Symmetrical ULF made from available parts based on V. Korol. Powerful transistor amplifier Low frequency power amplifiers

Low Frequency Amplifiers

Low frequency amplifiers (LF) are relatively simple devices in their structure and at the same time very difficult to evaluate. There are still no objective parameters for comparing them, and it is not yet clear whether this is possible in principle. Thus, the debate between supporters and opponents of tube amplifiers is still ongoing. But, since amplifiers still need to be evaluated somehow, let’s take a closer look at their classification and the generally accepted parameters used to evaluate them. We will not touch upon other types of amplifiers except low-frequency AC power amplifiers, and these are what we will mean by the abbreviation ULF, although many parameters are the same for all types of amplifiers.

It is absolutely necessary to mention that we will be considering amplifiers designed for high-quality sound reproduction, therefore all assessments of amplifiers and their parameters, such as better or worse, will be based on this criterion. The ideal is Hi-End, classic Hi-End in the engineering, not audiophile sense of the word, a development of good old Hi-Fi - high fidelity in terms of technical parameters and scientific terms, measurable and reproducible.

These lectures are entirely devoted to integrated low-frequency amplifiers. Nobody knows what will happen tomorrow, but today there are no integrated ULFs that could compare in terms of reproduction quality with amplifiers using discrete elements. Their advantages are low cost (thousands and tens of thousands of times), small dimensions and ease of use. There are a number of other advantages arising from production technology. It is impossible to achieve such identical parameters of differential pair transistors as those grown on a single crystal with discrete elements. Automatic control of the thermal and electrical conditions of the most important power structures located on the same chip with the rest of the circuit is easy and simple. All the benefits and all the experience gained in the operational amplifier manufacturing process are at your service. The disadvantage of integrated ULFs is, first of all, the difficulty of heat removal and the difficulty of working with large and small currents simultaneously on the same substrate. In addition, when developing them, the goal is not to achieve something exclusive. This is, first of all, a cheap mass product that allows you to easily, cheaply and conveniently obtain excellent results.

To make it easier to understand what we are talking about, it is necessary to recall a number of general questions. Experts, of course, may not read this, but most readers would like to refresh their memory on a number of issues, especially since there is little modern literature on this issue in Russian. For beginners, these questions will probably seem insufficiently covered, but this is not a textbook.

Basic parameters of amplifiers

An electrical signal amplifier is a device that, using the energy of a power source, provides an increase in the amplitude of the current and/or voltage at the output compared to the input signal, without changing its shape. This is probably not the best definition, but for our purposes it is quite suitable (by the way, I have not come across absolutely correct definitions). Already from the definition, a number of conclusions can be drawn. People often talk about voltage amplifiers, current amplifiers and power amplifiers. In principle, these are not entirely correct expressions. They can be used when talking about the main task of a given amplifier or about a specific load. When we talk about ULF, we always mean power amplification. In what units is amplification measured? Today, the generally accepted global standard is decibels (dB). Decibels were first introduced into practice to indicate power ratios.

This is due to the fact that loudness to the human ear is perceived as a direct increase in the intensity of the acoustic effect (i.e., the output power of the amplifier), and as its logarithm. It was believed that a decibel is the minimum value perceptible to humans. Today, the generally accepted norm has become 0.5 dB as the minimum sensitivity of the ear. This is what we should proceed from when evaluating the various characteristics of amplifiers. Somewhat later, the decibel began to be used to simply denote the voltage ratio, although this is not entirely correct, and then other quantities. From the above, the following conclusion follows: an amplifier whose power is 10 times greater sounds only twice as loud. This must be remembered when choosing the output power of the amplifier.

The voltage gain for amplifiers is defined for a sinusoidal input signal as the ratio of the output voltage to the input voltage and, generally speaking, is a complex quantity that depends on frequency.

In technology, gain refers to its modulus.

where Uo is the output voltage, aUiN is the input voltage.

Gain measurements, like all other parameters of an amplifier or any other device, are made under conditions previously specified by the manufacturer, and these conditions are not always the same for different manufacturers.

The current gain is determined in the same way as the voltage, but this ULF characteristic is rarely used, just like the power gain, so in the future, by gain we will understand the voltage gain.

