What Does a Stereo Amplifier Do? | Powering Your Speakers

Every music system with passive speakers has one. The stereo amplifier takes the small signal from your turntable, CD player, computer, or phone and increases its voltage and current until it can physically move the speaker drivers. Understanding what a stereo amplifier does matters when you’re piecing together a system, matching components, or wondering why your records sound thin.

The Core Job: Amplification

A stereo amplifier does one primary job: it increases the amplitude of an electrical audio signal. Sources like CD players and turntables output a very weak line-level signal—roughly 150 millivolts to 2 volts. That’s not enough to drive a speaker. The amplifier’s power stage boosts that signal to around 20–40 volts at speaker level, supplying the current that moves the drivers.

Here’s the sequence inside the box:

• The source sends a low-power audio signal into the amplifier.
• The preamp section selects the input and applies volume, tone, and balance controls.
• The power amplifier stage increases the signal’s voltage and current.
• The output drives the passive speakers, which convert electricity into sound.

It’s two-channel by design, meaning it powers a left and right speaker for proper stereo imaging.

Integrated Amplifier vs. Power Amplifier vs. Receiver

These three terms cause the most confusion. An integrated amplifier combines the preamp and power amp in one chassis. The preamp lets you switch between sources and provides volume, tone, and phono equalization. A power amplifier alone only amplifies—it has no input switching or volume control. A stereo receiver is an integrated amplifier with a built-in radio tuner.

An AV receiver is a different category entirely. It handles multi-channel surround sound and video switching, whereas a stereo amplifier focuses on two-channel audio only. If you need surround sound, a stereo amp is the wrong choice.

Phono Inputs and Speaker Compatibility

Turntables need special handling. A turntable’s cartridge produces a very low signal that requires equalization (RIAA curve) before it sounds correct. Some stereo amplifiers include a phono input with this built in. If yours doesn’t, you need a separate phono preamp—without it, vinyl playback sounds thin, quiet, and wrong.

Speaker matching matters too. Passive speakers require external amplification; powered speakers have amps built in and don’t need a stereo amplifier at all. For the listening side, the amplifier also regulates power delivery, preventing distortion and potential speaker damage when levels stay within reasonable limits.

FAQs

Is a stereo amplifier the same as a receiver?

Not exactly. A stereo receiver is a stereo amplifier with a built-in AM/FM tuner. If you don’t listen to radio, an integrated amplifier gives you the same two-channel performance without paying for a tuner you won’t use.

Can I connect a turntable to any stereo amplifier?

Only if the amplifier has a phono input. Many modern amps skip it. Without phono equalization, a turntable sounds quiet and thin. You’ll need an amp with a phono stage or a separate phono preamp between the turntable and any line-level input.

Do I need a stereo amplifier if my speakers are powered?

No. Powered speakers have their own built-in amplification. A stereo amplifier only adds value with passive speakers that need an external source of power to produce sound.