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An instrument amplifier is an electronic amplifier designed for use with an electric or electronic musical instrument, such as an electric guitar.

1 Most common forms

Instrument amplifiers come in two main forms. The combo amplifier contains both the amplifier and suitable loudspeakers in a single unit. In the other form, the amplifier is separate from the loudspeakers, and joined to them by cables. The separate amplifier is called an amplifier head and is commonly placed on top of one or more loudspeaker enclosures, the amplifier head and loudspeaker enclosures together forming an amplifier stack.

An amplifier stack consisting of a head and two loudspeaker cabinets is sometimes called a double stack.

2 History

The first instrument amplifiers were guitar amplifiers designed for use with electric guitars. Traditional guitar amplifiers provided a great deal of treble boost, and no high treble or low bass response at all. Some better models also provided a spring reverb and/or an electronic tremolo unit which electric guitarists (following the lead of the Fender company) have confusingly always called vibrato (and similarly they call a device designed to produce real vibrato a tremolo arm, see electric guitar, tremolo).

In the 1960s guitarists experimented with distortion produced by deliberately overloading (or overdriving) their amplifiers. The Kinks guitarist Dave Davies was quoted as saying "you just turn it up and it sounds like that, s'loovly". At one stage Davies was producing distortion by connecting the output of one amplifier into the input of another, an abuse which the designers could never have imagined (but see Maton).

Later, many guitar amplifiers were provided with distortion controls, and fuzz boxes and other effects pedals were engineered to safely and reliably produce these sounds. Today distortion is an accepted part of nearly all styles of electric guitar playing.

Guitar amplifiers were at first used with limited success with bass guitarThe electric bass guitar is a stringed instrument similar to the electric guitar, but larger in size and with a lower range. It is also closely related to—and inspired by—the double bass, and shares things in common with a range of bass instruments. It iss and electronic keyboardElectronic keyboards include synthesizers (notably the Moog synthesizer), samplers and frequency divider organs. With the use of sampled sounds and MIDI, true synthesizers have become rare, and more and more the general term electronic keyboard is being us, but it was quickly recognised that other instruments had different requirements to the electric guitar.

3 Present day

A wide range of instrument amplifiers is now available, some general purpose and some designed for specific instruments and even for particular sounds. These include:

• Traditional guitar amplifiers, with a clean undistorted sound, a sharp treble roll off at 5KHz or less and bass roll off at 60-100Hz, and often built-in reverb and "vibrato" units.
• Rock-style guitar amplifiers, intended for distortion.
• Bass amplifiers, with extended bass response and tone controls optimised for bass guitars.
• Keyboard amplifiers, with very low distortion and extended, flat frequency response in both directions.
• Acoustic amplifiers, similar in many ways to keyboard amplifiers but designed specifically to produce an "acoustic" sound when used with acoustic instruments with built-in pickupThis article is about pickups for musical instruments. For a small truck used by both business and consumers, see pickup truck. For a scene which is filmed after the main production of a film has finished and which will be edited into the rest (commonly cs. (Note that there was once also a brand of guitar and bass amplifier called AcousticAcoustic Control Corporation was a manufacturer of instrument amplifiers, based at Van Nuys, California. They are particularly remembered for the 270-watt Acoustic 361 bass stack, consisting of an Acoustic 360 bass head and one or two Acoustic 301 W-bins,, still seen second-hand.)

Some amplifiers are designed to fill more than one of these roles, and may have multiple inputs.

Some also have a microphoneA microphone sometimes called a "mic" (pronounced "mike"), is a device that converts sound into an electrical signal. Microphones are used in many applications such as telephones, tape recorders, hearing aids and in radio and television broadcasting. input. Guitar amplifier inputs typically have an impedance of about 1 Meg ohm, which is not ideal for use with low-impedance (typically 600 Ω)microphones. When a low-impedance input is provided this will generally be a balanced input and easily identified because it will use an XLR connector. Phantom power is not often provided, restricting the choice of microphones for use with these inputs.