Description of the operation of the sound power amplifier on MOSFET transistors. Amplifier protection schematic diagram

The editors of the site "Two Schemes" present a simple but high-quality low-frequency amplifier based on MOSFET transistors. Its circuit should be well known to radio amateurs and audiophiles, since it is already 20 years old. The circuit is the development of the famous Anthony Holton, therefore it is sometimes called that - ULF Holton. The sound amplification system has low harmonic distortion, not exceeding 0.1%, with a power per load of about 100 watts.

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

The big advantage of the system is simple construction and an output stage consisting of 2 inexpensive MOSFETs. The amplifier can work with speakers with impedance of both 4 and 8 ohms. The only adjustment that needs to be done during startup is to set the quiescent current value of the output transistors.

Schematic diagram of UMZCH Holton

Holton MOSFET Amplifier - Circuit

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

Printed circuit board

ULF printed circuit board - finished view

Here is an archive with PDF files printed circuit board -.

The principle of the amplifier

Transistors T4 (BC546) and T5 (BC546) operate in a differential amplifier configuration and are designed to be powered from a current source built on the basis of transistors T7 (BC546), T10 (BC546) and resistors R18 (22 kΩ), R20 (680 Ohm) and R12 (22 rooms). Input signal is fed to two filters: low-pass, built of elements R6 (470 Ohm) and C6 (1 nF) - it limits the high-frequency components of the signal and band pass filter consisting of C5 (1 μF), R6 and R10 (47 kΩ), limiting the signal components at infra-low frequencies.

The differential amplifier is loaded with resistors R2 (4.7 kΩ) and R3 (4.7 kΩ). Transistors T1 (MJE350) and T2 (MJE350) are another amplification stage, and its load is transistors T8 (MJE340), T9 (MJE340) and T6 (BD139).

Capacitors C3 (33pF) and C4 (33pF) counteract amplifier excitation. Capacitor C8 (10 nF) in parallel with R13 (10 kΩ / 1 V) improves the ULF transient response, which is important for fast-rising input signals.

Transistor T6, together with elements R9 (4.7 ohms), R15 (680 ohms), R16 (82 ohms) and PR1 (5 ohms), allows you to set the correct polarity of the amplifier output stages at rest. Using a potentiometer, it is necessary to set the quiescent current of the output transistors within 90-110 mA, which corresponds to a voltage drop across R8 (0.22 Ohm / 5 W) and R17 (0.22 Ohm / 5 W) within 20-25 mV. The total quiescent current consumption of the amplifier should be in the region of 130 mA.

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

Resistors R8 and R17 were mainly used to quickly measure the quiescent current of power amplifier transistors without interfering with the circuit. They can also come in handy in the case of expanding the system to one more pair of power transistors, due to the differences in the resistance of the open channels of the transistors.

Resistors R5 (470 Ohm) and R19 (470 Ohm) limit the charging rate of the capacitance of the pass-through transistors, and, therefore, limit frequency range amplifier. Diodes D1-D2 (BZX85-C12V) protect power transistors. With them, the voltage at startup relative to the power supplies for the transistors should not exceed 12 V.

The amplifier board provides places for the power filter capacitors C2 (4700 μF / 50 V) and C13 (4700 μF / 50 V).

Homemade transistor ULF on MOSFET

The control is powered through an additional RC filter built on the 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 power that reaches real 100 watts (effective sinusoidal), with an input voltage in the region of 600 mV and a load resistance of 4 ohms.

Holton amplifier on board with details

The recommended transformer is a 200 W toroid with a voltage of 2x24 V. After rectification and smoothing, a two-polar power supply of the power amplifiers should be obtained in the region of +/- 33 Volts. The design shown here is a mono amplifier module with very good parameters, built on MOSFET transistors, which can be used as a separate unit or as part of.

This quality amplifier is completely transistor-based. Powerful bipolar transistors are used in the output stage, which provide output power up to 150 watts with a load of 4 ohms. The main characteristics of the audio amplifier are presented below:

E.g. power supply, V - +/- 35
- Current consumed. in cold mode - 80mA
- In.opr., KOhm - 24
- Sens., V - 1.25
- Out. power (KG = 0.03%), W - 85
- Diap. frequencies, Hz - 10 ... 35000
- Noise - 75dB

This type of amplifiers can operate on a load of 8 ohms and provide the same power as with a load of 4 ohms, for this you need to raise the supply voltage to +/- 42 V, the main thing is not to increase more than the specified value, otherwise the transistors of the amplifier's output stage may overheat and fail. In the circuit, you can also use domestic parts, for example, the final stage transistors are quite replaceable with a pair of 818 / 819GM, this series of transistors was produced in metal cases... Transistors must be reinforced on the heat sink by placing an insulating film between the heat sink and the transistor case in advance. It is recommended to use a heat sink with an area of 400 sq. cm for each transistor. Before - the output stage also needs to be reinforced with small heat sinks with an area of 100 sq. Cm

In the circuit, the resistor R11 is used to set the quiescent current of the output transistors within 70-100 mA. Capacitor C4 determines the upper limit of the amplification and it is not worth reducing its value - it is possible with excitation at high frequencies.

