The editors of the site "Two Schemes" are simple, but quality amplifier LF 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) connected in parallel with R13 (10 kΩ / 1 V) improves the transient response of the ULF, 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 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 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.
After mastering the basics of electronics, a novice radio amateur is ready to solder his first electronic designs. Audio power amplifiers are generally the most repeatable designs. There are a lot of schemes, each one differs in its parameters and design. This article will consider several of the simplest and completely 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 up to 7 watts of output power into a 4 ohm load. I want to say that the standard switching circuit of this microcircuit contains a small number of components, but a couple of years ago I came up with another circuit on this microcircuit. In this circuit, the number of component parts is minimized, but the amplifier has not lost its sound parameters... After developing this circuit, I began to make all my amplifiers for low-power speakers on this circuit.
The circuit of the presented amplifier has a wide range of reproducible frequencies, the supply voltage range is from 4.5 to 18 volts (typical 12-14 volts). The microcircuit is installed on a small heat sink, since the maximum power reaches up to 10 watts.
The microcircuit is capable of operating on 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 of 0.01 to 4.7 μF (preferably from 0.1 to 0.47 μF); both film and ceramic capacitors can be used. 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 a PC. It is very convenient to use a microcircuit for stand-alone speakers to mobile phone etc.
The amplifier works immediately after switching on, it does not need additional adjustment. It is recommended to additionally connect the minus power supply to the heatsink. All electrolytic capacitors are preferably 25 volts.
The second circuit is assembled on low-power transistors, and is more suitable as a headphone amplifier.
This is probably the highest quality circuit of this kind, the sound is clear, all frequency spectrum... WITH good headphones, it feels like you have a full-fledged subwoofer.
The amplifier is assembled on only 3 reverse conduction transistors, as the cheapest option, transistors of the KT315 series were used, but their choice is wide enough.
The amplifier can operate on a low-impedance load, up to 4 ohms, which makes it possible to use the circuit to amplify the signal of a player, radio, etc. A 9-volt krone-type battery is used as a power source.
In the final stage, KT315 transistors are also used. To increase the output power, you can use KT815 transistors, but then you will have to increase the supply voltage to 12 volts. In this case, the power of the amplifier will reach up to 1 Watt. The output capacitor can have a capacitance from 220 to 2200 μF.
The transistors in this circuit do not heat up, therefore no cooling is needed. When using more powerful output transistors, you may need small heatsinks for each transistor.
And finally, the third scheme. An equally simple, but proven version of the amplifier structure is presented. The amplifier is capable of operating from a reduced voltage of up to 5 volts, in which case the output power of the PA will be no more than 0.5 W, and the maximum power when powered by 12 volts reaches up to 2 watts.
The output stage of the amplifier is built on a domestic complementary pair. Adjust the amplifier by selecting the resistor R2. For this, it is advisable to use a 1kOhm trimmer. Slowly rotate the regulator until the quiescent current of the output stage is 2-5 mA.
The amplifier does not have a high input sensitivity, so it is advisable to use a preamplifier before the input.
A diode plays an important role in the circuit, it is here to stabilize the mode of the output stage.
The transistors of the output stage can be replaced with any complementary pair of the corresponding parameters, for example, KT816 / 817. The amplifier can drive low-power stand-alone speakers with a load impedance of 6-8 ohms.
