Sound frequency amplifiers on transistors. Description of the sound power amplifier on MOSFET transistors. Amplifier work class

The editorial board "Two Schemes" is simple, but high-quality amplifier HF on MOSFET transistors. Its scheme should be well known to radio amphibians, since she has already been 20 years old. The scheme is the development of the famous Anthony Holton, so it is sometimes called it - Uncle Holton. The sound amplification system has low harmonic distortion, not exceeding 0.1%, with power to load about 100 watts.

This amplifier is an alternative for popular TDA series amplifiers and similar pop, because with a slightly greater cost you can get an amplifier with clearly better characteristics.

The big advantage of the system is simple design and the output cascade consisting of 2 inexpensive MOS transistors. The amplifier can work with resistance speakers both 4 and 8 Ohm. The only setting that needs to be performed during start-up will be setting the value of the reservoir of the output transistors.

Holton Ump Circuit

Holton Amplifier on MOSFET - Scheme

The scheme is a classic two-stage amplifier, it consists of a differential input amplifier and a symmetric power amplifier in which one pair of power transistors operates. The system scheme is presented above.

Printed circuit board

UHR printed circuit board - Ready View

Here is the archive S. PDF files PCB -.

Principle of operation of the amplifier

T4 transistors (BC546) and T5 (BC546) are operating in the configuration of the differential amplifier and are calculated on power from the current source built on the basis of T7 transistors (BC546), T10 (BC546) and resistors R18 (22 com), R20 (680 Ohms) and R12 (22 com). The input signal is fed into two filters: the lower frequencies constructed from the elements R6 (470 Ohms) and C6 (1 NF) - it limits the RF components of the signal and the bandage filter consisting of C5 (1 μF), R6 and R10 (47 com), Limiting the components of the signal on the infusion frequencies.

The load of the differential amplifier are R2 resistors (4.7 com) and R3 (4.7 com). T1 (MJE350) and T2 (MJE350) transistors are another amplification cascade, and its load is T8 (MJE340), T9 (MJE340) and T6 (BD139) transistors.

Capacitors C3 (33 PF) and C4 (33 PF) counteract the excitation of the amplifier. Capacitor C8 (10 NF) Included parallel to R13 (10 kΩ / 1 B), improves the transition characteristic of UNG, which matters for fast increasing input signals.

The T6 transistor together with the elements R9 (4.7 kΩ), R15 (680 Ohms), R16 (82 Ohms) and PR1 (5 com) allows you to set the correct polarity of the output stage of the amplifier's output cascades at rest. Using the potentiometer, it is necessary to establish a rest current of the output transistors within 90-110 mA, which corresponds to the voltage drop on R8 (0.22 Ohm / 5 W) and R17 (0.22 Ohm / 5 W) within 20-25 mV. The total current consumption in the amplifier rest mode should be around 130 mA.

The output elements of the amplifier are MOS transistors T3 (IRFP240) and T11 (IRFP9240). These transistors are installed as a voltage repeater with a large maximum output current, thus, the first 2 cascades must split a sufficiently large amplitude for the output signal.

R8 and R17 resistors were applied mainly to quickly measure the current of the transistors of power amplifier without interference in the circuit. They can also come in handy in case of expanding the system to another pair of power transistors, due to differences in the resistance of open channels of transistors.

Resistors R5 (470 Ohms) and R19 (470 Ohms) limit the cost of charging the capacitance of passing transistors, and, therefore, limit the frequency range of the amplifier. D1-D2 diodes (BZX85-C12V) protect powerful transistors. With them, voltage at startup relative to power sources in transistors should not be more than 12 V.

The amplifier board provides spaces for C2 filter capacitors C2 (4700 μF / 50 B) and C13 (4700 μF / 50 V).

Homemade transistor UH on Mosfet.

Control powered through an additional RC filter built on elements R1 (100 Ohm / 1 V), C1 (220 μF / 50 V) and R23 (100 Ohm / 1 V) and C12 (220 μF / 50 V).

Power supply for umzch

The amplifier circuit provides a power that reaches a real 100 W (efficient sinusoidal), with input voltage in the area of \u200b\u200b600 mV and the load resistance of 4 Ohm.

Holton amplifier on card with details

The recommended transformer - 200 W toroid with a voltage of 2x24 V. After straightening and smoothing, two polar power supply power amplifiers should be obtained in the +/-3 volt area. The design presented here is a mono amplifier module with very good parameters built on MOSFET transistors, which can be used as a separate unit or part.

- a neighbor stalled on the battery to knock. Made music louder to hear it.
(From the folklore of audiophiles).

The epigraph is ironic, but the audiophile is not necessarily "patient on the whole head" with the physiognomy Josh Ernest at a briefing on relationships with the Russian Federation, which "rushing" because neighbors "happy." Someone wants to listen to serious music at home as in the hall. The quality of the equipment for this you need this, which lovers of the volumetric volume as such simply does not fit there, where the mind of people's mind, but the latter it comes from prices for suitable amplifiers (umzch, sound frequency power amplifier). And someone simultaneously arises a desire to join the useful and fascinating areas of activity - the technique of playing sound and generally electronics. Which in the age of digital technologies is inextricably linked and can become a highly profitable and prestigious profession. Optimal in all respects the first step in this business is to make an amplifier with your own hands: it is a worn that allows with initial training on the basis of school physics on the same table to go through the path from the simplest structures on the Polevochor (which, nevertheless, "sing well") to the most complex aggregates, through which a good rock band will play with pleasure. The purpose of this publication is light the first stages of this path for beginners and, perhaps, to report something new experienced.

Simplest

So, first, let's try to make a sound amplifier that just works. In order to thoroughly in to sound, you will have to gradually master quite a lot of theoretical material and do not forget as we move to enrich the luggage of knowledge. But any "mentality" is assumed easier when you see and taught how it works "in the gland." In this article further, too, without the theory will not cost - in what you need to know at first and what is possible to clarify without formulas and graphs. In the meantime, there will be a skill and use the multi-seater.

Note: If you still have not soldered electronics, keep in mind - its components can not be overheated! The soldering iron is up to 40 W (better than 25 W), the maximum permissible time soldering without a break - 10 s. The soldered output for the heat sink is held at 0.5-3 cm from the place of soldering from the body of the device with a medical tweezers. Acid and other active fluxs can not be applied! Solder - Pos-61.

Left in fig. - The simplest umzch, "which just works." It can be collected both in Germany and silicon transistors.

On this crumb, it is convenient to master the basics of adjusting UMP with direct connections between cascades, giving the most pure sound:

Before the first power turning on the load (speaker) turn off;
Instead of R1 we give a chain from permanent resistor at 33 com and alternating (potentiometer) at 270 com, i.e. First approx. four times smaller, and the second approx. twice the greatest nominal against the initial scheme;
Supply power and, rotating the potentiometer engine, at a point marked with a cross, set the specified current collector VT1;
Remove the food, we drop the time resistors and measure their overall resistance;
As R1, we put the resistor of the nominal from the standard range, the nearest to the measured;
Replace R3 on the chain constant 470 Ohm + potentiometer 3.3 com;
Just like according to PP. 3-5, in t. And set the voltage equal to half the supply voltage.

Point A, where the signal is removed in the load is T. Naz. The average point of the amplifier. In Umzch S. unipolar nutrition It is set to half its meaning, and in the UMR two-polar nutrition - zero relative to the common wire. This is called the adjustment of the boalance of the amplifier. In unipolar cleansing with capacitive loading of the load, it is not necessary to turn it off at the time of adjustment, but it is best to get used to do it reflexively: a unbalanced 2-polar amplifier with a connected load can burn its powerful and expensive output transistors, and even "new, good" and very Dear powerful speaker.

