Transistor Audio Amplifier

The transistor amplifiers, despite the appearance of more modern ICs, have not lost their relevance. Sometimes it is not so easy to get a microcircuit, but transistors can be evaporated from almost any electronic device, which is why inveterate radio amateurs sometimes have mountains of these parts. In order to find an application for them, I propose to build a simple transistor power amplifier, the assembly of which even a beginner can master.

Circuit

Transistor Audio Amplifier
The circuit consists of 6 transistors and can develop a power of up to 3 watts when powered by 12 volts. This power is enough to sound a small room or workplace. Transistors T5 and T6 on the circuit form the output stage, in their place you can put the common domestic counterparts KT814 and KT815. The 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 the 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 the speakers of the speaker system will remain intact. Separation capacitor C1 at the input is better to use a film, but if this is not at hand, the ceramic one will do. The analogue of the diodes D1 and D2 in this scheme 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. The
Transistor Audio Amplifier

Amplifier Assembly

A circuit is assembled on a PCB with dimensions of 50x40 mm, a picture in Sprint-Layout format is attached to the article. Given the printed circuit board when printing is necessary to mirror. After etching and removing toner from the board, the holes are drilled, it is best to use a 0.8–1 mm drill bit, and for holes for output transistors and a terminal block of 1.2 mm.
Sound amplifier transistors
After drilling the holes, it is desirable to trick all the tracks, thereby reducing their resistance and protect the copper from oxidation.Then soldered small parts - resistors, diodes, followed by output transistors, terminal board, capacitors. According to the scheme, the collectors of the output transistors must be connected; on this board, this connection is made by closing the backs of the transistors with a wire or a radiator, if used. The radiator should be installed in the event that the circuit is loaded on a speaker with a resistance of 4 Ohms, or if a large volume signal is input to the input. In other cases, the output transistors almost do not heat up and do not require additional cooling.
Audio Transistor Amplifier
Sound amplifier on transistors
After the assembly, it is necessary to wash off the flux residues from the tracks, check the board for assembly errors or short circuits between adjacent tracks.

Configure and test the amplifier

After the assembly is completed, you can power up the amplifier board. In the gap of one of the supply wires you need to include an ammeter to control the current consumption. We supply power and look at the readings of the ammeter; without applying a signal to the input, the amplifier should consume approximately 15-20 mA.The quiescent current is given by resistor R6; to increase it, the resistance of this resistor must be reduced. It is not necessary to raise the quiescent current too much, because the heat release at the output transistors will increase. If the quiescent current is normal, you can send a signal to the input, for example, music from a computer, phone or player, connect a speaker to the output and start listening. Although the amplifier is simple to perform, it provides a very acceptable sound quality. To play simultaneously two channels, left and right, the circuit must be assembled twice. Please note that if the signal source is far from the board, you need to connect it with a shielded wire, otherwise you will not be able to avoid interference and interference. Thus, this amplifier turned out to be completely universal due to the small current consumption and compact dimensions of the board. It can be used as part of computer speakers, and when creating a small stationary music center. Successful assembly.


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