A car stereo amplifier is a device installed in a car that receives a low-input audio signal and increases its amplitude, boosting the signal and making it stronger. This amplifier specifically receives its power from the car's deck or head unit and gives it more power before sending the signal to the car's speakers. Even the most basic of car stereos often include an amplifier, usually built into the head unit. Higher grade car stereo amplifiers are generally mounted externally, sometimes beneath the seat or in the trunk. These amplifiers generally provide more boost than built-in amplifiers and achieve a higher quality audio signal with more power.
Amplifiers are rated by wattage, which refers to the device's power level. Entry-level stock amplifiers are often rated at less than 50W, except in the case of premium original equipment manufacturer (OEM) sound systems. A number of companies specializing in stereo or car audio equipment manufacture OEM sound systems for car manufacturers. A premium car stereo amplifier is usually rated much higher, often at 200W or more.
The installation of externally-mounted car stereo amplifiers is one of the most common forms of automotive customization. Car audio enthusiasts often install external amplifiers in conjunction with upgraded speakers and a new head unit. The end result is a fully customized car sound system. A premium or aftermarket car stereo amplifier often includes a built-in fan cooling system, because of the excessive heat generated by the high powered systems. If the cooling system fails, the amplifier could overheat and cause a fire hazard.
A high-powered car stereo amplifier is not all that's needed to achieve a high-quality car audio system. This is why car stereo amplifiers are often installed alongside new speakers and head units; a high-quality amp will not overcome low-quality speakers or head unit. In some cases, the amp may be too powerful for the other components, resulting in distortion and poor audio quality.
Car stereo amplifier installation is usually taken care of by a car sound shop or an independent car audio technician. Consumers can install the systems on their own, but the process requires more than simply plugging in a few wires. Generally, when installing an aftermarket amplifier, a wiring guide must be used to ensure the amplifier's wires are correctly attached to the existing wires in the car stereo system.