Note: Components requiring selection when adjusting the device in the layout, in the schemes are designated or an asterisk (*), or a stroke apostrophe (').

In the center on the same rice. - Simple UMPs on transistors, developing already power up to 4-6 W at a load of 4 ohms. Although it works, like the previous one, in T. Naz. AB1 class not intended for Hi-Fi voicing, but if you replace a pair of such a class D amplifier (see below) in cheap Chinese computer speakers, their sound is noticeably improved. Here we know another trick: powerful weekend transistors need to be put on radiators. Components requiring additional cooling, in the schemes are driven by a dotted line; True, not always; Sometimes - indicating the necessary dissipation area of \u200b\u200bthe heat sink. Adjusting this UMP - balancing with R2.

Right in fig. - It's not a monster for 350 W (as was shown at the beginning of the article), but already quite solid beast: a simple amplifier on 100 W transistors. You can listen to music through it, but not Hi-Fi, the class of work is AB2. However, to voicing the platform for a picnic or a meeting in the open air, a school actor or a small shopping room, it is quite suitable. Amateur rock band, having such a worn to the tool, can successfully perform.

In this umzch, 2 more tricks are manifested: first, in very powerful amplifiers Cascade of a powerful outlet swing also need to cool, so VT3 put on a radiator from 100 square meters. See for the weekend VT4 and VT5, you need radiators from 400 square meters. See secondly, the umzch with two-polar nutrition is not balanced without load. Then one, then another output transistor goes into the cut-off, and conjugate in saturation. Then, on the full supply voltage, the current jump during balancing is able to deal with output transistors. Therefore, for balancing (R6, they guessed?) The amplifier is powered by +/- 24 V, and instead of loads include wire resistor 100 ... 200 ohms. By the way, the stokers in some resistors in the scheme - Roman numbers denoting them necessary power Heat scattering.

Note: The power source for this umzch is needed with a power of 600 W. Capacitors of the smoothing filter - from 6800 μF at 160 V. Parallel to electrolytic capacitors, IP are included in the Ceramic 0.01 μF to prevent self-excitation on ultrasound frequencies that can instantly burn output transistors.

On the fields

On the trail. Fig. - Another option is quite powerful umzch (30 W, and with a supply voltage of 35 V - 60 W) on powerful field transistors:

The sound from it already pulls on the requirements for Hi-Fi initial level (if, of course, UMPs works on acc. acustic systems, AC). Powerful bevels do not require high power for the swing, therefore there is no staple cascade. More powerful field transistors at no matter what faults do not burn the speakers - they are faster themselves. Also unpleasant, but still cheaper than changing the expensive bass head of the loudspeaker (GG). Balancing and generally adjusting this UMR is not required. The lack of him, like the design for beginners, is only one: powerful field transistors are much more expensive than bipolar for the amplifier with the same parameters. Requirements for IP - similar before. Case, but the power is needed from 450 W. Radiators - from 200 square meters. cm.

Note: No need to build powerful UMPs on field transistors for pulse sources Food, for example. Computer. When you try to "drive" them into the active mode, which is necessary for the umzch, they are or simply burned, or the sound is given weak, and in terms of "no". The same applies to powerful high-voltage bipolar transistors, for example of string scan Old TVs.

Immediately up

If you have already done the first steps, it will be quite natural will be the desire to build Hi-Fi class urzch, without going too deep into theoretical debris. To do this, you will have to expand the dashboard - the oscilloscope is needed, the sound frequency generator (GZH) and Millivoltmeter alternating current With the possibility of measuring the constant component. The prototype for the repetition is better to take the umzch by E. Gumeli, described in detail in Radio No. 1 for 1989. For its construction, it will take a little inexpensive component available, but the quality satisfies highly high requirements: power up to 60 W, a strip of 20-20,000 Hz, Non-uniformity frequency response 2 dB, coefficient nonlinear distortion (Books) 0.01%, the level of own noise -86 dB. However, to establish the amplifier of the rumelles is quite difficult; If you cope with it, you can take for any other. However, some of the currently known circumstances are much simplified by the establishment of this umzch, see below. Bearing in mind this and the fact that in the archives "Radio" will not do everything, it will be appropriate to repeat the highlights.

Schemes of simple high-quality umzch

Movement of the Gumeli and the specification to them are given on the illustration. Radiators output transistors - from 250 kV. See for umzch in fig. 1 and from 150 square meters. See for option in fig. 3 (Original numbering). Transistors of the prestigious cascade (CT814 / KT815) are installed on radiators bent from aluminum plates 75x35 mm thick 3 mm. Replacing the CT814 / KT815 on CT626 / KT961 is not worth it, the sound does not noticeably improve, but the establishment is seriously difficult.

This umzch is very critical to the power supply, installation topology and general, so it is necessary to establish it in constructively completed form and only with a standard power source. When trying to power from the stabilized IP, the output transistors burn immediately. Therefore, in Fig. Dana drawings are original printed circuit board and instructions on adjustment. It is possible to add to them that, firstly, if at the first inclusion noticeable "RUBID", it is struggling with it, changing the inductance L1. Secondly, the findings of the parts installed on the fees should be no longer 10 mm. Thirdly, changing the mounting topology is extremely undesirable, but if it is very necessary, on the side of the conductors, there must be a frame screen (earth loop, highlighted in color in Fig.), And the power supply paths must pass outside it.

Note: Rales in the tracks to which the bases are connected powerful transistors - technological, for establishing, after which the solder drops are searched.

The establishment of this umzch is a lot simplified, and the risk to face "RUB" in the process of use is reduced to zero if:

Minimize inter-block installation by placing cards on radiators of powerful transistors.
Fully abandon the connectors inside by performing all the installation only soldering. Then they do not need R12, R13 in a powerful version or R10 R11 in a less powerful (in the diagrams they are dotted).
Use for internal installation of an audio line from oxygen-free copper minimum length.

When performing these conditions with the excitation of problems, there is no problem, and the extension of UMPs is reduced to the routine procedure described in Fig.

Wires for sound

The audio line is not aware of the fiction. The need for their application is currently undoubted. In copper with an admixture of oxygen on the edges of the metal crystallites, the finest oxide film is formed. Metal oxides Semiconductors and, if the current in the wire is weak without constant component, its form is distorted. In theory, distortion on the myriads of crystallites should compensate each other, but the smallest (seems to be due to quantum uncertainties) remains. Sufficient to be noticed by the demanding listeners against the background of the purest sound of modern umzch.

Manufacturers and merchants without conscience are applied instead of an infectious conventional electrotechnical copper - it is impossible to distinguish one from the other to the eye. However, there is a scope of application where the fake is not definitely: the cable is twisted pair for computer networks. Put the grid with long segments "Levar", it will not start at all, or will be constantly buggy. Dispersion of pulses, you understand.

The author, when only the conversations about the audio enterprises, I realized that, in principle, this is not an empty chatter, especially since the octalless wires have been used for a long time in the technique of special substation, with which he was well acquainted. I took it then and replaced the regular cord of his headphones TDS-7 homemade from "Vituchi" with flexible stranded wires. Sound, for rumor, has consistently improved for through analog tracks, i.e. On the way from the studio microphone to the disk anywhere not exposed to digitization. Especially brightly sounded records on vinyl, made using DMM technology (Direct Meta Lmastering, direct application of metal). After that, the inter-block installation of all home audio was converted to "vituye". Then the improvement of the sound began to celebrate and completely random people, indifferent to music and not prevailing in advance.

