ULF circuits on microcircuits with printed circuit boards. The use of printed circuit boards in low frequency amplifier circuits

Evgenia Smirnova

To send light into the depths of the human heart - this is the purpose of the artist

Connecting speakers to a laptop, TV, or other music source sometimes requires amplifying the signal with a separate device. The idea of ​​building an amplifier is a good one if you are prone to PCB work at home and have some technical skills.

How to make a sound amplifier

Getting started on assembling an amplifying device for speakers of one type or another consists of finding tools and components. The amplifier circuit on a printed circuit board is assembled using a soldering iron on a heat-resistant support. It is recommended to use special soldering stations. If DIY assembly is for circuit testing purposes or for short term use, the on-wire option will do, but you will need more space to accommodate the components. The printed circuit board guarantees compactness of the device and convenience in further use.

A cheap and common amplifier for headphones or small speakers is created on the basis of a microcircuit - a miniature control unit with a pre-wired set of control commands electrical signal. It remains to add only a few resistors and capacitors to the circuit with a microcircuit. The total cost of an amateur-class amplifier is, as a result, much lower than the price of finished professional equipment from the nearest store, but the functionality is also limited to changing the output volume of the audio signal.

Remember the features of compact single-channel amplifiers assembled by yourself based on TDA series microcircuits and their analogues. Chip highlights a large number of heat during operation, so you must avoid or minimize its contact with other parts of the device. Radiator grill for heat dissipation is recommended for use. Depending on the model of the microcircuit and the power of the amplifier, the size of the required radiator increases. If the amplifier is assembled in a case, you should first plan a place for a heat sink.

Another feature of assembling a sound amplifier with your own hands is the low voltage consumption. This allows you to use a simple amplifier in cars (powered by a car battery), on the road or at home (powered by a special unit or batteries). Some simplified audio amplifiers require only 3 volts of current. The power consumption depends on how much amplification of the audio signal is required. The sound amplifier from the player for standard headphones consumes about 3 watts.

A novice radio amateur is recommended to use computer program to create and view circuit diagrams. Files for such programs may have *.lay extension - they are created and edited in a popular virtual instrument Sprint layout. Creating a DIY circuit from scratch makes sense if you have already gained experience and want to experiment with the knowledge gained. Otherwise, look for and download ready-made files, according to which you can quickly assemble a replacement for a low-frequency amplifier for a car radio or a digital combo amplifier for a guitar.

For laptop

A do-it-yourself sound amplifier is being assembled for a laptop in one of two cases: the built-in speakers are out of order, or their volume and sound quality are not enough for your needs. You will need a simple amplifier, designed for external speakers up to 2 watts, and winding resistance up to 4 ohms. To assemble it with your own hands, in addition to standard radio amateur tools (pliers, a soldering station), you will need a printed circuit board, a TDA 7231 chip, and a 9-volt power supply. Choose your own cabinet to house the components of the amplifier.

Add the following items to the list of purchased components:

• non-polar capacitor 0.1 uF - 2 pcs.;
• polar capacitor 100 uF - 1 pc.;
• polar capacitor 220 uF - 1 pc.;
• polar capacitor 470 uF - 1 pc.;
• constant resistor 10 KΩ - 1 pc.;
• resistor constant 4.7 Ohm - 1 pc.;
• two-position switch - 1 pc.;
• speaker output jack – 1 pc.

Determine the assembly order yourself, depending on which *.lay format wiring diagram you downloaded. Choose a radiator of such a size that its thermal conductivity allows you to keep the operating temperature of the microcircuit below 50 degrees Celsius. If the device is constantly used with a laptop outdoors, it will require a homemade case with slots or holes for air circulation. You can assemble such a case with your own hands from a plastic container or the remnants of old radio equipment, fixing the board with long screws.

For DIY headphones

The simplest stereo amplifier for portable headphones should have a small power, but the most important parameter will be power consumption. In an ideal example, the design is powered by AA batteries, in extreme cases, from a simple 3 volt adapter. You will need a high-quality TDA 2822 chip or its equivalent (for example, KA 2209), an electronic circuit for assembling an amplifier with your own hands on a TDA 2822. Additionally, take the following components:

• capacitors 100 uF (4 pcs.);
• up to 30 cm of copper wire;
• headphone jack.

