Rangemaster Treble Booster kit by Vintage Pedal Workshop. - YouTube
Dallas Rangemaster | DIY Fever
DIY Strat (and other guitar & audio projects): Building a quick Brian-May-style treble booster on Veroboard
Here are a couple more - the simple passive tone control that can be added to any circuit or used as a simple pa… | Treble booster, Diy guitar pedal, Diy guitar amp