JMI traces its roots to the original Jennings Musical Industries, founded by Tom Jennings in Dartford, Kent, England in the 1950s. Partnering with amplifier designer Dick Denney, Jennings launched the 15-watt AC15 in 1958 and the 30-watt AC30 in 1959 — amplifiers that became cornerstones of the British Invasion sound and were famously used by The Beatles and The Shadows. The original company folded in 1968, and the brand lay dormant for nearly three decades.

In 1997, Richard and Justin Harrison, then owners of Hiwatt amplification UK, purchased the JMI trademark and set about reviving the brand. The modern JMI builds hand-wired reproductions of the classic Jennings-Denney amplifier designs exclusively in Yorkshire, England. Their lineup includes faithful recreations of the AC10, AC15, and AC30, built to the original specifications with period-correct components like EL84 power tubes and Celestion speakers.

Beyond amplifiers, JMI produces effect pedals rooted in 1960s British circuit designs, including the MKII Tone Bender fuzz (using New Old Stock Mullard OC-75 transistors) and a Treble Booster based on the Dallas Rangemaster circuit. Artists who have played through the revived JMI amplifiers include Noel Gallagher and Billy Gibbons.

JMI has 12 products cataloged on Equipboard, including Fuzz Effects Pedals, Combo Guitar Amplifiers, and Bass Combo Amplifiers. Their gear is featured by 15 artists, with the strongest followings in Rock, Pop, and Blues. Notable users include J Mascis, Billy Corgan, and Jimmy Page.