MRB

This is an acronym for the Vox Mid-Range Boost circuit that was added to most Vox amps once they made the switch from vacuum tube to solid-state. By the time this feature was added, Vox amps that were sold in the U.S. were being built by the Thomas Organ Company. The Mid-Range Boost function was controlled by a 3-position rocker switch and loosely corresponded to three distinct positions on the new Vox wah-wah pedal. Position One was the darkest of the three, sounding like a wah almost in the full heel position, while Position 3 was the brightest, with a tone close to that of a wah not quite in the toe position. As you’d expect, Position Two was like a wah set in the middle of its range. The best recorded example of the MRB circuit can be heard on The Beatles’ song, “Fixing a Hole” from the Sgt. Pepper album. Despite this feature, sales of Vox amps plummeted, because the solid-state models simply did not have the clean, “chime” that the all-tube Vox amps were famous for.