The circuit is based on the shunt-series-feedback amplifier topology - a standard in engineering textbooks. Sola Sound and Vox had been using the same circuit topology for their Tone Bender pedals earlier in 1966. The Fuzz Face is particularly similar to the Sola Sound unit known today as the "Mk1.5" Tone Bender. The main difference is that the Fuzz Face is biased slightly colder, making it more usable in warm environments. The original instructions even described the Fuzz Face as a "Tone-Bending" unit.