There are basically three terminologies that are used to describe distorting guitar effects: distortion, fuzz, and overdrive. Over the years, these names have been mixed together.
For most manufacturers, categorizing is more a matter of taste and what they think a particular pedal sounds like rather than the actual physical differences in the electronic circuits. Essentially, ‘distortion’ covers everything that distorts a signal, whereas ‘overdrive’ relates to overdriving amp circuits, pushing a signal on the input of the amp that is hotter than what the amp is designed to cope with.
Today, most distortion and overdrive guitar effects on the market use clipping diodes to create the distorting effect of the guitar signal. Our TrueOverDrive™ pedals, Wise Guy, Big Fella and Three Stage Rocket, use a technique that have no clipping diodes in the signal chain at all. The overdrive comes exclusively from cascading gain stages, much like in a real tube amplifier. The result is a very transparent and tube-like sound with lots of sustain and body. The reactions we have received from many guitar players, who have tried our pedals, is that they sound like a hot-rodded Fender amp or a Marshall Plexi Head driven hard.