How to make inter-block wires from twisted pair, see the next. video.

Video: Inter-block wires from twisted pair do it yourself

Unfortunately, the flexible "Vituha" soon disappeared from the sale - poorly kept in the crimping connectors. However, to the information of readers, only from oxygen-free copper is made flexible "military" Wire MGTF and MGTFE (shielded). Fake is impossible, because On ordinary copper, ribbon fluoroplastic insulation is quite quickly spread. MGTF is now on a wide sale and is much cheaper than branded, with a guarantee, audio conductors. The lack of him is one: it is impossible to perform overlapping, but it can be corrected by tags. There are also oxygen-free winding wires, see below.

Theoretical intermedia

As you can see, at first, the development of sound engineers we had to face the concept of Hi-Fi (High Fidelity), high loyalty Play sound. Hi-Fi is different levels that are ranked by the next. Basic parameters:

Strip of reproducible frequency.
Dynamic range - relation in decibels (dB) of the maximum (peak) output power to the level of own noise.
The level of own noise in dB.
The coefficient of nonlinear distortion (books) on the nominal (long-term) output power. SC at peak power is taken 1% or 2% depending on the measurement techniques.
The unevenness of the amplitude-frequency characteristic (ACH) in the reproducible frequency band. For AC - separately on low (LF, 20-300 Hz), medium (sch, 300-5000 Hz) and high (HF, 5000-20 000 Hz) sound frequencies.

Note: The ratio of absolute levels of any values \u200b\u200bof i in (dB) is defined as P (dB) \u003d 20LG (I1 / I2). If i1

All the subtleties and nuances of Hi-Fi need to know, engaged in the design and construction of the speakers, and as for homemade Hi-Fi urzch for the home, then before switching to such, it is necessary to clearly understand the requirements for their power required for the sound of this room, Dynamic range (dynamics), level of own noise and books. To achieve from the umzch band frequency bands of 20-20,000 Hz with a bombardment at the edges of 3 dB and the non-uniformity of the frequency response to SCH in 2 dB on a modern elementary base is not large difficulties.

Volume

The power of the umzch is not an end in itself, it should provide the optimal volume of sound playback in this room. It is possible to determine it by curve equal volume, see Fig. Natural noise in residential premises quieter 20 dB does not happen; 20 dB is the forest wilderness in full calm. The volume level of 20 dB relative to the threshold of hearingness is a threshold of indestructible - the whisper is still possible, but the music is perceived only as the fact of its presence. An experienced musician can determine which tool plays, but what exactly is not.

40 dB - Normal noise of a well-insulated urban apartment in a quiet area or country house - represents the threshold of intelligibility. Music from the threshold of persistence to the threshold can be listened to the presence of deep correction ACH, primarily on bass. To do this, the Mute function is introduced into modern umzch (muzzle, mutating, not mutation!), Including acc. Corrective chains in UMP.

90 dB - the level of volume of the symphony orchestra in a very good concert hall. 110 dB can issue an extended composition orchestra in the hall with a unique acoustics, which in the world is not more than 10, this is a threshold of perception: the sounds are louder perceived as distinguishable in meaning with the effort of will, but already irritating noise. The volume zone in the residential premises 20-110 dB is a zone of complete hearing, and 40-90 dB - the zone of the best audibility, in which unprepared and inexperienced listeners fully perceive the meaning of sound. If, of course, he is in it.

Power

Calculation of the power of the equipment on a given volume in the audition zone is hardly the main and most difficult task of electroacoustics. For myself, it is better to go from acoustic systems (AC): calculate their power on a simplified technique, and take the nominal (long-term) power of the urzch of equal peak (musical) AU. In this case, the umzch will not add noticeably his distortions to such as, they are also the main source of nonlinearity in the sound tract. But it should not be too powerful to do: in this case, the level of its own noise may be above the threshold of hearingness, because It is considered from the voltage level of the output signal at maximum power. If you consider very simple, then for the room of a regular apartment or at home and speakers with a normal characteristic sensitivity (sound return) you can take a trail. The values \u200b\u200bof the optimal power of the umzch:

Up to 8 square meters M - 15-20 W.
8-12 square meters. M - 20-30 W.
12-26 sq. M. M - 30-50 W.
26-50 square meters M - 50-60 W.
50-70 square meters. M - 60-100 W.
70-100 kV. M - 100-150 W.
100-120 kV. M - 150-200 W.
More than 120 square meters. M - is determined by the calculation according to the data of acoustic measurements in place.

Dynamics

The dynamic range of UMPs is determined by the curves of equal volume and threshold values \u200b\u200bfor different degrees of perception:

Symphonic music and jazz with symphonic accompaniment - 90 dB (110 dB - 20 dB) Ideal, 70 dB (90 dB - 20 dB) is acceptable. The sound with a dynamics of 80-85 dB in the urban apartment does not differ from the ideal expert.
Other serious musical genres - 75 dB excellent, 80 dB "above the roof."
Pops of any kind and soundtracks for films - 66 dB for eyes enough, because These opuses are already compressed at levels of up to 66 dB and even up to 40 dB so that you can listen to anything.

The dynamic range of UMP, which is properly selected for this room, is considered to be equal to its level of own noise taken with a + sign, that's T. Naz. Signal / noise ratio.

Book

Nonlinear distortions (nor) UMPs are the components of the spectrum of the output signal, which was not in the input. Theoretically, neither best "shook" under the level of our own noise, but technically it is very difficult to implement. In practice, they take into account the T. Naz. The disguise effect: at the volume levels below approx. 30 dB The range of perceived by the human ear frequencies is narrowed as the ability to distinguish sounds in frequency. Musicians hear notes, but to evaluate the sound of sound difficult. In humans without a musical hearing, the disguise effect is already observed at 45-40 dB of volume. Therefore, the umzch from the book 0.1% (-60 dB from the volume of the volume in 110 dB) will evaluate as a Hi-Fi ordinary listener, and from the book 0.01% (-80 dB) can be considered not distorting sound.

Lamp

The last statement may cause rejection, right up to the fierce, the adepts of the lamp circuit circuitry: they say, the real sound is given only lamps, and not just some, but separate types of octal. Calm down, gentlemen - a special lamp sound is not a fiction. The reason is fundamentally different spectra of distortion in electronic lamps and transistors. Which, in turn, is due to the fact that in the lamp the electron flux is moving in vacuo and the quantum effects are not manifested in it. The transistor is a quantum device, there are non-core charge carriers (electrons and holes) move in a crystal that it is impossible without quantum effects. Therefore, the spectrum of lamp distortion is short and clean: only the harmonics are clearly traced in it to the 3rd - 4th, and the combination components (sums and differences of the frequencies of the input signal and their harmonic) are very small. Therefore, during the time of vacuum scheme engineering of the books called the harmonic coefficient (kg). In transistors, the spectrum of distortion (if they are measured, the reservation is random, see below) can be traced until the 15th and higher components, and the combination frequencies in it are even debt.

At first, the solid-state electronics constructors of transistor umzch took for them the familiar "lamp" book in 1-2%; The sound with a lamp spectrum of distortion of such a magnitude by ordinary listeners is perceived as pure. By the way, and the very concept of Hi-fidene has not yet been. It turned out - dull and deaf sound. In the process of developing transistor equipment and developed an understanding of what Hi-Fi is and what is needed for it.