A heat sink element is needed if you want to make the amplifier compact and with a closed case. You can assemble the amplifier on a finished or home-made printed circuit board or by surface mounting. The pulse transformer in the power supply may generate noise, so do not use it in this option amplifier. The finished amplifier will provide a pleasant and powerful sound from the player (recordings or radio signal), tablet or phone.

Subwoofer amplifier circuit

The low-frequency amplifier is assembled by hand on a TDA 7294 chip. It is used both to create powerful acoustics with basses in the apartment, and as a car amplifier - in this case, however, you need to purchase a bipolar power supply for 30-35 volts. The figures below describe the location of components, as well as the rating of resistors and capacitors. Such an amplifier for a subwoofer will provide output power up to 100 watts with prominent low frequencies.

Mini speaker amplifier

As a sound amplification device for domestic or foreign home speakers, the design described above for laptops is suitable. Stationary placement of the device will allow you to choose any power adapter available. Miniature and acceptable appearance You can provide an inexpensive amplifier by observing a few rules:

1. Ready-made high-quality printed circuit board.
2. Durable plastic or metal case (order from the master).
3. The placement of components is pre-planned.
4. The amplifier is soldered neatly, without extra drops of solder.
5. The heatsink only touches the chip.
6. Ready-made sockets for signal output and power input are used.

DIY tube sound amplifier

Tube audio amplifiers are expensive devices, provided that you purchase all the components with your own funds. Older radio amateurs sometimes keep collections of lamps and other parts. Collect tube amplifier at home with your own hands is relatively easy if you are willing to spend a few days looking for detailed diagrams in the Internet. The sound amplifier circuit in each case is unique and depends on the sound source (old tape recorder, modern digital technology), power source, estimated dimensions and other parameters.

Transistor audio amplifier

Assembling a sound preamplifier with your own hands without the use of complex microcircuits is possible on transistors. An amplifier based on germanium transistors is easily built into modern audio systems, it does not require additional settings. The disadvantage of transistor circuits is the larger size of the assembled boards. Dependence on the "purity" of the background is also unpleasant - you will need a shielded cable, or additional circuit suppression of noise and ripples from the network.

Video: do-it-yourself sound power amplifier

This article deals with specific design and usage issues. printed circuit boards in relation to power amplifiers, especially those that operate in class B. All power amplifiers incorporate power amplification stages as such and associated control and protection circuits. Most amplifiers also have a small-signal low-frequency stage, output amplifiers with balanced output, subsonic filter, output meters, etc.

Other issues related to the design of printed circuit boards are also considered, such as grounding, safety issues, reliability, etc. The performance of a low-frequency power amplifier depends on a large number of factors, in all cases, careful study of the printed circuit board is decisive, primarily for the risk of distortion caused by inductive interference; The possible interaction between the signal paths and the power rails can very easily cause the linearity of the amplifier to be limited, so the importance of this problem cannot be overestimated. The chosen layout (component layout and trace pattern) of the printed circuit board will largely determine both the level of distortion and the level of crosstalk of the amplifier.

In addition to the amplifier performance considerations outlined above, PCB layout will have a significant impact on buildability, ease of inspection, repairability, and reliability. All of the above aspects of the problem are discussed below.

Successful amplifier PCB design requires a certain amount of electronics knowledge to understand the intricacies of the effects described below, so that the PCB design process runs smoothly and efficiently. It is already considered generally accepted when developing printed circuit boards for various areas of electronics to surrender to the power of professionals who, being very knowledgeable in the intricacies of working with automated systems design engineers have a very vague or even complete lack of understanding of the intricacies of how electronic circuits work. For some areas, this approach is acceptable; when designing a power amplifier, it turns out to be completely inadequate due to the fact that the main characteristics, such as crosstalk and distortion level, are very dependent on the wiring diagram. A little lower, the PCB designer will be able to understand what, in fact, is at stake.

Crosstalk

Crosstalk (or the phenomenon of a signal "flowing" from one channel to another, electrical interference caused by the passage of a signal in adjacent wires) is characterized primarily by a signal source (which can be any complex resistance) and a receiver, usually having a higher value of complex resistance , or the potential of a virtual, "floating" earth. When crosstalk in communication channels is discussed, it is common to refer to the transmit and receive channels as speech and non-voice channels, respectively.