It is advisable to use the LED that is indicated in the diagram, since all LEDs have different drop and glow voltages, it is advisable to solder the LED directly to the board.

We put the output transistors on the radiators with a useful area. for each. Transistors MJL4281 and MJL4302 can also be replaced with another pair of analogs, for example, a pair of MJL21193 and MJL21194. Fuses for 3 amperes can be replaced with others (more powerful) or completely excluded from the circuit.

This amplifier is an excellent option for a home or car subwoofer, but I do not recommend fitting it to the subwoofer, since the amplifier is very high quality, distortions are not observed even at maximum volume, a separate voltage converter is needed to power the car, the designs of which you can find on our website.

The design presented here is a ready-made module for a high power mono LF amplifier with very good parameters. This amplifier is modeled after a popular design by an engineer. The circuit has low harmonic distortion, which does not exceed 0.05%, with a load power of about 500 watts. This amplifier is useful and necessary when organizing various outdoor concert events and has proven to be indispensable many times during these events. The big advantage of the system is its simple design and an inexpensive 10-MOSFET output stage. UMZCH can work with speakers with impedance of 4 or 8 ohms. The only adjustment that needs to be made during startup is to set the quiescent current of the output transistors.

The article provides only a diagram and a description of the operation of the power amplifier itself, but do not forget that the complete audio complex also contains other modules:

UMZCH terminator
Preamplifier
Power Supply
Level indicator
Soft start system
Cooling control system
Speaker protection box

Schematic diagram of ULF on transistors 500 watts

The power amplifier circuit is shown in the figure above. This is a classic circuit design consisting of a differential input amplifier and a balanced power amplifier, in which 5 pairs of transistors operate. Transistors T2 (MPSA42) and T3 (MPSA42) operate in a differential amplifier circuit powered by resistors R8 (10k) and R9 (10k). The voltage in the middle of this divider is stabilized with a Zener diode D2 (15V / 1W) and filtered by a capacitor C4 (100uF / 100V). The input signal is fed to the GP1 (IN) connector and filtered through elements R1 (470R), R3 (22k), C1 (1uF) and C2 (1nF), which limit the frequency range of the amplifier both above and below.

The differential amplifier is loaded with transistors T1 (MPSA42) and T4 (MPSA42) operating in a common base system, as well as resistors R5 (1.2 k) and R6 (1.2 k). The polarity of the load is set by the Zener diode D1 (15V / 1W) and the resistor R7 (10k). The main task of the system consisting of transistors T1 and T4 is to match the impedance of the output signal for the ULF stage. Another stage, built on transistors T5 (MJE350) and T6 (MJE350), acts as a differential voltage amplifier. It is powered through a resistor R11 (100P / 2W). Its load will be transistors T14 (MJE340) and T15 (MJE340), resistors R13 (100P / 2W) and R14 (100P / 2W), and transistor T7 (BD139).

Capacitor C15 (47nF) connected in parallel with resistor R44 (10k / 2W) improves transmission pulse signals, while small capacitors C7 (56pF) and C8 (56pF) counteract self-excitation of the UMZCH. Transistor T7 together with resistors R10 (4.7k), R45 (82R) and potentiometer P1 (4.7k) allows you to set the correct polarity of the output transistors T9-T13 (IRFP240), T17-T21 (IRFP9240) at rest. With potentiometer P1, you can set the quiescent current, which should be about 100 mA for each pair of output transistors. Transistors T9-T13, like T17-T21, are connected in parallel and work as voltage followers for a large maximum output current. Therefore, the previous amplifier stages must provide all of the voltage gain, which is determined by the ratio of R4 (22k) to R2 (470R) and is about 47.

Resistors R30-R39 (0.33 R / 5W) included in the sources of the output transistors provide protection against damage that could occur in the case of different resistances of the transistor channels. Resistors R20-P29 (470R), connected in series with the outputs of transistors T9-T13, T17-T21, serve to reduce the charging rate of the capacitor and, therefore, limit the frequency range of the amplifier.