List of radioelements
| Designation | Type of | Denomination | Quantity | Note | Shop | My notebook | |
|---|---|---|---|---|---|---|---|
| Amplifier on the TDA2003 chip | |||||||
| Audio amplifier | TDA2003 | 1 | Into notepad | ||||
| C1 | 47 uF x 25V | 1 | Into notepad | ||||
| C2 | Capacitor | 100 nF | 1 | Film | Into notepad | ||
| C3 | Electrolytic capacitor | 1 μF x 25V | 1 | Into notepad | |||
| C5 | Electrolytic capacitor | 470 uF x 16V | 1 | Into notepad | |||
| R1 | Resistor | 100 ohm | 1 | Into notepad | |||
| R2 | Variable resistor | 50 kΩ | 1 | 10 kΩ to 50 kΩ | Into notepad | ||
| Ls1 | Dynamic head | 2-4 Ohm | 1 | Into notepad | |||
| Amplifier on transistors circuit number 2 | |||||||
| VT1-VT3 | Bipolar transistor | KT315A | 3 | Into notepad | |||
| C1 | Electrolytic capacitor | 1 uF x 16V | 1 | Into notepad | |||
| C2, C3 | Electrolytic capacitor | 1000 uF x 16V | 2 | Into notepad | |||
| R1, R2 | Resistor | 100 kΩ | 2 | Into notepad | |||
| R3 | Resistor | 47 k Ohm | 1 | Into notepad | |||
| R4 | Resistor | 1 kΩ | 1 | Into notepad | |||
| R5 | Variable resistor | 50 kΩ | 1 | Into notepad | |||
| R6 | Resistor | 3 kΩ | 1 | Into notepad | |||
| Dynamic head | 2-4 Ohm | 1 | Into notepad | ||||
| Amplifier on transistors circuit number 3 | |||||||
| VT2 | Bipolar transistor | KT315A | 1 | Into notepad | |||
| VT3 | Bipolar transistor | KT361A | 1 | Into notepad | |||
| VT4 | Bipolar transistor | KT815A | 1 | Into notepad | |||
| VT5 | Bipolar transistor | KT816A | 1 | Into notepad | |||
| VD1 | Diode | D18 | 1 | Or any low power | Into notepad | ||
| C1, C2, C5 | Electrolytic capacitor | 10 μF x 16V | 3 | ||||
There was a desire to collect more powerful amplifier"A" class. Having read a sufficient amount of relevant literature and chose the most latest version... It was a 30W amplifier that matched high-end amplifiers in terms of its parameters.
I did not intend to make any changes to the existing routing of the original printed circuit boards, however, due to the lack of the original power transistors, a more reliable output stage was chosen using 2SA1943 and 2SC5200 transistors. The use of these transistors ultimately made it possible to provide a large output power amplifier. Schematic diagram my version of the amplifier further.
This is an image of boards assembled according to this scheme with Toshiba 2SA1943 and 2SC5200 transistors.
If you look closely, you can see on printed circuit board along with all the components are bias resistors, they are 1 watt carbon type. It turned out that they are more thermally stable. During the operation of any high-power amplifier, a huge amount of heat is generated, therefore, compliance with the constancy of the nominal value of the electronic component when it is heated is an important condition for the high-quality operation of the device.
The assembled version of the amplifier operates at a current of about 1.6 A and a voltage of 35 V. As a result, 60 watts of continuous power is dissipated by the transistors in the output stage. I must admit that this is only a third of the power they can handle. Try to imagine how much heat is generated on radiators when they are heated to 40 degrees.
The body of the amplifier is made by hand from aluminum. Top plate and base plate 3 mm thick. The radiator consists of two parts. dimensions are 420 x 180 x 35 mm. Fasteners - screws, mainly with a countersunk head made of stainless steel and M5 or M3 threads. The number of capacitors has been increased to six, with a total capacity of 220,000 μF. A 500 W toroidal transformer was used for power supply.
Amplifier power supply
The amplifier device is clearly visible, which has copper busbars of the corresponding design. Added a small toroid for variable feed controlled by DC protection circuitry. There is also an RF filter in the power supply circuit. For all its simplicity, I must say deceptive simplicity, the topology of the board of this amplifier and the sound is produced by it as if without any effort, implying, in turn, the possibility of its infinite amplification.
Oscillograms of the amplifier
3 dB roll-off at 208 kHz
Sine wave 10 Hz and 100 Hz
Sine wave 1 kHz and 10 kHz
100 kHz and 1 MHz signals
Square wave 10 Hz and 100 Hz
Square wave 1 kHz and 10 kHz
60 W total power clipping symmetry at 1 kHz
Thus, it becomes clear that a simple and high-quality design of the UMZCH is not necessarily done using integrated circuits- only 8 transistors allow you to achieve decent sound with a circuit that can be assembled in half a day.