The gain (any) is not a constant value, but depends on many factors. In particular, it depends on the frequency of the input signal. The dependence of gain on frequency is one of the most important characteristics of an amplifier and is called amplitude-frequency response (AFC) or bandwidth (frequencyresponse).

An ideal amplifier has a completely flat frequency response, but real amplifiers are far from this. All amplifiers have a decrease in frequency response in the high frequency region for a number of reasons, the main one of which is the limited frequency properties of active elements: transistors, lamps, etc. Many amplifiers have low-frequency rolloff due to the influence of coupling capacitors. It should be noted that for ULF the ideal characteristic is not a straight line at all. For them, only the range from 16 Hz to 20 kHz is of interest, i.e. the range of sound vibrations that the human ear can hear. Extra frequency regions, in which there is no useful signal, but only noise from both internal and external sources, only worsen the operation of the amplifier, reducing its efficiency, and the high-frequency region, in the case of not very successful circuit solutions, even poses some danger for output stages and acoustics when self-oscillation occurs. However, in high-end amplifiers, some frequency headroom is necessary for a number of reasons, both psychoacoustic and technical. Therefore, the upper limit of the ideal characteristic is set in the region of 25...50 kHz. There is no absolute standard here. We can only say that if the characteristics of a particular device go beyond these limits, then it is artificially limited. In some cases, this area is narrowed much more if the output device fundamentally cannot reproduce the entire frequency spectrum, such as a megaphone or telephone, or the area contains a large amount of interference from external sources, as in automotive technology.

Frequency responses look different even within the information provided by one developer. Sometimes this is a graph of gain versus frequency, sometimes it is the attenuation of the output signal. There are also normalized characteristics, when the Y-axis shows the ratio of the output voltage or gain to the same value measured at the average frequency. Recently, the term POWERBANDWIDTH (BW), which is the power bandwidth, has become widespread. The most important thing when assessing these characteristics is to remember that the frequency response limit is determined by a level of 0.5 from the level at medium frequencies, if this is a power characteristic (i.e., by a level of -3 dB) and by a level of 0.707 (or -6 dB), if this is tension. Since these characteristics of modern amplifiers are very uniform, most often their graphs are not even given, but simply tabulated data on the bandwidth or cutoff frequencies, i.e. about those frequencies at which the frequency response decay reaches the values mentioned above. Thus, the upper and lower limit frequencies (fн, fL) differ.

The second characteristic of complex gain is the phase shift introduced by the amplifier. The dependence of the phase shift on the signal frequency is called the phase-frequency characteristic of the amplifier or simply the phase characteristic. Since this dependence always occurs, it means that different spectral components pass through the amplifier at different times, which leads to distortion of the output signal shape. Phase characteristics are never given either for integrated amplifiers or for finished products, because their measurement is extremely difficult and there are no common standards for making such measurements. In addition, there is no consensus on how phase distortion affects the perception of acoustic signals, and therefore there are no uniform requirements. All waveform distortions described by frequency and phase characteristics are linear, i.e. can be described by functions of the form

where A and B are constants. This is due to the fact that they are caused by linear reactive elements and, accordingly, do not lead to the appearance of new components in the signal spectrum, but only change the ratio of phases and amplitudes of existing ones.

Circuit of a powerful five-channel low-frequency amplifier for a home audio center at minimal cost

In this article on the site Radio amateur, we will look at another simple amateur radio circuit - low frequency amplifier for home audio center.

Feature of this amplifier at low cost with fairly high parameters. Amplifier built according to a combined circuit, in which there is one powerful low-frequency channel (40 W), reproducing frequencies up to 400 Hz, and a stereo amplifier, the channels of which are made according to a two-channel midrange (300-4000 Hz) - high-frequency (3000-30000 Hz) circuit with a power of 2x18 Tue Thus the total output power of the amplifier is 106 W. For each channel, separate acoustic systems are used, made in separate housings. There are five acoustic systems in total: a low-frequency bottom and two each for mid and high frequencies.

The amplifier is made on the same type and inexpensive element base - TDA2030A (KR174UN19A) microcircuits and two transistors KT818GM and KT819GM. The amplifier is powered by a 200 W transformer.