The amplifier has two simple protections:

The first is directed against overload and is implemented using zener diodes D3 (7.5 V / 1W) and D4 (7.5 V / 1W), which prevent voltage growth between sources and outputs. powerful transistors above 7.5 volts.
The second protection is built using transistors T7, T16 and (BD136), resistors R16-R17 (33k) and R18-R19 (1k) and diodes D7-D10 (1N4148). It prevents an excessive increase in the current of the power transistors, which could lead to exceeding the permissible power. The section of the circuit consisting of transistors T7, T16 monitors the voltage drop across R30 (0.33 R / 5W) and R35 (0.33 R / 5W) and limits the voltage rise of powerful transistors in case of exceeding the permissible current passing through it.

The power supply is not stabilized two-pole, consisting of a Br1 diode bridge (25A) and capacitors C9-C14 (10000uF / 100V). The amplifier power supply is protected by fuses F1-F2 (10A). Behind the fuses, the voltage is additionally filtered by capacitors C18-C19 (1000uF / 100V). The power supply of the input circuits is separated from the power supply of the power amplifier using diodes D5-D6 (1N4009), resistors R12 (100P / 2W), R15 (100P / 2W) and is filtered by capacitors C3 (100uF / 100V) and C6 (100uF / 100V). This prevents the voltage drop that can occur at power peaks under heavy loads. LEDs D11-D12, together with terminal current-limiting resistors R40-R41 (16K / 1W), are indicators of the presence of power on the diagram.

Power Supply

The figure below shows a diagram of a power supply - a source of several auxiliary voltages. It is not required for the power amplifiers themselves, but is very useful for powering the rest of the complete audio complex, such as: preamplifier, fans, level indicator, soft start system or speaker protection. All these modules are integrated into one common amplifier in a large enclosure.

Power supply unit for auxiliary voltage ULF - diagram

The power supply is divided into several separate sections, each with its own separate ground circuit. The first section is a 2 × 15 V symmetrical power supply, it is used to supply preamplifier... Connector A4 is used to connect the bipolar winding of the transformer. The voltage is rectified using a rectifier bridge Br2 (1 A) and filtered by stabilizers U2 (LM317), U6 (LM337) using C1 (100nF), C7 (100nF) and C24-C25 (4700uF). The output filter is capacitors C8-C9 (100nF) and C19-C20 (100uF). The output voltage of this unit is set using resistors R2-R3 (220R) and R9-R10 (2.4 k). Transistors T1 (BC546), T2 (BC556); resistors R4-R5 (10k) and R7-R8 (3.3k) are a power cut-off circuit, or rather, they reduce the supply voltage to 2 × 1.25 V, which will allow the preamplifier to be turned off. During normal work, short circuit The GP8 connector ensures correct operation of the preamplifier.

PSU printed circuit board - drawing

The next two modules are 12 V power supplies assembled using stabilizers U4 (7812) and U5 (7812) and designed to power other circuit elements. Two separate sources are required because the amplifier is equipped with two pairs of level meters, each on a separate ground. One pair works at the input, controlling the input signal level, and the second pair is connected to the output and allows you to determine the current power level of the UMZCH.

Power Supply PCB - Etched and Drilled

Both power supplies are very simple, the first consists of a Br3 (1A) diode bridge, filter capacitors C5-C6 (100nF), C18 (100uF) and C22 (1000uF), and a stabilizer U4. The transformer windings must be connected to the A2 connector, and the power supply output will be the GP6 and GP7 connectors.

The second 12V channel works exactly the same and consists of elements: Br4 (1A), C10-C11 (100nF), C23 (1000uF), C21 (100uF) and U5.

The last module of the PSU system is the power supply circuit for other amplifier devices and cooling fans. A transformer should be connected to the A1 connector. The voltage is rectified using a rectifier bridge Br1 (5A) and filtered by capacitors C27 (4700uF), C12 (4700uF) and C2 (100nF). The U1 (LM317) microcircuit works here in the role of a stabilizer, which sets the required voltage using resistors R1 (220R) and R6 (2.7 k).

Capacitors C3 (100nF) and C16 (100uF) filter the voltage at the output of the stabilizer, which goes through the GP1 and GP2 connectors to the fan control system. The same voltage goes through the diode D1 (1N5819), to the stabilizer U3 (7812), whose task is to provide power for other amplifier devices connected to the GP3-GP5 connectors. Capacitors C28 (4700uF), C13 (4700uF), C4 (100nF) and C17 (100uF) filter the voltage before the regulator.

