DIY transistor amplifier for a computer. Amplifier built into the computer. Tube sound amplifier

For a computer user, a laptop is undoubtedly a convenient, compact and quite functional device. But, unfortunately, this device is not without flaws.

Surely many users of laptops and netbooks have encountered the problem of quiet sound playback through the built-in speakers of these devices.

If at home you can connect an external stereo system, then outside the home walls this may be impossible and you have to limit yourself to headphones. In this case, there is no talk of collective viewing of any film or series.

How to fix the situation?

Portable computer speakers powered by USB port. Now there is a huge selection of these devices on store shelves, but their quality can vary significantly.

The price of portable computer speakers powered by a USB port is quite low and affordable to a wide segment of the population. Despite this, the purchase of this device may be unsuccessful, since the quality of sound reproduction by such a system will leave much to be desired. Oddly enough, among the cheap devices of this class there are devices of very good quality, both in design and in sound reproduction quality.

Let’s perform an “opening” of a portable speaker system powered by a USB port and examine the electronic components of this device. From the point of view of a radio amateur, it is interesting to know from what electronic components such devices are assembled. The knowledge gained can be useful when independently constructing portable audio speakers powered by USB or repairing them.

We will disassemble portable multimedia USB speakers of the brand Sven 315. Despite their cheapness, this model of portable speakers showed good quality reproduction and sound power sufficient to sound a small room.

Disassembling computer USB speakers

Portable speakers are easy to disassemble. To open the case, you must carefully remove the front decorative panel.

In order to remove the amplifier circuit board, you need to unscrew the fixing nut, which is hidden under the plastic volume control knob. After this, the electronic board can be freely removed from the housing.

Electronic filling

The composition of the electronic filling of the device turned out to be quite simple. An integrated circuit of a stereo amplifier based on a microcircuit is mounted on a small printed circuit board LM4863D. With a supply voltage of 5 volts, this microcircuit can produce 2.2 W of output power per channel with a speaker voice coil resistance of 4 ohms. Based on the description (datasheet) THD + noise ( THD+N) at maximum output power is 1%.

Amplifier board and speaker

Based on these data, we can conclude that based on the LM4863D chip you can assemble a pretty good stereo amplifier with low voltage power supply (5V) and output power of 2 W per channel. Many who are not yet familiar with modern microcircuits believe that the TDA2822 will be suitable instead of the LM4863D. It's a delusion! The TDA2822 is very power hungry (compared to the LM4863) and produces severe signal distortion at maximum power. Also, the optimal power supply for the TDA2822 is about 12 volts, which is not good for portable equipment. The TDA2822 can be recommended as a readily available replacement if the LM4863 is not available. This can happen, for example, during repairs.

It is worth noting that the LM4863 chip was developed specifically for compact systems, so the chip requires a minimum of external elements (the so-called harness). The microcircuit is available in different packages, from the usual DIP to compact SOIC.

If you want to independently assemble an amplifier based on the LM4863 chip, you may encounter a problem. Finding this microcircuit on radio markets is not so easy (as it was at the time of writing this article). But it was not difficult to find such a microcircuit on online trading platforms. For example, in the AliExpress.com online store, the LM4863 chip can be easily found in all kinds of packages and in any quantity. The price of 1 microcircuit is less than $1, if you buy 10 pieces at once.

I told you how to buy radio components on Aliexpress.

In addition to the amplifier chip itself, the printed circuit board contains a connector for connecting a passive audio speaker (without a built-in amplifier), a dual variable resistor for adjusting the input audio signal, and an electrolytic capacitor. From the side of printed conductors circuit board SMD trim elements are installed, which are necessary for the operation of the integrated amplifier. The microcircuit is powered from a USB connector, which connects to any free port of a laptop or desktop computer.

A typical connection diagram for the LM4863 microcircuit is taken from the description (datasheet) for this microcircuit and is shown in the figure.

Typical circuit diagram for connecting the LM4863 chip (taken from the description)

Based on the typical connection diagram for the LM4863 chip, it can be seen that it can also work with regular headphones ( Headphone), whose resistance is 32 Ohms. The chip provides a circuit for detecting the connection of headphones and pin 16 (HP-IN) is allocated to implement this function.

For those who understand electronics and datasheets on English language They are not afraid, they can easily find LM4863 chips on the Internet at alldatasheet.com.

Amplifier circuit for portable USB speakers

The circuit diagram of the amplifier is made manually from the printed circuit board of Sven-315 USB computer speakers. The diagram shows one capacitor C2 instead of two (C7, C9) that are actually present on the printed circuit board (see below). This was done because on the printed circuit board the capacitors are connected in parallel (C7 and C9), and in the summarized diagram, capacitor C2 indicates the total capacity of these two capacitors.

Schematic diagram of an amplifier based on LM4863D (manually assembled)

As we see, typical diagram from the description differs from the one that was manually assembled from the printed circuit board of the computer speaker amplifier. The diagram does not include elements that are installed if a headphone jack is added to the diagram. Otherwise, the circuit corresponds to the standard one given in the description for the LM4863 chip.

Placing elements on a printed circuit board

If you plan to use portable speakers without a laptop, for example, together with an MP3 player, then a 5-volt power adapter is quite suitable for powering the speakers. The main thing is that the power adapter can provide sufficient load current (as a rough guide: the standard load current for USB ports is no more than 500 mA). According to the description for the LM4863 chip, the maximum quiescent current (when no sound signal is supplied to the chip) is 20 mA. Naturally, during playback the current consumption will be higher.

The photo shows an option for powering portable speakers SVEN-315 from a 5-volt adapter, which is used to charge an iPod. The maximum load current of the adapter is 1A, which is more than enough for regular work portable speakers.

As it turned out, high-quality sound reproduction of SVEN-315 portable speakers lies in the rational design of the housing. As you know, the quality of sound acoustic systems is influenced not only by the loudspeakers used in them, but also by the housing. To verify this, just pull the speaker out of the case and turn on playback. The quality and sound power of playback will be much worse. This remark was not made by chance, since a comparison was made of the sound reproduction quality of portable speakers SVEN-315 and similar, but more expensive USB speakers SVEN PS-30.

Despite the fact that SVEN PS-30 sound speakers are mounted on the basis of an integrated USB audio chip CM6120-S, which includes a 16-bit DAC and class D audio amplifiers, the quality of their sound reproduction is subjectively (by ear) much worse due to poor performance of the speaker system housing.

