Low-voltage low-frequency transistors. Low frequency amplifier on powerful transistors. Economical ULF on three transistors

Having bought good laptop or a cool phone, we are happy with the purchase, admiring the many features and speed of the device. But as soon as you connect the gadget to the speakers to listen to music or watch a movie, we understand that the sound produced by the device, as they say, “let us down”. Instead of a full and clear sound, we hear an unintelligible whisper with background noise.

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

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

Do not forget about the features of compact single-channel amplifiers based on TDA series chips, the main of which is the generation of a large amount of heat. Therefore, try with the internal structure of the amplifier to exclude the contact of the microcircuit with other parts. For additional cooling of the amplifier, it is recommended to use a radiator grill to remove heat. The size of the grating depends on the model of the microcircuit and the power of the amplifier. Plan in advance a place for a heat sink in the amplifier case.
Another feature self-manufacturing sound amplifier, is low power consumption. This, in turn, allows you to use the amplifier in the car by connecting it to the battery or on the road using battery power. Simplified amplifier models require a voltage of only 3 volts.

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

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

Headphone Amplifier

The portable headphone amplifier is not very powerful, but consumes very little power. This is an important factor for mobile amplifiers that are powered by batteries. You can also put a connector on the device for mains power through a 3 volt adapter.

To make a headphone amplifier you will need:

• Chip TDA2822 or equivalent KA2209.
• Amplifier assembly diagram.
• Capacitors 100uF 4 pieces.
• Headphone jack.
• Connector for adapter.
• Approximately 30 centimeters of copper wire.
• Heat sink element (for closed case).

The amplifier is made on a printed circuit board or surface-mounted. Do not use in this type of amplifier pulse transformer as it may interfere. After manufacturing, this amplifier is able to provide a powerful and pleasant sound from a phone, player, or tablet.
You can see another version of a homemade headphone amplifier in the video:

Notebook sound amplifier

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

To assemble the amplifier you will need:

• Printed circuit board.
• Chip TDA 7231.
• 9 volt power supply.
• Case for housing components.
• Capacitor non-polar 0.1 uF - 2 pieces.
• Capacitor polar 100 microfarad - 1 piece.
• Capacitor polar 220 microfarad - 1 piece.
• Capacitor polar 470 microfarad - 1 piece.
• Resistor constant 10 Kom - 1 piece.
• Resistor constant 4.7 Ohm - 1 piece.
• Two-position switch - 1 piece.
• Speaker input jack - 1 piece.

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

Sound amplifier for car radio

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

The microcircuit has the following declared characteristics:

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

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

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

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

Transistor audio amplifier

As a blueprint for transistor amplifier use the diagram below:

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

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

Start assembling the amplifier with power. Split two channels for stereo into two secondary windings coming from one transformer. On the layout, make bridges on Schottky diodes for the rectifier. After the bridges, there are CRC filters of two 33,000 microfarad capacitors and a 0.75 ohm resistor between them. A powerful cement resistor is needed in the filter, with a quiescent current of up to 2A it will dissipate 3 W of heat, so it is better to take it with a margin of 5-10 W. For the rest of the resistors in the circuit, a power of 2 W will be enough.

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

approximate cost Supplies for transistor audio amplifier:

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

The result is the amount - 12100 rubles.
You can also watch a video on assembling an amplifier based on germanium transistors:

Tube Sound Amplifier

Scheme of a simple tube amplifier consists of two cascades - preamplifier on 6N23P and power amplifier on 6P14P.

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

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

Classification of audio amplifiers

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

• • Class A- amplifiers of this class operate without signal cutoff in the linear section of the current-voltage characteristic of amplifying elements, which ensures a minimum non-linear distortion. But this comes at the cost of large amplifier size and huge power consumption. Class A amplifier efficiency is only 15-30%. This class includes tube and transistor amplifiers.

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

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

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

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

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

After mastering the basics of electronics, a novice radio amateur is ready to solder his first electronic designs. Audio power amplifiers tend to be the most repeatable designs. There are a lot of schemes, each differs in its parameters and design. This article will look at some of the simplest and most fully working amplifier circuits that can be successfully repeated by any radio amateur. The article does not use complex terms and calculations, everything is simplified as much as possible so that there are no additional questions.

