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Description

This article is from the Car Audio FAQ, by Ian D. Bjorhovde (ianbjor@mobileaudio.com) with numerous contributions by others.

3.31 What is a Line Driver? Do I need one? [LC,IDB]


A line driver is a device that amplifies a signal, such as the low-level
signal output from a head unit. Line drivers are made to amplify the
line level signal to as much as 10 volts or higher. This, of course, is
useless unless the receiving end can handle 10 volts as input. To solve
this problem, there are line receivers which bring the line level
voltage down from 10 volts or more to about 1 volt. Usually, the line
driver and receiver are placed as close to the sending signal source and
destination as possible, to minimize noise pick up.

The automobile is an inherently noisy electrical environment. So RCA
cables may pick up noise as it makes its way to the amplifier. Note
that noise here refers to the induced noise, not ground loop noise such
as engine whine. A simple way to fight against this noise is to make
the signal level carried in the RCA cable very high, thus increasing the
signal's resistance to induced noise and resulting in a higher signal to
noise ratio at the destination of the RCA cable. Most head units
produce a fairly low output voltage (< 1.5 V), although recently high
end head units advertise 4 volt or higher output, and won't usually need
a line driver.

Read more: 3.31 What is a Line Driver? Do I need one? [LC,IDB]

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The other advantage to having a higher line voltage from your pre-outs is a higher resolution signal. The more amplitude (Y axis) you have in your source signal, the more detail you'll be able to squeeze into that waveform. Think of it like zooming in on a JPG image. If the original image is high resolution to start with, then when you expand the image to a larger size (as the amplifier does with the audio signal) then your resulting, larger image will be sharper, whereas if the original image is a low resolution thumbnail type image, then when it's enlarged, the image will not be as clear or detailed.

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