The body of the SVEN-315 portable speakers is made of ABS plastic. Perhaps it is the design of the housing that allows you to “squeeze” all their modest capabilities out of small-sized speakers.

Factory-made devices for amplifying the audio signal are expensive and may not be powerful enough. Looking at the photos of homemade sound amplifiers, it is obvious that they are in no way inferior in appearance to finished products. In addition, their manufacture on their own does not require special skills or large material costs.

Device base

Beginner radio amateurs first of all ask themselves: what can they use to assemble a simple sound amplifier at home? The operation of the device is based on transistors or microcircuits, or a rare option is possible - on lamps. Let's take a closer look at each of them.

Microcircuits

The TDA series microcircuit and a similar one can be purchased in stores or you can use a microcircuit from an unnecessary TV.

Using car amplifier chips with a 12-volt power supply, it is very easy to achieve high-quality sound without the use of special skills and with a minimum of parts.

Transistors

The advantages of transistors are low power consumption. The device produces excellent sound performance, is easily integrated into any equipment and does not require additional configuration. In addition, there is no need to search for and use complex microcircuits.

Lamps

Today, the outdated assembly method based on tubes provides high-quality sound, but has a number of disadvantages:

• increased energy intensity
• dimensions
• cost of components

Recommendations for properly assembling a sound amplifier with your own hands

A device for enhancing sound quality, assembled at home based on TDA series microcircuits and their analogues, generates a lot of heat. For cooling, you need a radiator grille of a suitable size, depending on the model of the microcircuit itself and the power of the amplifier. There must be a place for it in the case.

The advantage of a self-made device is its low energy consumption, which allows it to be used in cars by connecting to a battery, as well as on the road or at home using a battery. Power consumption depends on the required degree of signal amplification. Some manufactured models require a voltage of only 3 Volts.

We take a serious and responsible approach to assembling a sound amplifier in order to avoid short circuit and failure of components.

Necessary materials

During the assembly process you will need the following tools and components:

• chip
• frame
• capacitors
• power unit
• plug
• switch button
• wires
• cooling radiator
• screws
• hot glue and thermal paste
• soldering iron and rosin

Circuits and instructions for making an amplifier at home

Each circuit is unique and depends on the sound source (old or modern digital technology), power supply, and expected final dimensions. It is assembled on a printed circuit board, which will make the device compact and more convenient. During the assembly process, you cannot do without a soldering iron or soldering station.

The British John Linsley-Hood circuit is based on four transistors without microcircuits. It allows you to similarly repeat the shape of the input signal, resulting in only pure gain and a sine wave at the output.

The simplest and most common option for manufacturing a single-channel amplifier is to use a microcircuit based on it, supplemented with resistors and capacitors.

Algorithm of actions for production

• install radio components on the printed circuit board, taking into account the polarity
• assemble the body (providing space for additional parts, for example, a radiator grille)

It is permissible to use a ready-made case or create it yourself, as well as install the board into the speaker case.

• run the device in test mode (identify and eliminate malfunctions if they occur)
• amplifier assembly (connection to the power supply and other components)

Note!

DIY home and car amplifiers

At home, there is often a lack of powerful sound when watching movies on a laptop or listening to music on headphones. Let's look at how to properly make a sound amplifier with your own hands.

For laptop

The sound wave amplifier must take into account the power of external speakers up to 2 watts and the winding resistance up to 4 ohms.

Assembly components:

• 9 volt power supply
• printed circuit board
• chip TDA 7231
• frame
• non-polar capacitor 0.1 µF - 2 pcs.
• polar capacitor 100 µF
• polar capacitor 220 µF
• polar capacitor 470 µF
• constant resistor 10 Kom m 4.7 Ohm
• two-position switch
• input socket

Manufacturing scheme

The assembly algorithm is selected depending on the selected scheme. It is necessary to consider the appropriate size of the cooling radiator so that the operating temperature inside the case does not rise above 50 degrees Celsius. When using a laptop outdoors, you need to provide holes in the case for air access.

For car radio

An amplifier for a car radio can be assembled using the common TDA8569Q microcircuit. Its characteristics:

• supply voltage 6-18 volts
• input power 25 watts per channel into 4 ohms and 40 watts per channel into 2 ohms
• frequency range 20-20000 Hz

Note!

It is imperative to provide, in addition to the circuit, a filter against interference created by the operation of the car.

First, draw a printed circuit board, then drill holes in it. Then the board must be etched with ferric chloride. After tinning and soldering all the parts of the microcircuit. To avoid power additives, a thick layer of solder will need to be applied to the power traces. Provide a cooling system using a cooler or radiator grille.

At the end of the assembly, it is necessary to make a filter against interference from the ignition system and poor noise insulation according to the following scheme: on a ferrite ring with a diameter of 20 mm, wind a choke with a wire with a cross-section of 1-1.5 mm in 5 turns.

Assembling a device to improve sound quality at home is not difficult. The main thing is to decide on the circuit and have on hand all the components from which you can easily assemble a simple sound amplifier.

DIY sound amplifier photo

Note!

Homemade amplifier and speakers for a computer, player or mobile phone from available parts. ULF, part 1.

Analyzing the traffic to the resource, I discovered that many people use search phrases like: “do-it-yourself amplifier for a computer”, “speakers for a computer”, “homemade amplifier for a player”, etc.

This seemed very strange to me. Is there really not enough information on this topic on the entire Russian Internet? It turned out, indeed, that normal descriptions for making a small audio system for a computer, player or mobile phone cannot be found, even if you search for a very long time. They increasingly describe speakers with the volume of a small refrigerator and amplifiers with the power of a small electric fireplace.

The most interesting videos on Youtube

Other articles devoted to the construction of this ULF.

At first I thought it would be nice to write a manual for making an amplifier. But it seemed to me that building an amplifier on a modern element base is a little easier than manufacturing speaker systems. Therefore, I decided to split the article into two parts and first make a simple stereo acoustic system from the most available parts.

You know, there are such plastic active acoustic systems (hereinafter referred to as “AS”), one of which already has a built-in amplifier on a chip in a DIP8 package. I also received this kit with my first computer. It is simply impossible to use these speakers without first removing low and mid frequencies in the audio card's equalizer. But I would like, on the contrary, to be able to raise high and low frequencies when listening to music or watching movies.

But let's get back to our homemade products.

