Expresso FX Silicon Fuzz

The Expresso FX Silicon Fuzz is a hand-wired fuzz pedal from UK builder Expresso FX. Expresso FX describes it as "a refined dual-Silicon-transistor-based fuzz pedal," and the manual explains its place in the range plainly: "Silicon Fuzz is very similar to our Germanium Fuzz but with silicon transistors instead"¹². Where the Germanium Fuzz uses germanium transistors, this version is built from an array of top grade NOS silicon transistors made by Toshiba and Philips¹.

The maker says the swap changes the character: "The results are a pedal that produces edgier fuzz tones with a brighter sound and more gain on tap"¹. The list price is £ 239.00 GBP².

A Germanium Fuzz circuit with silicon transistors

The Silicon Fuzz shares its circuit with the Expresso FX Germanium Fuzz, with silicon transistors substituted for germanium ones¹. Expresso FX offers a choice of silicon transistors on the product page, each with the maker's own description of its character³:

The pedal is hand wired by Expresso FX, which says it follows "our same tradition of extreme attention to detail when putting these pedals together"³. The manual describes the build as a high quality aluminum enclosure, professionally powder coated in a Copper Hammerite finish¹.

The idea of mixing germanium and silicon stages in one fuzz is one Expresso FX has explored elsewhere in its range. The Custom Dual Germanium/Silicon Fuzz with Filter Control is a custom fuzz pedal using hand-selected NOS germanium and silicon transistors, with germanium options that include a matched pair of Mullard OC42 at no surcharge, or a Newmarket NKT271 paired with a Newmarket OC84 for a £60 surcharge⁴. Expresso FX says the extra silicon transistor in that pedal "gives a fantastic alternative tone," and it adds a Filter control for controlling the circuit's low end⁵. Guitar Pedal X's Stefan Karlsson described his own custom Expresso FX Germanium/Silicon Fuzz, built in 2020 with a pair of MilSpec CV7351 germanium and CV10806 silicon transistors, as "a quite superb 2-stage germanium/silicon transistor switching fuzz"⁶.

Bias knob and trimpots

Some versions of the Silicon Fuzz carry an external bias knob. The manual explains how it works: the stock setting is 12 o'clock, turning it clockwise increases the bias voltage and anti-clockwise decreases it. The range is deliberately limited, designed to help correct the bias in less than optimal conditions rather than as a full sweep control¹.

Inside the pedal there may also be trimpots, depending on the version¹:

• Clean trimpot: located inside the pedal on the left hand side, on pedals fitted with one.
• Bias trimpot: the trimpot on the right hand side is for tweaking the bias, and the manual says it is best left stock unless changing the pedal's gain response is desired.

The external bias knob approach also appears on the Custom Dual Germanium/Silicon Fuzz with Filter Control, which is fitted with an external bias knob on top of the classic Volume and Fuzz knobs, to help compensate for the variation between different transistors⁴.

How it differs from the Germanium Fuzz

The core difference is the transistor type, and Expresso FX says it shows up in two ways. First, tone: the silicon version produces edgier fuzz tones with a brighter sound and more gain on tap¹. Second, cleanup: the manual states that "the circuit interacts well with the guitar's volume pot, though not as well as Germanium Fuzz does"¹. For players who use the guitar's volume knob as part of their sound, the germanium circuit remains the more responsive of the two in the maker's own account.

Versions and the Silicon Boost

Expresso FX builds the Silicon Fuzz in a range of enclosure finishes: Antique Copper Hammertone, Emerald Sparkle, Red Sparkle and Teal Sparkle². The pedal shares its 121 x 66 x 40 mm enclosure size with other pedals in the range, including the Silicon Boost⁵.

The Silicon Boost is a separate treble booster pedal from the same maker, designed by Sofiane Tebboune. Expresso FX says it "is based on the early treble boosters that were fitted with a single silicon transistor," and it features a Range knob for subtly tweaking the boosted frequencies, going from a full on treble boost setting to a more midrangy tone⁷. Like the fuzz, it is true bypass and carries the same 3 year warranty⁸.

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