In this final paper, transistor power amplifiers and their classes are described. Given that transistor circuits in the connection of a common emitter or source are most often used in the construction of audio amplifiers, I decided to describe their principle of operation. When dividing amplifiers by class I listed their advantages and disadvantages and explained the principle of operation so that the user of the circuit from chapter no. 4 had a better understanding of the operation of the circuit. We have described class A, B and AB amplifiers in more detail because these classes have the widest application in audio amplifiers. We managed the maintenance of the static operating point in the designed circuit through a negative feedback connection with the inverting operational amplifier, whose principle of operation is described in chapter no. 3. Simulation of the circuit from chapter no. 4 was performed in the Electronics Workbench program, where we used an oscilloscope to measure the input and output signal of the circuit and the negative feedback signal. Using simulation, we measured the output current and voltage gain of the circuit, in order to determine the value of the passive components needed to power a 5 Ω consumer with 10 W of effective output power.