I made homemade speakers only twice and both times in my youth. Even then, I was sorely lacking low frequencies, and my first speaker was, as it would now be called, a subwoofer.

To implement the project, I made only the front panel, and as the body I used the lower compartment of the bedside table from the TV with a volume of fifty liters. Two 4GD-28 speakers were installed diagonally and draped with radio fabric. As a low-pass filter, I used a spool of thread No. 10 with a wire of unknown cross-section wound around it. I made holes in the back wall of the nightstand. In the early seventies, this design impressed my friends.

Now you can also use this experience if you add something similar to the existing plastic speakers. Believe me, such a simple design will easily “make” any subwoofer from a budget home theater and other Chinese crafts.

But this time I decided to make a traditional pair of speakers, since free space there is no more furniture left.

The idea to use sewer pipes as a housing for the column came by chance when I saw an article on the Internet, the author of which, apparently taking inspiration from Home Depot, used similar pipes to make a wind generator propeller.

Since I had never heard how a round speaker works, before buying sewer pipes, I glued a pipe of the required diameter from cardboard. I used three-liter glass canning jars as a template.

The very first activation of the speaker layout gave a positive result, and I boldly went to the store.

Homemade single-way speakers for a stereo system.

So, I present a concept loudspeaker in the style of “Could you play a nocturne on a drainpipe flute?”

Building such a loudspeaker is not easy, but very simple. The entire assembly should take at most one hour.

Construction and details.

The housing of these loudspeakers is made of plastic 45-degree angles from an external sewer with a diameter of 160 mm, which cost me about $7.5. You can buy such pipes at big hardware store. It is in a large store, since in small stores they sell pipes only up to a diameter of 110 mm, which are intended for laying internal sewerage.

When selling, each square is given a rubber seal. The seal has a groove into which a plastic ring is inserted (in the picture it is red).

This is the inscription embossed on the surface of the squares I bought.

The speakers use speakers that can be borrowed from old Soviet TVs.

In color tube and thyristor (UPIMTST) televisions, a set of two speakers was installed, broadband - 3GD-38 (3GD-45, 5GDSH-4) and high-frequency (tweeters) - 2GD-36K. In integrated TVs with a screen size of 61 cm, only one speaker was installed - 3GD-38 (3GD-45, 5GDSH-4).

Speakers 3GD-38 (3GD-45, 5GDSH-4) in different years were issued under different names, but did not undergo any serious design changes. These are full-range speakers with a diameter of 160 mm and are designed for a nominal input sinusoidal power of 3 Watts. It is not recommended to apply more than 10 watts of power to this speaker, even briefly.

The resistance of 3GD-38 (3GD-45, 5GDSH-4) is 4 Ohms, and 2GD-36K is 8 Ohms.

Fasteners

1. Nut M2.5
2. Grover M2.5
3. Washer M2.5
4. Screw M2.5x10
5. Bracket Ø8mm
6. Washer M4 (Ø12mm)
7. Tube (cambric) Ø6mm.

Loudspeaker assembly.

When installing the dynamic head into the pipe, be careful to avoid damaging the diffuser. Do not bring metal objects to the center of the diffuser, as they may be attracted by the speaker's magnetic system.

We insert a rubber seal into the inner groove of the pipe.

Insert a plastic ring into the groove of the rubber seal.

We fix the position of the seal with a piece of wire of a suitable diameter.

First, we simply attach the fasteners and secure the end of the cable in the bracket. Then we solder the cable to the speaker. If you have already soldered a specialized connector to the cable for connecting to an amplifier, then immediately phase the speaker. The “plus” on the speaker can be marked either by a “+” (plus) sign, or by a marking dot, or even by a bump squeezed out on the body. You can read more about speaker phasing.

Be sure to secure the cable to the speaker body using a steel bracket or other in a reliable way. If this is not done, the very first tug of the cable will damage the speaker.

Now that the cable is soldered, you can insert the speaker into the groove of the rubber seal. When the speaker takes its place in the groove of the seal, you need to tighten the fastening screws.

The picture shows the position of one of the four washers that ensure centering of the speaker in the o-ring, before and after tightening the mounting screw.

Different ways to install a loudspeaker.

When using loudspeakers, it is advisable to provide a gap between the rear extension of the pipe and surrounding objects, since we have assembled an open-type speaker system.

Desktop option.

Floor option.

You can use anything as legs, for example, bicycle spokes bent in a “P” shape.

I also made the legs from pieces of a bicycle spoke and fastening washers from PEV-type resistors. Bicycle spokes are good because they already have a galvanic coating.

The speakers, if desired, can be hung on the wall using a cable if your room is decorated in a techno style.

Homemade two-way loudspeakers (columns).

As I mentioned above, in addition to the 3GD-38 wideband speakers (3GD-45, 5GDSH-4), 2GD-36K speakers were also installed in Soviet televisions. Having a pair of such speakers, I decided to improve the design by assembling a two-way speaker with coaxial speakers.

Electrical diagram.

The high-frequency and low-frequency speakers are decoupled using a filter. This made it possible to slightly level out the amplitude-frequency response (AFC) and improve the reproduction of high frequencies at the edge of the range.

Construction and details.

In this speaker system, the signal to the high-frequency speaker is supplied through current-carrying rods, with which it is attached to the low-frequency speaker. The rods are made of PEV-2 copper wire with a diameter of 1.5 mm. The length of each piece is 65mm. At the junction with the current-carrying petals, the rod is cleaned of varnish and tinned.

To prevent the signal from shorting to the speaker housing, insulating bushings and washers are used.

Mounting unit for the rod to the HF head.

Mounting unit for the rod and bracket to the woofer head.

The picture shows the fasteners and parts used to assemble the speaker.

The filter coil is wound with copper insulated wire PEL-2 with a diameter of 1 mm. on the boss from self-adhesive tape (scotch tape) and has 95 turns, wound in four layers. When winding, the layers were secured with BF-4 glue.

The capacitor and coil are attached to a bracket, which in turn is attached to the speakers.

The bracket is made of a steel strip 8mm wide, 1mm cross-section according to this drawing. The dotted line indicates bending points.

This is what the assembled speaker assembly looks like. Centering of the low-frequency speaker in the groove of the rubber seal is carried out by two insulating and two steel bushings with a diameter of 8 mm.

Spring washers (grower) were used as locking elements when assembling the speakers. Instead, you can use any nitro paint or BF glue.

Tests.