The schematic diagram of the low-frequency channel is shown in Fig. 1:

Terminals X1, X2, X3 receive a stereo signal with a nominal level of 0.8 volts. The microcircuit is capable of developing power up to 18 W and to increase this value, the output of the microcircuit is enhanced by a push-pull cascade on transistors VT1, VT2, which begins to operate at a power of more than 15 W. The cascade circuit is distinguished by the fact that the collectors of the transistors are connected together, which allows the use of one common radiator for the output stage. The A1 chip requires a separate heatsink.

The amplifier board (Fig. No. 4) is made so that the microcircuit and transistors are located at opposite edges.

The circuit of the mid-high-frequency amplifier is shown in Figure No. 2:

The diagram of only one stereo channel is shown, the second is exactly the same. The audio frequency of one of the stereo channels is supplied to terminals X1, X2. The mid-frequency amplifier is made on the A1 chip, and the high-frequency amplifier is made on the A2 chip. The microcircuits are installed on one common radiator. Therefore, on the printed circuit board (Fig. No. 5), the microcircuits are located at one edge.

There are two such boards in the amplifier - one for each stereo channel. There are three jumpers on the board, made with mounting wire. One feeds the signal to the RF amplifier (it is advisable to make it with a shielded wire), and the other two supply power to the RF amplifier. The jumpers are located on the side of the printed conductors and are laid in the shortest direction.

The inter-board connections and power supply diagram are shown in Figure 3. The power supply is not stabilized; it is made of a power transformer, a bridge rectifier and a bank of smoothing capacitors.

The stereo signal from the output of the preamplifier with a nominal level of 0.8 V is supplied to the XP1 connector. Directly next to the connector, trimming resistors R1-R5 are installed to set the ratio of the sound levels of stereo amplifiers and the low-frequency channel for a specific room. The transformer is made on the basis of the TS200 transformer from an old tube TV. All secondary windings were removed and two new ones were wound in their place - 50 turns of PEV 1.06 each. Connect the windings according to the diagram.

Radiators are made of U-shaped aluminum profile, which is used for suspended ceilings. For each radiator, two pieces approximately 15 cm long are cut. To increase the surface area over the entire surface, a hole is drilled through every centimeter and an M4 thread is cut. M4 screws 55 mm long are screwed into these holes, thus creating a needle-plate radiator (Fig. No. 6):

The speaker systems use the most affordable dynamic loudspeakers with 4 ohm voice coils. Each speaker system contains 4 speakers (Fig. No. 7). The low-frequency speaker contains 4 10GDSH-2 speakers, high-frequency speakers - four 4-GDV-1, mid-frequency speakers - 5GDSH-4.

Acoustic systems are made of 20 mm thick chipboards, used in the manufacture of cabinet furniture. The dimensions of the workpieces shown in Figures No. 8, 9, 10 take into account exactly this chipboard thickness.

The phase inverter pipe is made of 100 mm plastic gray sewer pipe 150 mm long. The pipe is glued into the hole with Moment-1 glue.

High input impedance and shallow feedback are the main secret of warm tube sound. It's no secret that the highest quality and most expensive amplifiers, which belong to the HI-End category, are manufactured using tubes. Let's understand what a quality amplifier is? A low-frequency power amplifier has the right to be called high-quality if it completely repeats the shape of the input signal at the output without distorting it; of course, the output signal is already amplified. On the Internet you can find several circuits of really high-quality amplifiers, which can be classified as HI-End and do not necessarily require tube circuitry. To obtain maximum quality, you need an amplifier whose output stage operates in pure class A. Maximum linearity of the circuit gives a minimum amount of distortion at the output, therefore, in the design of high-quality amplifiers, special attention is paid to this factor. Tube circuits are good, but not always available even for self-assembly, and industrial tube UMZCHs from branded manufacturers cost from several thousand to several tens of thousands of US dollars - this price is certainly not affordable for many.
The question arises: can similar results be achieved from transistor circuits? the answer will be at the end of the article.

There are quite a lot of linear and ultra-linear circuits of low-frequency power amplifiers, but the circuit that will be considered today is a high-quality ultra-linear circuit, which is implemented with only 4 transistors. The circuit was created back in 1969 by British audio engineer John Linsley-Hood. The author is the creator of several other high-quality circuits, in particular class A. Some experts call this amplifier the highest quality among transistor ULFs, and I was convinced of this a year ago.

