(EDIT: fixed the link below, using reTrEaD's correction in the following post. sumgai, 2/1/18)
A German research group, called Gitec, that dedicates itself to the science of electric guitar has been translating portions of their work into the English language in order to reach a broader audience, and they have just published a translated chapter on the circuitry of "Overdrive, Fuzz & Distortion" stomp boxes. Here's a link to the PDF: Gitec's treatise on distortion
The PDF covers the a little history of distorted guitar, discusses the circuit topography, and resulting clipping characteristics and frequency response of the Range Master, the Fuzz Face and the Tube Screamer. While this isn't a great number of pedals, it makes for a fine introduction as to what's happening on a technical level with fuzz boxes in general. The illustrations are of top notch quality, it's well written and well translated.