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

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

The microcircuit is capable of operating at a load of 2 ohms, which means that 2 heads with a resistance of 4 ohms can be connected to the amplifier output.
The input capacitor can be replaced with any other, with a capacitance from 0.01 to 4.7 uF (preferably from 0.1 to 0.47 uF), both film and ceramic capacitors can be used. All other components should not be replaced.

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

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

This is probably the most quality scheme this kind, the sound is clear, the whole frequency spectrum is felt. FROM good headphones, it feels like you have a full-fledged subwoofer.

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

The amplifier can operate on a low-impedance load, up to 4 ohms, which makes it possible to use the circuit to amplify the signal of a player, radio receiver, etc. A 9 volt battery was used as a power source.
KT315 transistors are also used in the final stage. To increase the output power, you can use KT815 transistors, but then you will have to increase the supply voltage to 12 volts. In this case, the power of the amplifier will reach up to 1 watt. The output capacitor can have a capacitance from 220 to 2200 uF.
The transistors in this circuit do not heat up, therefore, no cooling is needed. When using more powerful output transistors, you may need small heatsinks for each transistor.

And finally - the third scheme. A no less simple, but proven version of the amplifier structure is presented. The amplifier is capable of operating undervoltage up to 5 volts, in this case, the output power of the PA will be no more than 0.5 W, and the maximum power when powered by 12 volts reaches up to 2 watts.

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

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

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

List of radio elements

Portable speaker for a player or phone on a tda2822m chip Amplifier test photo:

The following figure lists the required parts:

You can use almost any of the bipolar transistors medium and high power n-p-n structures, for example, KT 817. It is desirable to put a film capacitor at the input, with a capacity of 0.22 - 1 μF. An example of film capacitors in the following photo:

I bring a drawing of a printed circuit board from the program Sprint layout :


The signal is taken from the output of an mp3 player or telephone, ground and one of the channels are used. In the following figure, you can see the wiring diagram for the Jack 3.5 plug, for connecting to a signal source:


If desired, this amplifier, like any other, can be equipped with a volume control by connecting a 50 KΩ potentiometer according to the standard scheme, 1 channel is used:


In parallel with the power supply, if there is no high-capacity electrolytic capacitor in the power supply after the diode bridge, you need to supply an electrolyte of 1000 - 2200 uF, with an operating voltage greater than the supply voltage of the circuit.
An example of such a capacitor:

You can download the printed circuit board of an amplifier on a single transistor for the sprint-layout program in the My files section of the site.

You can evaluate the sound quality of this amplifier by watching the video of its work on our channel.

This audio amplifier circuit was created by everyone's favorite British engineer (electronics engineer) Linsley-Hood. The amplifier itself is assembled on only 4 transistors. It looks like an ordinary bass amplifier circuit, but this is only at first glance. An experienced radio amateur will immediately understand that the output stage of the amplifier works in class A. It's ingenious that it's simple and this circuit is proof of that. This is a super-linear circuit where the shape of the output signal does not change, that is, at the output we get the same waveform as at the input, but already amplified. The scheme is better known as JLH - class A ultra-linear amplifier, and today I decided to present it to you, although the scheme is far from new. Any ordinary radio amateur can assemble this sound amplifier with his own hands, due to the absence of microcircuits in the design, which makes it more affordable.

How to make a speaker amplifier

Sound amplifier circuit

In my case, only domestic transistors were used, since it was not easy to find with imported ones, and even standard circuit transistors. The output stage is built on powerful domestic transistors of the KT803 series - it is with them that the sound seems better. To build up the output stage, a medium-power transistor of the KT801 series was used (it was difficult to find). All transistors can be replaced with others (KT805 or 819 can be used in the output stage). Changes are not critical.

Advice: who decides to taste this homemade sound amplifier - use germanium transistors, they sound better (IMHO). Several versions of this amp have been made, they all sound… divine, I can't find any other words.

The power of the presented circuit is not more than 15 watts(plus minus), current consumption 2 Amperes (sometimes a little more). The output stage transistors will get warm even without a signal being applied to the input of the amplifier. Strange phenomenon, isn't it? But for class amplifiers. And, this is quite normal, a large quiescent current - business card literally all known schemes of this class.

The video shows the operation of the amplifier itself, connected to the speakers. Please note that the video was filmed on mobile phone, but the sound quality can be judged in this way. To test any amplifier, you just need to listen to just one melody - Beethoven's "Fur Elise". After turning it on, it becomes clear what kind of amplifier is in front of you.

