Principles[edit | edit source]
An amplifier uses a small weak electronic signal and a power supply to produce a larger strong signal. This task can be done the new way using solid-state devices usually called transistors or an older way using electron tubes, also called valves. Amplification can also be done in an even older way mechanically using a horn of some type as in the Victrola and similar devices. The principles of amplification are ancient as in the medical stethescope and who knows how far back?
- Wikipedia: An electronic amplifier is a device for increasing the power of a signal.
Types and kinds[edit | edit source]
All amplification methods have common aspects most of which are expressed as ratios:
- Gain - the ratio between input and output energy
- Signal to Noise - Generally, the ratio between harmonic content that is desireable to that which is undesirable
- Efficiency - An amalgamation of factors used to measure energy that is used productively or dissipated as heat or other incidental loss
- Frequency response - A measure of an amplifier's ability to respond to various types of periodic change.
- ...several others
Electronic amplification can happen over a wide band of frequencies and physical conditions ranging from audible sound to electromagnetic radiation. The design parameters and objectives of an amplifier circuit are methodically built to a variety of types and kinds. For this discussion, we shall begin with an elementary examination of the Audio Amplifier.
- Point to ponder: Can visible and invisible light be amplified? Some might argue that anything that can be modulated, can be amplified. spoil
Sound transducers[edit | edit source]
A sonic signal enters and exits an amplifier by means of a sound transducer. Input devices such as microphones, magnetic pickups and piezo-electric devices faithfully translate sound, mechanical vibration or other type of audible energy into variable electrical energy that can enter the input stage or circuit. Output devices for converting amplified electrical energy back into sound are most commonly called loudspeakers.
The first electronic amplifiers used evacuated glass tubes containing four basic types of conducting members:
- filament - also called heaters, these innermost elements usually composed of tungsten, emmited energy in the form of heat producing the orange glow seen from behind a vintage w:guitar amplifier.
- cathode - this electrode connected directly or through a resister to the negative side of a DC Power source supplies a stream of w:electrons knocked off of it by the heat from the filament toward an outermost electrode called the...
- plate - this electrode is connected to the positive side of the power supply through a resistive or inductive load componant used to develop the amplified power of the tube (valve).
- grid - One or more screen-like elements are placed between the cathode and plate and present to the tube an input signal that represents a varying voltage that is biased somewhere between the negative potential of the cathode and the positive postential of the plate.
The kinetic energy allowed to flow between the cathode and the plate varies indirectly but at the same rate as the potential energy on the grid. To understand the operation of an amplifier tube, one should thing in terms of voltage with repect to ground. In most classic tube designes, the negative side of the power supply was connected with the chassis of the aparatus which was in turn connected (for best results) to Earth ground. Earth ground is nearly always at a 0-volt potential, unless of course a lightning strike or other anomoly is nearby.