What A Power Amplifier Is

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

The Home Theater Receiver Workhorse

In most home theater setups, a home theater receiver is used to provide all the connectivity and switching needed for source components, such as Blu-ray/DVD/CD players, Cable/Satellite Boxes, external media streamers, and a VCR (if you still have one), as well as providing all needed audio processing (and sometimes video processing), as well as providing power to your speakers.

That is definitely a lot for a single component to handle, and for some, separating the input switching and audio/video processing from the actual task of providing power for, and connection of, loudspeakers is best handled by a separate device.

The Separates Solution Alternative To The Home Theater Receiver

For those consumers, instead of a home theater receiver, a "separates" solution is employed in which a preamplifier or AV preamp processor handles all the input connection, switching and AV processing tasks, and the task of providing power to the speakers is handled by another external component referred to as a Power Amplifier.

The Power Amp

The power amplifier supplies power to a speaker or speakers but does not have any other functions, except, in some cases, a master gain control (gain is analogous to volume). However, volume control (as well as output level settings for each channel, is can be handled by a preamp or AV preamp/processor.

To get the audio signals to the Power Amplifier, the Preamp or AV preamp/processor provides line outputs in the form of either the familiar RCA-type connections or, in some higher-end preamp/power amplifier combinations, XLR connections. Both options transfer an analog audio signal that has already been processed by the Preamp or AV Preamp/Processor and is ready to be sent to the speakers.

Terminals, in turn, are provided to connect speakers to the power amplifier.

Power amplifiers come in several types of channel configurations, from one channel (referred to as a monoblock) to two (stereo) channels, or, for surround applications, 5, 7, or more channels. Sometimes, when, let's say 9 channels are needed, a user might employ both 7 and 2 channel power amplifiers and in the case where 11 channels are needed, a 7 channel amplifier is teamed with two 2-channel amplifiers. In fact, there are some that use a monoblock amplifier for each channel - Now that is a lot of amplifiers!

The Subwoofer Factor

However, in home theater applications, in addition to providing power to your speakers, you also have to take the subwoofer into account. If the subwoofer is powered (the most common type), then it has its own internal amp. If it a passive subwoofer then it would require power from a power amplifier, but usually, it is a specific type of power amplifier (referred subwoofer amplifier) that is only used to power the subwoofer and not used to power the rest of the speakers. Read more about the difference between Powered and Passive Subwoofers

Using A Home Theater Receiver As A Preamp In Combination With A Power Amp

Getting back to home theater receivers, although they provide their own built-in amplifiers that can power speakers, there are some (usually high-end) that also provide a set of preamp outputs that can be connected to one, or more power amps to provide a greater power output than its own built-in amplifiers may have, effectively turning the receiver into a preamp.

However, it must be noted that in this type of setup, the receiver's own internal amplifiers are bypassed - in other words, you cannot use the built-in amplifiers of a home theater receiver and external amplifiers to power the same channels at the same time.

Also, 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 amps(s) for powering a set of speakers that may be placed in a different location, while still retaining used of the receiver's own built-in amplifiers for use in the main zone.

For example, if the receiver is a 7.1 channel receiver and has preamp outputs available to run a two channel independent zone - then 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.