90% of microcircuit amplifiers will not pass the test, the sound will be “broken off”, wheezing and distortion can be observed when high frequencies. But the above does not apply to John Linsley's circuit, the ultra-linearity of the circuit allows you to completely repeat the shape of the input signal, thus obtaining only pure gain and a sinusoid at the output.

- The neighbor got tired of knocking on the battery. He turned the music up louder so that he could not be heard.
(From audiophile folklore).

The epigraph is ironic, but the audiophile is not necessarily “sick in the head” with the physiognomy 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 the hall. The quality of the equipment for this is necessary, which for fans of the decibel of loudness as such simply does not fit where sane people have a mind, but for the latter, this mind comes 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 - the technique of sound reproduction and electronics in general. Which in the digital age are inextricably linked and can become a highly profitable and prestigious profession. The first step in this matter, optimal in all respects, is to make an amplifier with your own hands: it is UMZCH that allows, with initial training based on 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 play with pleasure. The purpose of this publication is to cover the first stages of this path for beginners and, perhaps, to tell something new to experienced ones.

Protozoa

So, for starters, let's try to make a sound 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 do not forget to enrich your knowledge base as you progress. But any “smartness” is easier to digest when you see and feel how it works “in hardware”. In this article, further, too, it will not do without theory - 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 use the multitester.

Note: if you have not soldered electronics yet, please note that its components must not be overheated! Soldering iron - up to 40 W (better than 25 W), the maximum allowable soldering time without interruption is 10 s. The soldered lead for the heat sink is held 0.5-3 cm from the place of soldering from the side of the device case with medical tweezers. Acid 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 the first power-up, the load (speaker) is turned off;
• Instead of R1, we solder a chain of a constant resistor of 33 kOhm and a variable (potentiometer) of 270 kOhm, i.e. first note. four times smaller, and the second approx. twice the face value against the original according to the scheme;
• We supply power and, by rotating the potentiometer slider, at the point marked with a cross, set the specified collector current VT1;
• We remove the power, solder the temporary resistors and measure their total resistance;
• As R1, we set the nominal resistor 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 according to paragraphs. 3-5, incl. a set the voltage equal to half the supply voltage.

Point a, from where the signal is taken to the load, is the so-called. middle point of the amplifier. In UMZCH with unipolar power, half of its value is set in it, and in UMZCH in bipolar power supply- zero relative to the common wire. This is called adjusting the balance of the amplifier. In unipolar UMZCH with capacitive load decoupling, it is not necessary to turn it off during setup, but it is better to get used to doing it reflexively: an unbalanced 2-polar 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 a device in a layout are indicated on the diagrams either with an asterisk (*) or an apostrophe dash (‘).

In the center in the same Fig.- a simple UMZCH on transistors, which already develops 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 such class D amplifier (see below) in cheap Chinese computer speakers, their sound improves markedly. Here we learn another trick: powerful output transistors must be placed on radiators. Components that require additional cooling are circled in the diagrams with a dotted line; however, not always; sometimes - with an indication of the required dissipating area of ​​the heat sink. Adjustment of this UMZCH - balancing with 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 100 W transistor amplifier. You can listen to music through it, but not Hi-Fi, the work class is AB2. However, for scoring a picnic area or an outdoor meeting, a school assembly or a small trading floor, it is quite suitable. An amateur rock band, having such an UMZCH for an instrument, can perform successfully.

In this UMZCH, 2 more tricks appear: firstly, in a very powerful amplifiers the powerful output buildup cascade also needs to be cooled, so VT3 is placed on a radiator from 100 sq. see. For output VT4 and VT5, radiators from 400 square meters are needed. 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 conjugated one goes into saturation. Then, at full supply voltage, current surges during balancing can destroy the output transistors. Therefore, for balancing (R6, did you guess?), the amplifier is powered from +/-24 V, and instead of the load, a 100 ... 200 Ohm wire resistor is included. By the way, the squiggles in some of the resistors in the diagram are Roman numerals, denoting their required heat dissipation power.

