Shunt Feedback Clipping Diodes

The "Minimalist" Variation. Both ac and dc flow from collector to base.

In a discrete transistor single stage, this type of clipping is caused by connecting the collector to base via a diode. I've seen this stage featured in a home brew fuzz from Ethan Winer he claims he was building for friends in the mid 1960s. The modern Bazz Fuss makes use of this to create the most minimalist example of a fuzz circuit (the circuit above is pretty much a Bazz Fuss). In the minimalist circuit, both ac and dc feedback flow through the diode. The only commercial vintage fuzz example I know of using dc diode feedback is in the Fender Blender 3 Knob.

AC only clipping, due to the added capacitor

Connecting the diode in series with a capacitor ensures that only ac signals are clipped, and the dc conditions are left stable.

Shunt feedback clipping diodes were first used for distortion by the Electro Harmonix Big Muff Pi. This famous 4 transistor circuit includes two cascaded stages of shunt feedback clipping diodes. The Big Muff straddles the fence between fuzz and distortion/overdrive. It can be considered a "smooth fuzz."

In the 1970s, op amp distortion replaced discrete transistor distortion/fuzz. Op amp feedback clipping diodes are discussed here:

Op Amp Feedback Clipping Diodes

Examples:

Ethan Winer Fuzztone (circa 1966)

Electro Harmonix Big Muff Pi (1969)

Colorsound Supa Tone Bender (1973)

Colorsound Jumbo Tone Bender (1975)

Maxon 801 D&S Distortion and Sustain (1974)

Ibanez 850 Overdrive (1974)

Fender Blender 3 Knob (1976?)

Boss OD-2 Turbo Overdrive (1985)

Boss DS-2 Distortion (1987)

Boss OD-2R Turbo Overdrive (1994)

Boss OD-3 Overdrive (1997)