Amplifier circuits for computer speakers. A simple and inexpensive do-it-yourself amplifier for acoustics

Sometimes connecting speakers to a TV, laptop or other similar music source needs signal amplification through a certain device. If you have basic technical knowledge, you can make an amplifier at home with your own hands.

How to create a sound amplifier correctly

First of all, to assemble such a device for speakers, you will need tools, as well as the required components. The circuits of the simplest amplifiers are assembled by means of a soldering iron equipped on a support of a high degree of stability. It is advisable to use certain soldering stations.

In the process of assembling an amplifier with your own hands to test the corresponding circuit, or use it for a short period of time, a model on a wire would be a good option, but it will require a lot of free space for the arrangement of component elements.

The printed-circuit board serves as a guarantee of maximum compactness of the device and convenient use in the future.

A demanded and affordable amplifier for headphones or small speakers is made on the basis of a microcircuit representing a small-sized control unit with an embedded set of commands for controlling the electrical signal.

A pair of resistors and, of course, capacitors should be connected to the circuit with the desired microcircuit. In total, the price of a self-assembled amplifier will be much lower than the cost of equipment purchased in a specialized store, while the limitation of the functionality consists in changing the signal volume.

Do not forget about the features of single-channel amplifiers, the independent production of which is carried out on the basis of both TDA circuits and their analogues.

The circuit emits a lot of heat during the working process, it is for this reason that its contact with the elements of the device should be minimized. A radiator grill designed for heat dissipation is desirable for use.

Depending on the purchased microcircuit, as well as the power of the device, the size of the required radiator increases. When assembling the amplifier inside the case, you need to think in advance about the place provided under the heat sink.

Another feature of creating an amplifier with your own hands, as shown in the photo, is the minimum power consumption, which makes it possible to use a simplified amplifier in cars, on the road, or at home. Some simple amplifiers only need a few volts.

The power that is consumed directly depends on the required level of signal amplification. The audio amplifier from the player used for the necessary headphones consumes about 3 watts.

For making circuits, an inexperienced radio amateur is better off using a special program for which the files have the required extension.

Handwritten creation of the necessary scheme is possible if you have certain knowledge and a desire to experiment with them. Otherwise, it is better to download files for quick assembly of replacement of the amplifier with the lowest possible frequency.

For laptop

The instructions on how to make an amplifier for a laptop with your own hands provide for the assembly of such a device in such cases: the built-in type speakers are broken or have a low volume quality.

You will need a conventional amplifier with a power of several watts with a winding resistance of 40 ohms. In addition to the usual assembly tools, a printed circuit board, power supply and microcircuit are required. Choose your own case where the amplifier elements will be located.

The assembly process should depend on the downloaded microcircuit format. The radiator is chosen such a parameter that the thermal conductivity makes it possible to maintain the required temperature regime of the microcircuit.

If the device is constantly used along with a laptop outside the room, then it will need a self-made case with certain slots or holes so as not to impede air circulation.

The assembly of such a case is made from a plastic container, or the remains of failed equipment, while the board is fastened with screws.

Tube amplifier

This do-it-yourself amplifier, as in the photo, refers to a rather expensive device if you completely buy the components.

Some radio amateurs have lamps and other necessary parts in stock. Assembling a tube-type amplifier at home is not a difficult matter if you can spend time searching for the necessary circuits on the Runet.

If you need to find out what amplifiers are, it is important to understand that their circuit in each individual version is unique, and also depends directly on the sound source, size, and other important parameters.

DIY photo amplifiers

On Habré there were already publications about DIY-tube amplifiers, which were very interesting to read. No doubt, they sound wonderful, but for everyday use it is easier to use a device with transistors. Transistors are more convenient, since they do not require warming up before operation and are more durable. And not everyone dares to start a lamp saga with anode potentials under 400 V, and transformers for transistor ones of a couple of tens of volts are much safer and simply more affordable.

As a circuit for reproduction, I chose a circuit from John Linsley Hood in 1969, taking the author's parameters based on the impedance of my speakers of 8 ohms.

The classic diagram from a British engineer, published almost 50 years ago, is still one of the most reproducible and receives extremely positive reviews about itself. There are many explanations for this:
- the minimum number of elements simplifies installation. It is also believed that the simpler the design, the better the sound;
- despite the fact that there are two output transistors, they do not need to be sorted into complementary pairs;
- 10 watts output with a margin is enough for ordinary human dwellings, and the input sensitivity of 0.5-1 volts is very well matched with the output of most sound cards or turntables;
- class A - it is also class A in Africa, if we are talking about good sound. Comparison with other classes will be a little lower.

Interior design

The amplifier starts with power. Separation of two channels for stereo is most correct to carry out already from two different transformers, but I limited myself to one transformer with two secondary windings. After these windings, each channel exists on its own, so we must not forget to multiply by two everything mentioned below. On the breadboard we make bridges on Schottky diodes for the rectifier.

It is possible on ordinary diodes or even ready-made bridges, but then they must be shunted with capacitors, and the voltage drop across them is greater. After the bridges, there are CRC filters from two 33000 uF capacitors and a 0.75 Ohm resistor between them. If you take less capacity and a resistor, then the CRC filter will become cheaper and less heated, but the ripple will increase, which is not comme il faut. These parameters, IMHO, are reasonable in terms of price-effect. 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. For the rest of the resistors in the circuit, 2 W is sufficient.

Next, we move on to the amplifier board itself. A bunch of ready-made whales are sold in online stores, but there are no fewer complaints about the quality of Chinese components or illiterate layouts on boards. Therefore, it is better to do it yourself, under your own "loose powder". I made both channels on a single breadboard, so that later I would attach it to the bottom of the case. Run with test items:

Everything except the Tr1 / Tr2 output transistors is on the board itself. Output transistors are mounted on radiators, more on that below. To the author's scheme from the original article, you need to make the following remarks:

Not everything needs to be soldered tightly right away. 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. Setting is reduced to the following operations. First, with the help of R6, it is set so that the voltage between X and zero is exactly half of the voltage + V and zero. In one of the channels, 100 kOhm was not enough for me, so it's better to take these trimmers with a margin. Then, with the help of R1 and R2 (keeping their approximate ratio!), The quiescent current is set - we put the tester to measure direct current and measure this very current at the input point of the power supply plus. I had to significantly reduce the resistance of both resistors to obtain the desired quiescent current. 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, according to the author's recommendation, should be 1.2 A at a voltage of 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 and die. For they are mainly heated.

It is possible that, as an experiment, you will want to compare the sound of different transistors, so you can also leave the possibility of a convenient replacement for them. I tried 2N3906, KT361 and BC557C inputs, there was a slight difference in favor of the latter. In the pre-weekend we tried KT630, BD139 and KT801, stopped at imported ones. Although all of the above transistors are very good and the difference can be rather subjective. At the exit, I put 2N3055 (ST Microelectronics) right away, since many people like them.

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. A Russian picture-diagram "Ultra-linear class A amplifier" is still walking on the Network, where this capacitor is generally proposed as 0.1 microfarad, which is fraught with a cut of all bass at 90 Hz:

They write that this circuit is not prone to self-excitation, but just in case, a Zobel circuit is placed between point X and the ground: R 10 Ohm + C 0.1 microfarad.
- fuses, they can and should be installed both on the transformer and on the power input of the circuit.
- it would be very appropriate to use thermal paste for maximum contact between the transistor and the radiator.

