• 20.09.2014

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• 21.09.2014

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• 12.12.2015

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• 23.09.2014

  A clock with a static indication has a brighter glow of indicators compared to a dynamic indication, the diagram of such a clock is shown in Figure 1. The K176ID2 decoder is used as an indicator control device, this microcircuit will provide a sufficiently high brightness of the glow LED indicator... K561IE10 microcircuits are used as counters, each contains 20a four-bit ...

By purchasing good laptop or a cool phone, we are delighted with the purchase, admiring the many features and the speed of the device. But it is worth connecting the gadget to the speakers to listen to music or watch a movie, we understand that the sound produced by the device, as they say, "pumped up". Instead of full and clear sound, we hear unintelligible whispers with background noise.

But do not get upset and scold the manufacturers, the sound problem can be solved on your own. If you know a little about microcircuits and know how to solder well, then it will not be difficult for you to make your own sound amplifier. In our article we will tell you how to make a sound amplifier for each type of device.

At the initial stage of work on creating an amplifier, you need to find tools and buy component parts. The amplifier circuit is made on a printed circuit board using a soldering iron. To create microcircuits, use special soldering stations that you can buy at the store. The use of a printed circuit board allows you to make the device compact and easy to use.

Audio amplifier

Do not forget about the features of compact single-channel amplifiers based on TDA series microcircuits, the main of which is the selection a large number heat. So try with internal structure amplifier, exclude contact of the microcircuit with other parts. For additional cooling of the amplifier, it is recommended to use a radiator grill for heat dissipation. The size of the grid depends on the chip model and the power of the amplifier. Plan ahead for the heat sink location in the amplifier enclosure.
Another feature self-made audio amplifier is low power consumption. This in turn allows the amplifier to be used in a car by connecting it to a battery or on the road using battery power. Simplified amplifier models require a voltage of only 3 volts.

The main elements of the amplifier

If you are a beginner radio amateur, then for more comfortable work, we recommend that you use the special computer program- Sprint Layout. With this program, you can independently create and view diagrams on your computer. Please note that creating your own schema only makes sense if you have sufficient experience and knowledge. If you are an inexperienced radio amateur, then use ready-made and proven circuits.

Below we give diagrams and descriptions of different options for a sound amplifier:

Headphone audio amplifier

The audio amplifier for portable headphones is not very powerful, but consumes very little power. This is an important factor for battery powered mobile amplifiers. You can also place a connector on the device to power it from the mains through a 3 volt adapter.

Homemade headphone amplifier

To make a headphone amplifier you will need:

• Chip TDA2822 or analogue KA2209.
• Amplifier assembly diagram.
• Capacitors 100 uF 4 pieces.
• Headphone plug socket.
• Adapter connector.
• Approximately 30 centimeters of copper wire.
• Heat dissipating element (for a closed case).

Headphone audio amplifier circuit

The amplifier is manufactured on a printed circuit board or surface-mounted. Do not use a pulse transformer with this type of amplifier as it may cause interference. Once manufactured, this amplifier is capable of delivering powerful and enjoyable sound from your phone, player or tablet.
You can check out another version of a homemade headphone amplifier in the video:

Sound amplifier for laptop

An amplifier for a laptop is assembled in cases where the power of the built-in speakers is not enough for normal listening, or if the speakers are out of order. The amplifier should be rated for external speakers up to 2 watts and winding resistance up to 4 ohms.

Sound amplifier for laptop

To assemble the amplifier you will need:

• Printed circuit board.
• Chip TDA 7231.
• 9 volt power supply.
• Component housing.
• Non-polar capacitor 0.1 μF - 2 pieces.
• Polar capacitor 100 μF - 1 piece.
• Polar capacitor 220 uF - 1 piece.
• Polar capacitor 470 uF - 1 piece.
• Constant resistor 10 Kom - 1 piece.
• Constant resistor 4.7 Ohm - 1 piece.
• Two-position switch - 1 piece.
• Loudspeaker input jack - 1 piece.

Sound amplifier circuit for laptop

The assembly order is determined independently, depending on the scheme. The cooling heatsink must be sized so that the operating temperature inside the amplifier enclosure does not exceed 50 degrees Celsius. If you plan to use the device outdoors, then you need to make a case for it with holes for air circulation. For the case, you can use a plastic container or plastic boxes from under the old radio equipment.
You can see a visual instruction in the video:

Sound amplifier for car radio

This amplifier for a car radio is assembled on a TDA8569Q microcircuit, the circuit is not complicated and very common.

