The Expresso FX Custom Ge/Si Fuzz is a custom-built, fully hand wired fuzz pedal from Expresso FX, the boutique builder Sofiane Tebboune. It is a two-stage hybrid design: a germanium/silicon fuzz on one side and a germanium boost on the other, with transistor switching that lets the player choose between germanium and silicon in the circuit. It belongs to a family of custom germanium fuzz builds from the same maker, including the Expresso FX Germanium Fuzz, the Expresso FX Germanium CV7005 Fuzz and the Expresso FX Custom Dual Germanium/Silicon Fuzz with Filter Control.1
The controls and transistor choices
The general release Custom Dual Ge/Si Fuzz & Ge Boost pairs a Ge/Si fuzz with a germanium boost. The fuzz's first transistor (Q1) is switchable between a Newmarket CV7005 (germanium) and a low-gain Mullard OC202 (silicon), and the boost side is fitted with a Mullard OC45 germanium transistor. The maker's full transistor set is hand selected NOS germanium and silicon: 1x Newmarket CV7005, 1x Mullard OC202 (silicon), 1x Texas Instruments or GE 2N1307, and 1x Mullard OC45.31
The reviewed two-stage version puts the switching in both stages. Guitar Pedal X listed its controls as "Volume, Fuzz, Q1 : Ge CV7351 / Si CV10806, Bias, Q2 : Ge CV7351 / Si CV10806", meaning each fuzz stage can select between a germanium CV7351 and a silicon CV10806, both MilSpec CV type transistors.4
| Control | What it does |
|---|---|
| Volume | Output level |
| Fuzz | Fuzz amount |
| Q1 selector | Switches stage one between Ge CV7351 and Si CV108064 |
| Bias | Bias control, one of the classic fuzz controls on this design5 |
| Q2 selector | Switches stage two between Ge CV7351 and Si CV108064 |
Bias is a control Expresso FX uses across its fuzz designs: the maker's Custom Dual-Switching FF Ge/Si, reviewed in 2020, carried "the more classic Volume, Fuzz and Bias" layout.5 On the related germanium boost circuit in the Custom Ge Fuzz / Ge Boost / Octave Up, a 7-way rotary switch provides seven tonal settings from treble-focused, to mid-focused, and to bass-focused options.6
One-off unit and the general release model
The pedal Guitar Pedal X reviewed is a one-off. The reviewer wrote that Tebboune "built this one-off to my preferences", and that Tebboune "selected the CV7351 as the Germanium type, and the very complementary CV10806 as the Silicon Type", in a compact Green/Purple color-switching Gørva enclosure from a period when Tebboune favored those enclosures.4
The general release model differs from that custom unit. As of August 2026, Guitar Pedal X noted that "The current model that's on more general release is only Transistor-switching on one Stage, but has an additional Filter" control, so it would not qualify for the article's selection of two-stage switching fuzzes.4
The maker's current product page describes the release version as "a custom dual-circuit pedal with a Ge/Si Fuzz on the right side and a Ge Boost on the left", fully hand wired, with the Mullard AC188 in Q2 on the fuzz side and a Mullard OC45 germanium transistor on the boost side.31
What reviewers said
Guitar Pedal X placed the pedal among its superior germanium and silicon transistor-switching two-stage fuzzes and compared it directly with a rival design4:
"It has one fewer knob than the DanDrive, and one fewer toggle-switch - but sounds every bit as good."
In the same review the pedal was described as another Top-Tier superb sounding pedal overall, sounding every bit as good as the DanDrive equivalent.4
Related Expresso FX fuzzes
Expresso FX builds a range of custom germanium fuzz pedals around NOS transistors234:
- Custom Ge Fuzz / Ge Boost / Octave Up: a custom-built pedal combining a Germanium Fuzz, a Germanium Boost, and an Octave UP effect, built around a matched pair of Mullard CV7005 germanium transistors in the fuzz, with hand selected NOS germanium transistors: 2x Mullard CV7005 and 1x Mullard AC107. Fully hand wired, listed at £449.00 GBP as of October 2024.62
- Custom Dual-Switching FF Ge/Si: listed at £229 in December 2020, with the classic Volume, Fuzz and Bias control set.5
- Germanium CV7005 Fuzz: listed by Guitar Pedal X at $325 in June 2024 as a pair with a Silicon BC183 Fuzz.7
For the wider category, see the site's Fuzz Pedals page.
Videos
Edge of Breakup 🎥 Guitars, Pickups, Amps & Pedals
Edge of Breakup 🎥 Guitars, Pickups, Amps & Pedals
Questions
What transistors are in the Expresso FX Custom Ge/Si Fuzz?
The general release Custom Dual Ge/Si Fuzz & Ge Boost uses hand selected NOS germanium and silicon transistors: a Newmarket CV7005, a Mullard OC202 (silicon), a Texas Instruments or GE 2N1307, and a Mullard OC45. The fuzz's first transistor (Q1) is switchable between the germanium CV7005 and the low-gain silicon OC202, and the boost side carries a Mullard OC45 germanium transistor.
How much does the Expresso FX Custom Ge/Si Fuzz cost?
Guitar Pedal X listed the Custom Ge/Si Switching 2-Stage Hybrid Fuzz at £299, which the review gave as $405, as of August 2026. The maker's product page for the Custom Dual Ge/Si Fuzz & Ge Boost shows £399.00 GBP as of August 2026. Prices are given in the currency the source states and are not converted.
Is the Expresso FX Ge/Si Fuzz hand wired?
Yes. Expresso FX describes the Custom Dual Ge/Si Fuzz & Ge Boost as fully hand wired, and the same description appears on the maker's Custom Ge Fuzz / Ge Boost / Octave Up page. The pedals are custom built by Sofiane Tebboune.
How does the general release differ from the custom unit?
The one-off unit reviewed by Guitar Pedal X has transistor switching on both stages, with selectable germanium or silicon in Q1 and Q2. According to Guitar Pedal X, the current general release model has transistor switching on only one stage, but adds an additional Filter control. The reviewer's unit was also built to his preferences in a Green/Purple colour-switching Gørva enclosure.
What does the Bias knob do on this fuzz?
Bias is one of the classic fuzz controls on this design, appearing alongside Volume and Fuzz on Expresso FX's dual-switching Ge/Si fuzzes. On the related germanium boost circuit in the Custom Ge Fuzz / Ge Boost / Octave Up, a 7-way rotary switch provides seven tonal settings ranging from treble-focused to mid-focused to bass-focused options.
Sources (7)
- Custom Dual Ge/Si Fuzz & Ge Boost, Expresso FX, 2024-09-15
- Custom Ge Fuzz / Ge Boost / Octave Up, Expresso FX, 2024-07-18
- Custom Dual Ge/Si Fuzz & Ge Boost, Expresso FX, 2024-09-15
- Guitar Pedal X, Guitar Pedal X, 2026-08-14
- Guitar Pedal X, Guitar Pedal X, 2020-12-18
- Custom Ge Fuzz / Ge Boost / Octave Up, Expresso FX, 2024-07-18
- Guitar Pedal X, Guitar Pedal X, 2024-06-24