ULF printed circuit board - drawing

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

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

The simplest

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

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

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

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

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

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

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

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

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

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

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

On the field workers

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

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

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

Straight up

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

Schemes of a simple high-quality UMZCH

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

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

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

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

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

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

Sound wires

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

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

The author, when they were just talking about audio lines, realized that, in principle, this was not idle chatter, especially since oxygen-free wires had long been used in special purpose equipment by that time, with which he was well familiar by his occupation. Then I took and replaced the standard cord of my TDS-7 headphones with a homemade one made of "vitukha" with flexible stranded wires. The sound, by ear, has steadily improved for loop-through analog tracks, i.e. on the way from studio microphone to the disk that have not been digitized anywhere. Recordings on vinyl made using DMM technology (Direct Meta lMastering, direct metal deposition) sounded especially brightly. After that, interconnect editing of all home audio was converted to "vitush". Then the improvement in sound began to be noted by completely random people, indifferent to music and not forewarned in advance.

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

Video: do-it-yourself twisted pair interconnect wires

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

Theoretical interlude

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

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

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

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

Volume

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

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

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

Power

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

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

Dynamics

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

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

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

KNI

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

Lamps

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

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

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

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

Experienced stand

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

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

For guitarists and rockers

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

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

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

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

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

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

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

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

How to make a transformer?

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

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

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

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

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

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

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

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

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

On microcircuits

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

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

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

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

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

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

UMZCH for subwoofer

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

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

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

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

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

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

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

A little about acoustics

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

Headphone Amplifier

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

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

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

A long time ago, two years ago, I bought an old Soviet speaker 35GD-1. Despite its initially poor condition, I repaired it, painted it a nice blue, and even made a plywood box for it. A large box with two bass reflexes greatly improved its acoustic qualities. The only thing left is a good amplifier that will pump this column. I decided to do it differently than most people do - buy a ready-made D-class amplifier from China and install it. I decided to make an amplifier myself, but not some generally accepted one on the TDA7294 microcircuit, and indeed not on a microcircuit, and not even the legendary Lanzar, but a very rare amplifier on field-effect transistors. And there is very little information on the network about amplifiers on field workers, so it became interesting what it is and how it sounds.

Assembly

This amplifier has 4 pairs of output transistors. 1 pair - 100 watts of output power, 2 pairs - 200 watts, 3 - 300 watts and 4, respectively, 400 watts. I don't need all 400 watts yet, but I decided to put all 4 pairs in order to distribute the heat and reduce the power dissipated by each transistor.

The diagram looks like this:

On the diagram, exactly those component denominations are signed that are installed with me, the diagram is checked and works properly. I am attaching the printed circuit board. Lay6 board.

Attention! All power tracks must be tinned with a thick layer of solder, since a very large current will flow through them. We solder carefully, without snot, we wash the flux. Power transistors must be installed on a heatsink. The advantage of this design is that the transistors can not be isolated from the radiator, but sculpted all on one. Agree, this greatly saves mica heat-conducting pads, because 8 transistors would take 8 pieces of them (surprising, but true)! The radiator is the common drain of all 8 transistors and the audio output of the amplifier, so when installing in the case, do not forget to somehow isolate it from the case. Despite the absence of the need to install mica gaskets between the flanges of the transistors and the radiator, this place must be smeared with thermal grease.

Attention! It is better to check everything right away before installing the transistors on the radiator. If you screw the transistors to the radiator, and there are any snot or non-soldered contacts on the board, it will be unpleasant to unscrew the transistors again and get smeared with thermal grease. So check everything at once.

Bipolar Transistors: T1 - BD139, T2 - BD140. It also needs to be screwed to the radiator. They don't get very hot, but they still get warm. They also need not be isolated from heat sinks.

So, we proceed directly to the assembly. The parts are located on the board as follows:

Now I am attaching a photo of the different stages of the amplifier assembly. First, cut out a piece of PCB to fit the board.

Then we overlay the image of the board on the textolite and drill holes for the radio components. We sand and degrease. We take a permanent marker, stock up on a fair amount of patience and draw paths (I don’t know how to do LUT, so I’m suffering).

We arm ourselves with a soldering iron, take the flux, solder and tinker.

