High-quality bass amplifier using transistors. Powerful transistor amplifier. Push-pull audio amplifier

The editors of the “Two Schemes” website present a simple but high-quality low-frequency amplifier based on MOSFET transistors. His circuit should be well known to radio amateurs and audiophiles, since it is already about 20 years old. The circuit was developed by the famous Anthony Holton, which is why it is sometimes called ULF Holton. The sound amplification system has low harmonic distortion, not exceeding 0.1%, with a load power of about 100 watts.

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

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

Schematic diagram of UMZCH Holton

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

Printed circuit board

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

Amplifier operating principle

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

The load of the differential amplifier is resistors R2 (4.7 kΩ) and R3 (4.7 kΩ). Transistors T1 (MJE350) and T2 (MJE350) represent another gain stage, and its load is transistors T8 (MJE340), T9 (MJE340) and T6 (BD139).

Capacitors C3 (33 pf) and C4 (33 pf) counteract the excitation of the amplifier. Capacitor C8 (10 nf) connected in parallel with R13 (10 kom/1 V) improves the transient response of the ULF, which is important for rapidly 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 current consumption in idle mode of the amplifier should be around 130 mA.

The output elements of the amplifier are MOSFETs 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 drive a sufficiently large amplitude for the output signal.

Resistors R8 and R17 were used mainly for quickly measuring the quiescent current of power amplifier transistors without interfering with the circuit. They may also be useful in case of expanding the system with another pair of power transistors, due to 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 pass transistor capacitance, and, therefore, limit the frequency range of the amplifier. Diodes D1-D2 (BZX85-C12V) protect powerful transistors. With them, the voltage at startup relative to the power supplies of the transistors should not be more than 12 V.

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

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

Power supply for UMZCH

The amplifier circuit provides power that reaches a real 100 W (effective sine wave), with an input voltage of around 600 mV and a load resistance of 4 ohms.

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

Scheme No. 1

Selecting an amplifier class . Let us immediately warn the radio amateur - we will not make a class A amplifier using transistors. The reason is simple - as stated in the introduction, the transistor amplifies not only the useful signal, but also the bias applied to it. Simply put, it amplifies direct current. This current, together with the useful signal, will flow through speaker system(AC), and the speakers, unfortunately, are able to reproduce this direct current. They do this in the most obvious way - by pushing or pulling the diffuser from its normal position to an unnatural one.

Try to press the speaker cone with your finger - and you will see what a nightmare the sound produced will turn into. Direct current in its action successfully replaces your fingers, so it is absolutely contraindicated for a dynamic head. You can separate direct current from an alternating signal by only two means - a transformer or a capacitor - and both options, as they say, are worse than the other.

Schematic diagram

The circuit of the first amplifier that we will assemble is shown in Fig. 11.18.

This is a feedback amplifier, the output stage of which operates in mode B. The only advantage of this circuit is its simplicity, as well as the uniformity of the output transistors (no special complementary pairs are required). However, it is quite widely used in low-power amplifiers. Another advantage of the scheme is that it does not require any configuration, and if the parts are in good working order, it will work immediately, and this is very important for us now.

Let's consider the operation of this circuit. The amplified signal is supplied to the base of transistor VT1. The signal amplified by this transistor from resistor R4 is supplied to the base of the composite transistor VT2, VT4, and from it to resistor R5.

Transistor VT3 is turned on in emitter follower mode. It amplifies the positive half-waves of the signal on resistor R5 and supplies them through capacitor C4 to the speaker.

The negative half-waves are enhanced by the composite transistor VT2, VT4. In this case, the voltage drop across diode VD1 closes transistor VT3. The signal from the amplifier output is fed to the feedback circuit divider R3, R6, and from it to the emitter of the input transistor VT1. Thus, transistor VT1 plays the role of a comparison device in the feedback circuit.

It amplifies direct current with a gain equal to unity (because the resistance of the capacitor C DC theoretically infinite), and the useful signal - with a coefficient equal to the ratio R6/R3.

As you can see, the capacitance value of the capacitor is not taken into account in this formula. The frequency from which the capacitor can be neglected in calculations is called the cutoff frequency of the RC circuit. This frequency can be calculated using the formula

F = 1 / (R×C).

For our example, it will be about 18 Hz, i.e. the amplifier will amplify lower frequencies worse than it could.

Pay . The amplifier is assembled on a board made of single-sided fiberglass 1.5 mm thick with dimensions 45×32.5 mm. The PCB layout in a mirror image and the parts layout can be downloaded. You can download a video about the operation of the amplifier in MOV format for viewing. I want to immediately warn the radio amateur - the sound reproduced by the amplifier was recorded in the video using the microphone built into the camera, so, unfortunately, it will not be entirely appropriate to talk about the sound quality! Appearance amplifier is shown in Fig. 11.19.

Element base . When manufacturing an amplifier, transistors VT3, VT4 can be replaced with any transistors designed for a voltage not less than the supply voltage of the amplifier, and a permissible current of at least 2 A. The diode VD1 must also be designed for the same current.