Sound amplifier for car radio

The microcircuit has the following declared characteristics:

• Input power 25 watts per channel at 4 ohms and 40 watts per channel at 2 ohms.
• Supply voltage 6-18 volts.
• The range of reproducible frequencies is 20-20000 Hz.

For use in a car, a filter must be added to the circuit against interference that is created by the generator and the ignition system. The microcircuit is also protected against short circuit at the outlet and overheating.

Sound amplifier circuit for car radio

Checking the presented diagram, make a purchase necessary components... Next draw printed circuit board and drill holes in it. Then etch the board with ferric chloride. In conclusion, we tinker and begin to solder the components of the microcircuit. Please note that it is better to cover the power tracks with a thicker layer of solder so that there are no drawdowns in the power supply.
You need to install a radiator on the microcircuit or organize active cooling using a cooler, otherwise the amplifier will overheat at increased volume.
After assembling the microcircuit, it is necessary to make a filter for power supply according to the diagram below:

Anti-interference filter circuit

The choke in the filter is wound in 5 turns, with a wire with a cross section of 1-1.5 mm, on a ferite ring with a diameter of 20 mm.
Also, this filter can be used if your radio tape recorder catches "pickups".
Attention! Be careful not to reverse the polarity of the power supply, otherwise the microcircuit will burn out instantly.
How to make an amplifier for a stereo signal, you can also learn from the video:

Transistor Sound Amplifier

As a schema for transistor amplifier use the diagram below:

Transistor audio amplifier circuit

The scheme, although old, has a lot of fans, for the following reasons:

• Simplified installation due to the small number of elements.
• There is no need to sort out transistors in complementary pairs.
• 10 watts of power, with a margin is enough for living rooms.
• Good compatibility with new sound cards and players.
• Great sound quality.

Start assembling the amplifier from the power supply. Separate the two channels for stereo with two secondary windings coming from the same transformer. On the model, make bridges on Schottky diodes for the rectifier. After the bridges, there are CRC filters from two 33000 uF capacitors and a 0.75 Ohm resistor between them. The resistor in the filter needs a powerful cement one, at a quiescent current of up to 2A it will dissipate 3W of heat, so it is better to take it with a margin of 5-10W. The rest of the resistors in the circuit, 2 W of power will be enough.

Transistor amplifier

Moving on to the amplifier board. Everything except the Tr1 / Tr2 output transistors is on the board itself. The output transistors are mounted on heatsinks. It is better to first put resistors R1, R2 and R6 with trimmers, after all adjustments, evaporate, measure their resistance and solder the final constant resistors with the same resistance. The setting is reduced to the following operations - using R6, it is set so that the voltage between X and zero is exactly half of the voltage + V and zero. Then, using R1 and R2, the quiescent current is set - we put the tester to measure the direct current and measure the current at the input point of the power supply plus. The quiescent current of the amplifier in class A is maximum and, in fact, in the absence of an input signal, all goes into thermal energy. For 8 ohm speakers, this current should be 1.2 A at 27 volts, which means 32.4 watts of heat per channel. Since setting the current can take several minutes, the output transistors must already be on the cooling heatsinks, otherwise they will quickly overheat.
When adjusting and underestimating the resistance of the amplifier, the cutoff frequency of the low-frequency can increase, therefore, for a capacitor at the input, it is better to use not 0.5 microfarads, but 1 or even 2 microfarads in a polymer film. It is believed that this circuit is not prone to self-excitation, but just in case, a Zobel circuit is placed between point X and ground: R 10 Ohm + C 0.1 μF. Fuses must be installed both on the transformer and on the power input of the circuit.
It is a good idea to use thermal paste to maximize contact between the transistor and the heatsink.
Now a few words about the case. The size of the case is set by radiators - NS135-250, 2500 square centimeters per transistor. The body itself is made of plexiglass or plastic. Having assembled the amplifier, before you start enjoying the music, you need to properly ground the ground to minimize the background. To do this, connect the SZ to the minus of the input-output, and bring the remaining minuses to the "star" near the filter capacitors.