Locksmith and carpentry

Now about the traditionally the most difficult part in DIY - the case. The dimensions of the case are set by the radiators, and they should be large in class A, remember about 30 watts of heat on each side. At first I underestimated this power and made a case with average radiators of 800 cm² per channel. However, with a set quiescent current of 1.2A, they heated up to 100 ° C in 5 minutes, and it became clear that something more powerful was needed. That is, you need to either install larger radiators or use coolers. I didn’t want to make a quadrocopter, so I bought giant beauties HS 135-250 with an area of ​​2500 cm² for each transistor. As practice has shown, such a measure turned out to be a little redundant, but now the amplifier can be easily touched with your hands - the temperature is only 40 ° C even in rest mode. Drilling holes in the radiators for fasteners and transistors became a certain problem - the originally purchased Chinese drills for metal were drilled extremely slowly, each hole would take at least half an hour. Cobalt drills with a sharpening angle of 135 ° from a well-known German manufacturer came to the rescue - each hole is drilled in a few seconds!

I made the body itself from plexiglass. We immediately order cut rectangles from the glaziers, make the necessary holes for fasteners in them and paint them on the back with black paint.

Plexiglas painted on the back looks very nice. Now all that remains is to collect everything and enjoy the muses ... oh yes, during the final assembly it is still important to properly dilute the ground to minimize the background. As it was found out decades before us, C3 needs to be connected to the signal ground, i.e. to the minus input-input, and all other minuses can be sent to the "star" near the filter capacitors. If everything is done correctly, then no background can be heard, even if you bring your ear to the speaker at maximum volume. Another "ground" feature that is characteristic of sound cards that are not galvanically isolated from the computer is interference from the motherboard, which can crawl through USB and RCA. Judging by the Internet, the problem is often encountered: in the speakers you can hear the sounds of the HDD, printer, mouse and the background of the system unit's power supply unit. In this case, the easiest way to break the earth loop is to tape the earth on the amplifier plug with electrical tape. There is nothing to fear here, tk. there will be a second ground loop through the computer.

I didn’t do the volume control on the amplifier, because I couldn’t get any high-quality ALPS, and I didn’t like the rustling of Chinese potentiometers. Instead, a normal 47K resistor was installed between ground and the input signal. Moreover, the external sound card's regulator is always at hand, and every program also has a slider. Only the turntable doesn’t have a volume control, so I attached an external potentiometer to the connecting cable to listen to it.

I will guess this container in 5 seconds ...

Finally, you can start listening. Foobar2000 → ASIO → external Asus Xonar U7 is used as a sound source. Columns Microlab Pro3. The main advantage of these speakers is a separate block of their own amplifier on the LM4766 microcircuit, which can be immediately removed somewhere further away. Much more interesting with this acoustics was the amplifier from the Panasonic mini-system with the proud Hi-Fi inscription or the amplifier of the Soviet Vega-109 turntable. Both of the aforementioned devices operate in class AB. JLH, presented in the article, outplayed all of the above comrades in one wicket, based on the results of a blind test for 3 people. Although the difference could be heard with the naked ear and without any tests, the sound is clearly more detailed and transparent. It is quite easy, for example, to hear the difference between MP3 256kbps and FLAC. I used to think that the lossless effect was more like a placebo, but now the opinion has changed. Likewise, it has become much more pleasant to listen to files that are not compressed from loudness war - a dynamic range of less than 5 dB is not ice at all. Linsley Hood is worth the investment of time and money, as a similar branded amp will cost much more.

Material costs

Transformer 2200 r.
Output transistors (6 pcs. With a margin) 900 r.
Filter capacitors (4 pcs) 2700 rub.
"Loose" (resistors, small capacitors and transistors, diodes) ~ 2000 r.
Radiators 1800 r.
Plexiglas 650 r.
Paint 250 rub.
Connectors 600 rub.
Boards, wires, silver solder, etc. ~ 1000 r.
TOTAL ~ 12100 p.

How to achieve high-quality sound of your favorite music? Arm yourself with the necessary knowledge, a tool, after which you can assemble a sound amplifier with your own hands.

Which amplifier is better?

How many radio amateurs exist, so many opinions. Basically, the choice depends on the person, so it is very difficult to draw any specific conclusions. Today you can assemble a sound amplifier with your own hands on:

• Transistors. They have low power consumption and compact size. Provides excellent performance in sound quality.
• Lamps. The old old-fashioned way of assembling radio equipment. Despite the monstrous gluttony, weight and size, it surpasses semiconductor counterparts in sound quality.

Where to begin?

Before making a sound amplifier, you must clearly understand in what conditions and for what purpose it will be used. It directly depends on how much power it should have. In order to listen to your favorite compositions at home, a small device is enough, which will provide high-quality sound with a power of 30 - 50 W. The situation will be completely different if it is necessary to create equipment for holding large-scale events. In this case, it becomes necessary to assemble a more complex sound amplifier with your own hands. 200W is far from the limit of the power that will be needed during operation.

You should also stock up on everything you need:

• Soldering iron.
• Multimeter.
• Screwdriver Set.
• Textolite for the manufacture of microcircuits.
• Material for the body of the future amplifier.
• Electrical parts that are indicated in the schematic diagram of the product.
• Schematic of the printed circuit board of the amplifier selected for assembly.

DIY printed circuit board

Each case has its own subtleties. Making a PCB at home is no exception. It is she who will subsequently become the basis for all further work and will allow you to assemble a sound amplifier with your own hands. First, let's go over everything we need:

• Textolite with copper foil.
• Household iron.
• Silit detergent.
• Laser printer.
• Chinese self-adhesive film with substrate marking 333.
• Drills for making holes in PCB.
• A swab made of gauze and a piece of cotton cloth.

• We cut out the necessary piece of PCB so that about one centimeter of stock remains on each side.
• We treat it with detergent until the copper foil turns pink.
• We wash the processed board and send it to dry.
• We take a piece of self-adhesive necessary in size, use glue to glue it with a substrate to an A4 sheet, remove the film layer, print a drawing of the future board on the glazed side of the resulting blank. In this case, the toner supply must be set to maximum.
• Lay out a sheet of plywood, an old unnecessary book on the desktop, and on top - a board with the foil facing up.
• We cover the board with ordinary office paper and warm it up with a pre-heated iron. The approximate warm-up time is one minute.
• Next, we remove the iron, a sheet of paper, apply the printed drawing and smooth it with a swab.
• Cover with a sheet of paper again, place the iron on top and wait for about 30 seconds. If the surface of the board is larger than the sole of the iron, then you need to iron the entire part evenly.
• Remove a sheet of paper and smooth the drawing with a swab for 30 seconds. Movement should be both along and across. In this case, it is necessary to slightly press on the workpiece.
• After the workpiece has cooled down, carefully remove the backing.

How and with what to poison the board

In order to properly assemble a sound amplifier with your own hands, it is not enough to correctly apply a board drawing or solder a wire. You need to be able to qualitatively etch all the tracks on the microcircuit.

Ferric chloride has always been used for these purposes. However, this solution is very expensive and not readily available commercially. For this reason, it can be replaced with a home-made solution of copper sulfate and sodium chloride, which are not in short supply. The proportions for the mixture are as follows:

• A liter of warm water.
• 100 g of copper sulfate.
• 200 g of table salt.

When all the components are dissolved, clean and fat-free metal items (for example, a couple of nails), the workpiece itself, a small motor with blades or a compressor from the aquarium are dropped into the container. To enhance the reaction, it is necessary to place the container with the solution in warm water. The approximate etching time of the lanes is 25-30 minutes.

