The most common way to build amplifiers is by using transistors. Depending on topology, the amplifiers can be voltage or current ones. For power amplifiers we need both voltage and current gain, therefore we use several amplifiers (stages) connected in cascade. Three main stages are usually used: input stage, voltage amplifier stage (VAS) and current amplifier stage (output stage). Special type of power amplifiers are audio power amplifiers that are optimized for driving loudspeakers and for amplifying frequency band that humans can hear. Audio amplifiers can come in different forms, but what makes them different from one another is a way how current amplifier stage is designed. That defines amplifier class. Push-pull configuration is most commonly used as it enables B and AB class amplifiers to be used as audio amplifiers, and it also improves class A amplifiers efficiency. For small output power, an amplifier can be made with a simple common collector or, rarely, a common emiter topology. For larger output power we use drivers, smaller signal transistors with greater current gain that drive large output power transistors. Output transistors and drivers can be arranged in three basic configurations: double common collector (Darlington configuration), complementary feedback pair (CFP) and quasi-complementary pair. CFP configuration is the most linear with the smallest distortion level. On the other hand, quasi-complementary pair is the worst one regarding distortion. Two amplifiers with double common collector topology, one class A and one class AB, were built as part of this thesis so we could compare them. Simulations and measurements confirm that class A amplifiers are more linear, therefore they produce less harmonic distortion, but with cost in terms of efficiency and large heatsink. Both amplifiers sound well connected to the speakers, but class A amplifiers are better options for audiophiles, although special conditions are necessary to distinguish two well-made class A and AB amplifiers.