Do-it-yourself amplifier: a master class on building a simple and effective device for signal amplification. The simplest sound amplifier DIY low-frequency sound amplifier

In this article we will talk about amplifiers. They are also ULF (low frequency amplifiers), they are also UMZCH (audio frequency power amplifiers). These devices can be made on both transistors and microcircuits. Although some radio amateurs, paying tribute to the vintage fashion, make them the old fashioned way - using lamps. We recommend you look here. I would like to draw special attention of beginners to car amplifier microcircuits with 12-volt power supply. Using them you can get a fairly high-quality sound output, and for assembly, knowledge of a school physics course is practically enough. Sometimes from the body kit, or in other words, those parts on the diagram without which the microcircuit will not work, there are literally 5 pieces on the diagram. One of these, an amplifier on a chip TDA1557Q shown in the figure:

Such an amplifier was assembled by me at one time; I have been using it for several years together with Soviet 8 Ohm 8 W acoustics, together with a computer. The sound quality is much higher than that of Chinese plastic speakers. True, in order to feel a significant difference, I had to buy a creative sound card; the difference with the built-in sound was insignificant.

The amplifier can be assembled by hanging mounting

The amplifier can also be assembled by hanging mounting, directly on the terminals of the parts, but I would not recommend assembling using this method. It’s better to spend a little more time, find a wired printed circuit board (or wire it yourself), transfer the design to the PCB, etch it and end up with an amplifier that will work for many years. All these technologies have been described many times on the Internet, so I will not dwell on them in more detail.

Amplifier attached to radiator

I’ll say right away that amplifier chips get very hot during operation and need to be secured by applying thermal paste to the radiator. For those who just want to assemble one amplifier and do not have the time or desire to study programs for PCB layout, LUT technologies and etching, I can suggest using special breadboards with solder holes. One of them is shown in the photo below:

As can be seen in the photo, connections are made not by tracks on a printed circuit board, as is the case with printed wiring, but by flexible wires soldered to the contacts on the board. The only problem when assembling such amplifiers is the power supply, which produces a voltage of 12-16 volts, with a current consumption by the amplifier of up to 5 amperes. Of course, such a transformer (5 amperes) will have rather large dimensions, so some use switching power supplies.

Transformer for amplifier - photo

I think many people at home have computer power supplies that are now obsolete and are no longer used as part of system units, but such power supplies are capable of delivering +12 volts through circuits, currents much greater than 4 amperes. Of course, such power supply among sound connoisseurs is considered worse than a standard transformer one, but I connected a switching power supply to power my amplifier, then changed it to a transformer one - the difference in sound can be said to be imperceptible.

After leaving the transformer, of course, you need to install a diode bridge to rectify the current, which must be designed to work with the large currents consumed by the amplifier.

After the diode bridge there is a filter on an electrolytic capacitor, which should be designed for a noticeably higher voltage than in our circuit. For example, if we have a 16 volt power supply in the circuit, the capacitor should be 25 volt. Moreover, this capacitor should be as large as possible; I have 2 capacitors of 2200 uF each connected in parallel, and this is not the limit. In parallel with the power supply (bypass), you need to connect a ceramic capacitor with a capacity of 100 nF. At the input of the amplifier, film decoupling capacitors with a capacity of 0.22 to 1 µF are installed.

Film capacitors

Connecting the signal to the amplifier, in order to reduce the level of induced interference, should be done with a shielded cable; for these purposes it is convenient to use a cable Jack 3.5- 2 Tulips, with corresponding sockets on the amplifier.