Assembling the amplifier

The first step that needs to be done in order to assemble a sound amplifier with your own hands is to install all radio components on a printed circuit board. Pay particular attention to polarity here. It will also be useful to note that all work should be carried out with special care and attention. Otherwise, a short circuit may occur, which will lead to inevitable failure of the components of the future amplifier.

The above procedure is followed by the assembly of the body. Its dimensions will directly depend on the dimensions of the amplifier board, power supply, and how the volume control and balance between channels are implemented. At this stage, you can use a ready-made factory case with the introduction of some design changes. However, the best way is still to manually make the shell of the electrical appliance. Thus, you can realize the possibility of creating a unique design. The option of installing the board into the case of one of the speakers also has the right to life.

Before putting everything together, it is necessary to conduct a test run of the future electrical appliance and, if necessary, eliminate all problems.

The last step is assembling the amplifier, which consists in installing the board, power supply and all other components.

A little off topic

Collecting sound power amplifiers with your own hands, it is not always possible to achieve the desired effect. The secret lies in the fact that the so-called acoustics is not able to cope with the tasks assigned to it. For this reason, sometimes it is necessary to additionally make self-assembly even of the speakers. Such an approach to the issue will allow not only to guarantee the maximum satisfaction of all wishes, but also help to get rid of a stand-alone device by hiding the amplifier in the speaker case.

Recently, a certain person approached with a request to assemble an amplifier of sufficient power and separate amplification channels for low, medium and high frequencies. before that, I had already collected for myself more than once as an experiment and, I must say, the experiments were very successful. The sound quality of even inexpensive speakers of a not very high level is noticeably improved in comparison, for example, with the option of using passive filters in the speakers themselves. In addition, it becomes possible to quite easily change the frequency of the division of the bands and the gain of each individual band and, thus, it is easier to achieve a uniform frequency response of the entire sound-amplifying path. In the amplifier, ready-made circuits were used, which had previously been tested more than once in simpler designs.

Structural scheme

The figure below shows the circuit for channel 1:

As you can see from the diagram, the amplifier has three inputs, one of which provides for the simple possibility of adding a preamplifier-equalizer for a vinyl player (if necessary), an input switch, a preamplifier-timbre (also three-band, with adjustable HF / MF / LF levels), a volume control, a three-band filter unit with adjustable gain for each band with the ability to turn off filtering and a power supply for high-power final amplifiers (unstabilized) and a stabilizer for the "low-current" part (preliminary amplification stages).

Pre-amplifier-timbre block

As it, a scheme was used, which had been tested more than once before, which, with its simplicity and availability of parts, shows fairly good characteristics. The scheme (like all subsequent ones) was at one time published in the magazine "Radio" and then more than once published on various sites on the Internet:

The input stage on DA1 contains a gain level switch (-10; 0; +10 dB), which simplifies matching the entire amplifier with signal sources of different levels, and a tone control is directly assembled on DA2. The circuit is not capricious to a certain range of element ratings and does not require any adjustment. As an op-amp, you can use any microcircuits used in the sound paths of amplifiers, for example, here (and in subsequent circuits) I tried imported BA4558, TL072 and LM2904. Anything is suitable, but it is better, of course, to choose op-amp options with the lowest possible noise level and high speed (input voltage slew rate). These parameters can be found in reference books (datasheets). Of course, here it is not at all necessary to use this particular scheme, it is quite possible, for example, to make not a three-band, but a regular (standard) two-band tone block. But not a "passive" circuit, but with cascades of amplification-matching at the input and output on transistors or op-amp.

Filter block

You can also find a lot of filter circuits, if you wish, since there are now enough publications on the topic of multiband amplifiers. To facilitate this task and just for example, I will present here several possible schemes found in various sources:

- the circuit that was applied by me in this amplifier, since the frequency of the crossover turned out to be exactly what the "customer" needed - 500 Hz and 5 kHz, and there was no need to recalculate anything.

- the second scheme, simpler on the op-amp.

And one more possible circuit, on transistors:

As yours already wrote, I chose the first scheme because of the rather high-quality filtering of the bands and the correspondence of the frequency separation of the bands to the given ones. Only at the outputs of each channel (strip) were simple gain controls added (as is done, for example, in the third circuit, on transistors). Regulators can be supplied from 30 to 100 kOhm. Operational amplifiers and transistors in all circuits can be replaced with modern imported ones (taking into account the pinout!) To obtain the best circuit parameters. All these circuits do not require any tuning, if you do not need to change the frequency of the crossover. Unfortunately, I am not able to give information on recalculating these frequencies of the section, since the circuits were searched for "ready-made" examples and detailed descriptions were not attached to them.

In the filter block circuit (the first circuit of the three), the ability to turn off filtering on the MF and HF channels was added. For this, two push-button switches of the P2K type were installed, with the help of which you can simply close the connection points of the filter inputs - R10C9 with their corresponding outputs - "high-frequency output" and "mid-frequency output". In this case, a complete audio signal is sent through these channels.

Power amplifiers

From the output of each channel of the filter, the HF-MF-LF signals are fed to the inputs of the power amplifiers, which can also be assembled according to any of the known schemes, depending on the required power of the entire amplifier. I made UMZCH according to the well-known scheme from the magazine "Radio", No. 3, 1991, p. 51. Here I give a link to the "primary source", since about this scheme there are many opinions and disputes on the grounds of its "quality". The fact is that at first glance this is a class B amplifier circuit with the inevitable presence of crossover distortion, but this is not the case. The circuit uses current control of the transistors of the output stage, which makes it possible to get rid of these drawbacks with a normal, standard connection. At the same time, the circuit is very simple, not critical to the parts used, and even transistors do not require special preliminary selection in terms of parameters. In addition, the circuit is convenient because powerful output transistors can be installed on one heat sink in pairs without insulating gaskets, since the collector leads are connected at the point " output ”, which greatly simplifies the installation of the amplifier:

When setting up, it is only IMPORTANT to select the correct operating modes for the transistors of the pre-terminal stage (by selecting resistors R7R8) - on the bases of these transistors in the "rest" mode and without load at the output (speaker) there should be a voltage within 0.4-0.6 volts. The supply voltage for such amplifiers (there should be 6 of them, respectively) was raised to 32 volts with the replacement of the output transistors by 2SA1943 and 2SC5200, the resistance of the resistors R10R12 should also be increased to 1.5 kΩ (to "make life easier" for the zener diodes in the circuit supply of input op-amps). The op-amps were also replaced by VA4558, thus the "zero setting" circuit is no longer needed (outputs 2 and 6 in the diagram) and, accordingly, the pinout changes when soldering the microcircuit. As a result, during testing, each amplifier according to this scheme produced power up to 150 watts (for a short time) with a completely adequate degree of heating of the radiator.

ULF power supply

As a power supply unit, two transformers with rectifier and filter units were used according to the usual, standard scheme. To power the low-frequency band channels (left and right channels) - a 250-watt transformer, a rectifier on diode assemblies such as MBR2560 or similar, and capacitors 40,000 microfarads x 50 volts in each power supply arm. For the MF and HF channels - a 350-watt transformer (taken from a burnt-out Yamaha receiver), a rectifier - a TS6P06G diode assembly and a filter - two capacitors of 25,000 microfarads x 63 volts for each power arm. All electrolytic capacitors of the filters are shunted with film capacitors with a capacity of 1 μF x 63 volts.

In general, a power supply unit can be with one transformer, of course, but with its corresponding power. The power of the amplifier as a whole in this case is determined solely by the capabilities of the power source. All preamplifiers (tone block, filters) are also powered from one of these transformers (it is possible from any of them), but through an additional block of a bipolar stabilizer assembled on a KREN type MC (or imported) or according to any of the standard circuits on transistors.

