A power trio is a rock and roll band format having a lineup of electric guitar, bass guitar and drum kit (drums and cymbals), leaving out the second rhythm guitar or keyboard instrument (e.g., Hammond organ) that are used in other rock music bands that are quartets and quintets. Larger rock bands use one or more additional rhythm section to fill out the sound with chords and harmony parts.
Most power trios in hard rock and heavy metal music use the electric guitar player in two roles; during much of the song, they play rhythm guitar, playing the chord progression for the song and performing the song's important riffs, and then switching to a lead guitar role during the guitar solo. While one or more band members typically sing while they play their instruments, power trios in hard rock and heavy metal music generally emphasize instrumental performance and overall sonic impact over vocals and lyrics. An example of a power trio is Motorhead, which consisted of a bassist, guitarist and drummer, with Lemmy, the bass guitarist, singing lead vocals simultaneously while he played bass.
The rise of the power trio in the 1960s was made possible in part by developments in amplifier technology that greatly enhanced the volume of the electric guitar and bass. Particularly, the popularization of the electric bass guitar defined the bottom end and filled in the gaps. Since the amplified bass could also now be louder, the rest of the band could also play at higher volumes, without fear of being unable to hear the bass. This allowed a three-person band to have the same sonic impact as a large band but left far more room for improvisation and creativity, unencumbered by the need for detailed arrangements. As with the organ trio, a 1960s-era soul jazz group centered on the amplified Hammond organ, a three-piece group could fill a large bar or club with a big sound for a much lower price than a large rock and roll band. A power trio, at least in its blues rock incarnation, is also generally held to have developed out of Chicago-style blues bands such as Muddy Waters' trio.
In addition to technological improvements, another impetus for the rise of the power trio was the virtuosity of guitarists such as Eric Clapton, Jimi Hendrix, and Rory Gallagher, who could essentially cover both the rhythm guitar and lead guitar roles in a live performance. In 1964, Frank Zappa played guitar in a power trio The Muthers, with Paul Woods on bass and Les Papp on drums. In 1966, the prototypical blues-rock power trio Cream was formed, consisting of Eric Clapton on guitar/vocals, Jack Bruce on bass/vocals, and Ginger Baker on drums. Other influential 1960s-era blues rock/hard rock power trio bands were The Jimi Hendrix Experience,Blue Cheer, Grand Funk Railroad, the James Gang featuring Joe Walsh, and Taste.
Well-known 1970s-era power trios include the Canadian progressive rock groups Rush and Triumph, the American band ZZ Top, the British heavy metal band Motörhead, and Robin Trower. Emerson, Lake & Palmer (as well as its offshoot Emerson, Lake & Powell), while replacing the guitarist by a keyboardist, is usually considered as a power trio, as Keith Emerson fulfilled the rhythm and lead playing on the keyboards that would usually fall on the guitarist, while bassist (and occasional guitarist) Greg Lake was the vocalist. In 1968, the power trio Manal was formed in Argentina, and were the first group that composed blues music in Spanish.
After the 1970s, the phrase "power trio" was applied to the new wave group The Police,grunge band Nirvana, post-punk band Hüsker Dü, mod revivalists The Jam, hard rock/progressive metal band King's X, progressive rock band Rush, post-grunge band Silverchair, alternative bands The Presidents of the United States of America, Goo Goo Dolls, Primus, Everclear and Eve 6, pop punk bands such as Green Day, Blink-182, Alkaline Trio and MxPx, and Argentine rock bands like Soda Stereo, Divididos and From Power Project. Also, by the 1990s, rock trios began to form around different instrumentation, from the band Morphine featured a baritone saxophone instead of an electric guitar, while Ben Folds Five replaced the guitar with various keyboards, principally the piano.
In the late 1960's, two music groups, Taste and Cream, blazed trails as definitive examples of rock's power-trios.