Multiple meanings, but in hi-fi generally refers to a separate section of circuitry that includes source switching, volume and balance controls (as well as tone controls in many cases). Used to raise the level from tape decks, turntables, CD players and other music sources to a level suited to the power amplifier.

being still or at rest, in an inactive state. The quiescent current in an amplifier is that current drawn when the amplifier is "at rest" - i.e. not amplifying a signal, but supplied with power.

Silicon (or various other materials) that are specially treated so as to form diodes, transistors, MOSFETs, light emitting diodes (LEDs) etc. The basis of all modern electronics.

the sum of all amplifier distortion components, plus system noise. THD measurements are sometimes quoted as THD+noise. Usually measured at specified frequencies and power levels.

a situation that occurs in conductors that are close to another conducting material. For example, a coaxial cable has an inner and outer conductor, with insulation between the two. The velocity factor of such cables varies from 0.7 to 0.9 (i.e. the signal travels slower than in free space).

The basic unit of power. 1 Volt across 1 Ohm (giving 1 Amp) dissipates 1 Watt (all as heat with a resistive load).

[A]  [B]  [C]  [D]  [E]  [F]  [G]  [H]  [I]  [J]  [K]  [L]  [M]  [N]  [O]  [P]  [Q]  [R]  [S]  [T]  [U]  [V]  [W]  [X]  [Y]  [Z]

A current whose polarity alternates from positive to negative over time. The rate of such "alternations" is measured in cycles per second - more commonly known as Hertz (Hz)

a measurement of the capacity of a storage medium (a single cell or a battery). A cell which can supply 1 Amp for 1 hour before it is discharged to a specified minimum level is said to have a capacity of 1 Amp hour

An electronic device which generates a high power signal based on the information supplied by a lower powered signal. A perfect amplifier would add or subtract nothing from the original except additional power - these have not been invented yet