Homemade amplifier design

This, perhaps, was the most difficult moment in the manufacture, since there was no suitable finished case and I had to invent possible options :-)) In order not to sculpt a bunch of separate radiators, I decided to use a radiator case from a car 4-channel amplifier, rather large, something like this:

All the "insides" were, of course, extracted and the layout turned out to be something like this (unfortunately I did not take the corresponding photo):

- as you can see, six terminal UMZCH boards and a pre-amplifier-timbre block board were installed in this radiator cover. The filter block board did not fit anymore, so it was fixed on the then added construction from an aluminum corner (you can see it in the figures). Also, in this "frame" were installed transformers, rectifiers and power supply filters.

The front view with all the switches and controls looks like this:

Rear view, with speaker output pads and a fuse box (since no electronic protection circuits were made due to lack of space in the design and so as not to complicate the circuit):

Subsequently, the frame from the corner is supposed, of course, to be covered with decorative panels to give the product a more "marketable" appearance, but this will be done by the "customer" himself, according to his personal taste. In general, in terms of sound quality and power, the design turned out to be quite decent. Author of the material: Andrey Baryshev (specially for the site site).

- The neighbor started knocking on the battery. Made the music louder so I couldn't hear it.
(From the folklore of audiophiles).

The epigraph is ironic, but the audiophile is not at all necessarily “sick in the head” with the face of Josh Ernest at a briefing on relations with the Russian Federation, who is “rushing” because the neighbors are “happy”. Someone wants to listen to serious music at home as in a hall. The quality of the equipment for this needs such a thing that lovers of decibels of loudness as such simply do not fit where sane people have a mind, but for the latter, it goes beyond the price of suitable amplifiers (UMZCH, audio frequency power amplifier). And someone along the way has a desire to join useful and exciting areas of activity - sound reproduction technology and electronics in general. Which in the digital age are inextricably linked and can become a highly profitable and prestigious profession. The optimal first step in all respects in this matter is to make an amplifier with your own hands: it is UMZCH that allows, with initial training on the basis of school physics, on the same table to go from the simplest structures for half an evening (which, nevertheless, “sing” well) to the most complex units through which a good rock band will also play with pleasure. The purpose of this publication is to highlight the first steps of this path for beginners and, possibly, to communicate something new to the experienced.

The simplest

So, first let's try to make an audio amplifier that just works. In order to thoroughly delve into sound engineering, you will have to gradually master quite a lot of theoretical material and not forget to enrich your knowledge base as you progress. But any “cleverness” is assimilated easier when you see and feel how it works “in hardware”. In this article, further, too, the theory will not do - in what you need to know at first and what can be explained without formulas and graphs. In the meantime, it will be enough to be able to and use a multitester.

Note: If you have not soldered the electronics before, please note that its components must not be overheated! Soldering iron - up to 40 W (better than 25 W), the maximum permissible soldering time without interruption is 10 s. The soldered lead for the heat sink is held 0.5-3 cm from the soldering point on the side of the device case with medical tweezers. Acidic and other active fluxes must not be used! Solder - POS-61.

On the left in Fig.- the simplest UMZCH, "which just works." It can be assembled on both germanium and silicon transistors.

On this crumb it is convenient to master the basics of setting up the UMZCH with direct connections between the cascades, which give the clearest sound:

• Before turning on the power for the first time, turn off the load (speaker);
• Instead of R1, we solder a chain of a 33 kΩ constant resistor and a 270 kΩ variable (potentiometer) resistor, i.e. first approx. four times smaller, and the second approx. twice the denomination against the initial one according to the scheme;
• We supply power and, rotating the potentiometer slider, at the point indicated by the cross, set the specified collector current VT1;
• We remove the power supply, solder the temporary resistors and measure their total resistance;
• As R1, we put a resistor of the nominal value from the standard row closest to the measured one;
• We replace R3 with a constant 470 Ohm chain + 3.3 kOhm potentiometer;
• The same as in PP. 3-5, including setting the voltage equal to half the supply voltage.

Point a, from where the signal is taken to the load is the so-called. midpoint of the amplifier. In UMZCH with unipolar power, half of its value is set in it, and in UMZCH in bipolar power - zero relative to the common wire. This is called amplifier balance adjustment. In unipolar UMZCH with capacitive decoupling of the load, it is not necessary to disconnect it during setup, but it is better to get used to doing it reflexively: an unbalanced 2-pole amplifier with a connected load can burn its own powerful and expensive output transistors, or even "new, good" and very expensive powerful speaker.

Note: components that require selection when setting up the device in the layout are indicated on the diagrams either by an asterisk (*) or by an apostrophe (’).

In the center in the same fig.- a simple UMZCH on transistors, which already develops a power of up to 4-6 W at a load of 4 ohms. Although it works, like the previous one, in the so-called. class AB1, not intended for hi-fi sound, but if you replace a pair of such class D amplifiers (see below) in cheap Chinese computer speakers, their sound is noticeably improved. Here we learn one more trick: powerful output transistors must be installed on radiators. Components requiring additional cooling are circled in dashed lines in the diagrams; true, not always; sometimes - with an indication of the required dissipative area of ​​the heat sink. The adjustment of this UMZCH is balancing using R2.

On the right in Fig.- not yet a 350 W monster (as shown at the beginning of the article), but already quite a solid beast: a simple 100 W transistor amplifier. You can listen to music through it, but not Hi-Fi, the class of work is AB2. However, it is quite suitable for sounding a picnic area or outdoor meeting, a school assembly or a small trading floor. An amateur rock group, having such an UMZCH for an instrument, can perform successfully.

In this UMZCH, 2 more tricks are manifested: firstly, in very powerful amplifiers, the swing stage of the powerful output also needs to be cooled, therefore VT3 is placed on a radiator from 100 sq. see For output VT4 and VT5 radiators from 400 sq. see Secondly, UMZCH with bipolar power supply are not balanced at all without load. Either one or the other output transistor goes into cutoff, and the conjugate transistor goes into saturation. Then, at full supply voltage, current surges during balancing can damage the output transistors. Therefore, for balancing (R6, you guessed it?), The amplifier is powered from +/– 24 V, and instead of the load, a wire resistor of 100… 200 Ohm is included. By the way, the squiggles in some of the resistors on the diagram are Roman numerals, indicating their required heat dissipation power.

Note: a power source for this UMZCH needs a power of 600 watts. Smoothing filter capacitors - from 6800 uF to 160 V. In parallel to the electrolytic capacitors of the PS, ceramic capacitors of 0.01 uF are switched on to prevent self-excitation at ultrasonic frequencies, which can instantly burn out the output transistors.

On the field workers

On the trail. rice. - another option for a fairly powerful UMZCH (30 W, and at a supply voltage of 35 V - 60 W) on powerful field-effect transistors:

The sound from it already pulls on the requirements for the entry-level Hi-Fi (if, of course, the UMZCH works on the corresponding speaker systems, speakers). Powerful field workers do not require a lot of power for swinging, therefore there is no pre-power cascade. Even powerful field-effect transistors do not burn out the speakers under any malfunctions - they themselves burn out faster. It is also unpleasant, but still cheaper than changing an expensive bass head of a loudspeaker (GG). Balancing and, in general, adjustment of this UMZCH is not required. It has only one drawback, like a design for beginners: powerful field-effect transistors are much more expensive than bipolar ones for an amplifier with the same parameters. Requirements for IP - similar to the previous one. occasion, but its power is needed from 450 watts. Radiators - from 200 sq. cm.