Currently, the growth of transistor technology has been successfully overcome and side frequencies at the output of good urzch with difficulty are captured by special measurement methods. And the lamp circuit engineering can be considered the art that passed into the category. Its basis can be any, why can not electronics do there? This will be appropriate an analogy with a photo. No one can deny that the modern digital car gives a picture of an immeasurably clearer, detailed, deep on the range of brightness and color than plywood boxes with harmonica. But someone's woven Nikon "clasters pictures" like "This is my fat koshak drove up as a reptile and raging his paws," and someone shifting-8m on the coaching ch / w film takes a picture, which is crowded in the prestigious exhibition.

Note: And even once calm down - not everything is so bad. Today, at least one application remains at least one application, and not the latest importance for which they are technically needed.

Experienced stand

Many audio lovers, barely learned to solder, immediately "go to the lamps." This is no case deserves the censure, on the contrary. Interest in the origins is always justified and useful, and the electronics has become such on the lamps. The first computers were lamp, and the onboard electronic equipment of the first spacecraft was also a lamp: transistors were already there, but could not withstand extraterrestrial radiation. By the way, then lamps were created under the strictest secret ... microcircuits! On microlams with a cold cathode. The only well-known mention of them in open sources is in the rare book of Mitrofanov and Pickersgil "Modern receiving and amplifying lamps".

But enough lyrics, to business. For lovers, tinker with lamps in fig. - A scheme of a bench lamp UMP, designed specifically for experiments: SA1 switches the operation of the output lamp, and SA2 is the supply voltage. The scheme is well known in the Russian Federation, a small refinement touched only the output transformer: now you can not only "drive" in different modes native 6P7S, but also pick up the turning on the on-screen grid in ulralinear mode for other lamps; For the overwhelming majority of the output pents and radiation tetrods, it or 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 without lamps can not do. As you know, the electric guitar has become a full-fledged soling tool after the pre-enhanced signal from the pickup began to skip through a special console - the fuser is a deliberately distorting spectrum. Without this, the sound of the string was too sharp and short, because The electromagnetic pickup reacts only on the modes of its mechanical oscillations in the plane of the tool deck.

Soon an unpleasant circumstance was revealed: the sound of electric guitar with a fouther takes full force and brightness only on large losses. This is especially manifested for guitars with a hambaker type pickup, giving the most "angry" sound. And how to be a beginner, forced to rehearse at home? Do not go to the hall to speak, not knowing exactly how the instrument will sound there. And simply fans of rock you want to listen to your favorite things in complete juice, and rockers people in general are decent and non-conflict. At least those who are interested in the rock music, and not an entourage with outrageous.

So, it turned out that the fatal sound appears at the volume levels acceptable for residential premises, if the umzch lamp. The reason is the specific interaction of the signal spectrum from the fuser with a clean and short spectrum of lamp harmonics. The analogy is relevant here: a photo can be much more expressive than color, because leaves for viewing only the outline and light.

Those to whom the lamp amplifier is not needed for experiments, and due to the technical necessity, long to learn the subtleties of the lamp electronics underwitch, they are most passionate about. Umzch, in this case, it is better to make a blowranxiformator. More precisely, with a one-acting matching output transformer operating without constant additions. Such an approach simplifies and accelerates the manufacture of the most complex and responsible node of the lamp UMP.

"TRANSFORMATORAL" LAMP OUTPUT CASCADE UMPS and PREVIOUS ACIDS TO HIM

Right in fig. A diagram of a tranfactory output cascade of a lamp ukluch, and on the left - options for the pre-amplifier for it. At the top - with a tone controller according to the classic Baxandal scheme, providing a sufficiently deep adjustment, but bringing small phase distortion into the signal, which may be significantly when the UMP is working on a 2-band speaker. Below is a preamplifier with the adjustment of the timbre, not distorting the signal.

But back to the "final". In a number of foreign sources, this scheme is considered to be revelation, but it is identical to it, with the exception of the capacity of electrolytic capacitors, is found in the Soviet "radio amateur reference book" of 1966. Tolstinized booking of 1060 pages. There was no Internet and databases on disks.

In the same place, on the right in Fig., Briefly, but clearly describes the shortcomings of this scheme. Advanced, from the same source, given to the next. Fig. on right. In it, the on-screen mesh L2 is powered from the middle point of the anode rectifier (the anode winding of the power transformer is symmetrical), and the L1 screen grid through the load. If instead of high-resistant speakers include a consigning transformer with conventional speakers, as in before. Scheme, output power to make approx. 12 W, because The active resistance of the primary winding of the transformer is much less than 800 ohms. Of the book of this terminal cascade with transformer exit - approx. 0.5%

How to make a transformer?

The main enemies of the quality of the powerful signaling LC (sound) transformer - the magnetic field of scattering, the power lines of which are closed, bypassing the magnetic circuit (core), vortex currents in the magnetic circuit (Foucault currents) and, to a lesser extent, magnetostriction in the core. Because of this, the phenomenon is a carelessly assembled transformer "sings", buzzing or beats. Face-fight currents are struggling, reducing the thickness of the magnetic pipe plates and additionally isolating them with varnish when assembling. For output transformers, the optimal thickness of the plates is 0.15 mm, the maximum allowable is 0.25 mm. To take a plate thinner for the output transformer: the coefficient of filling the core (central rod of the magnetic pipeline) Steel will fall, the magnetic pipeline cross-section will have to increase the distortion and loss in it will only increase.

In the core of a sound transformer operating with constant additions (for example, the anode current of the one-bit output cascade) should be small (determined by the calculation) a non-magnetic clearance. The presence of a non-magnetic gap, on the one hand, reduces the distortion of the signal from constant additions; On the other hand, in the magnetic content of the usual type increases the scattering field and requires a core of a larger cross section. Therefore, the non-magnetic gap must count on the optimum and perform as accurate as possible.

For transformers working with appreciation, the optimal type of the core is from the plates of the SP (spin), pos. 1 in fig. In them, the non-magnetic clearance is formed at the boring of the core and therefore stable; Its value is indicated in the passport on the plate or measured by a set of probe. The scattering field is minimal, because Side branches through which the magnetic flow is closed, solid. From the plates of the SP, the cores of transformers without additions are also assembled, because SP plates are made from high-quality transformer steel. In this case, the core is collecting ahead (the plates are placed in one, then in the other direction), and its cross section increases by 10% against the calculated one.

Transformers without additions are better to wind on ears cores (reduced height with extended windows), pos. 2. A decrease in the scattering field is achieved by reducing the magnetic path length. Because the OSH plates are more accessible to the SP, of which the cores of transformers with appliances are often typing. Then the core assembly leads to Vnakroy: they collect a package of W-plates, put a strip of non-conductive non-magnetic material with a thickness of a non-magnetic clearance, are covered with a yarm from the jumper package and tighten everything together by the rope.

Note: "Sound" signal magnetic pipelines type SCLM for output transformers of high-quality lamp amplifiers are little suitable, they have a large scattering field.

On pos. 3 is given a diagram of the sizes of the core to calculate the transformer, on the pos. 4 Design frame windings, and on pos. 5 - patterns of its details. As for the transformer for a "batranformator" output cascade, it is better to do it on the SHLME, because The addition is negligible (addition current is equal to the current mesh current). The main task is here - to make windings as compact as possible in order to reduce the scattering field; Their active resistance will still work out a lot less than 800 ohms. The more free space will remain in the windows, the better the transformer turned out. Therefore, the windings shake the turn to the turn (if there is no winding machine, it is terrible) from as little thin wire, the installation coefficient of the anode winding for mechanical calculation of the transformer takes 0.6. Winding wire - MARODS OF PHTV or PEMM, they lived oxless. PTTV-2 or PEMM-2 is not necessary, they have an enlarged outer diameter and the field of scattering will be larger. The primary winding shake first, because It is its scattering field that affects the sound.

