assembled using a voltage-controlled current source (VCS) circuit, intrigued me. As a result, I assembled the UMZCH according to the following scheme.

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

Amplifier characteristics when operating at a 4 Ohm load:

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

– Supply voltage (V) – ±30;

– Nominal input voltage (V) – 0.6;

– Nominal output power (W) – 73;

– Input resistance (kOhm) – 9.4;

– THD at 60W, no more (%) – 0.01.

A 12V parametric stabilizer is installed on the printed circuit board to power service circuits 9 and 10 of the TDA7294, shown in the figure.

In the “Play!” position, the amplifier is in an unlocked state and is ready for use every second. In the “Mute” position, the input and output stages of the microcircuit are blocked, and its consumption is reduced to the minimum standby currents. The capacitances of C11 and C12 are doubled compared to standard ones to provide greater turn-on delay and prevent clicking in the speakers even when charging the power supply capacitors for a long time.

Amplifier parts

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

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

Both output terminals of the amplifier are “hot”, neither of them is grounded, because The acoustic system is also a feedback link. The speaker turns on between and .

Below is a board layout with views from the elements and conductors, created using the Sprint-Layout_6.0 program.

Probably any radio amateur is familiar with the microcircuit: simple circuit, good quality sound, low price. I recently decided to take a different perspective when I once again came across an article about the "MF-1" amplifier from Lincor.

This is my first article, it is intended for beginner lovers of good sound. Also presented is a drawing of the PCB and a manufacturing option for the amplifier housing.

My acquaintance did not go very smoothly. At that time there were a lot of fakes. They sometimes burned immediately when the power was first applied, and if they started up, they produced not a sound, but something vaguely reminiscent of it, which made me want to pour gasoline on the board and set it on fire, get rid of this ULF and never think about it. Maybe the reason for this was also my inexperience, or maybe the topology of the board I made myself, measuring 35x45 mm (when I remember that board, the author gets big goose bumps all over his body).

After reading, the decision was made to build according to the following criteria:
1) a clean terminal without a volume control (the amplifier works in conjunction with a PC, and the sound is regulated from it),
2) 2 amplification channels according to the double mono scheme (there were 2 transformers from UM Vega,
3) lower coefficient. interpenetration of channels and beautiful stereo),
4) forced cooling using 2 computer coolers and fans at low speeds,
5) and all this must be in the case in the form of a finished structure, which is not a shame to post on Datagor.

My version of PP

The corps served, oddly enough, homemade amplifier my neighbor, a former radio amateur, assembled in the body of an unknown laboratory device. The amp was placed on the landing because... He no longer needed it, and it was a pity to throw it in the trash. I remembered this case when I decided to assemble the MF-1.

In the process of finalizing the body, simple and inexpensive parts were used:
Aluminum corner 15x15 x 1 mm, bought at HomeCenter.
M3 bolts with a countersunk head, nuts.
Metal spacers with M3 thread.

And this is what we got:

Transformers and filter

Rectifiers

Terminals with coolers

Now it's time for the panels. Because We use a fan for cooling, the air must come out somewhere and come in from somewhere. First of all, I started sawing the back panel with a hole for air outlet:

Everything was done using a drill, jigsaw, engraver and needle files. Now we cut out the grille from the computer power supply case and clean the edges of the hole:

Now we take soldering acid, a soldering iron with a power of at least 100 W and solder the grille to the panel in several places:

We place input and output connectors on the panel, BE SURE TO ISOLATE THEM FROM THE CASE:

Solder the housing shielding lead to the panel. This will be the ONLY point where the chassis connects to the common power wire. We connect the case with the ground contacts of the input connectors through 1-2 W resistors with a nominal value of 1.5-2 Ohms. These measures are needed in order not to catch the “ground loop”, which will spoil us in the form of a 50 Hz background.

Rear panel in place:

Now we transfer the Zobel circuit from the board to the output connectors of the PA. It doesn’t really have a place on the board, because... it (the circuit) is a resonant system:

Now it's up to the front panel. There is only a power switch on it. The panel itself is made of aluminum, behind it there is a false panel made of moderately soft plastic, on which you can fasten anything with M3 screws with countersunk heads. The button was used from an old dead Wilma-104-Stereo cassette deck:

The panel is mounted on tin corners using hex bolts. That's all, the amplifier is ready!

Results

Guys, I did NOT find out! I didn’t think I’d ever say this, but it’s true! Nice soft bass, distinct highs (now I can distinguish percussion and handclaps on tracks that I know by heart), and all this pleasure on homemade three-way ZY with 8" bass drivers.
Everyone who is repulsed increased level HF, I want to reassure you: aurally this is felt not as a rise in the highs, but as an increase in the quality of the source, an increase in “transparency”.

In my version, the board is slightly redesigned. The choice of “mute” and “standby” modes has been removed as unnecessary, the main capacitor bank has been moved closer to the MS.

Power supply 2×23 V. The rectifier uses KD213B diodes. The electrolytes are shunted with a capacity of 100 nF, the secondary of the transformer is 47 nF.
Each MS is isolated from the radiators by a mica plate, and the radiators, in turn, are grounded to the case.
All wires are twisted together to reduce interference.