Note: no need to build powerful UMZCH on field-effect transistors for switching power supplies, for example. computer. When trying to "drive" them into the active mode, which is necessary for the UMZCH, they either simply burn out, or the sound is weak, but in terms of quality "none". The same applies to high-power high-voltage bipolar transistors, for example. from the line scan of old TVs.

Straight up

If you have already taken the first steps, then it will be quite natural to want to build UMZCH class Hi-Fi, without going too deep into the theoretical jungle. To do this, you will have to expand the instrument park - you need an oscilloscope, an audio frequency generator (GZCH) and an AC millivoltmeter with the ability to measure the DC component. The prototype for repetition is better to take UMZCH E. Gumeli, described in detail in "Radio" No. 1, 1989. For its construction, you will need a few inexpensive available components, but the quality meets very high requirements: power up to 60 W, bandwidth 20-20,000 Hz, non-uniformity of frequency response 2 dB, coefficient of nonlinear distortion (THD) 0.01%, self-noise level –86 dB. However, it is quite difficult to adjust the Gumeli amplifier; if you can handle it, you can take on any other. However, some of the currently known circumstances greatly simplify the establishment of this UMZCH, see below. Bearing in mind this and the fact that not everyone manages to get into the archives of "Radio", it would be appropriate to repeat the main points.

Schemes of a simple high-quality UMZCH

Schemes UMZCH Gumeli and the specification for them are given in the illustration. Output transistor radiators - from 250 sq. see for UMZCH in fig. 1 and from 150 sq. see for option according to fig. 3 (original numbering). The transistors of the pre-output stage (KT814 / KT815) are installed on radiators bent from aluminum plates 75x35 mm with a thickness of 3 mm. It is not worth replacing KT814 / KT815 with KT626 / KT961, the sound does not noticeably improve, but the establishment is seriously hampered.

This UMZCH is very critical to power supply, installation topology and general, therefore, it needs to be adjusted in a constructively finished form and only with a standard power source. When trying to supply power from a stabilized power supply, the output transistors burn out immediately. Therefore, in Fig. the drawings of the original printed circuit boards and instructions for setting up are given. To them we can add that, firstly, if at the first turn-on the "excitement" is noticeable, they are struggling with it, changing the inductance L1. Secondly, the leads of the parts installed on the boards should be no longer than 10 mm. Thirdly, it is extremely undesirable to change the installation topology, but if it is really necessary, there must be a frame screen on the side of the conductors (an earth loop, highlighted in color in the figure), and the power supply paths must go outside it.

Note: gaps in the tracks to which the bases of powerful transistors are connected - technological, for adjustment, after which they are soldered with drops of solder.

The establishment of this UMZCH is much simplified, and the risk of encountering "excitement" in the process of use is reduced to zero if:

• Minimize interconnect wiring by placing boards on heat sinks of power transistors.
• Completely abandon the connectors inside, performing the entire installation only by soldering. Then R12, R13 in a powerful version or R10 R11 in a less powerful version will not be needed (they are dotted in the diagrams).
• Use for indoor installation an oxygen-free copper audio wire of minimum length.

When these conditions are met, there are no problems with the initiation, and the establishment of the UMZCH is reduced to the routine procedure described in Fig.

Sound wires

Audio piping is not an idle invention. The need for their application is currently undeniable. In copper with an admixture of oxygen, the thinnest oxide film is formed on the faces of the metal crystallites. Metal oxides are semiconductors and, if the current in the wire is weak without a constant component, its shape is distorted. In theory, the distortions on the myriads of crystallites should compensate for each other, but the smallest amount (it seems, due to quantum uncertainties) remains. Sufficient to be noticed by discerning listeners against the background of the purest sound of modern UMZCH.

Manufacturers and traders, without a twinge of conscience, slip ordinary electrical copper instead of oxygen-free - it is impossible to distinguish one from the other by eye. However, there is an area of ​​application where counterfeiting does not go unambiguously: a twisted-pair cable for computer networks. Putting the grid with long segments "left-handed", it will either not start at all, or will be constantly buggy. Dispersion of impulses, you know.

The author, when they were just talking about audio wires, realized that, in principle, this was not empty chatter, especially since oxygen-free wires had already been used for a long time in special purpose equipment, with which he was familiar by his occupation. Then I took and replaced the standard cord of my TDS-7 headphones with a homemade one made of "vitukha" with flexible stranded wires. The sound, by ear, has steadily improved for loop-through analog tracks, i.e. on the path from studio microphone to disc that has never been digitized anywhere. Recordings on vinyl made using DMM technology (Direct Meta lMastering, direct metal deposition) sounded especially brightly. After that, interconnect editing of all home audio was converted to "vitush". Then the improvement in sound began to be noted by completely random people, indifferent to music and not forewarned in advance.

How to make interconnect wires from twisted pair, see next. video.

Video: do-it-yourself twisted pair interconnect wires

Unfortunately, the flexible "vitukha" soon disappeared from the market - it did not hold well in crimped connectors. However, for the information of readers, flexible "military" wire MGTF and MGTFE (shielded) is made only from oxygen-free copper. Counterfeiting is impossible, because on ordinary copper, tape fluoroplastic insulation creeps out rather quickly. MGTF is now widely sold and is much cheaper than branded, with a guarantee, audio wires. It has only one drawback: it cannot be done colored, but this can be corrected with tags. There are also oxygen-free winding wires, see below.

Theoretical interlude

As you can see, already at the very beginning of mastering sound technology, we had to face the concept of Hi-Fi (High Fidelity), high fidelity of sound reproduction. Hi-Fi comes in different levels, which are ranked by next. main parameters:

1. Band of reproducible frequencies.
2. Dynamic range is the ratio in decibels (dB) of the maximum (peak) output power to the noise floor.
3. Intrinsic noise level in dB.
4. The coefficient of nonlinear distortion (THD) at the nominal (long-term) output power. THD at peak power is taken as 1% or 2%, depending on the measurement technique.
5. Irregularities of the amplitude-frequency characteristic (AFC) in the reproducible frequency band. For speakers - separately at low (LF, 20-300 Hz), medium (MF, 300-5000 Hz) and high (HF, 5000-20,000 Hz) sound frequencies.

Note: the ratio of the absolute levels of any I values ​​in (dB) is defined as P (dB) = 20lg (I1 / I2). If I1

You need to know all the subtleties and nuances of Hi-Fi when designing and building speakers, and as for a home-made Hi-Fi UMZCH for the home, before moving on to such, you need to clearly understand the requirements for their power required for sounding a given room. dynamic range (dynamics), noise floor and THD. To achieve from the UMZCH a frequency band of 20-20,000 Hz with a blockage at the edges of 3 dB and an uneven frequency response at the midrange of 2 dB on a modern element base is not very difficult.

Volume

The power of the UMZCH is not an end in itself, it should provide the optimal volume of sound reproduction in a given room. It can be determined by curves of equal loudness, see fig. Natural noise in residential premises is not quieter than 20 dB; 20 dB is a forest wilderness in complete calm. A loudness level of 20 dB relative to the threshold of audibility is the threshold of intelligibility - a whisper can still be discerned, but music is perceived only as a fact of its presence. An experienced musician can tell which instrument is playing, but which one is not.

40 dB - the normal noise of a well-insulated city apartment in a quiet area or a country house - represents the threshold of intelligibility. Music from the threshold of intelligibility to the threshold of intelligibility can be listened to in the presence of deep correction of the frequency response, especially in the bass. To do this, the MUTE function is introduced into modern UMZCH (mute, mutation, not mutation!), Including, respectively. corrective circuits in UMZCH.