The first version of such an amplifier was presented at. A successful attempt to implement the circuit forced me to create a two-channel ULF using the same circuit, assemble everything in a housing and use it for personal needs.

Features of the scheme

Despite its simplicity, the scheme has several features. Correct operation may be disrupted due to incorrect board layout, poor placement of components, incorrect power supply, etc.
It is the power supply that is a particularly important factor - I strongly advise against powering this amplifier from all kinds of power supplies; the best option is a battery or a power supply with a battery connected in parallel.
The amplifier power is 10 watts with a 16 Volt power supply into a 4 Ohm load. The circuit itself can be adapted for 4, 8 and 16 Ohm heads.
I created a stereo version of the amplifier, both channels are located on the same board.

The second one is intended for driving the output stage, I installed KT801 (it was quite difficult to get hold of it.
In the output stage itself, I installed powerful bipolar switches of reverse conduction - the KT803 received undoubtedly high-quality sound with them, although I experimented with many transistors - KT805, 819, 808, and even installed powerful composite switches - KT827, with it the power is much higher, but the sound is not compare with KT803, although this is just my subjective opinion.

An input capacitor with a capacity of 0.1-0.33 μF, you need to use film capacitors with minimal leakage, preferably from well-known manufacturers, the same with the output electrolytic capacitor.
If the circuit is designed for a 4 Ohm load, then you should not increase the supply voltage above 16-18 Volts.
I decided not to install a sound regulator; it, in turn, also affects the sound, but it is advisable to install a 47k resistor parallel to the input and minus.
The board itself is a prototype board. I had to tinker with the board for a long time, since the lines of the tracks also had some influence on the sound quality as a whole. This amplifier has a very wide frequency range, from 30 Hz to 1 MHz.

Setup couldn't be easier. To do this, you need to use a variable resistor to achieve half the supply voltage at the output. For more precise settings, it is worth using a multi-turn variable resistor. We connect one multimeter lead to the minus power supply, put the other one to the output line, i.e. to the plus of the electrolyte at the output, thus, slowly rotating the variable we achieve half of the power supply at the output.

In this article we will analyze the scheme in detail DIY tube amplifier.

SE or single-ended circuits are amplifiers in which the signal is amplified by one amplifying element (tube, transistor) in series at each stage. These systems operate in pure Class A and are valued by many audiophiles for their good microdynamics and precision in detail presentation. Simplicity is also an advantage. The disadvantages of these circuits are: low energy efficiency (Class A), low gain, slightly higher distortion. We present here a prototype of such an amplifier.

tube amplifier

Tube amplifier it's not worth it cheap collect. But it is quite possible and realistic collect your own hands. But what to assemble, has been going for more than one year. It is in many ways better than semiconductor ones, and the sound is warmer. And so, let's get started - a diagram and a photo report of a tube amplifier with your own hands with all the files and descriptions.

DIY home theater with lamps

For every true audio connoisseur, a tube amplifier speaks volumes, but the latest in fashion is the creation of a complete multi-channel tube home theater. Believe me, with a 32" screen the effect is simply amazing! We use a classic single-ended circuit, with parallel connection of lamps at the output to increase the output power. The amplifier operates in class "A", which ensures maximum sound quality. The lamps can be used for input - 6N1P, 6N2P, 6N23P; for exit - 6P14P, 6P15P, 6P43P, 6P3S - shorter than rich.

Another low purity amplifier on TDA

Do-it-yourself low-frequency amplifier for tda

This amplifier is well suited for assembly and for those who recently began to be interested in radio engineering, have mastered the technology of how to apply tracks to a board and etch it.

The amplifier is assembled on a tda7377 and ne555 microcircuit.

Pout - maximum 20W per channel.
The output power will allow you to enjoy the tracks you like.

DIY low pass filter

Low pass filter for subwoofer circuit

We all know that a subwoofer low-frequency head without any filters, when connected to a power amplifier, will simply work like a regular speaker, of course reproducing low frequencies perfectly, but without low pass filters You can't build a good subwoofer.

DIY 50W tube amplifier

Good evening to all fans of radio tube sound! There are a lot of good sound amplifier circuits on the site, so I will publish a mono version of my LUNC. It took me a long time to assemble it, for almost a whole year I periodically took on the project and gradually completed it, and now, finally, the time has come to present the final version for your consideration. Purpose: the usage for the subwoofer channel was calculated.

