An instrument amplifier is an electronic amplifier designed for use with an electric or electronic musical instrument, such as an electric guitar or electric piano/keyboard. 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.
The first instrument amplifiers were probably 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 Fender) have confusingly always called vibrato, and similarly they call a device designed to produce real vibrato a tremolo arm. Nowadays called a whammy bar)
Guitar amplifiers were at first used with limited success with bass guitars and electronic keyboards, but it was quickly recognized that other instruments had different requirements to the electric guitar. A wide range of instrument amplifiers are now available, some general purpose and some designed for specific instruments, and even for particular sounds.
- 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 optimized 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 pickups.