90 dB is the loudness level of a symphony orchestra in a very good concert hall. 110 dB can be given by an expanded orchestra in a hall with unique acoustics, of which there are no more than 10 in the world, this is the threshold of perception: sounds are perceived louder still as discernible in meaning with an effort of will, but already annoying noise. The loudness zone in residential premises of 20-110 dB is the zone of complete audibility, and 40-90 dB is the zone of best audibility, in which untrained and inexperienced listeners fully perceive the meaning of the sound. If, of course, it is in it.

Power

Calculating the power of the equipment for a given loudness in the listening area is perhaps the main and most difficult task of electroacoustics. For yourself, in conditions, it is better to go from acoustic systems (AC): calculate their power using a simplified method, and take the nominal (long-term) power of the UMZCH equal to the peak (musical) speaker. In this case, the UMZCH will not add noticeably its distortions to those of the speakers, they are already the main source of nonlinearity in the sound path. But you should not make the UMZCH too powerful: in this case, the level of its own noise may turn out to be higher than the audibility threshold, because it is calculated from the voltage level of the output signal at maximum power. If it is very simple to consider, then for a room in an ordinary apartment or house and a speaker with normal characteristic sensitivity (sound output), you can take a trace. values ​​of the optimal power UMZCH:

• Up to 8 sq. m - 15-20 W.
• 8-12 sq. m - 20-30 W.
• 12-26 sq. m - 30-50 W.
• 26-50 sq. m - 50-60 W.
• 50-70 sq. m - 60-100 W.
• 70-100 sq. m - 100-150 W.
• 100-120 sq. m - 150-200 W.
• More than 120 sq. m - determined by calculation according to the data of acoustic measurements on site.

Dynamics

The dynamic range of the UMZCH is determined by the curves of equal loudness and threshold values ​​for different degrees of perception:

1. Symphonic music and jazz with symphonic accompaniment - 90 dB (110 dB - 20 dB) ideal, 70 dB (90 dB - 20 dB) acceptable. Sound with dynamics of 80-85 dB in a city apartment cannot be distinguished from ideal by any expert.
2. Other serious music genres - excellent 75 dB, 80 dB above the roof.
3. Pops of any kind and soundtracks for films - 66 dB for the eyes is enough, tk. These opuses are already compressed in levels up to 66 dB and even up to 40 dB during recording, so that you can listen on anything.

The dynamic range of the UMZCH, correctly selected for a given room, is considered equal to its own noise level, taken with a + sign, this is the so-called. signal-to-noise ratio.

KNI

Nonlinear distortion (NI) UMZCH is the components of the output signal spectrum, which were not in the input signal. Theoretically, it is best to "push" the NI to the level of its own noise, but technically it is very difficult to implement. In practice, they take into account the so-called. masking effect: at volume levels below approx. 30 dB, the range of frequencies perceived by the human ear is narrowed, as is the ability to distinguish sounds by frequency. Musicians hear notes, but find it difficult to assess the timbre of the sound. In people without a musical ear, the masking effect is observed already at 45-40 dB of loudness. Therefore, an UMZCH with a THD of 0.1% (–60 dB of a loudness level of 110 dB) will be assessed as a Hi-Fi by an ordinary listener, and with an THD of 0.01% (–80 dB) it can be considered not distorting sound.

Lamps

The latter statement, perhaps, will cause rejection, even furious, among the adherents of tube circuitry: they say, only lamps give real sound, and not just any, but individual types of octal. Calm down, gentlemen - a special tube sound is not a fiction. The reason is fundamentally different spectra of distortions in electronic tubes and transistors. Which, in turn, are due to the fact that the flow of electrons in the lamp moves in a vacuum and quantum effects do not appear in it. A transistor is a quantum device, where minority charge carriers (electrons and holes) move in the crystal, which is generally impossible without quantum effects. Therefore, the spectrum of tube distortions is short and clean: only harmonics up to the 3rd - 4th are clearly visible in it, and there are very few combination components (the sums and differences of the frequencies of the input signal and their harmonics). Therefore, at the time of vacuum circuitry, SOI was called the harmonic coefficient (CH). In transistors, the spectrum of distortions (if they are measurable, the reservation is random, see below) can be traced up to the 15th and higher components, and there are more than enough combination frequencies in it.

At the beginning of solid-state electronics, the designers of transistor UMZCH took for them the usual "tube" THD in 1-2%; sound with a tube distortion spectrum of this magnitude is perceived by ordinary listeners as pure. By the way, the very concept of Hi-Fi did not exist at that time. It turned out - they sound dull and dull. In the process of development of transistor technology, an understanding of what Hi-Fi is and what is needed for it was developed.

Currently, the growing pains of transistor technology have been successfully overcome and the side frequencies at the output of a good UMZCH are hardly captured by special measurement methods. And the lamp circuitry can be considered as having passed into the category of art. Its basis can be anything, why can't electronics go there? An analogy with photography is appropriate here. No one can deny that a modern digital mirror gives a picture that is immeasurably clearer, more detailed, deep in the range of brightness and color than a plywood box with an accordion. But someone with the coolest Nikon "clicks pictures" like "this is my fat cat got drunk like a bastard and is sleeping with his paws out," and someone with Smena-8M takes a picture on Svem's b / w film, in front of which people crowd at a prestigious exhibition.

Note: and calm down again - it's not all bad. Today, low-power lamp UMZCHs have at least one application, and not of the least importance, for which they are technically necessary.

Experienced stand

Many audio lovers, having barely learned how to solder, immediately "go to the lamps." This is by no means blameworthy, on the contrary. Interest in the origins is always justified and useful, and electronics have become such on lamps. The first computers were vacuum tubes, and the onboard electronic equipment of the first spacecraft was also vacuum tubes: transistors were already there, but they could not withstand extraterrestrial radiation. By the way, then tube ... microcircuits were also created under the strictest confidence! On microlamps with a cold cathode. The only known mention of them in open sources is in the rare book of Mitrofanov and Pickersgil "Modern receiving and amplifying tubes".

But enough lyrics, to the point. For those who like to tinker with the lamps in fig. - a circuit of a bench lamp UMZCH designed specifically for experiments: SA1 switches the operating mode of the output lamp, and SA2 switches the supply voltage. The circuit is well known in the Russian Federation, a slight revision has affected only the output transformer: now it is possible not only to "drive" the native 6P7S in different modes, but also to select the switching coefficient of the screen grid in the ultralinear mode for other lamps; for the vast majority of output pentodes and beam tetrodes, it is either 0.22-0.25, or 0.42-0.45. See below for the manufacture of the output transformer.

For guitarists and rockers

This is the case when you can't do without lamps. As you know, the electric guitar became a full-fledged solo instrument after the pre-amplified signal from the pickup was passed through a special attachment - a fuser - which deliberately distorted its spectrum. Without this, the sound of the string was too harsh and short, because the electromagnetic pickup reacts only to the modes of its mechanical vibrations in the plane of the instrument deck.

Soon an unpleasant circumstance came to light: the sound of an electric guitar with a fuser acquires full strength and brightness only at high volumes. This is especially true for guitars with a humbucker pickup, which gives the most "evil" sound. But what about a beginner who is forced to rehearse at home? Do not go to the hall to perform, not knowing exactly how the instrument will sound there. And just rock lovers want to listen to their favorite things in full juice, and rockers are generally decent and non-conflict people. At least those who are interested in rock music, and not outrageous entourage.