Since I do not have a measuring room, I had to remove (the frequency response) both from homemade speakers and from the industrial speaker “S-30” so that I could have at least some kind of reference point.

This is the frequency response of “White Noise” taken from the “S-30”.

The same goes for a homemade product with one full-range speaker.

Frequency response of a homemade two-way speaker.

To the ear, single-way speakers sound much louder than the S-30, and two-way speakers sound a little better high frequencies. Of course, both are inferior to the S-30 in terms of low frequencies. Actually, this is confirmed by the graphs.

To remove the hump in the frequency response around 400Hz, which is unpleasant to the ear, I had to use the audio card’s equalizer.

This is what happened after correcting the two-way speaker.

The disadvantages of "plumbing" speakers include a relatively small maximum permissible power, with relatively large dimensions. But this can be attributed to the costs of the budget decision.

As for comparing the sound quality with Chinese plastic speakers, the latter have already gone looking for another listener.

If anyone wants to repeat this design, be careful when connecting speakers to a high-power VLF. It is very easy to damage a speaker designed for use in open speakers, especially at low frequencies.

During the tests, I used a 30-watt amplifier and, through carelessness, I destroyed the coil of one of the heads, produced in 1978 (apparently some of the turns had come unglued).

Post Scriptum.

Today my wife made a change to the design of the speakers, adding dust collectors, which are the compartment of tights that fits on one of the largest and attractive parts female body.

To make a dust collector, it is enough to secure the indicated compartment with a thick thread and cut off the rest. The target part of the tights is thicker and has an elastic band that just fits the size of the tube.

Another improvement

One of my laptops did not have a standard equalizer, and I have long been planning to equalize the frequency response of these speakers by replacing the tweeters. When I removed these Jericho pipes from the wall, I found too much dust inside.

M. SAPOZHNIKOV, Ganei Aviv, Israel
Radio, 2002, No. 4

The author has proposed two simple two-way stereo UMZCHs with a common low-frequency channel, which work with a personal computer in a multimedia system. These same amplifiers can also be used in a car radio or portable music center.

In two-way or multi-band sound reproduction equipment, the bands are separated by filters of the second, third and higher orders. But in simple stereo devices it often makes sense to separate the bands at the output of UMZCH stereo channels, which in this case should be wideband. The capacitor separating the UMZCH and the mid-HF loudspeaker can be used as a low-pass filter element. In this case, the signal necessary for the operation of the low-frequency channel is generated directly on this capacitor. The increase in its reactance with a decrease in the signal frequency causes the same gradual increase in the voltage of the amplified signal on this capacitor. It is worth noting that broadband channels are not loaded at frequencies below the crossover frequency and at these frequencies the distortion in the amplifier is much lower than with a broadband load. In addition, due to more efficient electroacoustic conversion in dynamic heads in the mid-HF band, less power is required from the amplifier than for broadband heads.

On schematic diagram(Fig. 1) shows two broadband UMZCH channels on the DA1 chip.

The MF-HF acoustic system heads BA1 and BA2 with a common isolation capacitor C6 of small capacity are connected to the outputs of the microcircuit. As a result, a first-order low-pass filter is obtained from the active load resistances BA1, BA2 and capacitor C6. The signal of the low-frequency component is removed from it to a bridge low-frequency amplifier assembled on the DA2 chip.

The input circuits of the device consist of low-pass filters R1C1, R2C2, which weaken supra-tonal and radio frequency interference, and a dual volume control R3.1, R3.2. At the input of the low-frequency channel, a sensitivity regulator R5 is installed to adjust the tonal balance of signals in the low-frequency and mid-high frequency bands.

The TDA1519 series microcircuits were not chosen by chance. They provide good sound quality and at the same time have a minimum of external elements. The amplifier can be switched to standby mode using switch SB1. It should be taken into account that TDA1519Q microcircuits or those without a letter index have two non-inverting amplifiers inside; they are installed in place of DA1, and in microcircuits with indexes A and B, one of the amplifiers is inverting, which is necessary for switching on the bridge circuit DA2.

When the MF - HF channels are loaded with a resistance of 8 Ohms and the specified supply voltage, the nominal output power is about 2.5 W, and at a low-frequency channel load with a resistance of 4 - 8 Ohms - 9... 12 W with nonlinear distortion of no more than 0.1%. With a capacitance of capacitor C6 of about 220 μF, the crossover frequency was chosen to be about 180 Hz. Its value depends on the capacitance of this capacitor. If you use a load with a resistance of 4 Ohms in the MF - HF channels, then the power on it will double, but to maintain the crossover frequency, the capacitance of capacitor C6 should be doubled. Voltage gain of broadband channels - 40 dB.

Instead of the TDA1519 (DA1) chip, it is permissible to use the TDA1517 chip. Then the gain of broadband channels will be equal to 20 dB.

Another UMZCH (Fig. 2) is based on the same principle of dividing bands in the load circuits of the MF - HF channels, but it uses TDA2005 microcircuits, which are more familiar to many radio amateurs.

Here in broadband channels it is used Feedback in terms of current through the load, which provides higher parameters for the UMZCH and allows you to have a signal on the coupling capacitors (in this case there are two of them) identical to the input one, with a level independent of the load impedance (of course, at frequencies below the band crossover frequency). The common low-frequency channel is also assembled using a bridge circuit, where both amplifiers of the DA2 microcircuit are connected in an inverse circuit. The rheostat-activated regulator R10 changes the signal gain in the low-frequency channel.

The parameters of the UMZCH are approximately the same as in the previous device, but with a load resistance of 8 Ohms, the voltage gain of the broadband amplifier is 26 dB and depends on the load resistance. If necessary, its sensitivity is changed by selecting resistors R6, R8. To select the capacitance of capacitors C12, C13, the same recommendations apply here as for C6 in the circuit shown in Fig. 1.

In both the first and second amplifiers, the microcircuits must be installed on a heat sink with an effective area of ​​at least 200 cm2. Printed circuit boards were not developed by the author; It is quite simple to install the amplifier elements on a suitable breadboard.

– The neighbor stopped knocking on the radiator. I turned the music up so I couldn't hear him.
(From audiophile folklore).