The remaining transistors are any with a permissible voltage of at least the supply voltage, and a permissible current of at least 100 mA. Resistors - any with a permissible power dissipation of at least 0.125 W, capacitors - electrolytic, with a capacitance not less than indicated in the diagram, and an operating voltage less than the supply voltage of the amplifier.

Radiators for amplifier . Before we try to make our second design, let us, dear radio amateur, focus on radiators for the amplifier and present here a very simplified method for calculating them.

First, we calculate the maximum power of the amplifier using the formula:

P = (U × U) / (8 × R), W,

Where U- amplifier supply voltage, V; R- speaker resistance (usually it is 4 or 8 ohms, although there are exceptions).

Secondly, we calculate the power dissipated on the collectors of the transistors using the formula:

P race = 0.25 × P, W.

Thirdly, we calculate the radiator area required to remove the corresponding amount of heat:

S = 20 × P race, cm 2

Fourthly, we select or manufacture a radiator whose surface area will be no less than the calculated one.

This calculation is very approximate, but for amateur radio practice it is usually sufficient. For our amplifier, with a supply voltage of 12 V and an AC resistance of 8 Ohms, the “correct” radiator would be an aluminum plate measuring 2x3 cm and at least 5 mm thick for each transistor. Keep in mind that a thinner plate does not transfer heat well from the transistor to the edges of the plate. I would like to warn you right away - the radiators in all other amplifiers must also be of “normal” sizes. Which ones exactly - count for yourself!

Sound quality . After assembling the circuit, you will find that the amplifier's sound is not entirely clear.

The reason for this is the “pure” class B mode in the output stage, the characteristic distortions of which even feedback is not able to completely compensate. For the sake of experiment, try replacing transistor VT1 in the circuit with KT3102EM, and transistor VT2 with KT3107L. These transistors have a significantly higher gain than KT315B and KT361B. And you will find that the amp's sound has improved significantly, although some distortion will still be noticeable.

The reason for this is also obvious - a higher gain of the amplifier as a whole ensures greater accuracy of the feedback and a greater compensating effect.

Continue reading

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

How to make a speaker amplifier

Audio amplifier circuit

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

Advice: whoever decides to “taste” this homemade sound amplifier - use germanium transistors, they sound better (IMHO). Several versions of this amplifier have been created, all of them sound... divine, I can't find any other words.

The power of the presented circuit is no more than 15 watts(plus minus), current consumption 2 Amperes (sometimes a little more). The output stage transistors will heat up even without sending a signal to the amplifier input. A strange phenomenon, isn't it? But for class amplifiers. Ah, this is a completely normal phenomenon, a large quiescent current - business card literally all known circuits of this class.

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

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

After mastering the basics of electronics, the novice radio amateur is ready to solder his first electronic designs. Power amplifiers audio frequency, as a rule, the most repeatable designs. There are quite a lot of schemes, each with its own parameters and design. This article will discuss several simple and fully working amplifier circuits that can be successfully repeated by any radio amateur. The article does not use complex terms and calculations; everything is simplified as much as possible so that no additional questions arise.

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

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

The microcircuit is capable of operating at a load of 2 ohms, which means that 2 heads with a resistance of 4 ohms can be connected to the amplifier output.
The input capacitor can be replaced with any other one, with a capacity from 0.01 to 4.7 μF (preferably from 0.1 to 0.47 μF), you can use both film and ceramic capacitors. It is advisable not to replace all other components.

Volume control from 10 to 47 kOhm.
The output power of the microcircuit allows it to be used in low-power speakers for PCs. It is very convenient to use the chip for stand-alone speakers mobile phone and so on.
The amplifier works immediately after switching on and does not require additional adjustment. It is recommended to additionally connect the power supply minus to the heat sink. It is advisable to use all electrolytic capacitors at 25 Volts.

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

This is probably the most high-quality scheme This kind of sound is clear, the entire frequency spectrum is felt. WITH good headphones, it feels like you have a full-fledged subwoofer.

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

The amplifier can operate at a low-impedance load, up to 4 ohms, which makes it possible to use the circuit to amplify the signal of a player, radio, etc. A 9-volt Krona battery is used as a power source.
The final stage also uses KT315 transistors. To increase the output power, you can use KT815 transistors, but then you will have to increase the supply voltage to 12 volts. In this case, the amplifier power will reach up to 1 Watt. The output capacitor can have a capacity from 220 to 2200 µF.
The transistors in this circuit do not heat up, therefore, no cooling is needed. If you use larger output transistors, you may need small heat sinks for each transistor.

And finally - the third scheme. An equally simple, but proven version of the amplifier structure is presented. The amplifier is capable of operating from undervoltage up to 5 volts, in this case the output power of the PA will be no more than 0.5 W, and the maximum power with a 12 volt power supply reaches up to 2 Watts.

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

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

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

List of radioelements

Reading time ≈ 6 minutes

Amplifiers are probably one of the first devices that novice radio amateurs begin to construct. When assembling ULF transistors with their own hands using a ready-made circuit, many use microcircuits.