Iron for this transformer should be sought with holes in the corners of plates and tighter brackets (see Fig. Right), because "For complete happiness", the assembly of the magnetic pipeline is made in the next. order (of course, windings with conclusions and outer insulation should already be on the frame):

Prepare diluted halves acrylic varnish or, in the old manner, shellak;
Plates with jumpers quickly cover with varnish on the one hand and as quickly as possible, not pressed strongly, insert into the frame. The first plate is layered by a lacquered side inside, the following - non-plated side to lacquered first, etc.;
When the frame window is filled, apply brackets and tightly tighten with bolts;
1-3 minutes, when the squeezing of varnishes from the gaps apparently stops, the plates are added again before filling the window;
Repeat PP. 2-4, while the window is not tightly soldered with steel;
The core is tightly tightened again and dried on the battery, etc. 3-5 days.

The core assembled by such technology has very good insulation of plates and filling steel. Losses for magnetostriction is not detected at all. But consider - for the cores, their Permalloe this technique is not applicable, because From strong mechanical impacts, the magnetic properties of Permalloe are irreversibly deteriorating!

On microcircuits

UMPs on integrated chips (IC) make most often those that suggests sound quality to medium Hi-Fi, but more attracts cheapness, speed, simplicity of assembly and the complete absence of any adjustment procedures that require special knowledge. Simply, the amplifier on chips is the optimal option for "kettles". The classic of the genre is here - the umzch on the IC TDA2004, standing in the series, give God's memory, already 20 years old, left in Fig. Power - up to 12 W per canal, supply voltage - 3-18 in unipolar. Radiator area - from 200 square meters. See for maximum power. Advantage is the ability to work on very low-level, up to 1.6 ohms, the load, which allows you to remove the full power when powering from the onboard network of 12 V, and 7-8 W - with 6-volt nutrition, for example, on a motorcycle. However, the yield of TDA2004 in the class in the noncommmable (on the transistors of the same conductivity), so the tumors are definitely not Hi-Fi: Koke 1%, dynamics 45 dB.

More modern TDA7261 Sound gives no better, but more powerful, up to 25 watts, because The upper limit of the supply voltage is increased to 25 V. Nizhny, 4.5 V, still allows you to be powered from 6 to the boots, i.e. TDA7261 can be launched from almost all airlocks, except for airplane 27 V. With the help of mounted components (strapping, on the right in Fig.) The TDA7261 can work in mutation mode and with the ST-BY function (Stand By, wait), translating the UMP to the minimum power mode In the absence of an input signal for a certain time. Amenities are money, so the stereo will need a pair of TDA7261 with radiators from 250 kV. See for each.

Note: If you are attracted by the amplifiers with the ST-BY function, do not care - it is not worthwhile to wait for the speakers wider than 66 dB.

"Super Economic" powered by TDA7482, on the left in Fig. Operating in T. Naz. Class D. Such umzch is sometimes called digital amplifiers, which is incorrect. For real digitization from an analog signal, references levels of a level with a quantization frequency, not less than twice the greatest of the reproducible frequencies, the value of each reference is recorded by an obstacle code and is saved for further use. Ump class D - impulse. In them, the analogue is directly converted to a sequence of latitude-modulated pulses (PWM) high frequency, which is fed to the speaker through the low frequency filter (FNH).

The sound of class D with Hi-Fi has nothing to generally: books in 2% and dynamics of 55 dB for Class D is considered very good indicators. And TDA7482 Here, I must say, the choice is not optimal: other firms specializing in class D are produced by the ISSF cheaper and requiring smaller strapping, for example, the D-UMPs of the PAXX series, right in Fig.

From TDs, you should mark the 4-channel TDA7385, see fig. On which you can collect a good amplifier for columns to the average Hi-Fi inclusive, with the frequency separation by 2 bands or for a system with a subwoofer. The rainflection of the LF and SC-HF is also made at the input on a weak signal, which simplifies the design of the filters and allows you to separate the strips. And if the acoustics are subwoofer, then 2 channels TDA7385 can be highlighted under the sub-UHB of the bridge circuit (see below), and the remaining 2 to use for SC-HF.

Ump for subwoofer

Subwoofer, which can be translated as "sub-release" or, literally, "Podkavka" reproduces frequencies to 150-200 Hz, in this range, human ears are practically not able to determine the direction to the sound source. At the AC with the subwoofer "sub-mas" speaker put in the hotel acoustic design, this is a subwoofer as such. The subwoofer is placed in principle, as more convenient, and the stereo effect is ensured by separate SC-RF channels with their small-sized speakers, whose acoustic design is not particularly presented. The experts converge on the fact that the stereo is better to listen to the full separation of the channels, but subwoofer systems significantly save funds or work on the bass tract and facilitate the placement of acoustics in small rooms, why and are popular with consumers with ordinary hearing and not particularly demanding.

"Seeping" sch-high in the subwoofer, and from it into the air, spoils stereo strongly, but if the subbasy is sharply "chopping", which, by the way, is very difficult and expensive, then the sound of sound jumping effect will arise. Therefore, the polyvillation of the channels in subwoofer systems is performed twice. At the inlet by electric filters, the SC-HF with bass "tails", not overloading the SC-RF path, but providing a smooth transition to a subabass. Basz with the "tails" are combined and served on a separate UMP for a subwoofer. Misk is reaffected so that the stereo does not deteriorate, in the subwoofer are already acoustically: the sub-masted speaker, apply, for example, in the septum between the resonator chambers of the subwoofer, which do not produce the sch outward, see on the right in Fig.

A number of specific requirements are made to the subwoofer for a subwoofer, of which "kettles" are mainly considered to be greater power. This is completely wrong if, say, the calculation of acoustics under the room gave the peak power W for one column, then the power of the subwoofer is needed 0.8 (2W) or 1.6W. For example, if the AC S-30 is suitable for the room, the subwoofer is needed 1.6x30 \u003d 48 W.

It is much more important to ensure the lack of phase and transitional distortion: they will go - the sound of sound will necessarily be. As for the books, he will admit to 1% of their own distortions of bass of such a level are not heard (see curves of equal volume), and the "tailings" of their spectrum to the best of all the hearing area will not get out of the subwoofer.

To avoid phase and transitional distortions, the amplifier for the subwoofer build on the T. Naz. Bridge Scheme: Outputs of 2 identical UMPs include on the speaker; Input signals are fed in antiphase. The absence of phase and transitional distortion in the bridge circuit is due to the full electrical symmetry of the output paths. The identity of the amplifiers forming the shoulders of the bridge is ensured by using paired umzch on the IC, made on the same crystal; This is perhaps the only case when the amplifier on chips is better discrete.

Note: The power of the bridge is not doubled, as some think, it is determined by the supply voltage.

An example of a pavement scheme for a subwoofer in a room to 20 square meters. m (without input filters) on the IC TDA2030 is given in Fig. left. Additional filtering sch is carried out by chains R5C3 and R'5C'3. The TDA2030 radiator area is from 400 square meters. See the bridge urzch with an open output is an unpleasant feature: when the bridge is loss in the load current, a constant component appears, capable of inclusive speaker, and the protection circuits on subbasas are often buggy, turning off the speaker when it is not necessary. Therefore, it is better to protect the dear HF "Dubovo" head, non-polar batteries of electrolytic capacitors (highlighted by color, and the diagram of one battery is given on the insertion.

