The Dallas Rangemaster Treble Booster is a booster guitar pedal that especially emphasizes the upper mid and treble frequencies (coloring the signal). It was designed in London (UK) by Dallas Musical Ltd in 1965. At that time, the British tube amplifiers such as the Vox AC30 or Marshall JTM45, tended to produce a slightly dark, muddy tones when overdriven, this box fixed that issue. The effect became popular because of its sweet coloration, slightly bending the signal and giving a soft compression when maxed out.
The grey metal box was designed to sit on top of the amp and not on the floor as most of the pedals do nowadays, it features a simple ON/OFF sliding switch and a potentiometer to adjust the volume. The apparent simplicity of the circuit and the limited supply of this discontinued effect make it a perfect target for builder and guitar pedal enthusiasts.