An amplifier is used to boost the power of a weak signal, usually an audio signal. The most commonly known, and usually the most important type, is the electronic amplifier. These are used in a variety of machines, ranging from television and radio receivers to radar and HiFi systems.
All electronic amplifiers operate in a very similar way. However, they can vary greatly in their design and capabilities with regard to the degree of amplification which they can produce.
The heart of the amplifier is a series of transistors, sometimes
many thousand contained in a single integrated circuit or `chip'. These transistors are supported by other electronic components such as resistors, capacitors and diodes to construct the complete amplifier which usually includes circuits for tone and volume control.
The transistor operates as a variable switch. The flow of a small current through one part, can be utilised to control the flow of a larger one passing at another point. This means that when the smaller current flows, the larger one, which is drawn from a separate power source, will automatically flow too. Likewise, if the small current flow stops the larger one is shut down. This reaction guarantees that by proportion, the larger current is kept constant to the smaller one, the larger current being an amplified mirror image.
Using this technique, the very small signals received from, for example, a record deck, can be amplified many thousands of times to drive the speaker system connected to the amplifier.
