Seven Fuzz Topologies of the 1960s, Pt. 5: The Mosrite Fuzzrite

Part 5 of Seven Fuzz Topologies of the 1960s, a bench-reference series. New here? Pt. 1 covers the drawing conventions and how to read the clipping diagrams.

5

Parallel Phase-Blend (Subtractive Mix)

Mosrite Fuzzrite topology · 1966

Two inverting gain stages in series, but the DEPTH pot blends the output of stage one against the output of stage two. Because each stage inverts, the two signals are out of phase; mixing them partially cancels the fundamental and leaves the harmonics. The result is thin, nasal and buzzy on purpose.

Devices

PNP germanium ×2 (2N2613 / 2N408), 9 V, positive ground; later silicon

Supply as drawn

+9 V

Controls

DEPTH · VOLUME

Clipping

transistor saturation in each stage, then antiphase cancellation

Schematic drawn NPN / positive rail for comparison; see conventions above

How it clips signal at each point in the chain (dashed = what the wave would be without clipping)

Stage by stage

• Q1 is a high-gain stage (hFE 100–150) biased by a very large collector-to-base resistor; Q2 is deliberately a lower-gain device (hFE 40–60). Both are simple common-emitter stages that saturate when pushed.
• The DEPTH pot has one end tied through a 2.2 nF cap to Q1’s collector and the other end through another 2.2 nF cap to Q2’s collector. The wiper is the output.
• At either extreme you hear one stage on its own. In the middle you hear the sum of an inverted signal and a doubly-inverted (in-phase) one: the fundamental partly cancels, the odd harmonics and the sharp edges do not, and the tone gets thin and raspy. The tiny coupling caps also roll off everything below ~1 kHz, which is most of the Fuzzrite’s "Iron Butterfly" character.

Bench notes & values

• Values are from a trace of a 1966 germanium unit (as documented by Aion FX for their Orpheus project). The original silicon Fuzzrite uses different biasing and 2N3565-class NPN parts; the topology is identical.
• The gain ratio matters more than the absolute numbers: keep Q1 at least twice the hFE of Q2 or the blend stops doing anything interesting.
• Originals used a 350 k reverse-audio DEPTH pot; 500 k with a 1.2 M resistor across the outer lugs approximates the taper.
• Bench cost: under $3 silicon; two germanium PNPs $10–25.

Same topologyMosrite FuzzriteGuild Foxey Lady V1Guild Foxey Lady V2Shin-Ei Companion Fuzz FY-2Claybridge Fuzzmaster MKIV

Sources for values: Gibson patent US 3,213,181 (FZ-1); Arbiter Fuzz Face germanium schematic; Sola Sound Tone Bender Professional MkII (pedalparts.co.uk BOM, vero-p2p); Aion FX Orpheus (Fuzzrite) and Astra (Astrotone) documentation; fuzzcentral.ssguitar.com Octavia parts lists. Octavia and Boss Tone stage values are representative working designs, not traces.

Drawn with schemdraw and matplotlib. Made for Jason’s bench at Illicit Apothecary.