Hence we will require some form of Power Amplifier to 'boost' the signal power level from the source and make it big enough to play the music. This means we have to have some way of adjusting the overall Gain of the system. Sometimes all these functions are built into the same piece of equipment, however is often better to use a separate box which acts as a Pre-Amp to select inputs, adjust the volume, etc. In fact, even when built into the same box, most amplifier systems use a series of 'stages' which share the task of boosting and controlling the signals. The system shown in figure 1.2 is similar to the previous arrangement, but in this case is used for taking signals from microphones and 'mixing' them together to produce a combined output for power amplification.
Microphones tend to produce very small signal levels.
This is similar to many other forms of sensor employed by scientists and engineers to measure various quantities. It is usual for sensors to produce low signal power levels. So low, in fact, that detection and measurement can be difficult due to the presence of Noise which arises in all electronic system. For that reason it is a good idea to amplify these weak, sensor created, signals, as soon as possible to overcome noise problems and give the signal enough energy to be able to travel along the cables from the source to its destination. Due to the range of tasks, amplifiers tend to be divided into various types and classes.