I was talking to a friend about distortion boxes and the Box of Rock came up. Which got me thinking, I’d never heard one before, and Z Vex always makes good stuff. I found a schematic in the usual place. It looked like a pretty easy build.
The Box is basically two pedals in series, a distortion followed by a booster. The Box has two foot switches, The first switch engages the distortion and the second engages the booster. The controls for the distortion are Gain, Tone and Volume. The booster adds a fourth knob, Gain/Boost.
The distortion section is made of three BS170 MOSFet stages. The first stage is a SHO followed by a Marshall style high pass filter made of a 470p cap and a 470K resistor in parallel. Then come two more BS170s configured gains of approximately 51 and 15.
Next is a BMP style tone stack followed by an extra low pass filter. The low pass filter is exactly the same as used in the BSIAB II. The BSIAB II also uses the same Marshall style, 470p and 470K, high pass filter between the first two stages.
The B of R includes an SHO booster on the output. I had one of these built already so i decided not to build the stock B of R and instead build just the distortion section. I figure I can place my SHO or any other booster after it for different sounds.