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At the most basic level, a signal amplifier does exactly what you expect – it makes a signal
bigger! However, the way in which it is done does vary with the design of the actual amplifier,
the type of signal, and the reason why we want to enlarge the signal. [1] We can illustrate this by
considering the common example of a “Hi-Fi” audio system.
In a typical modern Hi-Fi: system, the signals will come from a unit like a CD player, FM
tuner, or a Tape/Minidisk unit. The signals they produce have typical levels of the order of
100 mV or so when the music is moderately loud. This is a reasonably large voltage, easy to
detect with something like an oscilloscope or a voltmeter. However, the actual power levels of
these signals are quite modest.