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A keyboard amplifier is a powered electronic amplifier and loudspeaker in a speaker cabinet used for the amplification of electronic keyboard instruments. Keyboard amplifiers are distinct from other types of amplification systems such as guitar amplifiers due to the particular challenges associated with making keyboards sound louder on stage; namely, to provide solid low-frequency sound reproduction for the deep basslines that keyboards can play and crisp high-frequency sound for the high-register notes. Another difference between keyboard amplifiers and guitar/bass amplifiers is that keyboard amps are usually designed with a relatively flat frequency response and low distortion. In contrast, many guitar and bass amp designers purposely make their amplifiers modify the frequency response, typically to "roll-off" very high frequencies, and most rock and blues guitar amps, and since the 1980s and 1990s, even many bass amps are designed to add distortion or overdrive to the instrument tone (for bass, this is called "fuzz bass").
Keyboard amplifiers differ from guitar amplifiers and bass amplifiers in that whereas guitar and bass amps are usually designed for use with one guitar at a time, keyboard amplifiers almost always have a mixer with inputs for two, three, or four keyboards, because many performers often use multiple keyboards. For example, a single player may perform with a stage piano, a keytar and a synthesizer keyboard. Each channel input typically has its own pre-amplifier and volume knob. Keyboard amps in the lower cost range and power output range may only provide equalization controls (for modifying the bass and treble response) for the overall mix. Higher-priced, higher power output keyboard amps designed for professionals may have equalizer controls for each channel. Keyboard amplifiers also differ from guitar amps and bass amps in that whereas many guitar and bass amplifier companies often sell standalone amplifier units (which contain a preamplifier and power amplifier) for use with one or more separate speaker enclosures, keyboard amplifiers are almost always combination (or "combo") amplifiers, so-named because they combine a preamplifier, power amplifier, full-range speaker, and a horn-loaded tweeter, all in a single wooden speaker cabinet.
Two notable exceptions to the "low distortion" rule are keyboard amplifiers designed for the Hammond organ or clonewheel organs and amps used with electric pianos such as the Fender Rhodes. With organs used in blues or hard rock, performers often use the vintage Leslie speaker cabinet and modern recreations, which have a tube amplifier which is often turned up to add a warm, "growling" overdrive to the organ sound. With electric pianos used in a rock or funk band, natural tube overdrive is often added to the sound.