Transistor audio amplifier housing

The approximate cost of consumables for a transistor sound amplifier:

• Filter capacitors 4 pieces - 2700 rubles.
• Transformer - 2200 rubles.
• Radiators - 1800 rubles.
• Output transistors - 6-8 pieces 900 rubles.
• Small elements (resistors, capacitors, transistors, diodes) about - 2000 rubles.
• Connectors - 600 rubles.
• Plexiglass - 650 rubles.
• Paint - 250 rubles.
• Board, wires, solder about - 1000 rubles

The result is an amount of 12,100 rubles.
You can also watch a video on assembling an amplifier on germanium transistors:

Vacuum tube amplifier

Simple scheme tube amplifier consists of two stages - preamplifier for 6N23P and a power amplifier for 6P14P.

Tube amplifier circuit

As can be seen from the diagram, both stages operate in a triode connection, and the anode current of the lamps is close to the limiting one. The currents are built up by cathode resistors - 3mA for the input and 50mA for the output lamp.
Parts used for the tube amplifier must be new and High Quality... The permissible deviation of the resistor ratings can be plus or minus 20%, and the capacitances of all capacitors can be increased by 2-3 times.
Filter capacitors must be rated for at least 350 volts. The interstage capacitor must be designed for the same voltage. Transformers for the amplifier can be conventional - TV31-9 or a more modern analogue - TWSE-6.

Vacuum tube amplifier

It is better not to install the volume and stereo balance control on the amplifier, since these adjustments can be made in the computer itself or the player. Input lamp is selected from - 6N1P, 6N2P, 6N23P, 6N3P. 6P14P, 6P15P, 6P18P or 6P43P (with increased cathode resistor resistance) are used as the output pentode.
Even if you have a working transformer, it is better to use a regular transformer with a 40-60 watt rectifier to turn on the foot amplifier for the first time. Only after successful testing and tuning of the amplifier can a pulse transformer be installed.
Use standard sockets for plugs and cables; to connect speakers it is better to install “pedals” on 4 pins.
A case for a claw amplifier is usually made from a shell of old technology or cases of system units.
You can watch another version of the tube amplifier in the video:

Classification of audio amplifiers

So that you can determine to which class of sound amplifiers the device you have assembled belongs, check out the UMZCH classification below:

Class A amplifier

• • Class A- amplifiers of this class operate without clipping the signal in the linear section of the current-voltage characteristics of the amplifying elements, which ensures a minimum of nonlinear distortion. But this comes at the price of a large amplifier and enormous power consumption. The efficiency of a class A amplifier is only 15-30%. This class includes tube and transistor amplifiers.

Class B amplifier

• • Class B- Class B amplifiers operate with a 90 degree cutoff. For such an operation, a push-pull circuit is used, in which each part amplifies its half of the signal. The main disadvantage of class B amplifiers is signal distortion due to the stepwise transition of one half-wave to another. The advantage of this class of amplifiers is considered to be high efficiency, sometimes reaching 70%. But despite high productivity, modern class B amplifier models, you will not find on the shelves.

Class AB amplifier

• • Class AB- this is an attempt to combine amplifiers of the classes described above, in order to achieve the absence of signal distortion and high efficiency.

Class H amplifier

• • Class H- designed specifically for vehicles that have limited voltage supply to the output stages. The reason for the creation of class H amplifiers is that the real sound signal has a pulse character and its average power is much lower than the peak. The circuit of this class of amplifiers is based on simple circuit for a class AB amplifier, operating in a bridge circuit. Added only a special circuit for doubling the supply voltage. The main element of the doubling circuit is a high-capacity storage capacitor, which is constantly charged from the main power source. At power peaks, this capacitor is connected by a control circuit with the main power supply. The power supply voltage of the amplifier's output stage is doubled, allowing it to cope with the transmission of signal peaks. The efficiency of class H amplifiers reaches 80%, with a signal distortion of only 0.1%.

Class D amplifier

• Class D is a separate class of amplifiers called "digital amplifiers". Digital conversion provides additional features on sound processing: from adjusting the volume and tone to the implementation of digital effects such as reverb, noise suppression, acoustic suppression feedback... Unlike analog amplifiers, the output of Class D amplifiers is rectangular. Their amplitude is constant, and their duration varies depending on the amplitude. analog signal input to the amplifier. The efficiency of amplifiers of this type can reach 90% -95%.

In conclusion, I would like to say that engaging in radio electronics requires a large amount of knowledge and experience that is acquired over a long time. Therefore, if something did not work out for you, do not be discouraged, reinforce your knowledge from other sources and try again!

This amplifier, in theory, is the most simple amplifier audio frequency. The power component is quite powerful transistor Darlington. Composite transistors have great amplification - it is this chip that is the basis for the operation of such an amplifier.