Note: a power source for this UMZCH needs a power of 600 watts or more. Smoothing filter capacitors - from 6800 uF to 160 V. In parallel with the electrolytic capacitors of the IP, ceramic ones of 0.01 uF are turned 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 draws on the requirements for Hi-Fi entry level(if, of course, UMZCH works on acc. Acustic systems, AS). Powerful field workers do not require much power for buildup, so there is no pre-power cascade. Even powerful field-effect transistors do not burn the speakers under any malfunctions - they themselves burn out faster. Also unpleasant, but still cheaper than changing an expensive bass speaker head (GG). Balancing and generally adjustment to this UMZCH are 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. IP requirements are the same as before. 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 necessary for the UMZCH, they either simply burn out, or they give a weak sound, but “none” in quality. The same applies to powerful high-voltage bipolar transistors, for example. from the horizontal scanning of old TVs.

Right 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. It is better to take the UMZCH E. Gumeli, described in detail in Radio No. 1 for 1989, as a prototype for repetition. To build it, you will need a few inexpensive affordable components, but the quality meets very high requirements: power up to 60 W, bandwidth 20-20,000 Hz, frequency response unevenness 2 dB, non-linear 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 circumstances now known greatly simplify the establishment of this UMZCH, see below. Bearing this in mind and the fact that not everyone succeeds in getting into the Radio archives, it would be appropriate to repeat the main points.

Schemes of a simple high-quality UMZCH

UMZCH Gumeli schemes and specifications for them are given in the illustration. Radiators of output transistors - from 250 sq. see for UMZCH according to fig. 1 and from 150 sq. see for variant according to fig. 3 (numbering is original). The transistors of the pre-output stage (KT814/KT815) are mounted on radiators bent from aluminum plates 75x35 mm 3 mm thick. It is not worth replacing KT814 / KT815 with KT626 / KT961, the sound does not noticeably improve, but it is seriously difficult to establish.

This UMZCH is very critical to the power supply, installation topology and general, therefore, it must be adjusted in a structurally finished form and only with a standard power source. When trying to power from a stabilized IP, the output transistors burn out immediately. Therefore, in fig. drawings of the original printed circuit boards and setup instructions. It can be added to them that, firstly, if “excitation” is noticeable at the first start, they fight with it by changing the inductance L1. Secondly, the leads of the parts installed on the boards must be no longer than 10 mm. Thirdly, it is highly undesirable to change the installation topology, but, if it is very necessary, there must be a frame screen 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 ones, for establishing, after which they are sealed with drops of solder.

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

• Minimize interconnect wiring by placing boards on high-power transistor heatsinks.
• Completely abandon the connectors inside, performing the entire installation only by soldering. Then you will not need R12, R13 in a powerful version or R10 R11 in a less powerful one (they are dotted on the diagrams).
• Use the minimum length of oxygen-free copper audio wires for indoor wiring.

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

Wires for sound

Audio wires are not idle fiction. The need for their use at the present time is undeniable. In copper with an admixture of oxygen, the thinnest 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 (it seems, due to quantum uncertainties) remains. Enough 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 copper - it is impossible to distinguish one from the other by eye. However, there is a scope where a fake does not go unambiguously: cable twisted pair for computer networks. Put a grid with long segments on the left, it will either not start at all, or it will constantly fail. Dispersion of impulses, you know.

The author, when there was still talk about audio wires, realized that, in principle, this was not empty chatter, especially since oxygen-free wires by that time had long been used in special-purpose equipment, with which he was well acquainted with the type of activity. Then I took it and replaced the regular cord of my TDS-7 headphones with a home-made one from a “vitukha” with flexible stranded wires. The sound, by ear, has steadily improved for analog tracks through, i.e. on the way from the studio microphone to the disc, never digitized. Recordings on vinyl made using DMM technology (Direct Meta lMastering, direct metal deposition) sounded especially bright. After that, the interblock editing of all home audio was converted to "vitushny". Then completely random people began to notice the improvement in sound, they were indifferent to music and not forewarned in advance.

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

Video: do-it-yourself twisted-pair interconnect wires

Unfortunately, the flexible "vituha" soon disappeared from sale - 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. Forgery is impossible, because. on ordinary copper, fluoroplastic tape insulation spreads rather quickly. MGTF is now widely available and is much cheaper than branded, guaranteed audio wires. It has 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 engineering, we had to deal with the concept of Hi-Fi (High Fidelity), high fidelity of sound reproduction. Hi-Fi are different levels, which are ranked in order. main parameters:

1. Band of reproducible frequencies.
2. Dynamic range - the ratio in decibels (dB) of the maximum (peak) output power to the level of self-noise.
3. Self-noise level in dB.
4. Nonlinear distortion factor (THD) at rated (long-term) output power. SOI at peak power is assumed to be 1% or 2% depending on the measurement technique.
5. Irregularities in 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) audio frequencies.

