What Is a Power Amplifier and How Is It Used?

A power amplifier is a type of amplifier that supplies power to one or more speakers. It doesn't have the extra features and connections you often find on a home theater receiver, such as a radio, input source switching, and audio/video (AV) processing. The only control you typically find on a power amplifier (apart from a power switch) is a primary gain control, which is analogous to volume.

Power Amplifier Channel Configurations

Power amplifiers come in several channel configurations, from one channel (referred to as a monoblock) to two (stereo) channels. For surround applications, power amplifiers may feature five, seven, or more channels.

When nine channels are needed, both seven and two-channel power amplifiers may be employed. When 11 channels are needed, a seven-channel amplifier is teamed with two two-channel amplifiers. A monoblock amplifier can be used for each channel, which calls for a lot of amplifiers.

How to Connect a Power Amplifier

A separate preamp or AV preamp/processor is required to get audio signals to a power amplifier.

The AV preamp/processor decodes or processes audio source signals and passes the signals to the power amp, which, in turn, sends the signals to the speakers. The signals are passed in analog form via line outputs using RCA-type connections or, in some higher-end preamp/power amplifier combinations, XLR connections.

Here is an example of a preamp/processor showing its source and line-out connections. Note there are no speaker connections.

Power Amplifiers and Subwoofers

For home theater, in addition to source devices and speakers, consider a subwoofer. If the subwoofer is self-powered (the most common type), it has an internal amp. To get sound to a powered subwoofer, connect a provided subwoofer preamp output from an AV preamp/processor or home theater receiver.

If the subwoofer is a passive type, connect a subwoofer preamp output to an external power amplifier (also called a subwoofer amplifier). This type of amplifier only powers the subwoofer and should not power the rest of the speakers.

How to Use a Power Amplifier With a Home Theater Receiver

Home theater receivers have built-in amplifiers to power speakers. Still, some receivers provide preamp outputs that can connect to one or more power amps to provide greater power output than the built-in amplifiers may have. This turns the receiver into an AV preamp/processor.

Suppose a home theater receiver has multi-zone capability. In that case, the Zone 2 (or 3 or 4) preamp outputs can be connected to an external power amp to power a set of speakers placed in different locations while using the receiver's built-in amplifiers for the main zone.

Suppose the receiver provides 7.1 channels and has preamp outputs available to run a two-channel independent zone. In that case, you can operate the main 7.1 channel zone and the 2-channel second zone at the same time, taking advantage of additional power amps connected to speakers in the additional zone.

Power Amplifiers vs. Integrated Amplifiers

An integrated amplifier differs from a power amplifier. The integrated amplifier features source input connectivity and switching, varying degrees of audio decoding or processing, and a built-in amplifier for powering speakers.

However, unlike a stereo or home theater receiver, an integrated amplifier doesn't receive AM/FM radio transmissions. In rare cases, it may be able to stream music from the internet. Such amplifiers are marketed as streaming amplifiers.

Why You Might Want to Use a Power Amplifier

In most home theater setups, an AV receiver provides the connectivity and switching for source components, all audio processing (and sometimes video processing), as well as power to the speakers. That's a lot for a single device to handle.

Some users prefer to separate input switching and AV processing from the task of providing power for, and connection of, loudspeakers through separate AV preamp/processors and power amplifiers.

Here are a few more points to consider:

• Amplifiers generate heat. Housing the amplifier circuitry and power supply in a separate device may be desired, rather than cramming it in the same cabinet as other receiver-type functions, especially when lots of amplifier output power is needed.
• A separate preamp and power amp results in more equipment and cable clutter. Still, more flexibility is provided as power amps don't go out of date as quickly as a preamp might.
• An older home theater receiver may have perfectly fine built-in amps. However, it may not meet current AV connectivity and processing standards. You may end up tossing out perfectly good amps to get newer features.