Homemade transistor amplifier. Do-it-yourself high-quality sound amplifier
Scheme simple amplifier sound on transistors, which is implemented on two powerful composite transistors TIP142-TIP147 installed in the output stage, two low-power BC556B in the differential path and one BD241C in the signal pre-amplification circuit - only five transistors for the entire circuit! This UMZCH design can be freely used, for example, as part of a home music center or for the buildup of a subwoofer installed in a car, at a disco.
The main attraction of this sound power amplifier lies in the ease of assembly even by novice radio amateurs, there is no need for any special settings, there are no problems in purchasing components at an affordable price. The PA circuit presented here has electrical characteristics with high linearity of operation in the frequency range from 20Hz to 20000Hz. p>
When choosing or self-manufacturing transformer for the power supply, the following factor must be taken into account: - the transformer must have a sufficient power reserve, for example: 300 W per one channel, in the case of a two-channel version, then naturally the power doubles. You can use your own separate transformer for each, and if you use the stereo version of the amplifier, then you will generally get a “double mono” type device, which will naturally increase the efficiency of sound amplification.
The effective voltage in the secondary windings of the transformer should be ~ 34v alternating, then constant pressure after the rectifier it will turn out in the region of 48v - 50v. In each power supply arm, it is necessary to install a fuse rated for a working current of 6A, respectively, for a stereo when working on one power supply - 12A.
The editors of the Two Circuits website present a simple but high-quality low-frequency amplifier based on MOSFET transistors. His circuit should be well known to audiophile radio amateurs, since she is already 20 years old. The circuit is the development of 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 power load of about 100 watts.
This amplifier is an alternative to 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 the simple design and the output stage, consisting of 2 inexpensive MOSFETs. The amplifier can drive both 4 and 8 ohm speakers. 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
Holton amplifier on MOSFET - circuit The circuit is a classic two-stage amplifier, it consists of a differential input amplifier and symmetrical amplifier power, in which one pair of power transistors operates. The scheme of the system is presented above.
Printed circuit board
printed ULF board- finished look Here is the archive from PDF files printed circuit board - .
The principle of operation of the amplifier
Transistors T4 (BC546) and T5 (BC546) operate in a differential amplifier configuration and are powered by a current source built on the basis of transistors T7 (BC546), T10 (BC546) and resistors R18 (22 kohm), R20 (680 ohms) and R12 (22 com). The input signal is fed to two filters: a low-pass filter, built from the elements R6 (470 ohms) and C6 (1 nf) - it limits the high-frequency components of the signal and a band-pass filter, consisting of C5 (1 uF), R6 and R10 (47 kohm), limiting signal components at infra-low frequencies.
The load of the differential amplifier is resistors R2 (4.7 kohm) and R3 (4.7 kohm). Transistors T1 (MJE350) and T2 (MJE350) are another amplification stage, and transistors T8 (MJE340), T9 (MJE340) and T6 (BD139) are its load.
Capacitors C3 (33pF) and C4 (33pF) counteract the excitation of the amplifier. 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-growing input signals.
Transistor T6, together with the elements R9 (4.7 kohm), R15 (680 ohms), R16 (82 ohms) and PR1 (5 ohms), allows you to set the correct polarity of the output stages of the amplifier 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 the rest mode of the amplifier should be in the region of 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 swing a large enough 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 if the system is expanded with another pair of power transistors, due to differences in the resistance of the open channels of the transistors.
Resistors R5 (470 ohms) and R19 (470 ohms) limit the charging rate of the capacitance of the pass transistors, 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 power supplies for transistors should not be more than 12 V.
The amplifier board provides places for power filter capacitors C2 (4700 uF / 50 V) and C13 (4700 uF / 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 Ω / 1 V) and C12 (220 μF / 50 V).
Power supply for UMZCH
The amplifier circuit delivers power that reaches a real 100 watts (effective sinusoidal), at input voltage in the region of 600 mV and a load resistance of 4 ohms.
Amplifier Holton on the board with details The recommended transformer is a 200 W toroid with a voltage of 2x24 V. After rectification and smoothing, you should get two-polar power amplifiers in the region of +/-33 Volts. The design shown here is a very good performance MOSFET mono amplifier module that can be used as a standalone unit or as part of a .
Transistor amplifiers, despite the emergence of more modern microcircuit amplifiers, have not lost their relevance. Sometimes it’s not so easy to get a microcircuit, but transistors can be soldered from almost any electronic device, which is why avid radio amateurs sometimes accumulate mountains of these details. In order to find a use for them, I propose to assemble an unpretentious transistor amplifier power, the assembly of which will be mastered even by a beginner.
Scheme
The circuit consists of 6 transistors and can develop power up to 3 watts when powered by 12 volts. This power is enough to sound a small room or workplace. Transistors T5 and T6 in the circuit form an output stage, in their place can be put widespread domestic analogues KT814 and KT815. Capacitor C4, which is connected to the collectors of the output transistors, separates the DC component of the output signal, which is why this amplifier can be used without a speaker protection board. Even if the amplifier fails during operation and a constant voltage appears at the output, it will not go beyond this capacitor and dynamics speaker system will remain intact. Isolating capacitor C1 at the input is better to use a film one, but if this is not at hand, a ceramic one is also suitable. The analogue of diodes D1 and D2 in this circuit are 1N4007 or domestic KD522. The speaker can be used with a resistance of 4-16 ohms, the lower its resistance, the more power the circuit will develop.(downloads: 686)
Amplifier Assembly
A circuit is being assembled on a printed circuit board measuring 50x40 mm, a drawing in the Sprint-Layout format is attached to the article. The given printed circuit board must be mirrored when printing. After etching and removing the toner from the board, holes are drilled, it is best to use a 0.8 - 1 mm drill, and for holes for output transistors and a 1.2 mm terminal block.