The epigraph is ironic, but the audiophile is not necessarily “sick in the head” with the face of Josh Ernest at a briefing on relations with the Russian Federation, who is “thrilled” because his neighbors are “happy.” Someone wants to listen to serious music at home as in the hall. For this purpose, the quality of the equipment is needed, which among lovers of decibel volume as such simply does not fit where sane people have a mind, but for the latter it goes beyond reason from the prices 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 age of digital technology are inextricably linked and can become a highly profitable and prestigious profession. The optimal first step in this matter in all respects 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 designs for half an evening (which, nevertheless, “sing” well) to the most complex units, through which a good rock band will play with pleasure. The purpose of this publication is highlight the first stages of this path for beginners and, perhaps, convey something new to those with experience.

Protozoa

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 easier to assimilate when you see and feel how it works “in hardware.” In this article further, too, we will not do without theory - about what you need to know at first and what can be explained without formulas and graphs. In the meantime, it will be enough to know how to use a multitester.

Note: If you haven’t soldered electronics yet, keep in mind that its components cannot be overheated! Soldering iron - up to 40 W (preferably 25 W), maximum allowable soldering time without interruption - 10 s. The soldered pin for the heat sink is held 0.5-3 cm from the soldering point on the side of the device body with medical tweezers. Acid and other active fluxes cannot be used! Solder - POS-61.

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

On this baby it is convenient to learn the basics of setting up an UMZCH with direct connections between cascades that 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 constant resistor of 33 kOhm and a variable resistor (potentiometer) of 270 kOhm, i.e. first note four times less, and the second approx. twice the denomination compared to the original according to the scheme;
• We supply power and, by rotating the potentiometer, at the point marked with a cross, we set the indicated collector current VT1;
• We remove the power, unsolder the temporary resistors and measure their total resistance;
• As R1 we set a resistor with a value from the standard series closest to the measured one;
• We replace R3 with a constant 470 Ohm chain + 3.3 kOhm potentiometer;
• Same as according to paragraphs. 3-5, V. And we set the voltage equal to half the supply voltage.

Point a, from where the signal is removed to the load, is the so-called. midpoint of the amplifier. In UMZCH with unipolar power supply half of its value is set in it, and in UMZCH with bipolar power supply - zero relative to the common wire. This is called adjusting the amplifier balance. In unipolar UMZCHs with capacitive decoupling of the load, it is not necessary to turn it off during setup, but it is better to get used to doing this reflexively: an unbalanced 2-polar amplifier with a connected load can burn out its own powerful and expensive output transistors, or even a “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 with an asterisk (*) or an apostrophe (‘).

In the center of the same fig.- a simple UMZCH on transistors, already developing power 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 these class D amplifiers (see below) in cheap Chinese computer speakers, their sound improves noticeably. Here we learn another trick: powerful output transistors need to be placed on radiators. Components that require additional cooling are outlined in dotted lines in the diagrams; however, not always; sometimes - indicating the required dissipative area of ​​the heat sink. Setting up this UMZCH is balancing using R2.

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

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

Note: A power source for this UMZCH needs a power of 600 W or more. Anti-aliasing filter capacitors - from 6800 µF at 160 V. In parallel electrolytic capacitors 0.01 µF ceramic PIs 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 with a supply voltage of 35 V - 60 W) on powerful field-effect transistors:

The sound from it already meets the requirements for entry-level Hi-Fi (if, of course, the UMZCH works on the corresponding acoustic systems, speakers). Powerful field drivers do not require a lot of power to drive, so there is no pre-power cascade. Even more powerful field-effect transistors do not burn out the speakers in the event of any malfunction - they themselves burn out faster. Also unpleasant, but still cheaper than replacing an expensive loudspeaker bass head (GB). This UMZCH does not require balancing or adjustment in general. As a design for beginners, it has only one drawback: powerful field-effect transistors are much more expensive than bipolar transistors for an amplifier with the same parameters. Requirements for individual entrepreneurs are similar to previous ones. case, but its power is needed from 450 W. Radiators – from 200 sq. cm.

Note: there is no need to build powerful UMZCHs on field-effect transistors for switching power supplies, for example. computer When trying to “drive” them into the active mode required for UMZCH, they either simply burn out, or the sound is weak and “no quality at all.” The same applies to powerful high-voltage bipolar transistors, eg. from line scan of old TVs.

Straight up

If you have already taken the first steps, then it is quite natural to want to build Hi-Fi class UMZCH, without going too deep into the theoretical jungle. To do this, you will have to expand your instrumentation - you need an oscilloscope, an audio frequency generator (AFG) and an AC millivoltmeter with the ability to measure the DC component. It is better to take as a prototype for repetition the E. Gumeli UMZCH, described in detail in Radio No. 1, 1989. To build it, you will need a few inexpensive available components, but the quality meets very high requirements: power up to 60 W, band 20-20,000 Hz, frequency response unevenness 2 dB, nonlinear distortion factor (THD) 0.01%, self-noise level –86 dB. However, setting up the Gumeli amplifier is quite difficult; 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 is able to get into the Radio archives, it would be appropriate to repeat the main points.

Schemes of a simple high-quality UMZCH

The Gumeli UMZCH circuits and specifications for them are shown in the illustration. Radiators of output transistors – from 250 sq. see for UMZCH in Fig. 1 and from 150 sq. see for option according to fig. 3 (original numbering). Transistors of the pre-output stage (KT814/KT815) are installed on radiators bent from 75x35 mm aluminum plates with a thickness of 3 mm. There is no need to replace KT814/KT815 with KT626/KT961; the sound does not noticeably improve, but setup becomes seriously difficult.

This UMZCH is very critical to power supply, installation topology and general, so it needs to be installed in a structurally complete form and only with a standard power source. When trying to power it from a stabilized power supply, the output transistors burn out immediately. Therefore, in Fig. Drawings of original printed circuit boards and setup instructions are provided. We can add to them that, firstly, if “excitement” is noticeable when you first turn it on, they fight it by changing the inductance L1. Secondly, the leads of parts installed on 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 shield on the side of the conductors (ground loop, highlighted in color in the figure), and the power supply paths must pass outside it.

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

Setting up this UMZCH is greatly simplified, and the risk of encountering “excitement” during use is reduced to zero if:

• Minimize interconnect installation by placing the boards on radiators of powerful transistors.
• Completely abandon the connectors inside, performing all installation only by soldering. Then there will be no need for R12, R13 in a powerful version or R10 R11 in a less powerful version (they are dotted in the diagrams).
• Use oxygen-free copper audio wires of minimum length for internal installation.

