What Is a Power Amplifier and How Is It Used?

How it's different than a home theater receiver

A power amplifier is a type of amplifier that supplies power to one or more speakers; it does not 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 an power switch), is a primary gain control, which is analogous to volume.

Marantz MM8077 7-Channel Power Amplifier
Image provided by D&M Holdings

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, they may feature 5, 7, or more channels. When 9 channels are needed, a user may employ both 7 and 2 channel power amplifiers. When 11 channels are needed, a 7-channel amplifier is teamed with two 2-channel amplifiers. Some use a monoblock amplifier for each channel, which calls for a lot of amplifiers.

How to Connect a Power Amplifier

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

The AV preamp/processor decodes or processes audio source signals and passes them to the power amp, which, in turn, sends them 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.

The AV preamp/processor is where you connect your source components (Blu-ray, DVD, CD, media streamer, etc...).

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

Marantz AV7702mkII AV Preamp/Processor
Images provided by D&M Holdings

Power Amplifiers and Subwoofers

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

Onkyo TX-NR787 Dual Subwoofer Output
Onkyo USA

If the subwoofer is a passive type, a subwoofer preamp output needs to be connected to an external power amplifier (aka subwoofer amplifier). This type of amplifier is only used to power the subwoofer and should not power the rest of the speakers.

How to Use a Power Amplifier With a Home Theater Receiver

Although home theater receivers have built-in amplifiers to power speakers, some receivers provide preamp outputs that can be connected to one or more power amps to provide greater power output than its own built-in amplifiers may have. This turns the receiver into an AV preamp/processor.

In this type of setup, the receiver's internal amplifiers are bypassed. This means you can't use the built-in amplifiers of a home theater receiver and external power amplifiers for the same channels at the same time.

Home Theater Receiver with Multichannel Analog Audio Outputs

If a home theater receiver has Multi-Zone capability, then the Zone 2 (or 3,4) 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.

If the receiver provides 7.1 channels and has preamp outputs available to run a two-channel independent zone, 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.

Onkyo TX-NR787 Home Theater Receiver – Zone 2 Analog Audio Outputs
Onkyo

Power Amplifiers vs. Integrated Amplifiers

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

However, unlike a stereo or home theater receiver, an integrated amplifier does not 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".

Integrated amplifiers typically only support a two-channel speaker configuration with an A/B switch option.

Yamaha A-S701 Integrated Amplifier – Front and Rear Views
Yamaha

Why You Might Want to Use a Power Amplifier

In most home theater setups, and 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 a lot of heat. This means 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.
  • Even though a separate preamp and power amp results in more equipment and cable clutter, 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, but it may not meet current AV connectivity and processing standards. You may end up tossing out perfectly good amps, just to get all those newer features.