music setting, which typically aim for a relatively flat frequency response (i.e., no added colouration of the sound) and little or no distortion of the signal. Types Guitar amplifiers A guitar amplifier amplifies the electrical signal of an electric guitar (or, less commonly, with acoustic amplifiers, an acoustic guitar) so that it can drive a loudspeaker at sufficient volume for the performer and audience to hear. Most guitar amplifiers can also modify the instrument's with controls that emphasize or de-emphasize certain frequencies and add electronic effects. String vibrations are sensed by a suitable microphone or pickup, depending on the type of guitar. For electric guitars, strings are almost always made of metal, and the pickup works by electro-magnetic induction (these are called magnetic pickups; they are the most widely used type of pickup on electric guitars). Acoustic guitars do not usually have a built-in pickup or microphone, at least with entry-level and beginner instruments. Some acoustic guitars have a small condenser microphone mounted inside the body, which designed to convert acoustic vibrations into an electrical signal, but usually they do so from direct contact with the strings (replacing the guitar's bridge) or with the guitar's body, rather than having a membrane like general-purpose microphones. Acoustic guitars may also use a piezoelectric pickup, which converts the vibrations of the instrument into an electronic signal. More rarely, a magnetic pickup may be mounted in the sound hole of an acoustic guitar; while magnetic pickups do not have the same acoustic tone that microphones and piezo pickups can produce, magnetic pickups are more resistant to acoustic feedback. Standard amps Standard amplifiers, such as the Fender "tweed"-style amps (e.g., the Fender Bassman) and Gibson amps, are often used by traditional rock, blues, and country musicians who wish to create a "vintage" 1950s-style sound. They are used by electric guitarists, pedal steel guitar players, and blues harmonica ("harp") players. Combo amplifiers such as the Fender Super Reverb have powerful, loud tube amplifiers, four 10" speakers, and they often have built-in reverb and "vibrato" effects units. Smaller guitar amps are also available, which have fewer speakers (some have only one speaker) and lighter, less powerful amplifier units. Smaller guitar amps are easier to transport to gigs and sound recording sessions. Smaller amps are widely used in small venue shows (nightclubs) and in recordings, because players can obtain the tone they want without having to have an