Crosstalk occurs and manifests itself in various forms:

1. Capacitive crosstalk is a consequence of the proximity in space of two electrical conductors and can be represented using a virtual (or effective) capacitor connecting the two circuits. The capacitance of such a capacitor increases with increasing frequency in proportion to the value of 6 dB/octave, although higher rates of capacitance increase are possible. Shielding the conductors with any conductive material completely solves the problem, although increasing the distance between such conductors turns out to be less expensive.
2. Resistive crosstalk occurs for the simple reason that the resistance of the ground rails is different from zero. Copper at room temperature is not a superconductor. Resistive crosstalk is independent of frequency.
3. Inductive crosstalk is rarely a problem in audio design; they can occur when two low-frequency transformers are recklessly placed too close together, but apart from this case, this problem can usually be forgotten. A significant exception to this rule is the low-frequency Class B power amplifier, where the currents flowing through the power rails are in the form of half-sine waves and which can seriously affect the level of distortion of the amplifier if they are allowed to interact with the input signal circuits, the circuit feedback or output stage circuits.

In most linear low frequency circuits, the main cause of crosstalk is unwanted capacitive coupling between different circuit circuits, and in the vast majority of cases it is determined by the pattern (routing) of wires and PCB traces. In contrast, class B power amplifiers suffer almost negligible or even negligible crosstalk due to capacitive effects, since the impedances of the circuits tend to be small, and the distances between them sufficiently large; much big problem represents an inductive coupling between the buses through which the supply currents flow and the circuits through which the signal passes. If such a coupling occurs between circuits of the same channel, then it manifests itself in the form of distortion and can lead to significant non-linearity in the characteristics of the amplifier. If this interaction extends to another (non-speech) channel, then it will appear as a distorted signal crosstalk. In any case, such a connection is highly undesirable and special measures must be taken to prevent its occurrence.

PCB routing is only one element of this struggle, since crosstalk must somehow not only be emitted, but also received somewhere. As a rule, the source of maximum radiation will be their own, internal electric wires due to their overall length and ubiquity, the wire routing pattern will probably be the most critical to achieve the best performance, so various clamps, cable clamps, etc. must be used to secure them. The receiving device is most often the input circuits and feedback circuits, which are also located on the printed circuit board. For the good operation of the device, it is necessary to study these issues in terms of maximum radiation protection.

Distortion caused by interference from power rails

The power rails of a class B power amplifier carry very large and very distorted currents. As emphasized earlier, if due to induction their interaction is allowed on the circuits through which the acoustic signal passes, then the level of distortion will increase sharply. This applies to PCB conductors as well as cable connections, the sad truth is that it is easy enough to make an amplifier PCB that will be absolutely perfect in every way except for this one requirement, and the only solution will be to use the second one. fees. However, for optimal results, the following requirements should be followed:

1. Minimize electromagnetic emissions from the power rails by placing the positive and negative voltage rails as close to each other as physically possible. They should be located as far as possible from the input circuits of the amplifier stage and the connecting output terminals; the best method is to run the power rail wires to the output stage on one side and the rest of the amplifier wires on the other. Then you should run wires from the output to power the rest of the amplifier; they will no longer carry a current that has a half-wave form, so it will not cause problems.
2. Absorption must be minimized electromagnetic radiation power rails by minimizing the area of ​​the circuits covered by the wires of the input circuit and the feedback circuit. They form closed loops through the ground, so the area of ​​the loops covered by them should be kept to a minimum. Often enough best result can be obtained by maximum separation and routing the input circuits and the feedback loop across the LF ground trace that runs through the center of the PCB from the input to the output point of the ground loop. Inductive distortion can also occur when interacting with output wires and output ground wires. The latter case presents a rather serious problem, since it is usually difficult to change its position in space without updating the printed circuit board itself.

Installing Output Semiconductors

The most important policy decision is whether or not to install high power output devices on the amplifier's main PCB. There are a number of strong arguments in favor of such a decision, but, nevertheless, such a choice is not always the best one.