If these conditions are met, there are no problems with excitation, and setting up the UMZCH comes down to the routine procedure described in Fig.

Wires for sound

Audio wires are not an idle invention. The need for their use at present is undeniable. In copper with an admixture of oxygen, a thin oxide film is formed on the faces of 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, distortions on myriads of crystallites should compensate each other, but very little (apparently 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 shamelessly substitute ordinary electrical copper instead of oxygen-free copper - it is impossible to distinguish one from the other by eye. However, there is an area of ​​application where counterfeiting is not clear: twisted pair cable for computer networks. If you put a grid with long segments on the left, it will either not start at all or will constantly glitch. Momentum dispersion, you know.

The author, when there was just talk about audio wires, realized that, in principle, this was not idle chatter, especially since oxygen-free wires by that time had long been used in special-purpose equipment, with which he was well acquainted by his line of work. Then I took and replaced the standard cord of my TDS-7 headphones with a homemade one made from “vitukha” with flexible multi-core wires. The sound, aurally, has steadily improved for end-to-end analogue tracks, i.e. on the way from the studio microphone to the disc, never digitized. Vinyl recordings made using DMM (Direct Metal Mastering) technology sounded especially bright. After this, the interconnect installation of all home audio was converted to “vitushka”. Then completely random people, indifferent to the music and not notified in advance, began to notice the improvement in sound.

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

Video: do-it-yourself twisted pair interconnect wires

Unfortunately, the flexible “vitha” soon disappeared from sale - it did not hold well in the crimped connectors. However, for the information of readers, flexible “military” wire MGTF and MGTFE (shielded) is made only from oxygen-free copper. Fake is impossible, because On ordinary copper, tape fluoroplastic insulation spreads quite quickly. MGTF is now widely available and costs much less than branded audio cables with a guarantee. It has one drawback: it cannot be done in color, but this can be corrected with tags. There are also oxygen-free winding wires, see below.

Theoretical Interlude

As we can see, already in the early stages of mastering audio technology, we had to deal with the concept of Hi-Fi (High Fidelity), high fidelity sound reproduction. There are hi-fi different levels, which are ranked next. main parameters:

1. Reproducible frequency band.
2. Dynamic range - the ratio in decibels (dB) of the maximum (peak) output power to the noise level.
3. Self-noise level in dB.
4. Nonlinear distortion factor (THD) at rated (long-term) output power. The SOI at peak power is assumed to be 1% or 2% depending on the measurement technique.
5. Unevenness of the amplitude-frequency response (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 absolute levels of any values ​​of I in (dB) is defined as P(dB) = 20log(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 homemade Hi-Fi UMZCH for the home, before moving on to these, you need to clearly understand the requirements for their power required to sound a given room, dynamic range (dynamics), noise level and SOI. It is not very difficult to achieve a frequency band of 20-20,000 Hz from the UMZCH with a roll off at the edges of 3 dB and an uneven frequency response in the midrange of 2 dB on a modern element base.

Volume

The power of the UMZCH is not an end in itself; it must provide the optimal volume of sound reproduction in a given room. It can be determined by curves of equal loudness, see fig. There are no natural noises in residential areas quieter than 20 dB; 20 dB is the wilderness in complete calm. A volume level of 20 dB relative to the threshold of audibility is the threshold of intelligibility - a whisper can still be heard, but music is perceived only as the fact of its presence. An experienced musician can tell which instrument is being played, but not what exactly.

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

90 dB is the volume level of a symphony orchestra in a very good concert hall. 110 dB can be produced by an extended orchestra in a hall with unique acoustics, of which there are no more than 10 in the world, this is the threshold of perception: louder sounds are still perceived as distinguishable in meaning with an effort of will, but already annoying noise. The volume zone in residential premises of 20-110 dB constitutes 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, he is in it.

Power

Calculating the power of equipment at a given volume 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 (AS): 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 noticeably add its distortions to those of the speakers; they are already the main source of nonlinearity in the audio path. But the UMZCH should not be made too powerful: in this case, the level of its own noise may be higher than the threshold of audibility, because It is calculated based on the voltage level of the output signal at maximum power. If we consider it very simply, then for a room in an ordinary apartment or house and speakers with normal characteristic sensitivity (sound output) we can take the trace. UMZCH optimal power values:

• 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 based on on-site acoustic measurements.

Dynamics

The dynamic range of the UMZCH is determined by 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. No expert can distinguish a sound with a dynamics of 80-85 dB in a city apartment from ideal.
2. Other serious music genres – 75 dB excellent, 80 dB “through the roof”.
3. Pop music of any kind and movie soundtracks - 66 dB is enough for the eyes, because... These opuses are already compressed during recording to levels of up to 66 dB and even up to 40 dB, so that you can listen to them on anything.

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

SOI

Nonlinear distortions (ND) of UMZCH are components of the output signal spectrum that were not present in the input signal. Theoretically, it is best to “push” the NI under the level of its own noise, but technically this is very difficult to implement. In practice, they take into account the so-called. masking effect: at volume levels below approx. At 30 dB, the range of frequencies perceived by the human ear narrows, as does 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 hearing for music, the masking effect is observed already at 45-40 dB of volume. Therefore, an UMZCH with a THD of 0.1% (–60 dB from a volume level of 110 dB) will be assessed as Hi-Fi by the average listener, and with a THD of 0.01% (–80 dB) can be considered not distorting the sound.

Lamps

The last statement will probably cause rejection, even fury, among adherents of tube circuitry: they say, real sound is produced only by tubes, and not just some, but certain types of octal ones. Calm down, gentlemen - the special tube sound is not a fiction. The reason is the fundamentally different distortion spectra of electronic tubes and transistors. Which, in turn, are due to the fact that in the lamp the flow of electrons 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 completely 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 combinational components (sums and differences in the frequencies of the input signal and their harmonics). Therefore, in the days of vacuum circuitry, SOI was called harmonic distortion (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, designers of transistor UMZCHs used the usual “tube” SOI of 1-2% for them; 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 yet exist. It turned out that they sound dull and dull. In the process of developing 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 side frequencies at the output of a good UMZCH are difficult to detect using special measurement methods. And lamp circuitry can be considered to have become an art. Its basis can be anything, why can’t electronics go there? An analogy with photography would be appropriate here. No one can deny that a modern digital SLR camera produces an image that is immeasurably clearer, more detailed, and deeper 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, he got drunk like a bastard and is sleeping with his paws outstretched,” and someone, using Smena-8M, uses Svemov’s b/w film to take a picture in front of which there is a crowd of people at a prestigious exhibition.

