The following scheme diagram is the circuit diagram of VOX treble booster effect. A treble booster is an effects unit used by guitarists to boost volume and especially the high end of their tonal spectrum, and was popular mostly during the 1960s.
VOX made a variety of boosters that were meant to be plugged directly into amplifiers or guitars. Roger McGuinn installed one into his Rickenbacker guitar in the 1960s.
Original VOX Treble Booster diagram:
The modified treble booster circuit diagram is purposed to be used as an overdrive/distortion unit.
The input capacitor is changed from 500pF to 0.01 uF (1000pF) or 0.022 uF (2200 pF) to allow more bass in. This usually overloads the booster and causes crunchy distortion.
Download VOX treble booster effect circuit in PDF format from the following link: