The simplest low-frequency amplifiers using transistors. Transistor amplifier: types, circuits, simple and complex Amplifier power supply

Board assembly

Amplifier characteristics when operating at a 4 Ohm load (TDA7294 IC):
Operating frequency range, Hz 20-20,000
Supply voltage @4 Ohm, V ±30
Supply voltage @8 Ohm, V ±40
Rated input voltage, V 0.6 rms.
Rated output power, W 73 rms.
Input impedance, kOhm 9.4
THD at 70W, no more, % 0.3 *
THD at 60W, no more, % 0.01 *
*manufacturer specifications

Details:

Resistors: All resistors, except R7 and R8, are carbon or metal film 0.125-0.25 W (it is advisable to take more precise resistors, where the spread varies + -1%).

Capacitors: C1 – film, the highest available quality, lavsan or polypropylene (MKT or MKP) for minimum voltage (usually 50V). In the absence of access to expensive thoroughbred components, the K73-17 at 63V will also give a satisfactory result. C4 C7 C8 C9 film type K73-17 at 63V.

Diodes: D1 – any 12..15V zener diode with a power of at least 0.5W.
Amplifier chip– any of the TDA729x line (7296..7293). When using TDA7293, you must bite off or bend and do not solder the 5th leg. In general, just in case, this applies to all microcircuits in the line.

ATTENTION! The amplifier's power supply is bipolar. Both output terminals of the amplifier are “hot”, neither of them is grounded, because The acoustic system is also a feedback link. The speaker is connected between OUT+ and OUT-. The radiator of the microcircuit should also be grounded. This is a prerequisite for stable operation of the microcircuit. It is afraid of static - it must be isolated from the radiator, and the radiator must be grounded to the middle power point. That is, there is a radiator, a layer of thermal paste, then a mica gasket, a layer of thermal paste, and a microcircuit. The microcircuit must be screwed to the radiator through a dielectric washer. We also screw the wire to the radiator and connect it to the board at the GND point

P.S: I personally liked the sound of the TDA7293 chip, the bass is stronger and its reliability seems to be better. If it is possible, instead of large electrolytes 2200x63v, put 3300x63v, then it will be even better, the main thing is that they fit on the board. And for power supply, it is advisable to use + -35V, although it is written that it works at + -40V, but this is its limit, with a strong voltage surge it can fail!

I wish you all success in the assembly and pleasant listening!

After mastering the basics of electronics, the novice radio amateur is ready to solder his first electronic designs. Audio power amplifiers are typically the most repeatable designs. There are quite a lot of schemes, each with its own parameters and design. This article will discuss several simple and fully working amplifier circuits that can be successfully repeated by any radio amateur. The article does not use complex terms and calculations; everything is simplified as much as possible so that no additional questions arise.

Let's start with a more powerful circuit.
So, the first circuit is made on the well-known TDA2003 microcircuit. This is a mono amplifier with an output power of up to 7 watts into a 4 ohm load. I want to say that the standard circuit for connecting this microcircuit contains a small number of components, but a couple of years ago I came up with a different circuit on this microcircuit. In this circuit, the number of components is reduced to a minimum, but the amplifier has not lost its sound parameters. After developing this circuit, I began making all my amplifiers for low-power speakers using this circuit.

The circuit of the presented amplifier has a wide range of reproducible frequencies, a supply voltage range from 4.5 to 18 volts (typical 12-14 volts). The microcircuit is installed on a small heat sink, since the maximum power reaches up to 10 Watts.

The microcircuit is capable of operating at a load of 2 ohms, which means that 2 heads with a resistance of 4 ohms can be connected to the amplifier output.
The input capacitor can be replaced with any other one, with a capacity from 0.01 to 4.7 μF (preferably from 0.1 to 0.47 μF), you can use both film and ceramic capacitors. It is advisable not to replace all other components.

Volume control from 10 to 47 kOhm.
The output power of the microcircuit allows it to be used in low-power speakers for PCs. It is very convenient to use the chip for stand-alone speakers for a mobile phone, etc.
The amplifier works immediately after switching on and does not require additional adjustment. It is recommended to additionally connect the power supply minus to the heat sink. It is advisable to use all electrolytic capacitors at 25 Volts.

The second circuit is assembled using low-power transistors and is more suitable as a headphone amplifier.

This is probably the highest quality circuit of its kind, the sound is clear, you can feel the entire frequency spectrum. With good headphones, it feels like you have a full-fledged subwoofer.

The amplifier is assembled with only 3 reverse conduction transistors; as the cheapest option, transistors of the KT315 series were used, but their choice is quite wide.

The amplifier can operate at a low-impedance load, up to 4 ohms, which makes it possible to use the circuit to amplify the signal of a player, radio, etc. A 9-volt Krona battery is used as a power source.
The final stage also uses KT315 transistors. To increase the output power, you can use KT815 transistors, but then you will have to increase the supply voltage to 12 volts. In this case, the amplifier power will reach up to 1 Watt. The output capacitor can have a capacity from 220 to 2200 µF.
The transistors in this circuit do not heat up, therefore, no cooling is needed. If you use larger output transistors, you may need small heat sinks for each transistor.

And finally - the third scheme. An equally simple, but proven version of the amplifier structure is presented. The amplifier is capable of operating from reduced voltage to 5 volts, in which case the PA output power will be no more than 0.5 W, and the maximum power with a 12 volt supply reaches up to 2 Watts.

The output stage of the amplifier is built on a domestic complementary pair. The amplifier is regulated by selecting resistor R2. To do this, it is advisable to use a 1 kOhm trimmer. Slowly rotate the regulator until the quiescent current of the output stage is 2-5 mA.

The amplifier does not have high input sensitivity, so it is advisable to use a pre-amplifier before the input.

The diode plays a significant role in the circuit; it is here to stabilize the mode of the output stage.
The output stage transistors can be replaced with any complementary pair of corresponding parameters, for example KT816/817. The amplifier can power low-power stand-alone speakers with a load resistance of 6-8 ohms.

List of radioelements

Typical mistakes when designing germanium amplifiers occur due to the desire to get a wide bandwidth, low distortion, etc. from the amplifier.
Here is a diagram of my first germanium amplifier, designed by me in 2000.
Although the circuit is quite functional, its sound qualities leave much to be desired.

Practice has shown that the use of differential cascades, current generators, cascades with dynamic loads, current mirrors and other tricks with environmental feedback do not always lead to the desired result, and sometimes simply lead to a dead end.
The best practical results for obtaining high sound quality are obtained by using single-ended cascades. amplification and the use of inter-stage matching transformers.
We present to your attention a germanium amplifier with an output power of 60 W, into a load of 8 ohms. Output transistors used in the amplifier are P210A, P210Sh. Linearity 20-16000Hz.
There is practically no subjective lack of high frequencies.
With a 4-ohm load, the amplifier produces 100 watts.

Amplifier circuit using P-210 transistors.

The amplifier is powered by an unstabilized power supply with a bipolar output voltage of +40 and -40 volts.
For each channel, a separate bridge of D305 diodes is used, which are installed on small radiators.
Filter capacitors, it is advisable to use at least 10,000 microns per arm.
Power transformer data:
-iron 40 to 80. The primary winding contains 410 vit. wires 0.68. Secondary at 59 vit. 1.25 wires, wound four times (two windings - the upper and lower arms of one amplifier channel, the remaining two - the second channel)
.Additionally regarding the power transformer:
iron w 40 by 80 from the power supply of the KVN TV. After the primary winding, a copper foil screen is installed. One open turn. A lead is soldered to it which is then grounded.
You can use any iron that has a suitable cross-section.
The matching transformer is made of Sh20 by 40 iron.
The primary winding is divided into two parts and contains 480 vit.
The secondary winding contains 72 turns and is wound in two wires simultaneously.
First, 240 vit of the primary is wound, then the secondary, then again 240 vit of the primary.
The diameter of the primary wire is 0.355 mm, the secondary wire is 0.63 mm.
The transformer is assembled into a joint, the gap is a cable paper gasket of approximately 0.25 mm.
A 120 Ohm resistor is included to ensure no self-excitation when the load is off.
Chains 250 Ohm +2 x 4.7 Ohm are used to supply the initial bias to the bases of the output transistors.
Using 4.7 Ohm trimmers, the quiescent current is set to 100mA. The resistors in the emitters of the output transistors are 0.47 Ohms, and there should be a voltage of 47 mV.
The output transistors P210 should be almost barely warm.
To accurately set the zero potential, 250 Ohm resistors must be precisely selected (in a real design they consist of four 1 kOhm 2W resistors).
To smoothly set the quiescent current, trimming resistors R18, R19 type SP5-3V 4.7 Ohm 5% are used.
The rear view of the amplifier is shown in the photo below.

May I know your impressions of the sound of this version of the amplifier, in comparison with the previous transformerless version on the P213-217?

Even more rich, juicy sound. I would especially like to emphasize the quality of the bass. The listening was carried out with open acoustics on 2A12 speakers.

- Jean, why exactly are P215 and P210, and not GT806/813, included in the diagram?

Carefully look at the parameters and characteristics of all these transistors, I think you will understand everything, and the question will disappear by itself.
I am clearly aware of the desire of many to make the germanium amplifier more broadband. But the reality is that many high-frequency germanium transistors are not entirely suitable for audio purposes. Of the domestic ones, I can recommend P201, P202, P203, P4, 1T403, GT402, GT404, GT703, GT705, P213-P217, P208, P210. The method of expanding the bandwidth is the use of circuits with a common base, or the use of imported transistors.
The use of circuits with transformers has made it possible to achieve excellent results on silicon. An amplifier based on 2N3055 has been developed.
I'll share it soon.

- What about the “0” at the output? With a current of 100 mA, it is hard to believe that it will be possible to keep it at an acceptable +-0.1 V during operation.
In similar circuits 30 years ago (Grigoriev’s circuit), this is solved either by a “virtual” midpoint or by an electrolyte:

Grigoriev amplifier.

The zero potential is maintained within the limit you specify. The quiescent current can be set to 50mA. Monitored with an oscilloscope until the step disappears. No more need. Further, all op-amps can easily handle a 2k load. Therefore, there are no special coordination problems with CD.
Some high-frequency germanium transistors require attention and additional study in audio circuits. 1T901A, 1T906A, 1T905A, P605-P608, 1TS609, 1T321. Try it and gain experience.
Sometimes there were sudden failures of transistors 1T806, 1T813, so I can recommend them with caution.
They need to install “fast” current protection, designed for a current greater than the maximum in a given circuit. To prevent protection from triggering in normal mode. Then they work very reliably.
I’ll add my version of Grigoriev’s scheme

Version of Grigoriev's amplifier circuit.

By selecting a resistor from the base of the input transistor, half the supply voltage is set at the point where the 10 ohm resistors connect. By selecting a resistor in parallel with the 1N4148 diode, the quiescent current is established.

- 1. In my reference books, D305 is normalized to 50V. Is it safer to use D304? I think 5A is enough.
- 2. Indicate real h21 for devices installed in this layout or their minimum required values.

You are absolutely right. If there is no need for high power. The voltage across each diode is about 30V, so there are no reliability issues. Transistors with the following parameters were used; P210 h21-40, P215 h21-100, GT402G h21-200.

Readers! Remember this author's nickname and never repeat his schemes.
Moderators! Before you ban me for insulting me, think that you “allowed an ordinary gopnik to the microphone, who should not even be allowed close to radio engineering and, especially, to teaching beginners.

Firstly, with such a connection scheme, a large direct current will flow through the transistor and speaker, even if the variable resistor is in the desired position, that is, music will be heard. And with a large current, the speaker is damaged, that is, sooner or later, it will burn out.

Secondly, in this circuit there must be a current limiter, that is, a constant resistor, at least 1 KOhm, connected in series with an alternating one. Any homemade product will turn the variable resistor knob all the way, it will have zero resistance and a large current will flow to the base of the transistor. As a result, the transistor or speaker will burn out.

A variable capacitor at the input is needed to protect the sound source (the author should explain this, because there was immediately a reader who removed it just like that, considering himself smarter than the author). Without it, only those players that already have similar protection at the output will work normally. And if it is not there, then the player’s output may be damaged, especially, as I said above, if you turn the variable resistor “to zero”. In this case, the output of the expensive laptop will be supplied with voltage from the power source of this cheap trinket and it may burn out. Homemade people love to remove protective resistors and capacitors, because “it works!” As a result, the circuit may work with one sound source, but not with another, and even an expensive phone or laptop can be damaged.

The variable resistor in this circuit should only be tuning, that is, it should be adjusted once and closed in the housing, and not brought out with a convenient handle. This is not a volume control, but a distortion control, that is, it selects the operating mode of the transistor so that there is minimal distortion and so that no smoke comes out of the speaker. Therefore it should under no circumstances be accessible from the outside. You CANNOT adjust the volume by changing the mode. This is something to kill for. If you really want to regulate the volume, it’s easier to connect another variable resistor in series with the capacitor and now it can be output to the amplifier body.

In general, for the simplest circuits - and to make it work right away and not to damage anything, you need to buy a TDA type microcircuit (for example TDA7052, TDA7056... there are many examples on the Internet), and the author took a random transistor that was lying around in his desk. As a result, gullible amateurs will look for just such a transistor, although its gain is only 15, and the permissible current is as much as 8 amperes (it will burn out any speaker without even noticing).

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 the amplifier microcircuits 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 volts. Moreover, this capacitor should be as large as possible; I have 2 capacitors of 2200 μF 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 need 3-5 volts to operate, others need 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 resistance of the speaker 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.