Seven Fuzz Topologies of the 1960s, Pt. 6: The Sam Ash Fuzz Box / Astrotone

Part 6 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.

6

Cascaded Boost → Clip → Buffer

Sam Ash Fuzz Box / Astrotone topology · 1966

The first fuzz to clip with diodes instead of transistors. One clean-ish gain stage, a pair of back-to-back silicon diodes to ground, and an emitter follower to drive the tone and level controls. The clipping is symmetric and the level is fixed by the diode drop, so it sounds the same at any input level once it is over the threshold.

Devices

Silicon NPN ×2 (2N3565), 9 V, negative ground

Supply as drawn

+9 V

Controls

ATTACK (input level) · TONE · LEVEL

Clipping

symmetric diode clipping at ±0.6 V

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

• The ATTACK pot is simply a volume control on the input, so it sets how far past the diode threshold the signal goes.
• Q1 has an unbypassed 1.8 k emitter resistor, which holds its gain to about ×12 and keeps it linear. Unlike every other circuit on this page, the transistor is not meant to clip.
• D1/D2 are 1N914-type silicon diodes in anti-parallel to ground. Above about +0.6 V one conducts, below −0.6 V the other does, so the wave is shaved flat at the same level top and bottom. That symmetry means odd harmonics dominate, giving a harder, more "distortion pedal" flavour than the germanium fuzzes.
• Q2 is an emitter follower: unity gain, low output impedance, so the tone stack and level pot do not load the clipper.

Bench notes & values

• Values follow the Aion FX Astra trace of an Astrotone. The original tone control (10 k pot with a cap to ground after Q2, not drawn) is widely considered poor; Analog Man’s reissue swaps R6 to 470 Ω and the coupling caps to 470 nF for more low end.
• Any general-purpose NPN works (2N3904, 2N2222, BC549). Swap the diodes to experiment: germanium (1N34A) clips at ~0.3 V and sounds softer, LEDs at ~1.7 V give more headroom and crunch.
• Bench cost: about $2.

Same topologyAstrotone FuzzSam Ash Fuzzz Boxx

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.