DIY tube amplifier for guitar

Recently there was a need to assemble a simple ULF for guitar, for which the standard was chosen LUNCH scheme using lamps such as 6n23p and 6p14p.

DIY hybrid ULF

At numerous requests from radio amateurs, I present an improved and more complete hybrid ULF diagram with a detailed description, parts list and power supply diagram. The lamp at the input of the hybrid ULF 6N6P circuit was replaced with 6N2P. You can also install the 6N23P, which is more common in old lamps, in this unit. Field-effect transistors are replaceable with other similar ones - with an insulated gate and a drain current of 5A and higher.

Variable R1 - 50 kOhm is a high-quality variable resistor for the volume control. You can set it up to 300 kOhm, nothing will worsen. Be sure to check the regulator for the absence of rustles and unpleasant friction during rotation. Ideally, you should use ALPS RG - this is a Japanese company producing high-quality regulators. Don't forget about the balance regulator.

Tube amplifier circuit

DIY lamp unch

Tube amplifiers are becoming increasingly popular among audio lovers. They differ in quality from transistor ones and in a more aesthetically pleasing retro style.

Shown in photo tube ULF not difficult assemble with your own hands.

The author decided to assemble the UMZCH using a push-pull circuit on 6P6S lamps. I’ll say right away that the sound is really not bad, although I haven’t listened to it thoughtfully for a long time. The power is enough for the eyes, although it was difficult to remove the background, especially in the right channel. I assembled it according to the attached diagram, only the rectifier was made on 5TS3S, after the kenatron the capacitor is 47 microfarads, each channel has its own D21 inductor, after each choke there is 330 microfarads of capacitance and it still buzzes a little.

DIY amplifier for K174UN14

This amplifier is easy to assemble, UZCH scheme collected on a fairly well-known microcircuit k174un14, which is also an analogue of imported tda2003 chips.

Even beginners in radio engineering can assemble this circuit. And so we look further at the characteristics and the circuit diagram of the device itself sent by Aidar Galimov

Evgenia Smirnova

To send light into the depths of the human heart - this is the purpose of the artist

Content

Connecting speakers to a laptop, TV, or other music source sometimes requires amplification of the signal using a separate device. The idea of building your own amplifier is a good one if you are inclined to work with printed circuit boards at home and have some technical skills.

How to make a sound amplifier

The beginning of work on assembling an amplification device for speakers of one type or another consists of searching for tools and components. The amplifier circuit is assembled on a printed circuit board using a soldering iron on a heat-resistant support. It is recommended to use special soldering stations. If you assemble it yourself for the purpose of testing the circuit or for use for a short period of time, the “on wires” option is suitable, but you will need more space to place the components. The printed circuit board guarantees the compactness of the device and ease of further use.

A cheap and widespread amplifier for headphones or small speakers is created on the basis of a microcircuit - a miniature control unit with a pre-wired set of commands for controlling an electrical signal. All that remains to be added to the circuit with the microcircuit is a few resistors and capacitors. The total cost of an amateur-grade amplifier is ultimately significantly lower than the price of ready-made professional equipment from the nearest store, but the functionality is limited to changing the output volume of the audio signal.

Remember the features of compact single-channel amplifiers that you assemble yourself based on TDA series microcircuits and their analogues. The microcircuit generates a large amount of heat during operation, so you should eliminate or minimize its contact with other parts of the device. A radiator grille for heat dissipation is recommended for use. Depending on the model of the microcircuit and the power of the amplifier, the size of the required heatsink increases. If the amplifier is assembled in a housing, you should first plan a place for the heat sink.

Another feature of assembling a sound amplifier with your own hands is the low voltage consumption. This allows you to use a simple amplifier in cars (powered by a car battery), on the road or at home (powered by a special unit or batteries). Some simplified audio amplifiers require a voltage of only 3 Volts. Power consumption depends on the degree of audio signal amplification required. The sound amplifier from the player for standard headphones consumes about 3 Watts.

It is recommended that a novice radio amateur use a computer program to create and view circuit diagrams. Files for such programs can have a *.lay extension - they are created and edited in the popular virtual tool Sprint Layout. Creating a circuit with your own hands from scratch makes sense if you have already gained experience and want to experiment with the knowledge you have gained. Otherwise, look for and download ready-made files that can be used to quickly assemble a replacement for a low-frequency amplifier for a car radio or a digital combo amplifier for a guitar.

