The Vox V8401 Treble/Bass Booster was a module that plugged into the input jack of a guitar to boost bass or treble frequencies. A standard 1/4" jack on the bottom of the booster accepted a standard guitar cord for connection to an amplifier. The V8401 Treble/Bass Booster was manufactured for Vox by JEN  of Pescara, Italy. JEN was established by Joe Benaron, the president of Thomas Organ in Sepulveda CA and Ennio Unchini, chairman of the company that imported Thomas Organs to Italy. The brand name "JEN" was an amalgamation of the first letters of their names, Joe and Ennio. In addition to three "booster modules" (Treble/Bass, Repeat Percussion and Distortion) JEN also produced wah and distortion pedals for Vox. The V8401 replaced the chrome plated Vox V840 Treble/Bass Booster manufactured by Vox in the UK. The V8401 Treble/Bass Booster utilized a rotary control that adjusted the boosted frequency. JEN also produced a version of the V8401 Treble/Bass booster that they sold under the JEN brand name. The faceplate of the JEN model even included the classic Vox diamond grill pattern from the Vox V8401.

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