Note: the ratio of the absolute levels of any values ​​of I 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 these, you need to clearly understand the requirements for their power required for scoring a given room, dynamic range (dynamics), self-noise level and SOI. To achieve a frequency band of 20-20,000 Hz from the UMZCH with a blockage at the edges of 3 dB and a frequency response unevenness 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 quieter than 20 dB; 20 dB is the wilderness in complete calm. The volume level of 20 dB relative to the threshold of hearing is the threshold of intelligibility - you can still make out the whisper, but the music is perceived only as a fact of its presence. An experienced musician can tell which instrument is playing, but not exactly what.

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 with a deep frequency response correction, primarily in bass. To do this, the MUTE function is introduced into modern UMZCH (mute, mutation, not mutation!), Which includes resp. corrective circuits in UMZCH.

90 dB is the volume level of a symphony orchestra in a very good concert hall. 110 dB can give out 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: louder sounds are perceived even as distinguishable 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 full audibility, and 40-90 dB is the zone of the best audibility, in which unprepared and inexperienced listeners fully perceive the meaning of the sound. If, of course, he is in it.

Power

Calculating the power of the equipment for 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) speakers. In this case, the UMZCH will not noticeably add its distortions to those speakers, they are already the main source of non-linearity in the audio path. But the UMZCH should not be made too powerful: in this case, the level of its own noise may be above the threshold of audibility, because. it is considered from the voltage level of the output signal at maximum power. If we consider it very simply, then for a room of an ordinary apartment or house and speakers with normal characteristic sensitivity (sound output), we can take a 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 watts.
• 70-100 sq. m - 100-150 watts.
• 100-120 sq. m - 150-200 watts.
• Over 120 sq. m - is determined by calculation according to acoustic measurements on site.

Dynamics

The dynamic range of UMZCH is determined by equal loudness curves 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 will not be distinguished from ideal by any expert.
2. Other serious musical genres - 75 dB is excellent, 80 dB is over the roof.
3. Pops of any kind and movie soundtracks - 66 dB for the eyes is enough, because. these opuses are already compressed in levels up to 66 dB and even up to 40 dB during recording, so that you can listen to 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.

SOI

Nonlinear distortions (NI) UMZCH are components of the spectrum of the output signal, which were not in the input. 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. 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 it is difficult to assess the timbre of the sound. In people without a musical ear, the masking effect is already observed at 45-40 dB of volume. Therefore, UMZCH with a THD of 0.1% (-60 dB from a volume level of 110 dB) will be assessed as a Hi-Fi by an ordinary listener, and with a THD of 0.01% (-80 dB) can be considered not distorting the sound.

Lamps

The last statement, perhaps, will cause rejection, up to furious, among adherents of tube circuitry: they say that only tubes give real sound, and not just any, but certain types of octal ones. Calm down, gentlemen - a special tube sound is not fiction. The reason is fundamentally different distortion spectra for electronic tubes and transistors. Which, in turn, are due to the fact that the electron flow in the lamp moves in a vacuum and quantum effects do not appear in it. A transistor is a quantum device, where minor charge carriers (electrons and holes) move in a 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 traced in it, and there are very few combination components (sums and differences of the frequencies of the input signal and their harmonics). Therefore, in the days of vacuum circuitry, SOI was called the harmonic coefficient (KH). In transistors, the distortion spectrum (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 transistorized UMZCH took for them the usual "tube" SOI of 1-2%; a sound with a tube distortion spectrum of this magnitude is perceived by ordinary listeners as clean. By the way, the very concept of Hi-Fi did not exist then. It turned out - they sound dull and deaf. In the process of the development of transistor technology, an understanding was developed of what Hi-Fi is and what is needed for it.

At present, the growing pains of transistor technology have been successfully overcome and side frequencies at the output of a good UMZCH are hardly captured by special measurement methods. And lamp circuitry can be considered to have passed into the category of art. Its basis can be any, why can't electronics go there? An analogy with photography would be appropriate here. No one can deny that a modern digital SLR gives an image immeasurably clearer, more detailed, deeper in terms of brightness and color range 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 sleeps with his paws spread", and someone with Smena-8M on a Svemov b / w film takes a picture in front of which people are crowding at a prestigious exhibition.

