When shopping for an amplifier or a preamplifier for your home stereo system, you may run across the term "line level." Power amplifiers are designed to take line level signals and amplify them into a signal that can be translated to sound by a loudspeaker.
What is Line Level?
Line level describes the strength of an audio signal and is the signal an amplifier needs to be able to power a pair of speakers. Line level signals are put out by sources such as CD players, tape decks and DVD players. Other sources, such as turntables, microphones and instrument pick-ups output a different strength signal that needs a preamplifier to be line level.
Measurement
The measurement of consumer audio line level is -10dBV. Professional audio gear has a much higher line level reading, +4dBu, so that the signal will carry over long cable runs. The measurement dBV describes decibels above or below a reference voltage of one volt required to produce a milliwatt of power over a 1 kilohm load, while dBu is the power needed to produce a milliwatt of power over a 600 ohm load. So, -10dBV is equivalent to 0.316 volts, while +4dBu is 1.23 volts.
Preamplifier
The job of the preamplifier is to boost the signal of lower-level audio signals to line level. A phono preamplifier, in addition to boosting the signal to line level, also removes the RIAA (Recording Industry Association of America) curve applied to the record when it is cut to vinyl.
Connecting
Since CD players, DVD players and tape decks output a line level signal, it is technically possible to connect them directly to an amplifier. However, it is best to run through a preamp, which can function as a switcher, switching between the components, and also give the listener volume control.
Headphone Amplifiers
A headphone amplifier is designed to amplify a line level signal to power a pair of headphones. A headphone amp puts out a signal greater than a line level signal.
Tags: line level, level signal, line level, line level signal, level signals
