An amplifier uses a small input signal to create a large output signal, while minimizing distortion of the waveform. Amplifiers are used for both electrical and optical signals.

Working of an Amplifier

Modern amplifiers use solid-state electronics, although some are still made with vacuum tubes. A basic amplifier can be made with transistors, while complex amplifiers use other components, like op-amps, for feedback correction. To reduce the electrical noise, most amplifiers use toroidal transformers for their power supply.

Features of an Amplifier

The important features of an amplifier are its gain, linearity, noise and dynamic range.

  • Gain is a measure of an amplifier's power, the ratio of input to output power.
  • Linearity is a measure of how well the output signal stays proportional to the input signal.
  • Noise is the amount of static (unwanted interference) added to the input signal by the amplifier.
  • Dynamicrange is the useful part of the output signal, between the noise and distortion levels.

Amplifier Stages

A typical audio setup will have a power amplifier and usually a preamplifier before it. There may also be an equalizer after the power amplifier. These may be in separate cases, or bundled together with a receiver in one big case. The preamplifier takes the weak signal from an input device, usually a microphone or turntable, and increases its voltage level so that the power amplifier can use it. Some preamplifiers merely switch inputs without changing the signal. The power amplifier increases the current of the signal so that it can drive the speakers. If the signal is amplified too much, it becomes distorted and it may need to be filtered through an equalizer before going to the speakers.

Hi-Fi Amplifier

Hi-Fi is short term for high fidelity. It is a standard for audio equipment that aims for perfect frequency response and zero signal noise, although this is never achieved in practice. This term is used to represent the very best in audio equipment, but these days, even a sub-standard equipment is labeled hi-fi.