Cable jack 3.5 - 2 tulips

The signal level (volume on the amplifier) ​​is adjusted using a potentiometer; if the amplifier is stereo, then dual. The connection diagram for the variable resistor is shown in the figure below:

Of course, amplifiers can also be made using transistors, while power supply, connection and volume control are used in them in exactly the same way as in amplifiers on microcircuits. Consider, for example, an amplifier circuit using a single transistor:

There is also a separating capacitor here, and the minus of the signal is connected to the minus of the power supply. Below is a diagram of a push-pull power amplifier with two transistors:

The following circuit also uses two transistors, but is assembled from two stages. Indeed, if you look closely, it seems to consist of 2 almost identical parts. Our first cascade includes: C1, R1, R2, V1. In the second stage C2, R3, V2, and the load headphones B1.

Two-stage transistor amplifier - circuit diagram

If we want to make a stereo amplifier, we will need to assemble two identical channels. In the same way, we can, by assembling two circuits of any mono amplifier, turn it into stereo. Below is a diagram of a three-stage transistor power amplifier:

Three-stage transistor amplifier - circuit diagram

Amplifier circuits also differ in supply voltage, some require 3-5 volts to operate, others require 20 or more. Some amplifiers require bipolar power to operate. Below are 2 amplifier circuits on a chip TDA2822, first stereo connection:

In the diagram, speaker connections are indicated in the form of resistors RL. The amplifier operates normally at 4 volts. The following figure shows a bridged circuit that uses one speaker, but produces more power than the stereo version:

The following figure shows the amplifier circuits, both circuits are taken from the datasheet. Power supply 18 volts, power 14 watts:

The acoustics connected to the amplifier can have different impedances, most often it is 4-8 ohms, sometimes there are speakers with a resistance of 16 ohms. You can find out the speaker's resistance by turning it over with its back side facing you; the rated power and resistance of the speaker are usually written there. In our case it is 8 ohms, 15 watts.

If the speaker is inside the column and there is no way to see what is written on it, then the speaker can be ringed with a tester in ohmmeter mode by selecting a measurement limit of 200 Ohms.

Speakers have polarity. The cables that connect the speakers are usually marked in red, for the wire that is connected to the positive of the speaker.

If the wires are not marked, you can check the correct connection by connecting the battery plus with plus, minus with minus of the speaker (conditionally), if the speaker cone moves out, then we guessed the polarity. More different ULF circuits, including tube ones, can be found in. It contains, we think, the largest selection of schemes on the Internet.

- this is a device using field-effect transistors in the output path, implemented according to a “floating ground” circuit. That is, a “floating” ground is formed when the common wire of some part of the system is not electrically connected to the ground bus. During the existence of this amplifier circuit, significant changes were made to it, which greatly improved the technical characteristics of the UMZCH.

Power amplifier circuit model 2016.

Creating a device with a “virtual zero” or, as they say, a “midpoint” has its own characteristics: DIY sound amplifier for speakers does not require setting the voltage to “zero”; there is no need to protect the speaker system from constant output; The manufacture of a power transformer is greatly facilitated. For a constant-midpoint terminal circuit, two pairs of separate windings are required on one core, or two trances with two windings are required.

A little about testing and measuring the characteristics of an early version of this device, which was also assembled using MOSFET transistors in the output stage. Measurement of parameters showed the obvious presence of interference from the network in the input circuit of the UMZCH. And if we compare it with an amplifier with an average constant point, then there is a huge amount of interference multiples of a frequency of 50 Hz in a range of up to 1 kHz.

Reduced interference

To radically reduce the amount of radio interference appearing in the input circuit of the amplifier through a constant resistor R3, it was decided: to implement a voltage bias circuit to the control electrode (gate) of field-effect transistor Q2 with complete symmetry in alternating voltage. Based on the fact that resistors R4 and R11 are identical and a capacitive circuit C4-C6 has also been added, then by selecting the value of resistors R5-R12 you can set an acceptable bias voltage for the input switch. In addition, capacitances C4-C6 included in the circuit filter out the alternating voltage appearing at the terminals of the current sources.