Note: and calm down again - not everything is so bad. Today, low-power lamp UMZCHs have at least one application left, and not the least important, for which they are technically necessary.

Experimental stand

Many audio lovers, having barely learned to solder, immediately “go into tubes.” This in no way deserves censure, on the contrary. Interest in the origins is always justified and useful, and electronics has become so with tubes. The first computers were tube-based, and the on-board electronic equipment of the first spacecraft was also tube-based: there were already transistors then, but they could not withstand extraterrestrial radiation. By the way, at that time lamp microcircuits were also created under the strictest secrecy! On microlamps with a cold cathode. The only known mention of them in open sources is in the rare book by Mitrofanov and Pickersgil “Modern receiving and amplifying tubes”.

But enough of the lyrics, let's get to the point. For those who like to tinker with the lamps in Fig. – diagram of a bench lamp UMZCH, intended 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 minor modification affected only the output transformer: now you can not only “drive” the native 6P7S in different modes, but also select the screen grid switching factor for other lamps in ultra-linear mode; for the vast majority of output pentodes and beam tetrodes it is either 0.22-0.25 or 0.42-0.45. For the manufacture of the output transformer, see below.

Guitarists and rockers

This is the very 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 began to be passed through a special attachment - a fuser - which deliberately distorted its spectrum. Without this, the sound of the string was too sharp and short, because the electromagnetic pickup reacts only to the modes of its mechanical vibrations in the plane of the instrument soundboard.

An unpleasant circumstance soon emerged: 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-type pickup, which gives the most “angry” sound. But what about a beginner who is forced to rehearse at home? You can’t go to the hall to perform without knowing exactly how the instrument will sound there. And rock fans just 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 shocking surroundings.

So, it turned out that the fatal sound appears at volume levels acceptable for residential premises, if the UMZCH is tube-based. The reason is the specific interaction of the signal spectrum from the fuser with the pure 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 the outline and light for viewing.

Those who need a tube amplifier not for experiments, but due to technical necessity, do not have time to master the intricacies of tube electronics for a long time, they are passionate about something else. In this case, it is better to make the UMZCH transformerless. More precisely, with a single-ended matching output transformer that operates without constant magnetization. This approach greatly simplifies and speeds up the production of the most complex and critical component of a lamp UMZCH.

“Transformerless” tube output stage of the UMZCH and pre-amplifiers for it

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

But let's get back to the end. In a number of foreign sources, this scheme is considered a revelation, but an identical one, with the exception of the capacitance of the electrolytic capacitors, is found in the Soviet Radio Amateur Handbook of 1966. A thick book of 1060 pages. There was no Internet and disk-based databases back then.

In the same place, on the right in the figure, the disadvantages of this scheme are briefly but clearly described. An improved one, from the same source, is given on the trail. 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 powered through the load. If, instead of high-impedance speakers, you turn on a matching transformer with regular speakers, as in the previous one. circuit, the output power is approx. 12 W, because the active resistance of the primary winding of the transformer is much less than 800 Ohms. SOI of this final stage with transformer output - approx. 0.5%

How to make a transformer?

The main enemies of the quality of a powerful signal low-frequency (sound) transformer are the magnetic leakage 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 carelessly assembled transformer “sings,” hums, or beeps. Foucault currents are combated by reducing the thickness of the magnetic circuit plates 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. You should not take thinner plates for the output transformer: the fill factor of the core (the central rod of the magnetic circuit) with steel will fall, the cross-section of the magnetic circuit will have to be increased to obtain a given power, which will only increase distortions and losses in it.

In the core of an audio 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 magnetization; on the other hand, in a conventional magnetic circuit it increases the stray field and requires a core with a larger cross-section. Therefore, the non-magnetic gap must be calculated at the optimum and performed as accurately as possible.

For transformers operating with magnetization, the optimal type of core is made of Shp (cut) plates, pos. 1 in Fig. In them, a non-magnetic gap is formed during core cutting and is therefore stable; its value is indicated in the passport for the plates or measured with a set of probes. The stray field is minimal, because the side branches through which the magnetic flux is closed are solid. Transformer cores without bias are often assembled from Shp plates, because Shp plates are made from high-quality transformer steel. In this case, the core is assembled across the roof (the plates are laid with a cut in one direction or the other), and its cross-section is increased by 10% compared to 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 USh plates are more accessible than Shp, transformer cores with magnetization are often made from them. Then the core assembly is carried out cut to pieces: a package of W-plates is assembled, a strip of non-conducting non-magnetic material is placed with a thickness equal to the size of the non-magnetic gap, covered with a yoke from a package of jumpers and pulled together with a clip.

Note:“sound” signal magnetic circuits of the ShLM type are of little use for output transformers of high-quality tube amplifiers; they have a large stray field.

At pos. 3 shows a diagram of the core dimensions for calculating the transformer, at pos. 4 design of the winding frame, and at pos. 5 – patterns of its parts. As for the transformer for the “transformerless” output stage, it is better to make it on the ShLMm across the roof, because the bias is negligible (the bias current is equal to the 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 be much less than 800 Ohms. The more free space left in the windows, the better the transformer turned out. Therefore, the windings are wound turn to turn (if there is no winding machine, this is a terrible task) from the thinnest possible wire; the laying coefficient of the anode winding for the mechanical calculation of the transformer is taken 0.6. The winding wire is PETV or PEMM, they have an oxygen-free core. There is no need to take PETV-2 or PEMM-2; due to double varnishing, they have an increased outer diameter and a larger scattering field. The primary winding is wound first, because it is its scattering field that most affects the sound.

You need to look for iron for this transformer with holes in the corners of the plates and clamping brackets (see figure on the right), because “for complete happiness,” the magnetic circuit is assembled as follows. order (of course, the windings with leads and external insulation should already be on the frame):

1. Prepare acrylic varnish diluted in half or, in the old fashioned way, shellac;
2. Plates with jumpers are quickly coated with varnish on one side and placed into the frame as quickly as possible, without pressing too hard. The first plate is placed with the varnished side inward, the next one with the unvarnished side to the first varnished, etc.;
3. When the frame window is filled, staples are applied and bolted tightly;
4. After 1-3 minutes, when the squeezing of varnish from the gaps apparently stops, add the plates again until the window is filled;
5. Repeat paragraphs. 2-4 until the window is tightly packed with steel;
6. The core is pulled tightly 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 losses are not detected at all. But keep in mind that this technique is not applicable for permalloy cores, because Under strong mechanical influences, the magnetic properties of permalloy irreversibly deteriorate!

