Modern electric guitar amplifiers are fascinating creations. The sheer quality and range of effects currently available is simply astounding. This article explains the basic components comprising the modern electric guitar amplifier followed by an explanation of how it works.
What's In The Box?
Electric guitar amplifiers consist of the following components.
A wooden box or cabinet which contains the following components. The loud-speaker (s), from 4-inches in diameter up to 18-inches in diameter in bass guitar amplifiers. A metal 'electronics-chassis', designed with either transistors in integrated circuit configurations, or utilizing the classic 'vacuum tube (s)'. Finally, the interconnecting wiring or circuit boards 'foil-paths', to facilitate mass-manufacturing.
Depending on the style of music played, an amplifier's design can incorporate many different types of loud-speakers, effects compliments and cabinet coversings. For an example, the standard Fender Twin-Reverb amplifier consists of two-each, 12-inch loud-speakers that can provide massive amounts of sound output, achieving 80+ watts of power or more in some models.
How Does It Work?
A guitar cord is plugged into the input jack on the guitar amplifier. The low-level signal (-10 decibels typically) present on this cord emanates from the pickup (s) mounted under the strings on the electric guitar itself. The vibrating strings, when the guitar is strummed or plucked, cause a magnetic-field excitement inside the pickup assembly.
The pickup assembly consists of one or more permanent magnets, surrounded by a coil of tiny wire in a continuous loop around the magnet (s). There are pole-pieces on each pickup assembly which are mounted within each pickup assembly, and provide the magnetic field for each of the electric guitar strings to excite.
The output from the pickups is sent to volume and tone-shaping control (s) mounted on the guitar, for bass and treble adjustments, and then to the output jack on the guitar. This jack is connected using a guitar cord, a standard 1/4-inch phone plug that is connected to the guitar amplifier input jack using the guitar cord's other end.
The signal at the input of the electric guitar amplifier enters a pre-amplifier stage, when the signal is boosted, any tone shaping such as bass-mid-treble, or effects for example 'reverb' or 'chorus' are applied, and then sent to the main power amplifier, where the signal is boosted many times louder than the original one coming from the guitar.
This is accomplished through the use of ever increasing 'power-handling' stages of amplification in the power amplifier, whether in transistor-based or vacuum-tube designs. The power amplifier's output is connected to loudspeakers, by heavy-gauge wiring, whose cone-assemblies move large volumes of air, matching the signals generated by the strings coming from the guitar.
So in summary, the guitar signal is introduced to a pre-amplifier by the input jack on the amplifier, then to tone-shaping circuits for bass-mid-treble and effects to be added to the guitar signal. This modified signal is then introduced to the power amplifier who job it is to cause the loud-speakers to deliver large-volume sound into the air.
The type of guitar amplifiers available today range from 1-watt to over 2,000-watts for a massive stadium show amplifier.
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