At the model construction stage DIY sound amplifier for speakers demanded a thorough study of the problem of generating a device at ultra-low frequencies in the range below 20 Hz. Namely, when the total capacitance of the capacitors in the power circuit is too small and the capacitance at the C1 input is significant. Thus, the amplifier’s disposition to self-excitation is determined by the R-C circuit along the supply voltage R16-C5 (R17-C3), and naturally by the capacitors in the power source. To provide the amplifier with conditions for stable and stable operation, the total capacitance of the electrolytic capacitors in each arm of the power supply must be set to 10,000 µF with C1 up to 0.15 µF, 15,000 µF with C1 = 0.22 µF and 20,000 µF with C1 = 0.33 µF.

For high-quality sound reproduction at low frequencies, the input resistance of the UMZCH was increased. For this purpose, instead of a bipolar transistor, a MOSFET transistor Q2 was installed at the input, and instead of a current reflector, a current source was implemented in the primary stage. The second stage of the amplifier is assembled using a common emitter circuit design.

Amplifier reliability

To ensure reliable operation of the device, a pair of bipolar transistors Q11-Q15 were included in each arm of the circuit, which perform the function of limiting the peak current passing in the circuit of output transistors 7A-8A. In addition, a 1N4148 rectifier diode (D7) was added to the circuit to limit the forward and reverse voltage relative to the terminals of transistor Q14.

Important technical characteristics of the power amplifier:

The quiescent current in the circuit is set by variable resistor R23a (100 Ohm). The optimal quiescent current for normal operation of the device is needed within 80 mA. Even with this value of the quiescent current, the signal distortion at the output of this end amplifier is within 0.09% with a short instantly reducing harmonic range.

Upgraded power supply.

Power transformer

A 140 W power transformer is assembled on a toroidal core with two secondary windings having a voltage of ~36v each. The rectifier block consists of two diode bridges designed for a rated voltage of 100v and a current of 10A. According to the circuit, the rectifier filters are implemented on four 10,000 F capacitors for a voltage of 63v with a midpoint. Moreover, they are separate for each channel, and also without galvanic connection with a common bus. It is to these middle points that the speaker wires with the “-” sign from the left and right channels are supplied. Depending on the design of your transformer housing, you can install two transformers with a power of 70-80 W each. On electrolytic capacitors C3-C4, shunts in the form of paper capacitors C1-C2 must be installed in parallel.

I'd say it's just a super simple amp that contains all four elements and puts out 40 watts of power into two channels!
4 parts and 40 W x 2 power output Karl! This is a godsend for car enthusiasts, since the amplifier is powered by 12 Volts, the full range is from 8 to 18 Volts. It can be easily integrated into subwoofers or speaker systems.
Everything is accessible today thanks to the use of modern element base. Namely the chip - TDA8560Q.

This is a PHILIPS chip. Previously, the TDA1557Q was in use, on which you can also build a stereo amplifier with an output power of 22 W. But it was later modernized by updating the output stage and the TDA8560Q appeared with an output power of 40 W per channel. Also similar is the TDA8563Q.

Car amplifier circuit on a chip

The diagram shows a microcircuit, two input capacitors and one filter capacitor. The filter capacitor is specified with a minimum capacity of 2200 uF, but the best solution would be to take 4 of these capacitors and parallel them, this will ensure more stable operation of the amplifier at low frequencies. The microcircuit must be installed on a radiator, the larger the better.

Building a simple amplifier

It is also possible to increase the number of components in the circuit that increase reliability during operation, but not fundamentally.

Five more details have been added here, I’ll explain why. Two 10K Ohm resistors will remove the hum if there are long wires going to the circuit. A 27 K Ohm resistor and a 47 uF capacitor provide a smooth start of the amplifier without clicks. A 220 pF capacitor will filter out high-frequency noise traveling along the power wires. So I recommend modifying the circuit with these nodes; it won’t be superfluous.
I would also like to add that the amplifier develops full power only at a 2 Ohm load. At 4 Ohms there will be somewhere around 25 W, which is also very good. So our Soviet acoustics will be rocked.
Low-voltage, single-polar power supply provides additional advantages: it can be used in car speakers, but at home it can be powered from an old computer power supply.
The minimum number of components allows you to build in an amplifier to replace an old one that has failed on a microcircuit of other brands.

