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preamplifier
Preamplifier. A device used in a stereo or multichannel system that selects from multiple inputs, control level to the system and is typically placed between the sources (CD, tuner, phono, DVD player) and the power amplifier.
A preamplifier can be broken down into its component sections quite easily. Typically, there is the input selection stage first. The input selection stage is usually nothing more that a number of input connectors, either RCA or Balanced (XLR), and a switch arrangement set up to choose one of the inputs (such as phono, tuner, tape, etc.). Once an input has been selected, it next goes to the volume and balance control.
These simple variable resistive elements (potentiometers or pots) vary the resistance the signal goes through thus making the level of the signal go higher or lower depending on the direction the control is turned.
If the preamp in question is a passive preamp (or ‘pots in a box’), the signal is then routed either through an electronic buffer or straight out to a set of jacks to meet the outside world. This type of arrangement has no gain. In other words, whatever level of signal goes into the passive preamp is the highest level that can come out. even if the volume control is turned all the way up.
A standard preamplifier, though, has a gain stage. This can be either a tube gain stage or a transistor gain stage, and there are literally hundreds of different designs to accomplish this. These gain stages provide amplification of signal, so output signals can be stronger than the signal fed into the inputs, depending on the volume control settings.