The output power, as with any amplifier, depends on the supply voltage. Our version starts working when the supply voltage is below 1 volt - this is enough to open the composite transistor.

The circuit works with an input signal above 0.5 Volts - the sound can be fed directly from the PC port, while no additional preamplifiers are needed.

The maximum output power of such an amplifier reaches 1 watt, note that the amplifier itself operates in pure class A!

The composite transistor was taken from the old motherboard, although any composite transistors, regardless of the conductivity, in our case, a direct transistor is used, in the case of the opposite, it will be necessary to change the polarity of the supply voltage.

The transistor can be successfully replaced with ours - KT829 or with more powerful ones - KT827, 825 and others.

Due to the operating mode of the amplifier, the transistor will always be open, therefore the heat generation on it will be quite large, therefore the transistor is attached to the heat sink.

The resistance of the limiting resistor is selected in the region from 6 to 56 ohms, the power is preferably 2-5 watts, part of the initial power will also be dissipated on it. The amplifier efficiency is 20-25%.

At the expense of sound quality - class A does its job. This amplifier sounds better by ear recently assembled amplifier Houston, velvet sound, no distortion.

Important! the amplifier operates on a high-impedance load - in my case, 16 Ohm, with low-impedance heads the result was not the best.

Best regards - AKA KASYAN

Good afternoon, dear habrauser, I want to tell you about the basics of building audio amplifiers. I think this article will be of interest to you if you have never been involved in radio electronics, and of course it will be funny to those who do not part with a soldering iron. And so I will try to tell about this topic as simply as possible and unfortunately omitting some of the nuances.

An audio frequency amplifier or a low frequency amplifier, in order to understand how it still works and why there are so many different transistors, resistors and capacitors, you need to understand how each element works and try to find out how these elements work. In order to assemble a primitive amplifier, we need three types of electronic elements: resistors, capacitors and, of course, transistors.

Resistor

So, our resistors are characterized by resistance to electric current and this resistance is measured in Ohms. Each electrically conductive metal or metal alloy has its own specific resistance. If we take a wire of a certain length with a high resistivity, then we get a real wirewound resistor. In order for the resistor to be compact, the wire can be wound around the frame. Thus, we get a wirewound resistor, but it has a number of disadvantages, so resistors are usually made of cermet material. This is how the resistors on electrical diagrams:

The upper version of the designation was adopted in the USA, the lower one in Russia and in Europe.

Capacitor

A capacitor consists of two metal plates separated by a dielectric. If we apply a constant voltage to these plates, then an electric field will appear, which, after turning off the power, will maintain positive and negative charges on the plates, respectively.

The basis of the design of the capacitor is two conductive plates, between which there is a dielectric

Thus, the capacitor is able to accumulate electric charge... This ability to accumulate an electric charge is called electrical capacity, which is the main parameter of a capacitor. Capacitance is measured in Farads. What is also characteristic is that when we charge or discharge a capacitor, it goes through electricity... But as soon as the capacitor is charged, it stops passing electric current, and this is because the capacitor has taken the charge of the power source, that is, the potential of the capacitor and the power source are the same, and if there is no potential difference (voltage), there is no electric current. Thus, a charged capacitor does not pass a direct electric current, but passes an alternating current, since when connected to an alternating electric current, it will be constantly charged and discharged. On electrical diagrams, it is designated as follows:

Transistor

In our amplifier, we will use the simplest bipolar transistors. The transistor is made from a semiconductor material. The property we need is this material - the presence in them of free carriers of both positive and negative charges. Depending on which charges are greater, semiconductors are distinguished into two types by conductivity: n-type and p-type (n-negative, p-positive). Negative charges are electrons released from the outer shells of atoms in the crystal lattice, and positive charges are the so-called holes. Holes are vacancies that remain in the electron shells after electrons leave them. Let us conventionally denote atoms with an electron in the outer orbit by a blue circle with a minus sign, and atoms with a vacant place - by an empty circle:


Each bipolar transistor consists of three zones of such semiconductors, these zones are called base, emitter and collector.


Let's look at an example of how a transistor works. To do this, connect two batteries for 1.5 and 5 volts to the transistor, with a plus to the emitter, and a minus to the base and collector, respectively (see the figure):

An electromagnetic field will appear at the contact between the base and the emitter, which literally rips out electrons from the outer orbit of the base atoms and transfers them to the emitter. Free electrons leave holes behind them, and occupy vacant places already in the emitter. The same electromagnetic field has the same effect on the atoms of the collector, and since the base in the transistor is rather thin relative to the emitter and collector, the collector electrons pass through it quite easily into the emitter, and in much larger quantities than from the base.