In order to connect several speakers to a device such as a laptop or player without losing signal quality, you need a simple sound amplifier. If you have the desire and some knowledge, you can make it yourself.

To do this, it’s important to understand a little about the specifics of working with printed circuit boards and adhere to clear recommendations. This article talks about how to make a sound amplifier with your own hands.

Peculiarities

To ensure that the final device does not take up much space, you will need the following:

• Printed circuit board.
• Soldering iron.
• Wires.

If desired, you can connect everything using the same wires. However, such an audio amplifier circuit will be inconvenient and cumbersome to use. It is used in cases where you need to test one specific node.

When assembling a small sound amplifier at home for headphones or small speakers, you can save a lot of money, but such a device will have a number of limitations, such as a low threshold for maximum volume and strong heating of individual parts. In order to get rid of the latter, you need to connect a radiator plate to the device.

The convenience of using such a circuit lies in the low power consumption and low voltage required for its operation. So, most of these devices consume no more than 3 V, so they can be used in a car.

On a laptop

In order to amplify the sound signal, you must purchase the following components:

• Capacitor n/a 0.1 uF 2 pcs
• Capacitor n 100.220, 470 uF 1 pc.
• Fixed resistor 10, 4.7 Ohm, 1 pc.
• Switch.
• Speaker connector.

There are many assembly schemes that are essentially no different. They can be downloaded from the Internet. After everything is connected, it is necessary to make a reliable case in which there will be holes for cooling the radiator.

Headphones

A not particularly powerful DIY sound amplifier that can be used for high-quality music playback in headphones. The key quality that you need to pay attention to is power consumption. In order for the device to operate on regular AA batteries, it is better to choose a TDA 2822 type microcircuit. You will also need:

• 100 uF capacitor 4 pieces.
• Copper wire 0.4 m.
• Headphone jack.

If the amplifier is placed in a sealed case, you need to organize a heat removal system. A radiator grill is suitable for this; it is also recommended to make small holes.

By assembling and connecting this device, you can not only enhance the sound, but also improve its quality. It is also suitable for a player or tablet.

Subwoofer

In order to fill your apartment with high-quality bass, it is enough to assemble a low-frequency amplifier according to the TDA 7294 circuit. Following the circuit, you need to connect all the components together on a printed circuit board. This device will allow you to use up to 0.1 kW output.

Assembly Rules

Before assembling a sound wave amplifier, you need to familiarize yourself with the basic rules. Failure to comply with them can be fraught not only with the lack of fruits of the work, but also with the possibility of the device catching fire.

What to pay attention to:

• The printed circuit board on which the components will be located must be in good condition.
• The entire structure must be placed in a reliable metal or plastic case, which can be ordered from a specialist or made independently.
• It is necessary to install all elements according to a pre-prepared diagram.
• You need to solder wires and components so that the solder does not connect two elements.
• The radiator should not roll around individual elements and the housing. It should be secured so that it only touches the microcircuit.

Lamp devices

Tube audio amplifiers look very stylish. They are able to work with both old tape recorders and modern equipment. However, finding components for assembly can be quite difficult.

Transistor amplifier

The advantage of these amplifiers is their simplicity and the absence of multi-component complex circuits. If you use germanium transistors for manufacturing, you can freely integrate them into any audio equipment.

However, they also have significant disadvantages. For example, the final device will have quite large dimensions. Or the sound quality will be acceptable only with proper settings, since there will be a direct dependence on the “Background”.

For assembly you will need a shielded cable or an additional device to suppress noise and interference.

Conclusion

Assembling a sound amplifier yourself is not difficult. To do this, you just need to understand the electrical circuit diagrams and find the required component connection option on the Internet. All other parts can be freely purchased on the market.

