Amplifiers and Audio Amplifier Technology

An amplifier is a circuit that increases the power, voltage or current of a signal while preserving its shape as faithfully as possible. The ratio of output to input is the gain, and an ideal amplifier multiplies the signal by a constant factor across its whole operating range. In audio, amplifiers are arranged in stages: low-level preamplifier stages raise weak signals from sources such as microphones, and a power amplifier finally drives the loudspeaker with enough current and voltage to move its cone.

Several properties define how well an amplifier performs. Bandwidth is the range of frequencies it reproduces accurately, and distortion measures how much it alters the waveform. The biasing of the transistors sets their operating point and strongly influences both linearity and efficiency, which is the basis of the amplifier classes A, AB, B, C and D. The Miller effect describes how the feedback capacitance of an amplifying device appears magnified at the input, reducing high-frequency response, an effect designers must account for in wideband stages.

Practical power amplifiers must also deal with heat and load matching. Because output devices dissipate power, they are mounted on heatsinks that carry the heat away and keep the junction temperature within safe limits. Amplifier bridging combines two channels to drive a single load with a larger voltage swing, increasing the available power. Levels and ratios throughout the design are commonly expressed in decibels, including units such as dBm and dBV that are referenced to fixed power or voltage values.

Frequently asked questions

What is amplifier gain?

Gain is the ratio of the output signal to the input signal. It expresses how many times larger the amplifier makes the voltage, current or power of the signal.

Why do power amplifiers need heatsinks?

Output transistors dissipate part of the supply power as heat. A heatsink conducts that heat away and keeps the devices within their safe operating temperature.

What does amplifier bridging do?

Bridging combines two amplifier channels to drive one loudspeaker with a larger voltage swing, which increases the power delivered to that single load.