If we turn off the voltage from the base, then there will be no electromagnetic field, and the base will act as a dielectric, and the transistor will be closed. Thus, by applying a sufficiently low voltage to the base, we can control a higher voltage applied to the emitter and collector.

The transistor we considered pnp-type, since he has two p-zones and one n-zone. There are also npn- transistors, the principle of operation in them is the same, but the electric current flows in them in the opposite direction than in the transistor we have considered. Like this bipolar transistors are indicated on the electrical diagrams, the arrow indicates the direction of the current:

ULF

Well, let's try to design a low-frequency amplifier out of all this. First, we need a signal that we will amplify, it can be sound card computer or any other audio device with line-out. Let's say our signal has a maximum amplitude of about 0.5 volts at a current of 0.2 A, something like this:

And in order for the simplest 4-ohm 10-watt speaker to work, we need to increase the signal amplitude to 6 volts, with a current I = U / R= 6/4 = 1.5 A.

So, let's try to connect our signal to a transistor. Remember our circuit with a transistor and two batteries, now instead of 1.5 volt battery we have a line-out signal. Resistor R1 acts as a load so that there is no short circuit and our transistor does not burn out.

But here two problems arise at once, firstly, our transistor npn-type, and opens only when the half-wave is positive, and closes when negative.

Secondly, a transistor, like any semiconductor device, has nonlinear characteristics with respect to voltage and current, and the lower the current and voltage values, the stronger these distortions:

Not only is there only a half-wave left of our signal, it will also be distorted:

This is the so-called crossover distortion.

To get rid of these problems, we need to shift our signal to the working area of ​​the transistor, where the entire sinusoid of the signal will fit and the nonlinear distortion will be insignificant. To do this, a bias voltage is applied to the base, say 1 volt, using a voltage divider composed of two resistors R2 and R3.

And our signal entering the transistor will look like this:

Now we need to extract our useful signal from the collector of the transistor. To do this, install capacitor C1:

As we remember, the capacitor passes alternating current and does not pass direct current, so it will serve as a filter for us, passing only our useful signal - our sinusoid. And the constant component that has not passed through the capacitor will be dissipated on the resistor R1. The alternating current, our useful signal, will tend to pass through the capacitor, since the resistance of the capacitor for it is negligible compared to the resistor R1.

So the first transistor stage of our amplifier turned out. But there are two more little nuances:

We do not know 100% what signal is entering the amplifier, all of a sudden the signal source is faulty, anything can happen, again, static electricity or a constant voltage passes along with the useful signal. This can cause the transistor to not work properly or even provoke its breakdown. To do this, we will install a capacitor C2, it, like capacitor C1, will block a direct electric current, and also the limited capacity of the capacitor will not allow peaks of large amplitude to pass through, which can damage the transistor. These power surges usually occur when the device is turned on or off.

And the second nuance, any signal source requires a certain specific load (resistance). Therefore, the input impedance of the stage is important for us. To adjust input impedance add resistor R4 to the emitter circuit:

We now know the purpose of each resistor and capacitor in the transistor stage. Let's now try to calculate what element denominations you need to use for it.

Initial data:

• U= 12 V - supply voltage;
• U bae~ 1 V - Voltage emitter-base of the operating point of the transistor;

We choose a transistor, it is suitable for us npn-transistor 2N2712

• P max= 200 mW - maximum power dissipation;
• I max= 100 mA - maximum constant collector current;
• U max= 18 V - the maximum allowable collector-base / collector-emitter voltage (We have a supply voltage of 12 V, so there is enough with a margin);
• U eb= 5 V - the maximum allowable emitter-base voltage (our voltage is 1 volt ± 0.5 volts);
• h21= 75-225 - base current amplification factor, the minimum value is taken - 75;

1. We calculate the maximum static power of the transistor, it is taken 20% less than the maximum dissipated power, so that our transistor does not work at the limit of its capabilities:

   P article max = 0,8*P max= 0.8 * 200mW = 160mW;

2. Determine the collector current in a static mode (without a signal), despite the fact that no voltage is supplied to the base through the transistor, an electric current still flows to a small extent.