Single transistor amplifier- here is the design of a simple ULF on one transistor. It was with such schemes that many radio amateurs began their journey. Once we have assembled a simple amplifier, we always strive to make a more powerful and high-quality device. And so everything goes on increasing, there is always a desire to make an impeccable power amplifier.
Shown below the simplest scheme amplifier is made on one bipolar transistor and six electronic components, including a speaker. This design of the device for amplifying the sound of low frequency, was created just for the novice radio amateurs. Its main purpose is to make it clear the simple principle of operation of the amplifier, therefore it is assembled using a minimum number of electronic elements.
This amplifier naturally has a small power, for a start it is large and is not needed. However, if you set more powerful transistor and raise the supply voltage a little, then at the output you can get about 0.5 watts. And this is already considered a pretty decent power for an amplifier with such a design. In the diagram, for clarity, a bipolar transistor with n-p-n conductivity is used, but you can use any and with any conductivity.
To get 0.5 W at the output, it is best to use powerful bipolar transistors such as KT819 or their foreign counterparts, for example 2N6288, 2N5490. You can also use silicon transistors such as KT805, their foreign counterpart - BD148, BD149. The capacitor in the output path circuit can be set to 0.1mF, although its nominal value does not play a big role. Nevertheless, it forms the sensitivity of the device relative to the frequency of the audio signal.
If you put a capacitor with a large capacity, then the output will be mainly low frequencies, and high frequencies will be cut off. Conversely, if the capacitance is small, then low frequencies will be cut, and high frequencies will be skipped. Therefore, this output capacitor is selected and installed based on your preference for the audio range. The supply voltage for the circuit must be selected in the range from 3v to 12v.
I would also like to clarify - this power amplifier is presented to you for demonstration purposes only, to show the principle of operation of such a device. The sound of this device will of course be at a low level and cannot be compared with high quality devices... When you increase the playback volume, distortion in the form of wheezing will occur in the speaker.
Readers! Remember the nickname of this author and never repeat his schemes.
Moderators! Before you ban me for insults, think that you have "let an ordinary gopnik near the microphone", who should not even be allowed close to radio equipment and, moreover, to teaching beginners.
Firstly, with such a switching scheme, a large direct current will flow through the transistor and speaker, even if the variable resistor is in the right position, that is, music will be heard. And with a large current, the speaker is damaged, that is, sooner or later, it will burn out.
Secondly, in this circuit, there must be a current limiter, that is, a constant resistor, at least 1 KOhm, connected in series with a variable. Any homemade product will turn the variable resistor regulator all the way, it will have zero resistance and a large current will go to the base of the transistor. As a result, the transistor or speaker will burn out.
A variable capacitor at the input is needed to protect the sound source (the author should explain this, for immediately there was a reader who removed it just like that, considering himself smarter than the author). Without it, only those players in which such protection is already installed on the output will work normally. And if it is not there, then the output of the player may be damaged, especially, as I said above, if you unscrew the variable resistor "to zero". In this case, the output of an expensive laptop will be supplied with voltage from the power source of this penny trinket and it may burn out. Self-made, very fond of removing protective resistors and capacitors, because "it works the same!" As a result, the circuit can work with one sound source, but not with another, and even an expensive phone or laptop can be damaged.
The variable resistor, in this circuit, should only be a trimmer, that is, it should be adjusted once and closed in the case, and not brought out with a convenient handle. This is not a volume control, but a distortion control, that is, it selects the operating mode of the transistor so that there is minimal distortion and that smoke does not come from the speaker. Therefore, in no case should it be accessible from the outside. You can NOT adjust the volume by changing the mode. For this you need to "kill". If you really want to control the volume, it's easier to turn on another variable resistor in series with the capacitor, and now it can be brought out to the amplifier case.
In general, for the simplest circuits - and in order to work immediately and in order not to damage anything, you need to buy a TDA-type microcircuit (for example, TDA7052, TDA7056 ... there are many examples on the Internet), and the author took a random transistor that was lying around in his desk. As a result, gullible amateurs will look for just such a transistor, although its gain is only 15, and the permissible current is as much as 8 amperes (it will burn any speaker without even noticing it).