Advantages:

1. The PCB of the amplifier can be calculated to form a complete unit that can be carefully checked before it is installed on the chassis. This approach greatly simplifies testing, as it provides access to various points of the circuit from all sides; it also eliminates the possibility of surface damage to the PCB itself (scratches, etc.) during inspection.
2. Incorrect connection of the output semiconductors is excluded, provided that the necessary semiconductors are installed in the correct positions. This is a fairly significant argument, since such errors usually disable output semiconductor devices, and also lead to other negative effects that develop according to the principle of falling dominoes, and which will take a lot of time (and money) to correct.
3. All connecting wires leading to the output semiconductors should be kept as short as possible. This helps to increase the stability of the output stage and resist the occurrence of high-frequency oscillations.

Disadvantages:

1. If the output devices of the amplifier require frequent replacement (which clearly indicates some very serious flaw), then repeated soldering operation will damage the PCB tracks. However, if the worst happens, the damaged section can always be replaced with a short conductor, so there is no need to scrap the PCB; rest assured that such a repair option is always possible.
2. It is possible that the output semiconductors can get very hot even if they are operating at nominal conditions; for instruments of type TO3, case temperatures of 90 °C are not unusual. If the mounting method used does not allow for some degree of resilience, then thermal expansion can generate mechanical forces that can tear off the PCB mounting gaskets.
3. The heat-removing radiator will have, as a rule, considerable dimensions and weight. Therefore, it is necessary to use a sufficiently rigid structure that secures the printed circuit board and the heatsink. IN otherwise the entire structure, due to the lack of sufficient rigidity, will vibrate during transportation, creating excessive forces at the soldering joints.

Manufacturing good amplifier power has always been one of the most difficult steps in the design of audio equipment. Sound quality, bass softness and clear mids and highs, musical instrument detail - all these are empty words without a quality low-frequency power amplifier.

Foreword

Out of variety homemade amplifiers LF 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 a variant 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, you can not hear softness and saturation in it, 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, 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. Very small details began to be heard in the compositions, 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 schemes 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. Transistor test circuit P-N-P structures and N-P-N for performance in 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 if something goes wrong.

It is desirable to connect a volume control to the input - one dual variable resistor or two separately. Front the inclusion of UMZCH we put the half-width 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 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, UMZCH will not interfere.

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 ground ( complete absence input signal), connect speaker systems to the outputs of the amplifiers.

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 powerful lamps incandescent. 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 acoustic systems, about the case and the front panel...

PRINTED CIRCUIT BOARD

I didn’t think about the board for a long time, all the boards of individual blocks were available, it was only necessary to transfer all the templates to foil fiberglass and etch. Board and schematic files. The templates were applied to the common board after a short calculation. For this process, I used a well-known one, I ironed each template for 90 seconds, you need to iron it carefully so that the toner firmly adheres to the foil surface of the textolite and does not peel off when the paper is removed.

Next, let the textolite cool for 5-10 minutes, then carefully remove the paper. First, you need to put the board in a vessel with water and wait a couple of minutes, then carefully remove the paper. I did not find reagents for etching in the town, I had to go for an alternative. The alternative solution consists of three main components - hydrogen peroxide , citric acid And table salt .

In general, I spent 12 bottles of hydrogen peroxide (3% hydrogen peroxide solution, each bottle 100 mg) - purchased at the pharmacy 12 packs of citric acid (pack - 40 mg) - bought at the grocery store 9 teaspoons of table salt - stolen from the kitchen of his own house. All components are mixed until the salt and citric acid are completely dissolved.

Due to the large size of the board, there were difficulties with the vessel in which the etching was planned. Here, too, I decided to go for an alternative. A plastic bag was purchased at the store, which I placed in a box from some kind of player, the board fit perfectly into such a "vessel". He poured the solution and put the whole thing in the sun.

The entire etching process lasted no more than an hour. Quite a violent reaction, so you need to carry out in clean air. Next, you need to erase the toner. To do this, use clean (or not so) rags and acetone. The already finished board must be thoroughly washed with warm water, then dried with a hairdryer.

Another problem is the disposal of the solution, I acted in a barbaric way by draining the entire solution into the sewer, when you do the same, make sure that no one sees, otherwise environmentalists will flood in, in my case this problem did not arise, since I myself am an ecologist ( lol ).

Next, you already need to start drilling holes, but there are a lot of them, a lot. I drilled half of the holes with a 3-kilogram drill, then specially for this idea at an auction ebay was bought a mini-drill with all amenities. In the drilling process, I used 0.8mm drills for small components (resistors, capacitors, microcircuits, etc.), 1mm drills for larger ones (amplifier output transistors, power diodes) and 5mm drills for pulse transformer winding leads.