A little about acoustics

Acoustic design of the subwoofer is a special topic, but since the drawing is given here, then you need an explanation. Case material - MDF 24 mm. Pipes of resonators - from sufficiently strong non-ringing plastic, eg, polyethylene. The inner diameter of pipes is 60 mm, protrusions inside 113 mm in a large chamber and 61 in small. Under the specific head of the loudspeaker, the subwoofer will have to migrate on the best bass and, at the same time, by the smallest effect on the stereo effect. To configure the pipe, they take obviously greater lengths and, raising-put forward, achieve the required sound. The protrusions of the pipes outside the sound do not affect, they are then cut off. Tuning the pipes is interdependent, so it will have to obey.

Headphone Amplifier

The headphone amplifier makes them most often in the 2nd reasons. The first - for the hearing "on the go", i.e. Outside the house when the power of the audio output player or smartphone lacks for the "Buttons" or "Lopukhov". Second - for high-class home headphones. Hi-Fi Umzch for the ordinary residential room is needed with dynamics up to 70-75 dB, but the dynamic range of the best modern stereo handphones exceeds 100 dB. The amplifier with such a dynamics is more expensive than some cars, and its power will be from 200 W in the channel, which is too much for the ordinary apartment: listening to the sound highly understated against the rated power, see above. Therefore, it makes sense to make a low-power, but with good dynamics a separate amplifier for headphones: Prices for domestic umzch with such an imminately overestimated is obviously impossible.

The circuit of the simplest amplifier for headphones on transistors is given on the pos. 1 Fig. Sound - except for Chinese "buttons", it works in class B. Economy is also no different - 13 mm lithium batteries are enough for 3-4 hours at full volume. On pos. 2 - TDA Classic for headphones "on the move." The sound, however, gives quite a decent, to medium Hi-Fi, looking through the parameters of the track digitization. Amateur improvements to the TDA7050 strapping to bear numbers, but no one has achieved sound transition to the next level of gravity: no one has achieved: "Microus" itself does not allow. TDA7057 (pos. 3) is simply functional, you can connect the volume control on the usual, non-dual, potentiometer.

Ump for headphones on TDA7350 (pos. 4) is already calculated on the spawn of good individual acoustics. It is on this IMA that the headphone amplifiers are collected in most domestic urzchs of the middle and high class. Ump for headphones on KA2206B (pos. 5) is considered to be professional: its maximum power of 2.3 W enough and for the swinging of such serious isoodanic "Lopukhov" as TDS-7 and TDS-15.

Now on the Internet you can find a huge number of circuits of various amplifiers on chips, mainly the TDA series. They possess quite good characteristics, good efficiency and are not so expensive, in connection with this, and are so popular. However, in their background, transistor amplifiers, which, although complex in the setting, are not less interesting are forgotten.

Amplifier scheme

In this article, consider the assembly process a very unusual amplifier working in the class "A" and containing only 4 transistors. This scheme was developed back in 1969 by the English engineer John Linsley, despite his old age, she still remains relevant to this day.

Unlike chip amplifiers, transistor amplifiers require a thorough setting and selection of transistors. This scheme is no exception, even though it looks extremely simple. Transistor VT1 - input, PNP structure. You can experiment with various low-power PNP transistors, including Germany, for example, MP42. It has been well proven in this scheme as VT1 such transistors as 2N3906, BC212, BC546, CT361. The transistor VT2 is the structure of NPN, medium or low power, CT801, KT630, CT602, 2N697, BD139, 2Sc5707, 2SD2165 are suitable. Particular attention should be paid to the output transistors VT3 and VT4, or rather, their gain. CT805, 2SC5200, 2N3055, 2SC5198 are well suited here. You need to select two identical transistors with as close as possible gain as possible, and it should more than 120. If the gain of the output transistors is less than 120, it means that the transistor with a large amplification (300 or more) must be put into the drive cascade (VT2).

Selection of rates of amplifier

Some denominations on the diagram are selected based on the supply voltage and load resistance, some possible options are shown in the table:

It is not recommended to raise the supply voltage of more than 40 volts, the output transistors may fail. The feature of the amplifiers of class A is a long rest current, and, therefore, a strong heating of transistors. With a supply voltage, for example, 20 volts and a rest of 1.5 amper, the amplifier consumes 30 watts, regardless of whether the signal is fed to its input or not. Each of the weekend transistors will dispel 15 watts heat, and this is the power of a small soldering iron! Therefore, the VT3 and VT4 transistors must be installed on a large radiator using a thermalcol.
This amplifier is inclined in the emergence of self-excitation, therefore the Tsobel chain is set at its output: a resistance resistor 10 ohms and a capacitor 100 NF, included in series between the ground and the common point of the output transistors (this chain is shown in the diagram).
When the amplifier is first turned on, it is necessary to enable an ammeter to control the rest of the rest. While the output transistors did not warm up to the operating temperature, it can swim a little, it is quite normal. Also, when you first turn on, you need to measure the voltage between the total point of the output transistors (collector VT4 and Emmitizer VT3) and the Earth, there should be half the supply voltage. If the voltage is different in a large or smaller side, you need to twist the R2 trick resistor.

Amplifier board:

(Dropping: 456)

The board is made by the LUT method.

I assembled amplifier

A few words about condensers, entrance and output. The capacitance of the input capacitor in the diagram is indicated by 0.1 μF, but this container is not enough. As an input, a film capacitor with a capacity of 0.68 - 1 μF should be supplied, otherwise a unwanted low-frequency cut is possible. The output capacitor C5 is worth taking the voltage not less than the supply voltage, it is also not worth greeding with a container.
The advantage of the scheme of this amplifier is that it does not represent hazards for the speakers of the speaker system, because the speaker is connected through a separator capacitor (C5), which means that when the constant voltage appears, for example, when the amplifier exits, the speaker will remain intact, After all, the capacitor will not miss a constant voltage.

Going into the past, and now to collect any simple amplifier, no longer need to suffer with calculations and rivet the printed circuit board of large sizes.

Now almost all cheap reinforcement is done on chips. The largest distribution was obtained by the TDA chips to enhance the audio signal. Currently, they are used in car radio, in active subwoofers, in home acoustics and in many other audiors and look like this:

Pluses of TDA chip

In order to assemble the amplifier on them, it is enough to supply power, connect speakers and several radio elements.
The dimensions of these microcircuits are very small, but it will be necessary to put them on the radiator, otherwise they will warm themselves.
They are sold in any radio market. On Ali, something expensive, if you retail.
They are built into various protection and other options, such as disconnecting sound and so on. But according to my observations, protection is not very good, so chips often die or overheating or from. So it is desirable not to climb the conclusions of the chips among themselves and do not overheat the chip, squeezing all the juices from it.
Price. I would not say that they are very expensive. For the price and the functions performed, they are not equal.

Single-channel amplifier on TDA7396

Let's collect a simple single-channel amplifier on the TDA7396 chip. At the time of writing, I took it at a price of 240 rubles. In the datashet on the chip, it was said that this chip could issue up to 45 watts in the load 2 Ohm. That is, if you measure the resistance of the coil of the speaker and it will be about 2 ohms, then on the dynamics it is quite possible to obtain peak power in 45 watts.This power is enough to arrange a disco in the room not only for yourself, but also for neighbors and at the same time get a mediocre sound that, of course, do not compare with Hi-Fi amplifiers.