   I k0 =P article max / U ke, where U ke- voltage of the collector-emitter junction. Half of the supply voltage is dissipated on the transistor, the second half will be dissipated on resistors:

   U ke = U / 2;

   I k0 = P article max / (U/ 2) = 160 mW / (12V / 2) = 26.7 mA;

3. Now let's calculate the load resistance, initially we had one resistor R1, which played this role, but since we added a resistor R4 to increase the input resistance of the stage, now the load resistance will be the sum of R1 and R4:

   R n = R1 + R4, where R n - total resistance loads;

   The ratio between R1 and R4 is usually taken as 1 to 10:

   R1 =R4*10;

   Let's calculate the load resistance:

   R1 + R4 = (U / 2) / I k0= (12V / 2) / 26.7 mA = (12V / 2) / 0.0267 A = 224.7 Ohm;

   The closest resistors are 200 and 27 ohms. R1= 200 Ohm, and R4= 27 ohms.

4. Now we find the voltage at the collector of the transistor without a signal:

   U k0 = (U ke0 + I k0 * R4) = (U - I k0 * R1) = (12V -0.0267 A * 200 Ohm) = 6.7 V;

5. Transistor control base current:

   I b = I to / h21, where I to- collector current;

   I to = (U / R n);

   I b = (U / R n) / h21= (12V / (200 Ohm + 27 Ohm)) / 75 = 0.0007 A = 0.07 mA;

6. The total base current is determined by the base bias voltage, which is set by the divider R2 and R3... The current set by the divider must be 5-10 times greater than the base control current ( I b) so that the actual base control current does not affect the bias voltage. Thus, for the divider current value ( I cases) we take 0.7 mA and calculate R2 and R3:

   R2 + R3 = U / I cases= 12V / 0.007 = 1714.3 Ohm

7. Now let's calculate the voltage at the emitter at rest of the transistor ( U uh):

   U uh = I k0 * R4= 0.0267 A * 27 Ohm = 0.72 V

   Yes, I k0 the quiescent current of the collector, but the same current passes through the emitter, so that I k0 consider the quiescent current of the entire transistor.

8. We calculate the total voltage at the base ( U b) taking into account the bias voltage ( U cm= 1B):

   U b = U uh + U cm= 0.72 + 1 = 1.72V

   Now, using the voltage divider formula, we find the values ​​of the resistors R2 and R3:

   R3 = (R2 + R3) * U b / U= 1714.3 Ohm * 1.72 V / 12 V = 245.7 Ohm;

   The closest resistor rating is 250 Ohm;

   R2 = (R2 + R3) - R3= 1714.3 Ohm - 250 Ohm = 1464.3 Ohm;

   We select the resistor value in the direction of decreasing, the closest R2= 1.3 kΩ.

9. Capacitors C1 and C2 usually set at least 5 μF. The capacity is chosen so that the capacitor does not have time to recharge.

Conclusion

At the output of the stage, we get proportionally amplified signal and by current and voltage, that is, by power. But one stage is not enough for the required gain, so we have to add the next and the next ... And so on.

The considered calculation is rather superficial and such an amplification scheme is certainly not used in the structure of amplifiers, we must not forget about the range of pass frequencies, distortions and much more.

Readers! Remember the nickname of this author and never repeat his schemes.
Moderators! Before you ban me for insults, think that you have "let an ordinary gopnik near the microphone", who should not even be allowed close to radio equipment and, moreover, to teaching beginners.

Firstly, with such a switching scheme, a large direct current will flow through the transistor and speaker, even if the variable resistor is in the right 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 a variable. Any homemade product will turn the variable resistor regulator all the way, it will have zero resistance and a large current will go 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, for immediately there was a reader who removed it just like that, considering himself smarter than the author). Without it, only those players in which such protection is already installed on the output will work normally. And if it is not there, then the output of the player may be damaged, especially, as I said above, if you unscrew the variable resistor "to zero". In this case, the output of an expensive laptop will be supplied with voltage from the power source of this penny trinket and it may burn out. Self-made, very fond of removing protective resistors and capacitors, because "it works the same!" As a result, the circuit can 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 a trimmer, that is, it should be adjusted once and closed in the case, 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 that smoke does not come from the speaker. Therefore, in no case should it be accessible from the outside. You can NOT adjust the volume by changing the mode. For this you need to "kill". If you really want to control the volume, it's easier to turn on another variable resistor in series with the capacitor, and now it can be brought out to the amplifier case.

In general, for the simplest circuits - and in order to work immediately and in order 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 any speaker without even noticing it).