The background is not audible even with the input open, even close to the speaker. The goal, so to speak, has been achieved!
Further plans include drilling holes for air intake on the right side of the bottom cover of the case, making a device for adjusting the fan speed with control of the temperature of the radiators, possibly building in a preamplifier with a tone control, and painting the case.

A low frequency amplifier (LFA) is a device for amplifying electrical oscillations corresponding to the frequency range audible to the human ear, i.e. the LFA should amplify in the frequency range from 20 Hz to 20 kHz, but some VLFs can have a range of up to 200 kHz. The ULF can be assembled in the form independent device, or used in more complex devices - televisions, radios, radios, etc.

The peculiarity of this circuit is that pin 11 of the TDA1552 microcircuit controls the operating modes - Normal or MUTE.

C1, C2 - pass-through blocking capacitors, used to cut off the DC component sine wave. It is better not to use electrolytic capacitors. It is advisable to place the TDA1552 chip on a radiator using heat-conducting paste.

In principle, the presented circuits are bridge ones, because in one housing of the TDA1558Q microassembly there are 4 amplification channels, so pins 1 - 2, and 16 - 17 are connected in pairs, and they receive input signals from both channels through capacitors C1 and C2. But if you need an amplifier for four speakers, then you can use the circuit option below, although the power will be 2 times less per channel.

The basis of the design is the TDA1560Q class H microassembly. The maximum power of this ULF reaches 40 W, with a load of 8 ohms. This power is provided by approximately twice the increased voltage due to the operation of the capacitors.

The output power of the amplifier in the first circuit assembled on the TDA2030 is 60W at a load of 4 Ohms and 80W at a load of 2 Ohms; TDA2030A 80W at 4 ohm load and 120W at 2 ohm load. The second circuit of the considered ULF is already with an output power of 14 Watts.

This is a typical two-channel ULF. With a little wiring of passive radio components, this chip can be used to build an excellent stereo amplifier with an output power of 1 W on each channel.

Microassembly TDA7265 - is a fairly powerful two-channel Hi-Fi amplifier class AB in a standard Multiwatt package, the microcircuit has found its niche in high-quality stereo technology, Hi-Fi class. The simple switching circuit and excellent parameters made the TDA7265 a perfectly balanced and excellent solution for building high-quality amateur radio equipment.

First, a test version was assembled on a breadboard exactly as shown in the datasheet in the link above, and successfully tested on S90 speakers. The sound is not bad, but something was missing. After some time, I decided to remake the amplifier using a modified circuit.

The microassembly is a quad class AB amplifier designed specifically for use in car audio devices. Based on this microcircuit, you can build several high-quality ULF options using a minimum of radio components. The microcircuit can be recommended to beginning radio amateurs for home assembly of various speaker systems.

The main advantage of the amplifier circuit on this microassembly is the presence of four channels independent of each other. This power amplifier operates in AB mode. It can be used to amplify various stereo signals. If desired, you can connect to speaker system car or personal computer.

The TDA8560Q is just more powerful analogue The TDA1557Q chip, widely known to radio amateurs. The developers have only strengthened the output stage, making the ULF perfectly suited to a two-ohm load.

The LM386 microassembly is a ready-made power amplifier that can be used in designs with low supply voltage. For example, when powering the circuit from battery. LM386 has a voltage gain of about 20. But by connecting external resistances and capacitances, the gain can be adjusted up to 200, and the output voltage automatically becomes equal to half the supply voltage.

Microassembly LM3886 is an amplifier High Quality with an output power of 68 watts at 4 ohms or 50 watts at 8 ohms. At peak moment, the output power can reach 135 W. A wide voltage range from 20 to 94 volts is applicable to the microcircuit. Moreover, you can use both bipolar and unipolar power supplies. The ULF harmonic coefficient is 0.03%. Moreover, this is over the entire frequency range from 20 to 20,000 Hz.

The circuit uses two ICs in a typical connection - KR548UH1 as a microphone amplifier (installed in the PTT switch) and (TDA2005) in a bridge connection as final amplifier(installed in the siren housing instead of the original board). A modified alarm siren with a magnetic head is used as an acoustic emitter (piezo emitters are not suitable). The modification consists of disassembling the siren and throwing out the original tweeter with an amplifier. The microphone is electrodynamic. When using an electret microphone (for example, from Chinese handsets), the connection point between the microphone and the capacitor must be connected via a ~4.7K resistor to +12V (after the button!). The 100K resistor in the K548UH1 feedback circuit is better set with a resistance of ~30-47K. This resistor is used to adjust the volume. It is better to install the TDA2004 chip on a small radiator.

Test and operate - with the emitter under the hood and the PTT in the cabin. Otherwise, squealing due to self-excitation is inevitable. A trimmer resistor sets the volume level so that there is no strong sound distortion and self-excitation. If the volume is insufficient (for example, a bad microphone) and there is a clear reserve of emitter power, you can increase the gain of the microphone amplifier by several times increasing the value of the trimmer in the feedback circuit (the one according to the 100K circuit). In a good way, we would also need a primabass that would prevent the circuit from self-exciting - some kind of phase-shifting chain or a filter for the excitation frequency. Although the scheme works fine without complications

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

Amplifier Specifications

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

Amplifier PCB

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Ready amplifier

power unit