On microcircuits

UMZCHs on integrated circuits (ICs) are most often made by those who are satisfied with the sound quality up to average Hi-Fi, but are more attracted by the low cost, speed, ease of assembly and the complete absence of any setup procedures that require special knowledge. Simply, an amplifier on microcircuits is the best option for dummies. The classic of the genre here is the UMZCH on the TDA2004 IC, which has been on the series, God willing, for about 20 years now, 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. The advantage is the ability to work with a very low-resistance, up to 1.6 Ohm, load, which allows you to extract full power when powered from a 12 V on-board network, and 7-8 W when supplied with a 6-volt power supply, for example, on a motorcycle. However, the output of the TDA2004 in class B is not complementary (on transistors of the same conductivity), so the sound is definitely not Hi-Fi: THD 1%, dynamics 45 dB.

The more modern TDA7261 does not produce better sound, but is more powerful, up to 25 W, because The upper limit of the supply voltage has been increased to 25 V. The lower limit, 4.5 V, still allows it to be powered from a 6 V on-board network, i.e. The TDA7261 can be started from almost all on-board networks, except for the aircraft 27 V. Using attached components (strapping, on the right in the figure), the TDA7261 can operate in mutation mode and with the St-By (Stand By) function, which switches the UMZCH to the minimum power consumption mode when there is no input signal for a certain time. Convenience costs money, so for a stereo you will need a pair of TDA7261 with radiators from 250 sq. see for each.

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

“Super economical” in terms of power supply TDA7482, on the left in the figure, operating in the so-called. class D. Such UMZCHs are sometimes called digital amplifiers, which is incorrect. For real digitization, level samples are taken from an analog signal with a quantization frequency that is no less than twice the highest of the reproduced frequencies, the value of each sample is recorded in a noise-resistant code and stored for further use. UMZCH class D – pulse. In them, the analogue is directly converted into a sequence of high-frequency pulse-width modulated (PWM), which is fed to the speaker through a low-pass filter (LPF).

Class D sound has nothing in common with Hi-Fi: a SOI of 2% and dynamics of 55 dB for a Class D UMZCH are considered very good indicators. And TDA7482 here, it must be said, is not the optimal choice: other companies specializing in class D produce UMZCH ICs that are cheaper and require less wiring, for example, D-UMZCH of the Paxx series, on the right in Fig.

Among the TDAs, the 4-channel TDA7385 should be noted, see the figure, on which you can assemble a good amplifier for speakers up to medium Hi-Fi, inclusive, with frequency division into 2 bands or for a system with a subwoofer. In both cases, low-pass and mid-high-frequency filtering 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 a sub-ULF bridge circuit (see below), and the remaining 2 can be used for MF-HF.

UMZCH for subwoofer

A subwoofer, which can be translated as “subwoofer” or, literally, “boomer,” reproduces frequencies up to 150-200 Hz; in this range, human ears are practically unable to determine the direction of the sound source. In speakers with a subwoofer, the “sub-bass” speaker is placed in a separate acoustic design, this is the subwoofer as such. The subwoofer is placed, in principle, as conveniently as possible, and the stereo effect is provided by separate MF-HF channels with their own small-sized speakers, for the acoustic design of which there are no particularly serious requirements. Experts agree that it is better to listen to stereo with full channel separation, but subwoofer systems significantly save money or labor on the bass path and make it easier to place acoustics in small rooms, which is why they are popular among consumers with normal hearing and not particularly demanding ones.

The “leakage” of mid-high frequencies into the subwoofer, and from it into the air, greatly spoils the stereo, but if you sharply “cut off” the sub-bass, which, by the way, is very difficult and expensive, then a very unpleasant sound jumping effect will occur. Therefore, channels in subwoofer systems are filtered twice. At the input, electric filters highlight midrange-high frequencies with bass “tails” that do not overload the midrange-high frequency path, but provide a smooth transition to sub-bass. Bass with midrange “tails” are combined and fed to a separate UMZCH for the subwoofer. The midrange is additionally filtered so that the stereo does not deteriorate; in the subwoofer it is already acoustic: a sub-bass speaker is placed, for example, in the partition between the resonator chambers of the subwoofer, which do not let the midrange out, see on the right in Fig.

A UMZCH for a subwoofer is subject to a number of specific requirements, of which “dummies” consider the most important to be as high a power as possible. This is completely wrong, if, say, the calculation of the acoustics for the 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 S-30 speakers are suitable for the room, then a subwoofer needs 1.6x30 = 48 W.

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

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

Note: The power of a bridge UMZCH does not double, as some people 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 midrange filtering is carried out by circuits R5C3 and R’5C’3. Radiator area TDA2030 – from 400 sq. see. Bridged UMZCHs with an open output have an unpleasant feature: when the bridge is unbalanced, a constant component appears in the load current, which can damage the speaker, and the sub-bass protection circuits 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 the diagram of one battery is given in the inset.

A little about acoustics

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

Headphone Amplifier

A headphone amplifier is most often made by hand for two reasons. The first is for listening “on the go”, i.e. outside the home, when the power of the audio output of the player or smartphone is not enough to drive “buttons” or “burdocks”. The second is for high-end home headphones. A Hi-Fi UMZCH for an ordinary living room is needed with dynamics of up to 70-75 dB, but the dynamic range of the best modern stereo headphones exceeds 100 dB. An amplifier with such dynamics costs more 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 much lower than 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: the prices for household UMZCHs with such an additional weight are clearly absurdly inflated.

The circuit of the simplest headphone amplifier using transistors is given in pos. 1 pic. The sound is only for Chinese “buttons”, it works in class B. It is also no different in terms of efficiency - 13 mm lithium batteries last for 3-4 hours at full volume. At pos. 2 – TDA’s classic for on-the-go headphones. The sound, however, is quite decent, up to average Hi-Fi depending on the track digitization parameters. There are countless amateur improvements to the TDA7050 harness, but no one has yet achieved the transition of sound to the next level of class: the “microphone” itself does not allow it. TDA7057 (item 3) is simply more functional; you can connect the volume control to a regular, not dual, potentiometer.

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