The already drilled board needs to be tinned. To do this, you need a hundred-watt soldering iron, pine rosin, and, of course, tin. I advise you to wear a mask during this process, the smoke from rosin is not toxic, but a whole cloud of smoke forms here, it is quite difficult to breathe under such conditions. The glossy tin layer gives the printed circuit board a beautiful appearance and keeps the copper tracks from oxidizing. Only after the completion of this process, we have a completely finished printed circuit board, and now we can Regards - AKA KASYAN.

Discuss the article HOME AMPLIFIER - SCHEMES AND PRINTED BOARDS

If you need to make simple, but enough powerful UMZCH- TDA2040 or TDA2050 chip will be the best and inexpensive solution. This small stereo AF amplifier is based on two well-known TDA2030A microcircuits. Compared to the classic inclusion, this circuit has improved power filtering and optimized PCB layout. After adding any preamp and power supply, the design is ideal for making a homemade homemade audio power amplifier, approximately 15 watts (each channel). The project is made on the basis of TDA2030A, but you can use TDA2040 or TDA2050, thereby increasing the output power by a factor of one and a half. The amplifier is suitable for speakers with an impedance of 8 or 4 ohms. The advantage of the design is that it does not require bi-polar power, like most. The scheme is distinguished by good parameters, ease of launch and reliability in operation.

Schematic diagram of ULF

TDA2030A allows you to solder a class AB low frequency amplifier. The microcircuit provides a large output current, while being characterized by low signal distortion. There is a built-in protection against short circuit, which automatically limits the power to a safe value, as well as traditional for such devices. thermal protection. The circuit consists of two identical channels, the operation of one of which is described below.

The principle of operation of the amplifier on the TDA2030

Resistors R1 (100k), R2 (100k) and R3 (100k) serve to create a virtual zero of amplifier U1 (TDA2030A), and capacitor C1 (22uF/35V) filters this voltage. Capacitor C2 (2.2 uF / 35V) cuts off the DC component - prevents constant voltage to the input of the amplifier microcircuit through the line input.

Elements R4 (4.7k), R5 (100k) and C4 (2.2 uF / 35V) operate in a negative feedback loop and have the task of forming the frequency response of the amplifier. Resistors R4 and R5 determine the gain level, while C4 provides unity gain for the DC component.

Resistor R6 (1R) together with capacitor C6 (100nF) work in a system that forms frequency response characteristic at the exit. Capacitor C7 (2200uF/35V) prevents the passage direct current through the speaker (passing the alternating audio signal of the music).

Diodes D1 and D2 prevent the occurrence of dangerous reverse polarity voltages that can occur in the speaker coil and ruin the chip. Capacitors C3 (100nF) and C5 (1000uF/35V) filter the supply voltage.

ULF printed circuit board

You can see the printed circuit board in the photos. with drawings can be archived (without registration). As for the assembly, it is convenient to first solder two jumpers on the power rails. If possible, use a thicker wire, and not a thin leg from a resistor, as is often the case. If the amplifier will work with AC 8 ohms, and not 4 ohms - capacitors C7 and C14 (2200uF / 35V) can have a value of 1000uF.

Radiators or one common radiator must be screwed onto the flanges, remembering that the TDA2030A microcircuit cases are internally connected to the ground.

On a printed circuit board, TDA2040 or TDA2050 microcircuits can be successfully used without any changes in the pinout. The board was designed in such a way that it can be cut at the point indicated by the dotted line if necessary, and only one half of the amplifier with the U1 chip can be used. In place of the AR2 (TB2-5) and AR3 (TB2-5) connectors, you can solder the wires directly if the audio connectors are fixed to the amplifier case.

Case and PSU

Take the power supply either with a transformer plus a rectifier, or a ready-made pulse one, for example, from a laptop. The amplifier must be powered with a non-stabilized voltage within 12 - 30 V. The maximum supply voltage is 35 V, which is naturally better not to reach a couple of volts, you never know what.

Making a case from scratch is very troublesome, so the easiest way is to pick up a finished box (metal, plastic) or even a finished case from electronic device(TV tuner satellite, DVD player).