Here is the pinout of the chip:

We will collect our amplifier according to a typical scheme that was attached in the datashet itself:

For the leg 8, we feed + vs, and I do not apply anything on the foot. Consequently, the scheme will take this kind:

VS is the supply voltage. It can be from 8 to 18 volts. "In +" and "In-" - here we give a weak beep. To 5 and 7 legs cling the speaker. Sadim's sixth leg on minus.

Here is my assembly mounted installation

Capacitors at the power supply of 100 NF and 1000MKF I did not use, since I have a clean voltage from the power supply.

Rasked the speaker with such parameters:

As you can see, the resistance of the coil 4 Ohm. The frequency band indicates that it is a subwoofer type.

And so I look like a sub in a self-mounted building:

I tried to shoot a video, but the sound on the video I removes very badly. But still, I can say that from the phone at the middle power it has already fallen so that the ears wrapped around, although the consumption of the entire scheme in the working form was only about 10 watts (multiply 14.3 by 0.73). In this example, I took the tension as in the car, that is, 14.4 volts, which is fully fitted into our working range from 8 and to 18 volts.

If you do not have a powerful power source, it can be collected according to this scheme.

Do not dwell precisely on this chip. These TDA chips, as I said, there are many species. Some of them enhance the stereo signal and can issue sound at once on 4 speakers, as is done in car radio. So do not be lazy to ride on the Internet and find a suitable thought. After completing the assembly, let the neighbors check your amplifier, twisting the volume knob to the entire balalaica and leaning the powerful speaker to the wall).

But in the article I collected the amplifier on the TDA2030A chip

It turned out very well, since TDA2030A has better characteristics than TDA7396

Also, I will also apply for a variety of still scheme from the subscriber who has an amplifier on TDA 1557Q for more than 10 years in a row:

Amplifiers on Aliexpress

On Ali, I also found a whale sets on TDA. For example, this stereo amplifier of 15 watts per canal at a price of $ 1. This power is enough to sweat under favorite tracks in the room

You can buy.

And here he is immediately ready

And in general, these amplifier modules on AliqPress are very much. Press on this link And choose any favorite amplifier.

The amplifier on the transistors, despite his already long history, remains a favorite subject of research both beginners and mastty radio amateurs. And this is understandable. It is an indispensable part of the most massive and amplifiers of low (sound) frequency. We will look at how the simplest amplifiers on transistors are built.

Frequency characteristic amplifier

In any television or radio receiver, in each music center or audio amplifier, you can find transistor sound amplifiers (low frequency - LF). The difference between sound transistor amplifiers and other species is their frequency characteristics.

The sound amplifier on the transistors has a uniform frequency response in the frequency band from 15 Hz to 20 kHz. This means that all input signals with a frequency inside of this range converts (enhances) approximately the same. In the figure below in the coordinates, the coefficient of amplification coefficient KU - the frequency of the input signal shows the perfect curve of the frequency response for the audio amplifier.

This curve is practically flat with 15 Hz in 20 kHz. This means that this amplifier should be used for input signals with frequencies between 15 Hz and 20 kHz. For input signals with frequencies above 20 kHz or below 15 Hz, the efficiency and quality of its work is rapidly reduced.

The type of frequency response of the amplifier is determined by electrical elements (ERE) of its scheme, and primarily the transistors themselves. The audio amplifier on the transistors is usually collected on the so-called low and mid-frequency transistors with a total bandwidth of input signals from tens and hundreds of Hz to 30 kHz.

Amplifier work class

As it is known, depending on the degree of continuity of current flow during its period through the transistor, the amplifying cascade (amplifier) \u200b\u200bdistinguish the following classes of its operation: "A", "B", "AB", "C", "D".

In the class of operation, the current "A" through the cascade occurs over 100% of the input period. The work of the cascade in this class illustrates the next drawing.

In the class of work of the amplifying stage "AB", the current through it proceeds by more than 50%, but less than 100% of the input period (see Figure below).

In the class of work of the cascade "in" the current through it exactly 50% of the input period proceeds, as the picture illustrates.

Finally, in the class of work of the cascade "C", the current flows through it less than 50% of the input period.

LF-amplifier on transistors: distortion in major work classes

In the workspace, the transistor amplifier of the class "A" has a small level of nonlinear distortion. But if the signal has pulsed voltage emissions, leading to the saturation of transistors, the highest harmonics appear around each "standard" harmonic of the output signal (up to 11th). This causes the phenomenon of the so-called transistor, or metallic, sound.

If the power amplifiers on the transistors have unstabilized power, their output signals are modulated by amplitude near the network frequency. This leads to the rigidity of the sound on the left edge of the frequency response. The various methods of stabilization of voltage make the construction of the amplifier more complex.

A typical efficiency of the one-stage amplifier of the class A does not exceed 20% due to the constantly open transistor and the continuous flow of the constant current. You can perform an amplifier of the class A two-stroke, the efficiency will increase somewhat, but the half-wave of the signal will become more asymmetric. The translation of the cascade from the class of work "A" to the class of work "AB" increases four of all nonlinear distortion, although the efficiency of its scheme is increasing.

In the amplifiers of the Classes "Av" and "in" distortion increases as the signal level decreases. Involuntarily, I would like to bring such an amplifier to the pogroms to complete the feelings of the power and dynamics of music, but it often helps it.

Intermediate classes of work

At the class of work "A" there is a variety - class "A +". At the same time, low-voltage input transistors of the amplifier of this class work in the class "A", and the high-voltage output transistors of the amplifier when they are exceeded by the input signals of a certain level go to the classes "in" or "av". The economy of such cascades is better than in a pure class "A", and non-linear distortions are less (up to 0.003%). However, the sound of them also "metallic" due to the presence of higher harmonics in the output signal.

At the amplifiers of another class - "AA" the degree of nonlinear distortion is even lower - about 0.0005%, but the highest harmonics are also present.

Return to transistor amplifier class "A"?

Today, many specialists in the field of high-quality sound reproduction will be advantageous for returning to lamp amplifiers, since the level of nonlinear distortion and higher harmonics introduced by them in the output signal are obviously lower than that of transistors. However, these advantages are largely leveled by the need to match the transformer between a high-resistant tube output cascade and low-level sound columns. However, a simple amplifier on the transistors can be made with a transformer output, which will be shown below.

There is also a point of view that the limit sound quality can only provide a hybrid lamp transistor amplifier, all cascades of which are uncommon, are not covered and operate in the class "A". That is, such a power repeater is an amplifier on one transistor. The scheme can have an extremely achievable efficiency (in the class "A") not more than 50%. But neither power nor the Empower efficiency is indicators of sound performance. At the same time, the quality and linearity of the characteristics of all ERA in the scheme are of particular importance.

Since disposable schemes receive such a perspective, we will consider below their possible options.

One-acting amplifier on one transistor

Its scheme made with a common emitter and R-c-links over input and output signals to work in the class "A", shown in the figure below.

It shows the transistor Q1 of the N-P-N structure. Its collector through a current-limiting resistor R3 is attached to the positive conclusion of + VCC, and the emitter is to -Vcc. The amplifier on the transistor structure P-N-P will have the same scheme, but the output of the power source will be changed in places.