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

Experimental stand

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

But enough of the lyrics, let's get down to business. For those who like to tinker with the lamps in fig. - a diagram 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 refinement touched only the output transformer: now you can not only “drive” your own 6P7S in different modes, but also select the screen grid switching ratio 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. See below for output transformer manufacturing.

Guitarists and rockers

This is the case when you can not 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 pass through a special prefix - fuser - deliberately distorting its spectrum. Without this, the sound of the string was too sharp and short, because. an electromagnetic pickup reacts only to the modes of its mechanical oscillations in the plane of the soundboard of the instrument.

An unpleasant circumstance soon emerged: the sound of an electric guitar with a fuser gains full strength and brightness only at high volumes. This is especially evident for guitars with a humbucker pickup, which gives the most "evil" sound. But what about a beginner, 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 surroundings.

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

Those who need a tube amplifier not for experiments, but because of technical necessity, have no time to master the intricacies of tube electronics for a long time, they are passionate about others. UMZCH in this case, it is better to do transformerless. More precisely, with a single-ended matching output transformer that operates without constant bias. This approach greatly simplifies and speeds up the manufacture of the most complex and critical assembly of the lamp UMZCH.

“Transformerless” UMZCH tube output stage and preamplifiers 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 options for a preamplifier 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 operating the UMZCH on a 2-way speaker. Below is a simpler preamplifier with tone control that does not distort the signal.

But let's get back to the end. In a number of foreign sources, this circuit is considered a revelation, however, identical to it, with the exception of the capacity of electrolytic capacitors, is found in the Soviet Radio Amateur's Handbook of 1966. A thick book of 1060 pages. There was no Internet then 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 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 through the load. If, instead of high-impedance speakers, you turn on a matching transformer with a conventional speaker, as in the previous. 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 a 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 stray 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", buzzes or squeaks. Foucault currents are fought by reducing the thickness of the plates of the magnetic circuit and additionally isolating them with varnish during assembly. For output transformers, the optimal thickness of the plates is 0.15 mm, the maximum allowable is 0.25 mm. Thinner plates should not be taken for the output transformer: the fill factor of the core (the central core 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 distortion and losses in it.

In the core of an audio transformer operating with a constant bias (eg, 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. 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 plates (punched), pos. 1 in fig. In them, a non-magnetic gap is formed during the penetration of the core and therefore is 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 closes are solid. Shp plates are often used to assemble transformer cores without magnetization, because Shp plates are made of high quality transformer steel. In this case, the core is assembled in 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, the reduction of 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 also made from them. Then the assembly of the core is carried out in a cut: a package of W-plates is assembled, a strip of non-conductive non-magnetic material is laid with a thickness equal to the value of the non-magnetic gap, covered with a yoke from a package of jumpers and pulled together by a clip.

Note:"Audio" 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 winding frame design, and on pos. 5 - patterns of its details. As for the transformer for the "transformerless" output stage, it is better to do it on the SLMme with an overlap, because. the bias is negligible (the bias current is equal to the current of the screen grid). 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 a terrible machine) from the thinnest possible wire, the anode winding laying coefficient for the mechanical calculation of the transformer is taken as 0.6. The winding wire is of the PETV or PEMM brands, they have an oxygen-free core. It is not necessary 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 stray field that most affects the sound.

Iron for this transformer must be looked for with holes in the corners of the plates and clamps (see the figure on the right), because. "For complete happiness" the assembly of the magnetic circuit is carried out in the next. order (of course, the windings with leads and outer 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 put into the frame as quickly as possible, without pressing hard. The first plate is placed with the lacquered side inward, the next - with the unvarnished side to the lacquered first, etc.;
3. When the frame window is full, staples are applied and tightened tightly with bolts;
4. After 1-3 minutes, when the extrusion of 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 tightly again and dried on a battery or the like. 3-5 days.

The core assembled using this technology has very good plate insulation and steel filling. Losses due to magnetostriction are 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 irreversibly deteriorate!

