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The amplifier
All car audio systems have an amplifier, even if it's a small one (and based upon the factory systems we've been listening to lately, a lot of them are really dinky).
Occasionally the amplifier will be attached to the rear of the head unit; however, in most systems it is hidden elsewhere in the car to better dissipate heat.
Signal amplification is actually a two-stage process, handled by two separate components. These are the preamplifier and the power amplifier.
The preamplifier (preamp, for short) is like that little voice whispering in your ear not to eat ice cream at midnight. It's a very tiny signal coming directly from the radio (in fact, the preamp resides inside the head unit). Whether it's reproducing a cassette signal, a CD signal, or an FM broadcast, the preamp puts out a signal inaudible to the human ear. This is where the power amplifier takes over.
It's the power amp's job to take the signal from the preamp and boost it into the audible range. We'll cover this in more depth in our Amplifier column in this series. Again, because of heat, most amplifiers are located away from the head unit.
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