A power amplifier is a hi-fi component that increases the power of an audio signal so that it can drive passive loudspeakers. It takes a relatively low-level signal from a preamplifier or another compatible source and produces a much more powerful electrical signal for the speakers.
In a traditional separates hi-fi system, the preamplifier and power amplifier perform different jobs. The preamplifier handles source selection and volume control, while the power amplifier provides the current and voltage required to operate the loudspeakers.
The amplified signal is sent from the power amplifier to the loudspeakers through loudspeaker cables. Inside each speaker, the electrical signal causes the drivers to move, converting the signal into the sound waves that we hear.
Power amplifiers are available with different numbers of channels. A stereo power amplifier contains two amplification channels, one for the left loudspeaker and one for the right. Mono power amplifiers, sometimes called monoblocks, provide a single amplification channel, so two are normally required for a stereo system.
The output of a power amplifier is commonly specified in watts per channel into a particular loudspeaker impedance, such as 8 ohms or 4 ohms. Power ratings can help when matching an amplifier with loudspeakers, although wattage alone does not determine an amplifier's performance or sound quality.
Different power amplifiers also use different amplifier designs and operating classes. Common examples include Class A, Class AB and Class D, each of which uses a different approach to amplification and has its own characteristics in areas such as efficiency, heat generation and power output.
Some power amplifiers offer balanced XLR inputs as well as conventional RCA connections. Other features can include multiple sets of speaker terminals, trigger connections and the ability to operate in bridged or mono configurations.
A power amplifier differs from an integrated amplifier because it generally does not provide the same level of source selection and volume control. An integrated amplifier combines a preamplifier and power amplifier within a single component, while a separate power amplifier concentrates primarily on supplying power to the loudspeakers.
The power amplifier is therefore a fundamental part of many separates-based hi-fi systems. Its role is to take the audio signal provided by the preceding components and amplify it sufficiently to control the loudspeakers and reproduce music at the required listening level.