We wash off the remnants of the flux, take a multimeter and ring for a short circuit between the tracks where it should not be. If everything is normal, we proceed to the installation of the parts.
Possible replacements.
First, I'll attach the parts list:
C1 = 1u
C2, C3 = 820p
C4, C5 = 470u
C6, C7 = 1u
C8, C9 = 1000u
C10, C11 = 220n

D1, D2 = 15V
D3, D4 = 1N4148

OP1 = KR54UD1A

R1, R32 = 47k
R2 = 1k
R3 = 2k
R4 = 2k
R5 = 5k
R6, R7 = 33
R8, R9 = 820
R10-R17 = 39
R18, R19 = 220
R20, R21 = 22k
R22, R23 = 2.7k
R24-R31 = 0.22

T1 = BD139
T2 = BD140
T3 = IRFP9240
T4 = IRFP240
T5 = IRFP9240
T6 = IRFP240
T7 = IRFP9240
T8 = IRFP240
T9 = IRFP9240
T10 = IRFP240

The first step is to replace the operational amplifier with any other, even imported, with the same pinout. Capacitor C3 is needed to suppress self-excitation of the amplifier. You can put more, which I did later. Any Zener diodes for 15 V and with a power of 1 W. Resistors R22, R23 can be set based on the calculation R = (Upit.-15) / Ist., Where Upit. - supply voltage, Ist. - stabilization current of the zener diode. Resistors R2, R32 are responsible for the gain. With these ratings, it is somewhere between 30 - 33. Capacitors C8, C9 - filter capacities - can be set from 560 to 2200 uF with a voltage not lower than Usup. * 1.2 so as not to exploit them at the limit of possibilities. Transistors T1, T2 - any complementary pair of average power, with a current of 1 A, for example, our KT814-815, KT816-817 or imported BD136-135, BD138-137, 2SC4793-2SA1837. Source resistors R24-R31 can be set to 2 W, albeit undesirable, with a resistance of 0.1 to 0.33 ohms. It is not advisable to change the power keys, although you can also IRF640-IRF9640 or IRF630-IRF9630; it is possible for transistors with similar passed currents, gate capacities and, of course, the same pin layout, although if you solder on the wires, this does not matter. There seems to be nothing more to change here.

First launch and setup.

The first start-up of the amplifier is made through a safety lamp to break the 220 V network. Be sure to short the input to ground and do not connect the load. At the moment of switching on, the lamp should flash and go out, and go out completely: the spiral should not glow at all. We turn it on, hold it for 20 seconds, then turn it off. We check if there is anything heating up (although if the lamp is off, it is unlikely that anything is heating up). If nothing really heats up, turn it on again and measure the constant voltage at the output: it should be in the range of 50 - 70 mV. For example, I have 61.5 mV. If everything is within the normal range, connect the load, give a signal to the input and listen to music. There should be no interference, extraneous hums, etc. If none of this is present, proceed to setting.

Setting up the whole thing is extremely simple. It is only necessary to set the quiescent current of the output transistors by rotating the trimming resistor slider. It should be approximately 60 - 70 mA for each transistor. This is done in the same way as on Lanzar. The quiescent current is calculated according to the formula I = Upfall / R, where Upfall. Is the voltage drop across one of the resistors R24 - R31, and R is the resistance of this very resistor. From this formula, we derive the voltage drop across the resistor required to set such a quiescent current. Upad. = I * R. For example, in my case it is = 0.07 * 0.22 = somewhere around 15 mV. The quiescent current is set on a “warm” amplifier, that is, the radiator must be warm, the amplifier must play for several minutes. The amplifier warmed up, disconnect the load, short-circuit the input to the common one, take the multimeter and carry out the previously described operation.

Characteristics and features:

Supply voltage - 30-80 V
Working temperature - up to 100-120 degrees.
Load resistance - 2-8 Ohm
Amplifier power - 400 W / 4 Ohm
SOI - 0.02-0.04% at a power of 350-380 W
Gain - 30-33
The range of reproducible frequencies - 5-100000 Hz

It is worth dwelling on the last point in more detail. Using this amplifier with noisy tone blocks such as the TDA1524 may result in the amplifier's seemingly unreasonable power consumption. In fact, this amplifier reproduces interference frequencies that are inaudible to our ears. It may seem that this is self-excitation, but most likely it is precisely interference. Here it is worth distinguishing between interference that is not audible to the ear from real self-excitation. I ran into this problem myself. Originally used as a pre-amplifier, the TL071 opamp. This is a very good high frequency imported op amp with low noise FET output. It can operate at frequencies up to 4 MHz - this is more than enough for reproducing interference frequencies and for self-excitation. What to do? One good person, thank him very much, advised me to replace the op-amp with another, less sensitive and reproducing a smaller frequency range, which simply cannot work at the self-excitation frequency. Therefore, I bought our domestic KR544UD1A, installed it and ... nothing has changed. All this prompted me to think that the variable resistors of the timbre block are making noise. The resistor motors make a little “rustling” noise, which causes interference. I removed the timbre block and the noise disappeared. So it's not self-agitation. With this amplifier, you need to put a low-noise passive timbre block and a transistor preamplifier in order to avoid the above.