So, it turned out that the fatal sound appears at loudness levels that are acceptable for living quarters, if the UMZCH is tube. The reason is the specific interaction of the signal spectrum from the fuser with the clean and short spectrum of tube harmonics. Here again an analogy is appropriate: a b / w photo can be much more expressive than a color one, because leaves only outline and light for viewing.

Those who need a tube amplifier not for experiments, but due to technical necessity, have no time to master the intricacies of tube electronics, they are carried away by others. UMZCH in this case, it is better to do transformerless. More precisely, with a single-ended matching output transformer operating without permanent bias. This approach greatly simplifies and speeds up the manufacture of the most complex and critical unit of the lamp UMZCH.

"Transformerless" tube output stage UMZCH and pre-amplifiers to it

On the right in Fig. a diagram of the transformerless output stage of the UMZCH tube is given, and on the left are the options for a pre-amplifier for it. Above - with a tone control according to the classic Baksandal scheme, which provides a fairly deep adjustment, but introduces small phase distortions into the signal, which can be significant when the UMZCH operates on a 2-way speaker. Below is a preamplifier with a simpler tone control that does not distort the signal.

But back to the “tip”. In a number of foreign sources, this scheme is considered a revelation, however, identical to it, with the exception of the capacity of electrolytic capacitors, is found in the Soviet "Handbook of a radio amateur" in 1966. A thick book of 1060 pages. Then there was no Internet and databases on disks.

In the same place, on the right in the figure, the shortcomings of this scheme are briefly but clearly described. Improved, from the same source, given on the next page. rice. on right. In it, the screen grid L2 is powered from the midpoint of the anode rectifier (the anode winding of the power transformer is symmetrical), and the screen grid L1 is fed through the load. If, instead of high-impedance speakers, you turn on a matching transformer with conventional speakers, as in the previous. circuit, output power approx. 12 W because the active resistance of the primary winding of the transformer is much less than 800 ohms. THD of this power stage with transformer output - approx. 0.5%

How to make a transformer?

The main enemies of the quality of a powerful signal LF (sound) transformer are the stray magnetic field, the lines of force of which are closed, bypassing the magnetic circuit (core), eddy currents in the magnetic circuit (Foucault currents) and, to a lesser extent, magnetostriction in the core. Because of this phenomenon, a casually assembled transformer "sings", buzzes or beeps. Foucault currents are fought by reducing the thickness of the plates of the magnetic circuit and additionally insulating them with varnish during assembly. For output transformers, the optimal plate thickness is 0.15 mm, the maximum allowable is 0.25 mm. It is not necessary to take thinner plates for the output transformer: the filling factor of the core (central core of the magnetic circuit) with steel will fall, the cross-section of the magnetic circuit will have to be increased to obtain the specified power, which will only increase the distortion and losses in it.

In the core of a sound transformer operating with constant bias (for example, the anode current of a single-ended output stage), there must be a small (determined by calculation) non-magnetic gap. The presence of a non-magnetic gap, on the one hand, reduces signal distortion from constant bias; on the other hand, in a conventional magnetic circuit it increases the stray field and requires a larger core section. Therefore, the non-magnetic gap must be expected to be optimal and performed as accurately as possible.

For transformers operating with magnetization, the optimal type of core is made of Shp plates (perforated), pos. 1 in fig. In them, a non-magnetic gap is formed during core punching and is therefore stable; its value is indicated in the passport for the plates or measured with a set of probes. The scattering field is minimal, because the side branches, through which the magnetic flux is closed, are solid. Cores of transformers are often assembled from Shp plates without magnetization, because Shp plates are made of high quality transformer steel. In this case, the core is assembled with an overlap (the plates are placed with a notch in one direction or the other), and its cross-section is increased by 10% against the calculated one.

It is better to wind transformers without magnetization on USH cores (reduced height with widened windows), pos. 2. In them, a decrease in the stray field is achieved by reducing the length of the magnetic path. Since the USH plates are more accessible than the Shp ones, the cores of transformers with magnetization are often recruited from them. Then the assembly of the core is carried out in close-up: a package of W-plates is assembled, a strip of non-conductive non-magnetic material with a thickness equal to the value of the non-magnetic gap is put, covered with a yoke from a package of jumpers and pulled together with a clip.

Note:"Sound" signal magnetic circuits of the ShLM type for output transformers of high-quality tube amplifiers are of little use, they have a large stray field.

At pos. 3 is a diagram of the dimensions of the core for calculating the transformer, at pos. 4 the structure of the winding frame, and in pos. 5 - patterns of its parts. As for the transformer for the "transformerless" output stage, it is better to do it on the ShLMme over the lid, because bias is negligible (bias current is equal to screen grid current). The main task here is to make the windings as compact as possible in order to reduce the stray field; their active resistance will still turn out to be much less than 800 ohms. The more free space left in the windows, the better the transformer turned out. Therefore, the windings wind turn to turn (if there is no winding machine, this is terrible) from the thinnest wire possible, the stacking factor of the anode winding for the mechanical calculation of the transformer is 0.6. The winding wire is of PETV or PEMM brands, they have an oxygen-free core. You do not need to take PETV-2 or PEMM-2, they have an increased outer diameter due to double varnishing and the scattering field will be larger. The primary winding is wound first, because it is its scattering field that most of all affects the sound.

The iron for this transformer must be looked for with holes in the corners of the plates and clamping brackets (see the figure on the right), since "For complete happiness" the assembly of the magnetic circuit is carried out in the next. order (of course, the windings with leads and external insulation should already be on the frame):

1. Prepare half-diluted acrylic varnish or, in the old fashioned way, shellac;
2. Plates with jumpers are quickly varnished on one side and as soon as possible, without pressing hard, put into the frame. The first plate is placed with the varnished side inward, the next - with the unlacquered side to the varnished first, etc .;
3. When the frame window is full, staples are applied and bolted tightly;
4. After 1-3 minutes, when the squeezing of the varnish from the gaps apparently stops, the plates are added again until the window is filled;
5. Repeat paragraphs. 2-4, until the window is tightly packed with steel;
6. The core is pulled tight again and dried on a battery, etc. 3-5 days.

The core assembled using this technology has very good plate insulation and steel filling. Magnetostriction loss is not detected at all. But keep in mind - for the cores of their permalloy, this technique is not applicable, because from strong mechanical influences the magnetic properties of permalloy are irreversibly deteriorated!

On microcircuits

UMZCH on integrated circuits (ICs) are made most often by those who are satisfied with the sound quality up to average Hi-Fi, but are more attracted by the cheapness, speed, ease of assembly and the complete absence of any setup procedures that require special knowledge. Quite simply, an amplifier based on microcircuits is the best option for dummies. The classics of the genre here - UMZCH on the IC TDA2004, standing on the series, God forbid, memory, for 20 years, on the left in Fig. Power - up to 12 W per channel, supply voltage - 3-18 V unipolar. Radiator area - from 200 sq. see for maximum power. Advantage - the ability to work on a very low-impedance, up to 1.6 Ohm, load, which allows you to remove the full power when powered by a 12 V on-board network, and 7-8 W - with a 6-volt power supply, for example, on a motorcycle. However, the output of TDA2004 in class B is non-complementary (on transistors of the same conductivity), so the sound is definitely not Hi-Fi: THD 1%, dynamics 45 dB.

The more modern TDA7261 gives no better sound, but more powerful, up to 25 W, tk. the upper limit of the supply voltage has been increased to 25 V. The lower, 4.5 V, still allows power supply from 6 V of the onboard network, i.e. The TDA7261 can be launched from almost all onboard networks, except for aircraft 27 V. With the help of attached components (strapping, on the right in the figure), the TDA7261 can work in mutation mode and with the St-By function (Stand By, wait), which transfers the UMZCH to the mode of minimum power consumption when there is no input signal for a certain time. Conveniences cost money, so for a stereo you will need a pair of TDA7261 with radiators from 250 sq. see for each.

