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A line amp is a small electronic amplifier placed in line with an existing audio or video signal path to compensate for weak signals or signal losses. For example, a sound system in a large building may consist of a CD/DVD player with an amplifier that channels music via cables to speakers placed throughout the facility. If the rooms at the far end of the complex are experiencing a lack of volume or sound quality due to signal losses caused by lengthy cable runs, a line amp may be used to boost the signal. The line amp would be placed in line with the speaker cables. Line amps may require a separate alternating current (AC) power supply or be battery operated.
Line amps are typically used to boost audio or video signals in domestic or commercial applications where the signal source and the end destination are separated by long lengths of cabling which rob the signal of power and quality. They can, however, be used successfully where the signal source is weak to begin with as is the case with bad TV reception. A line amp placed in line with the TV antenna coaxial cable can boost the signal to give far better reception.
The same principle applies to audio signals from weak sources. A common application of line amps in this regard is the headphone amplifier used to boost the signal to a set of headphones. Many musicians use a headphone amp to practice in environments where noise needs to be kept at a minimum. A guitar, for example, can be plugged into the input side of the line amp and the headphone jack into the output side. The resultant boost in signal allows the guitarist to practice without disturbing others.
The line amp is also often used in fairly high-tech applications such as L-band line amps used to boost satellite feed signals for commercial and military use. These line amps tend to be far more sophisticated, rack mount units with more complexity than the small in line amps. The basic principles are the same, however. These high-end amps usually also fulfill several other functions such as signal modification.
Another amplifier type that may be classified as a line amp is the audio pre-amplifier. The pre-amp is used to give weak audio signals such as those produced by acoustic instruments a boost in signal strength before they reach a venue's public address (PA) system. Pre-amps are also often used to increase the signals of microphones in the same way. They all, however, fulfill the same function of strengthening weak signals or compensating for signal losses in extensive cabling systems.