After drilling the holes, it is desirable to tin all the tracks, thereby reducing their resistance and protecting the copper from oxidation. Then small parts are soldered - resistors, diodes, after which the output transistors, terminal block, capacitors. According to the diagram, the collectors of the output transistors must be connected, on this board this connection occurs by closing the “backs” of the transistors with a wire or a radiator, if used. A radiator must be installed if the circuit is loaded on a speaker with a resistance of 4 ohms, or if a high volume signal is input. In other cases, the output transistors almost do not heat up and do not require additional cooling.
After assembly, it is imperative to wash off the flux residues from the tracks, check the board for assembly errors or short circuits between adjacent tracks.
Amplifier tuning and testing
After the assembly is completed, you can supply power to the amplifier board. An ammeter must be included in the break of one of the supply wires to control the current consumed. We turn on the power and look at the readings of the ammeter, without applying a signal to the input, the amplifier should consume about 15-20 mA. The quiescent current is set by resistor R6, to increase it, you need to decrease the resistance of this resistor. You should not raise the quiescent current too much, because. heat generation at the output transistors will increase. If the quiescent current is normal, you can input a signal, for example, music from a computer, phone or player, connect a speaker to the output and start listening. Although the amplifier is simple in execution, it provides a very acceptable sound quality. To play two channels simultaneously, left and right, the circuit must be assembled twice. Please note that if the signal source is far from the board, it must be connected with a shielded wire, otherwise interference and interference cannot be avoided. Thus, this amplifier turned out to be completely universal due to low current consumption and compact dimensions of the board. It can be used both as part of computer speakers and when creating a small stationary music center. Happy assembly.The amplifier offered to your precious attention is easy to assemble, terribly easy to set up (it actually does not require it), does not contain particularly scarce components, and at the same time has very good characteristics and easily pulls on the so-called hi-fi, so dearly loved by most citizens .The amplifier can operate on a load of 4 and 8 ohms, can be used in bridging into a load of 8 ohms, while it will give 200 watts to the load.
Main characteristics:
Supply voltage, V ............................................... .................±35
Current consumption in silent mode, mA .................................. 100
Input impedance, kOhm .............................................. ........... 24
Sensitivity (100 W, 8 Ohm), V.................................................. ...... 1.2
Output power (KG=0.04%), W...................................... ........ 80
Reproducible frequency range, Hz .............................. 10 - 30000
Signal-to-noise ratio (not weighted), dB...................................... -73
The amplifier is completely on discrete elements, without any op amps and other tricks. When operating on a load of 4 ohms and a power supply of 35 V, the amplifier develops power up to 100 watts. If there is a need to connect an 8 ohm load, the power can be increased to +/-42 V, in this case, we will get the same 100 watts.It is strongly not recommended to increase the supply voltage more than 42 V, otherwise you can be left without output transistors. When operating in bridge mode, an 8-ohm load must be used, otherwise, again, we lose all hope for the survival of the output transistors. By the way, it must be taken into account that there is no protection against short circuit in the load, so you need to be careful.To use the amplifier in bridged mode, it is necessary to fasten the MT input to the output of another amplifier, to the input of which the signal is applied. The remaining input is closed to a common wire. Resistor R11 is used to set the quiescent current of the output transistors. Capacitor C4 determines the upper limit of the gain and you should not reduce it - get self-excitation at high frequencies.
All resistors are 0.25W except for R18, R12, R13, R16, R17. The first three are 0.5 W, the last two are 5 W each. The HL1 LED is not for beauty, so you do not need to stick a super-bright diode into the circuit and output it to the front panel. The diode should be the most common green color - this is important, since LEDs of other colors have a different voltage drop.If suddenly someone was unlucky and he could not get the output transistors MJL4281 and MJL4302, they can be replaced with MJL21193 and MJL21194, respectively.It is best to take a variable resistor R11 multi-turn, although a regular one is also suitable. There is nothing critical here - it's just more convenient to set the quiescent current.
Readers! Remember the nickname of this author and never repeat his schemes.
Moderators! Before you ban me for insults, think that you "let an ordinary gopnik to the microphone", who should not even be allowed close to radio engineering and, moreover, to teaching beginners.
Firstly, with such a switching scheme, a large D.C., 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 KΩ, connected in series with a variable one. Any do-it-yourselfer 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 (this should be explained by the author, because 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 at the output will work normally. And if it is not there, then the player's output 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 energized from the power source of this penny trinket and it can burn out. Homemade ones are very fond of removing protective resistors and capacitors, because "it works!" 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 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 out of the speaker. Therefore, it should never be accessible from the outside. It is IMPOSSIBLE to adjust the volume by changing the mode. For this you need to "kill". If you really want to adjust the volume, it's easier to turn on another variable resistor in series with the capacitor, and now it can already be output to the amplifier case.
In general, for the simplest circuits - and in order to work right away and not to damage anything, you need to buy a TDA-type chip (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 allowable current is as much as 8 amperes (it will burn any speaker without even noticing).