Although there are a huge number of transistor amplifiers, every radio electronics engineer is constantly striving to make something new, more powerful, more complex, and interesting.

Moreover, if you need a high-quality, reliable amplifier, then you should look towards transistor models. After all, they are the cheapest, capable of producing clear sound, and any beginner can easily construct them.

Therefore, let's figure out how to make a homemade class B bass amplifier.

Note! Yes, yes, class amplifiersB can be good too. Many people say that only tube devices can produce high-quality sound. This is partly true. But, look at their cost.

Moreover, assembling such a device at home is far from an easy task. After all, you will have to search for a long time for the necessary radio tubes, and then buy them at a fairly high price. And the process of assembly and soldering itself requires some experience.

Therefore, let's consider the scheme of a simple, and at the same time quality amplifier low frequency, capable of producing sound power of 50 W.

An old but proven scheme from the 90s

The ULF circuit that we will assemble was first published in Radio magazine in 1991. It has been successfully collected by hundreds of thousands of radio amateurs. Moreover, not only for improving skills, but also for use in your audio systems.

So, the famous Dorofeev low-frequency amplifier:

The uniqueness and genius of this scheme lies in its simplicity. This ULF uses a minimum number of radio elements and an extremely simple power source. But, the device is capable of “taking” a load of 4 Ohms and providing output power 50 W, which is quite enough for a home or car speaker system.

Many electrical engineers improved and finalized this circuit. And for convenience, we took its most modern version, replacing the old components with new ones, so that it would be easier for you to design the ULF:

Description of the bass amplifier circuit

In this “reworked” Doroveevsky ULF, unique and most effective circuit solutions were used. For example, resistance R12. This resistor limits the collector current of the output transistor, thereby limiting the maximum power of the amplifier.

Important! No need to change the denominationR12 to increase the output power, since it is selected specifically for the components used in the circuit. This resistor protects the entire circuit from short circuits..

Transistor output stage:

The same R12 “live”:

Resistor R12 should have a power of 1 W, if you don’t have one at hand, take half a watt. It has parameters that provide a coefficient nonlinear distortion up to 0.1% at a frequency of 1 kHz, and no more than 0.2% at 20 kHz. That is, you will not notice any changes by ear. Even when operating at maximum power.

The power supply of our amplifier needs to be selected bipolar, with output voltages in the range of 15-25 V (+- 1%):

To “raise” the sound power, you can increase the voltage. But then you will have to simultaneously replace the transistors in the final stage of the circuit. They need to be replaced with more powerful ones, and then recalculate several resistances.

Components R9 and R10 must be rated according to the supplied voltage:

They, using a zener diode, limit the passing current. In the same part of the circuit, a parametric stabilizer is assembled, which is needed to stabilize the voltage and current in front of the operational amplifier:

A few words about the TL071 chip - the “heart” of our ULF. It is considered an excellent operational amplifier, which is found in both amateur designs and professional audio equipment. If there is no suitable op-amp, it can be replaced with TL081:

“Real” view on the board:

Important! If you decide to use any other operational amplifiers in this circuit, carefully study their pinout, because “legs” may have different meanings.

For convenience, the TL071 chip should be mounted on a plastic socket pre-soldered into the board. This way you can quickly replace the component with another if necessary.

Good to know! For your reference, we will present you with another circuit of this ULF, but without an amplifying microcircuit. The device consists exclusively of transistors, but is assembled extremely rarely due to obsolescence and irrelevance.

To make it more convenient, we tried to make printed circuit board minimal in size – for compactness and ease of installation in an audio system:

All jumpers on the board must be soldered immediately after etching.

Transistor blocks (input and output stages) must be mounted on a common radiator. Of course, they are carefully insulated from the heat sink.

Here they are in the diagram:

And here on the printed circuit board:

If ready-made ones are not available, radiators can be made from aluminum or copper plates:

The output stage transistors must have a power dissipation of at least 55 W, and even better - 70 or as much as 100 W. But, this parameter depends on the supply voltage supplied to the board.

From the diagram it is clear that 2 complementary transistors are used on the input and output stages. It is important for us to select them by amplification factor. To determine this parameter, you can take any multimeter with a transistor testing function:

If you don’t have such a device, then you’ll have to borrow a transistor tester from some specialist:

Zener diodes should be selected according to power by half a watt. Their stabilization voltage should be 15-20 V:

Power unit. If you plan to mount a transformer power supply on your ULF, then select filter capacitors with a capacity of at least 5,000 μF. Here the more the better.

The low-frequency amplifier we assembled belongs to B-class. It works stably, providing almost crystal clear sound. But it is best to select the BN so that it cannot operate at full capacity. The best option is a transformer overall power at least 80 W.

That's all. We figured out how to assemble a ULF on transistors with our own hands using a simple circuit, and how it can be improved in the future. All the components of the device will be found, and if they are not there, it’s worth disassembling a couple of old tape recorders or ordering radio parts on the Internet (they cost almost pennies).