For laptop

A do-it-yourself sound amplifier for a laptop is assembled in one of two cases: the built-in speakers are out of order, or their volume and sound quality are not enough for your needs. You will need a simple amplifier designed for a power of external speakers up to 2 Watts, and a winding resistance of up to 4 Ohms. To assemble it yourself, in addition to standard amateur radio tools (pliers, soldering station), you will need a printed circuit board, a TDA 7231 microcircuit, and a 9-volt power supply. Select your own housing to house the amplifier components.

Add the following items to the list of purchased components:

non-polar capacitor 0.1 µF – 2 pcs.;
polar capacitor 100 µF – 1 pc.;
polar capacitor 220 µF – 1 pc.;
polar capacitor 470 µF – 1 pc.;
constant resistor 10 KOhm – 1 pc.;
constant resistor 4.7 Ohm – 1 pc.;
two-position switch – 1 pc.;
jack for loudspeaker output – 1 pc.

Determine the assembly order yourself depending on which *.lay electrical diagram you downloaded. Select a radiator of such a size that its thermal conductivity allows you to maintain the operating temperature of the microcircuit below 50 degrees Celsius. If the device is constantly used outdoors with a laptop, it will need a homemade case with slots or holes for air circulation. You can assemble such a case with your own hands from a plastic container or the remains of old radio equipment, securing the board with long screws.

For DIY headphones

The simplest stereo amplifier for portable headphones should have low power, but the most important parameter will be power consumption. In an ideal example, the design is powered by AA batteries, or, in extreme cases, by a simple 3-volt adapter. You will need a high-quality TDA 2822 microcircuit or its analogue (for example, KA 2209), an electronic circuit for assembling an amplifier with your own hands using a TDA 2822. Additionally, take the following components:

capacitors 100 µF (4 pcs.);
up to 30 cm of copper wire;
headphone socket.

A heat sink element will be needed if you want to make the amplifier compact and with a closed housing. The amplifier can be assembled on a ready-made or home-made printed circuit board or by surface mounting. The pulse transformer in the power supply may cause interference, so do not use it in this amplifier. The finished amplifier will provide pleasant and powerful sound from the player (record or radio signal), tablet or phone.

Subwoofer amplifier circuit

The low-frequency amplifier is assembled with your own hands on the TDA 7294 microcircuit. It is used both to create powerful acoustics with bass in the apartment, and as a car amplifier - in this case, however, you need to purchase a bipolar power supply of 30-35 Volts. The figures below describe the location of components, as well as the values of resistors and capacitors. This subwoofer amplifier will provide an output power of up to 100 watts with outstanding low frequencies.

Mini sound amplifier for speakers

The design described above for laptops is suitable as a sound amplification device for domestic or foreign home speakers. Stationary placement of the device will allow you to choose any power adapter from those available. You can ensure the miniature size and acceptable appearance of an inexpensive amplifier by following several rules:

Ready-made high-quality printed circuit board.
Durable plastic or metal case (order from a specialist).
The placement of components is pre-planned.
The amplifier is soldered neatly, without unnecessary drops of solder.
The heatsink only touches the chip.
Ready-made sockets are used for signal output and power input.

DIY tube sound amplifier

Tube sound amplifiers are expensive devices, provided that you purchase all the components at your own expense. Old radio amateurs sometimes keep collections of tubes and other parts. Assembling a tube amplifier at home with your own hands is relatively easy if you are willing to spend a few days searching for detailed circuit diagrams on the Internet. The sound amplifier circuit in each case is unique and depends on the sound source (old tape recorder, modern digital equipment), power source, expected dimensions and other parameters.

Transistor sound amplifier

Assembling a sound preamplifier with your own hands without using complex microcircuits is possible using transistors. An amplifier based on germanium transistors can be easily integrated into modern audio systems; it does not require additional configuration. The disadvantage of transistor circuits is the larger size of the board assembly. The dependence on the “purity” of the background is also unpleasant - you will need a shielded cable, or an additional circuit for suppressing noise and ripple from the network.

Video: DIY audio power amplifier

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