On microchips

UMZCH on integrated circuits (ICs) is most often done by those who are satisfied with sound quality up to average Hi-Fi, but are more attracted by cheapness, speed, ease of assembly and the complete absence of any adjustment procedures that require special knowledge. Simply, an amplifier on microcircuits is the best option for dummies. The classic of the genre here is UMZCH on the TDA2004 IC, standing on the series, God forbid, 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. The advantage is the ability to work on a very low-resistance, up to 1.6 Ohm, load, which allows you to remove full power when powered from the 12 V on-board network, and 7-8 W - with a 6-volt power supply, for example, on a motorcycle. However, the TDA2004 output 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, because. the upper limit of the supply voltage has been increased to 25V. TDA7261 can be run from almost all on-board networks, except for aircraft 27 V. With the help of hinged components (strapping, on the right in the figure), TDA7261 can operate in mutation mode and with the St-By (Stand By, wait) function, which switches the UMZCH to the minimum power consumption mode when there is no input signal for a certain time. Amenities 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 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 TDA7482, on the left in the figure, working in the so-called. class D. Such UMZCH are sometimes called digital amplifiers, which is not true. For true digitization, level samples are taken from an analog signal at a quantization frequency of at least twice the highest of the reproducible frequencies, the value of each sample is recorded in an error-correcting code and stored for future use. UMZCH class D - pulsed. In them, the analogue 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 has nothing to do with Hi-Fi: THD of 2% and dynamics of 55 dB for UMZCH class D are considered very good indicators. And TDA7482 here, I must say, the choice is not optimal: other companies specializing in class D produce UMZCH ICs cheaper and require less strapping, for example, the Paxx D-UMZCH series, on the right in Fig.

Of the TDAs, it should be noted the 4-channel TDA7385, see the figure, on which you can assemble a good amplifier for speakers up to medium Hi-Fi inclusive, with frequency separation into 2 bands or for a system with a subwoofer. The filtering of low-frequency and mid-high frequencies in both cases is done at the input on a weak signal, which simplifies the design of the filters and allows for a deeper separation of the bands. And if the acoustics are subwoofer, then 2 channels of the TDA7385 can be allocated for the sub-ULF of the bridge circuit (see below), and the remaining 2 can be used for midrange-high frequencies.

UMZCH for subwoofer

A subwoofer, which can be translated as a "subwoofer" or, literally, "a subwoofer" 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 a separate acoustic design, this is the subwoofer as such. The subwoofer is placed, in principle, as it is more convenient, 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. Connoisseurs 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 make it easier to place acoustics in small rooms, which is why they are popular with consumers with normal hearing and not particularly demanding.

“Leakage” of midrange-high frequencies into the subwoofer, and from it into the air, greatly spoils the stereo, but if you sharply “cut off” the subbass, which, by the way, is very difficult and expensive, then a very unpleasant sound jump effect will occur. Therefore, channel filtering in subwoofer systems is done twice. At the input, MF-HF with bass "tails" are distinguished by electric filters, which do not overload the MF-HF 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, it is already acoustic in the subwoofer: the subwoofer is placed, for example, in the partition between the resonator chambers of the subwoofer that do 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 "dummies" consider the greatest possible power to be the main one. This is completely wrong, if, say, the calculation of acoustics for a room gave 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 the room, then a subwoofer is needed 1.6x30 \u003d 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 acceptable up to 1%. Bass distortions of this level are not audible (see equal loudness curves), and the “tails” of their spectrum in the best audible midrange region will not get out of the subwoofer.

In order 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 UMZCH are turned on in the opposite direction through the speaker; the signals to the inputs are 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 that form the shoulders of the bridge is ensured by the use of paired UMZCH 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 the 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 the R5C3 and R'5C'3 circuits. Radiator area TDA2030 - from 400 sq. see. Bridge UMZCHs with an open output have an unpleasant feature: when the bridge is unbalanced, a constant component appears in the load current that can disable the speaker, and protection circuits on the subbass often fail, turning off the speaker when not needed. Therefore, it is better to protect the expensive “dubovo” woofer with non-polar batteries of electrolytic capacitors (highlighted in color, and the diagram of one battery is given in the sidebar.

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 sufficiently 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 one. For a specific speaker 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 obviously longer lengths and, pushing in and out, achieve the desired sound. The outward protrusions of the pipes do not affect the sound, they are then cut off. The pipe settings are interdependent, so you have to tinker.

Headphone Amplifier

A headphone amplifier is made by hand most often for 2 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 build up "buttons" or "burdocks". 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 watts per channel, which is too much for an ordinary apartment: listening at a very low power level 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 a makeweight are obviously too high.

The diagram of the simplest headphone amplifier on transistors 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 for 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 track digitization. Amateur improvements to the TDA7050 strapping are innumerable, 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 the volume control on a regular, not dual, potentiometer.

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