DIY sound amplifier photo

I remember somewhere in the comments I promised to post photos of a homemade amplifier. I keep this promise.

In nature, there are a number of integrated audio frequency power amplifiers for various types of electronic equipment (radio and television receivers, communication and telephony equipment, stationary, portable and car radios, electronic toys, sound synthesizers, etc.). These devices are not at all difficult to use, and having at least theoretical skill in using a soldering iron, in about 40 minutes on your knees you can build a high-quality amplifier that can fit into a perfume box, if, of course, the idea of ​​putting an amplifier in there comes into your head :)

And it all started with the fact that my Odyssey 002 stopped transmitting sound through one of the channels (And it has 4 of them, or rather 2 parallel pairs). I found thyristors and capacitors on the market that had failed due to age, and nearby on the counter I found a TDA-based microcircuit (from Philips) that was interesting to me.

Having come home and reading information about it on the Internet, I discovered that this “centipede” the size of a small AAA battery is capable of delivering 35 watts per channel at a voltage of 18 V, and also has a protection device against short circuit, overload and overheating, loudness compensation, auto-shutdown when the signal source is turned off and many other useful things that I don’t even remember. And if you connect the channels into a bridge, you can get a 1-channel amplifier with a power of about 70 watts, which is more than enough to drive the huge S90. (However, as I later realized, the S90 was quite capable of driving a two-channel amplifier with a capacity of 2x35 watts).

Moreover, such microcircuits are used in serious car radios, stereos and other equipment (DO NOT forget that this was in 2003, now microcircuits may be used more seriously).

I will not go into details of soldering and selection of parts. It was not difficult for me to find everything on the market (4 resistors, 4 capacitors, the microcircuit itself, the board, and accessories for etching the board, sawing out its shape, + tin, rosin, beer and squid).

There is plenty of information and circuit diagrams for such amplifiers on more than a hundred sites on the Internet. You can search for the phrase "TDA chip", for example.

I bought a class D microcircuit. I didn’t know (and now I don’t know what classes there are and which is better, A or D), but I know that the main advantage of class D amplifiers is their high efficiency, reaching 90%, at a low supply voltage . In practice, the scope of application of Class D amplifiers is limited to car speakers and portable devices. Which is exactly what we need.

Also, when choosing, it is worth noting that the power is indicated at a certain voltage. This means that if you apply less voltage, your power will drop. For example, I connected the assembled amplifier to a computer power supply. There is 12V, which means that at the output I will no longer get 2x35 watts (rated power at 18 V), but approximately 2x22 watts with a load of 8 ohms.

Second point: I cut out all the “guts” from the S90 speakers. The filters that were there had already rotted over the years, dried out, and rotted again. And it seemed to me that they only spoiled the sound, although their purpose was to separate channels by frequency. I connected everything directly, although this is very incorrect, and replaced the standard tweeters with silk ones. The sound has changed for the better. Either because of the new amplifier, or because of the replacement of tweeters, or because of the exclusion of old “micro” circuits (the size of a bucket :)) from the circuit.

Here is a description, photo, review and diagram of a slightly simpler microcircuit than mine (And I don’t even remember the markings of mine):
link

Here's what it all looked like for me:
(The photo was taken in the corridor, a minute before one of the Hitforum visitors bought this amplifier, along with the speakers, from me). I hope he was pleased with the purchase and it has served him faithfully to this day.

It was torn out of the speaker body because at first I didn’t intend to sell it, but then I thought that I no longer needed it, and so I sold it, adding a little more money to the price of the speakers.

As you can see from the photos, the main size here is occupied by the radiator and cooler. By the way, the radiator is from the motherboard chipset. Now can you roughly imagine the size of the entire structure? :)

Of course, the assembly has a number of shortcomings, an experienced solderer will say. And she doesn't look respectable. Nevertheless, everything worked perfectly, and this was the first (and only) time I assembled a structure of this level.