An amplifier, or amp, is used in almost every electronic audio device with a speaker. Amplifiers make a stronger, larger version of an audio signal out of a weaker, smaller signal. When sound is generated or translated by an electronic device, the signal is often weak. In the device, the sound is simply an electronic signal, but in order for someone to hear it, the sound must be translated into a sound wave. Small amplifiers are used in items like telephone receivers and speaker phones; large amplifiers are used in stadium sound systems to allow thousands of people to hear a broadcast.
A sound wave is a physical change in pressure caused by vibrations. When something moves, it affects the air pressure around it as it moves in a series of waves; the ear detects the changes in pressure and interprets the variations as audible sound.
In an electronic audio device such as a radio or stereo, the signal is sent to a speaker to transform it into an audio wave and emit it so the ear can hear it. A traditional speaker uses a cone or dome that vibrates to cause the air pressure to change, creating audible sound. In order to control a speaker, the sound waves must be powerful enough to cause strong vibrations. An amplifier makes this possible.
An amplifier consists of two major components: a power supply that provides the energy to the signal and an amplifier that modifies the actual signal. The power supply takes energy from a battery or household current and smoothes it into an uninterrupted source of energy; the energy is used to move the speaker cones to create the physical sound wave.
This energy transmission is the output signal from the amplifier. The amplifier takes in an audio signal, known as the input signal, and processes it using an electronic device called a transistor. The transistor contains semiconductors; these relay electric currents at varying rates through the transistor.
By varying the current, the transistor helps the amplifier to mimic the original sound signal as closely as possible while increasing its strength. The transistor controls the energy contained in the output from the amplifier. Most amplifiers use multiple transistors to increase signals multiple times.
Different amplifiers are used for different goals. In general, it is important for an amplifier to create a sound that is true to the original audio signal without distorting it, varying it, or adding extra noise. Often additional electronic components such as capacitors and inductors are used to temper the output, for example by adjusting the speed.
A capacitor can hold energy and release it all at once; an inductor can resist a flow of energy by using a magnetic field. The combination of a capacitor and an inductor is known as an oscillator. Oscillators are useful for controlling the rate at which energy moves through the amplifier.
Amplifiers can be used to increase any electrical signal not just audio signals. So, many electronic devices use amplifiers to boost a signal as it is translated through the parts of the device.