Note: If you are attracted by amplifiers with the St-By function, keep in mind that you should not expect speakers wider than 66 dB from them.

"Supereconomic" in terms of power supply TDA7482, on the left in the figure, working in the so-called. class D. Such UMZCH is sometimes called digital amplifiers, which is incorrect. For real digitization, samples of the level are removed from the analog signal with a sampling frequency not less than twice the highest of the reproduced frequencies, the value of each sample is recorded with a noise-immune code and stored for further use. UMZCH class D - impulse. In them, the analog is directly converted into a sequence of high frequency pulse width modulated (PWM) pulses, which is fed to the speaker through a low pass filter (LPF).

Class D sound with Hi-Fi has nothing to do: THD of 2% and dynamics of 55 dB for class D UMZCH are considered very good indicators. And TDA7482 here, I must say, is not an optimal choice: other firms specializing in class D produce UMZCH ICs cheaper and requiring less strapping, for example, D-UMZCH of the Paxx series, on the right in Fig.

Of the TDAs, it should be noted the 4-channel TDA7385, see fig., On which you can assemble a good amplifier for speakers up to average Hi-Fi inclusive, with a frequency division into 2 bands or for a system with a subwoofer. Defiltering of LF and MF-HF in either case is done at the input on a weak signal, which simplifies the design of the filters and allows deeper separation of the bands. And if the acoustics are subwoofer, then 2 channels of the TDA7385 can be allocated for the sub-ULF bridge circuit (see below), and the remaining 2 can be used for the MF-HF.

UMZCH for subwoofer

The subwoofer, which can be translated as “sub-bass” or, literally, “pre-bass” reproduces frequencies up to 150-200 Hz, in this range human ears are practically unable to determine the direction to the sound source. In speakers with a subwoofer, the “subwoofer” speaker is placed in the hotel's acoustic design, this is the subwoofer itself. The subwoofer is placed, in principle, as it is more convenient, and the stereo effect is provided by separate mid-high-frequency channels with their own small-sized speakers, the acoustic design of which is not particularly demanding. Experts agree that it is still better to listen to stereo with full channel separation, but subwoofer systems significantly save money or labor on the bass path and facilitate the placement of acoustics in small rooms, which is why they are popular with consumers with ordinary hearing and not particularly demanding ones.

The "leakage" of the midrange-high frequency into the subwoofer, and from it into the air, greatly spoils the stereo, but if you abruptly "cut off" the subbass, which, by the way, is very difficult and expensive, then a very unpleasant sound jump effect will appear. Therefore, the channels are filtered twice in subwoofer systems. At the input, the MF-HF with bass tails are allocated with electric filters, which do not overload the MF-HF path, but provide a smooth transition to the sub-bass. Bass with midrange "tails" are combined and fed to a separate UMZCH for the subwoofer. The midrange is filtered, so as not to spoil the stereo, in the subwoofer it is already acoustically: the subwoofer is placed, for example, in the partition between the resonator chambers of the subwoofer, which does not let the midrange out, see on the right in Fig.

A number of specific requirements are imposed on the UMZCH for a subwoofer, of which the "teapots" consider the greatest possible power to be the main one. This is completely wrong, if, say, the calculation of acoustics for a room gave a peak power W for one speaker, then the power of the subwoofer needs 0.8 (2W) or 1.6W. For example, if speakers S-30 are suitable for a room, then a subwoofer is needed 1.6x30 = 48 watts.

It is much more important to ensure the absence of phase and transient distortions: if they go, there will definitely be a sound jump. As for THD, it is permissible up to 1%. Intrinsic bass distortions of this level are not audible (see curves of equal loudness), and the “tails” of their spectrum in the best audible midrange area will not get out of the subwoofer.

To avoid phase and transient distortions, an amplifier for a subwoofer is built according to the so-called. bridge circuit: outputs of 2 identical UMZCH turn on oppositely through the speaker; the signals to the inputs are applied in antiphase. The absence of phase and transient distortion in the bridge circuit is due to the complete electrical symmetry of the output signal paths. The identity of the amplifiers forming the bridge arms is ensured by the use of paired UMZCH on ICs, made on one crystal; this is perhaps the only case when an on-chip amplifier is better than a discrete one.

Note: the power of the bridge UMZCH does not double, as some think, it is determined by the supply voltage.

An example of a bridge UMZCH circuit for a subwoofer in a room up to 20 sq. m (without input filters) on the TDA2030 IC is given in Fig. left. Additional filtering of the midrange is carried out by the R5C3 and R'5C'3 circuits. Radiator area TDA2030 - from 400 sq. see. Bridge UMZCH with an open output have an unpleasant feature: when the bridge is unbalanced, a constant component appears in the load current that can damage the speaker, and the protection circuits on the subbases often fail, turning off the speaker when not needed. Therefore, it is better to protect the expensive “oak” bass head with non-polar batteries of electrolytic capacitors (highlighted in color, and a diagram of one battery is given in the inset.

A little about acoustics

The acoustic design of the subwoofer is a special topic, but since a drawing is given here, then explanations are also needed. Case material - MDF 24 mm. The resonator tubes are made of sufficiently durable non-ringing plastic, for example, polyethylene. The inner diameter of the pipes is 60 mm, the projections inward are 113 mm in the large chamber and 61 in the small one. For a specific loudspeaker head, the subwoofer will have to be reconfigured for the best bass and, at the same time, for the least impact on the stereo effect. To tune the pipes, they take a deliberately greater length and, pushing in and out, achieve the required sound. The protrusions of the pipes outward do not affect the sound, they are then cut off. The tuning of the pipes is interdependent, so you have to tinker.

Headphone Amplifier

A headphone amplifier is made by hand most often for 2 reasons. The first one is for listening "on the go", i.e. outside the home, when the audio output of the player or smartphone is not enough to swing "buttons" or "mugs". The second is for high-end home headphones. Hi-Fi UMZCH for an ordinary living room is needed with dynamics up to 70-75 dB, but the dynamic range of the best modern stereo headphones exceeds 100 dB. An amplifier with such dynamics is more expensive than some cars, and its power will be from 200 W per channel, which is too much for an ordinary apartment: listening at a power that is too low against the rated power spoils the sound, see above. Therefore, it makes sense to make a low-power, but with good dynamics, a separate amplifier specifically for headphones: prices for household UMZCH with such a makeweight are clearly absurdly overstated.

A diagram of the simplest transistor headphone amplifier is given in pos. 1 fig. Sound - except for Chinese "buttons", works in class B. It also does not differ in efficiency - 13-mm lithium batteries last 3-4 hours at full volume. At pos. 2 - TDA classic for on-the-go headphones. The sound, however, gives quite decent, up to average Hi-Fi, depending on the parameters of the digitization of the track. There are innumerable amateur improvements to the TDA7050 strapping, but no one has yet achieved the transition of sound to the next level of class: the "mikruha" itself does not allow. TDA7057 (pos. 3) is simply more functional, you can connect a volume control on a conventional, not dual, potentiometer.

UMZCH for headphones on the TDA7350 (pos. 4) is already designed to build good individual acoustics. It is on this IC that headphone amplifiers are assembled in most household UMZCHs of the middle and high class. UMZCH for headphones on the KA2206B (pos. 5) is already considered professional: its maximum power of 2.3 W is also enough to pump such serious isodynamic "mugs" as TDS-7 and TDS-15.