C1 is a separator capacitor by which the source of the variable input signal is separated from the VCC constant voltage source. At the same time, C1 does not interfere with the passage of the variable input current through the transistor - Emitter Q1 transistor. Resistors R1 and R2 in conjunction with the "E - B" transition resistance form VCC to select the operating point of the transistor Q1 in static mode. Typical for this scheme is the value R2 \u003d 1 com, and the position of the operating point is VCC / 2. R3 is a loading resistor of the collector chain and serves to create an output voltage on the collector.

Suppose that VCC \u003d 20 V, R2 \u003d 1 com, and the gain coefficient H \u003d 150. The voltage on the emitter is chosen ve \u003d 9 V, and the voltage drop at the "e - b" transition is taken equal to VBe \u003d 0.7 V. This value corresponds to the so-called silicon transistor. If we considered an amplifier on Germany transistors, the voltage drop in the open transition "E - B" would be equal to VBe \u003d 0.3 V.

Emitter current, approximately equal to the current collector

IE \u003d 9 b / 1 com \u003d 9 mA ≈ IC.

The current of the base IB \u003d IC / H \u003d 9 mA / 150 \u003d 60 μA.

Voltage drop on resistor R1

V (R1) \u003d VCC - VB \u003d VCC - (VBE + VE) \u003d 20 V - 9.7 V \u003d 10.3 V,

R1 \u003d V (R1) / IB \u003d 10.3 V / 60 MCA \u003d 172 com.

C2 is needed to create a circuit of passing a variable of the emitter current (actual collector current). If it were not, then the resistor R2 would strongly limit the variable component, so that the amplifier under consideration on the bipolar transistor would have a low current gain.

In our calculations, we assumed that Ic \u003d Ib H, where IB is the base current flowing into it from the emitter and occurs when the bias voltage is applied. However, through the database is always (as if there is a displacement, and without it), the current leakage from the ICB0 collector also flows. Therefore, the actual current of the collector is equal to IC \u003d IB H + ICB0 H, i.e. The leakage current in the Scheme with OE is amplified 150 times. If we considered an amplifier on Germany transistors, this circumstance would have to be considered when calculating. The fact is that there are essential ICB0 about several ICA. In the silicon, he is three orders of magnitude less (about several), so in the calculations they are usually neglected.

Single Amplifier with TIR transistor

Like any amplifier on the field transistors, the scheme under consideration has its own analogue among amplifiers on therefore, consider analogue of the previous scheme with a common emitter. It is made with a common source and R-c-links over input and output signals to work in the class "A" and shown in the figure below.

Here, C1 is the same separator capacitor, by which the source of the variable input signal is separated from the VDD constant voltage source. As you know, any amplifier on field transistors must have the potential of the shutter of its TIR transistors below the potentials of their origins. In this scheme, the shutter is grounded by a resistor R1, which is usually a large resistance (from 100 com by 1 mΩ) so that it does not shut the input signal. The current via R1 practically does not pass, therefore the potential of the shutter in the absence of the input signal is equal to the potential of the Earth. The potential of the source above the land potential due to the voltage drop on the R2 resistor. Thus, the potential of the shutter turns out to be lower than the potential of the source, which is necessary for normal operation Q1. Capacitor C2 and resistor R3 have the same purpose as in the previous scheme. Since this scheme with a common source, the input and output signals are shifted by a phase by 180 °.

Transformer Output Amplifier

The third single-stage simple amplifier on the transistors shown in the figure below is also made according to a circuit with a common emitter to work in the class "A", but with a low-voltage speaker, it is associated through the agreement transformer.

The primary winding of the transformer T1 is the load of the collector circuit of the transistor Q1 and develops the output signal. T1 transmits the output signal to the speaker and provides the coordination of the output impedance of the transistor with a low (order of several OM) resistance of the speaker.

The voltage divider of the collector power supply VCC, collected on the resistors R1 and R3, provides the choice of the operating point of the transistor Q1 (supply voltage to its database). The purpose of the remaining elements of the amplifier is the same as in the previous schemes.

Two-stroke sound amplifier

The two-stroke Amplifier on two transistors splits the input frequency into two antiphase half-waves, each of which is enhanced by its own transistor cascade. After performing this amplification, the half-wave is combined into a holistic harmonic signal, which is transmitted to the speaker system. A similar transformation of the NF signal (splitting and re-fusion), of course, causes irreversible distortions in it, due to the difference in frequency and dynamic properties of two transistors of the circuit. These distortions reduce the sound quality at the output of the amplifier.

Two-stroke amplifiers operating in the class "A" are not well reproducing complex sound signals well, since there is continuous current of increased values \u200b\u200bin their shoulders. This leads to the asymmetry of half-wave of a signal, phase distortions and ultimately to loss of sound integrity. Heating, two powerful transistors increase half the signal distortion in the low and infusion frequency area. But still the main advantage of the two-stroke scheme is its acceptable efficiency and an increased output power.

The two-stroke diagram of the power amplifier on the transistors is shown in the figure.

This is an amplifier to work in the class "A", but the class "AB" can also be used, and even "in".

BestranFormator transistor power amplifier

Transformers, despite the progress in their miniaturization, remain still the most bulky, heavy and expensive ERA. Therefore, the path to eliminate the transformer from the two-stroke scheme was found by performing it on two powerful complementary transistors of different types (N-P-N and P-N-P). Most of the modern power amplifiers use this particular principle and are designed to work in the class "B". The diagram of such a power amplifier is shown in the figure below.

Both of its transistors are included according to a circuit with a common collector (emitter repeater). Therefore, the diagram transmits the input voltage to the output without amplification. If there is no input signal, both transistors are on the border of the included state, but they are turned off.

When the harmonic signal is filed to the input, its positive half-wave opens the TR1, but transists the P-N-P TR2 transistor completely into the cutoff mode. Thus, only a positive half-wave of reinforced current flows through the load. The negative half-wave of the input signal opens only TR2 and locks TR1, so that the negative half-wave of the reinforced current is supplied. As a result, the load is allocated on the load (by gaining current) sinusoidal signal.

Amplifier on one transistor

To assimilate the above, we collect a simple amplifier on the transistors with your own hands and understand how it works.

As a load of a low-power transistor T type BC107, we will turn on the headphones with a resistance of 2-3 kΩ, the bias voltage to the base will be supplied with a high-resistant resistor R * 1 MΩ magnitude, unlocking the electrolytic capacitor with a capacity of 10 μF to 100 μF to be turned on to the base chain We will be from the battery 4.5 V / 0.3 A.

If the R * resistor is not connected, then there is no current base IB, no current collector IC. If the resistor is connected, the voltage on the base rises to 0.7 V and the current IB \u003d 4 μA proceeds through it. The gain of the current transistor is 250, which gives IC \u003d 250IB \u003d 1 mA.

By collecting a simple amplifier on the transistors with your own hands, we can now experience it. Connect the headphones and put a finger to the point 1 of the circuit. You will hear noise. Your body perceives the emission of the supply network at a frequency of 50 Hz. The noise heard from the headphones is and is this radiation only with a reinforced transistor. Let us explain this process more. AC voltage with a frequency of 50 Hz is connected to the base of the transistor through a Conductor S. The database voltage is now equal to the amount of constant offset voltage (approximately 0.7 V) coming from the resistor R *, and the voltage of the alternating current "from the finger". As a result, the collector current receives a variable component with a frequency of 50 Hz. This alternating current is used to shift the membrane of the speakers back and forth with the same frequency, which means that we can hear the tone of 50 Hz at the output.

Listening to the noise level of 50 Hz is not very interesting, so you can connect to points 1 and 2 low-frequency signal sources (CD player or microphone) and hear enhanced speech or music.