1 – Amplifying signals

Publisher Summary The purpose of an electronic amplifier is to make an electronic signal bigger without affecting it in any other way. Before considering exactly what is implied by this statement, the nature of a typical electronic signal must be understood. The first point is that a signal is a current, which varies in size and possibly in direction from instant to instant. When the signal represents a sound, the current changes too rapidly to be measurable with an ammeter. One way of examining it is to pass it through a resistor and connect an oscilloscope across it. According to Ohm's Law, a current flowing through a resistor causes a potential difference to appear between its two ends and that potential difference is exactly proportional to the current. The oscilloscope responds rapidly to the changing voltage and produces its display. If the sound is that of a clarinet, for example, a line with a very complicated shape can be seen.