The Catalinbread Formula 55 is a preamp pedal that reproduces the preamp section of the Fender Tweed Deluxe, specifically the 5E3 circuit, in a stompbox. It is a JFET-based overdrive, meaning it uses junction-gate transistors to emulate the behavior of the amp's tubes rather than the diode clipping many overdrives use12. Catalinbread launched it as the Formula No. 55 at the start of 2017, available to buy from the end of January that year, as part of the company's Foundation Overdrive range23.
Delicious Audio described it at launch as a "next-generation 5E3 Tweed Deluxe inspired overdrive with incredible range, from Grant Green to Crazy Horse!"2. The pedal sits in Catalinbread's Tweed-style amp-in-a-box line alongside the Formula 5F6 (Bassman) and, since 2023, the Formula 51 (Champ)4.
A Tweed Deluxe preamp in a pedal
The Formula 55 is a pedal reproduction of the preamp section of the Tweed Deluxe, the narrow-panel 5E3 amp prized for its touch-sensitive, mid-forward breakup82. Because it models the amp's preamp rather than adding diode clipping, it is built to respond to your guitar's volume knob and picking dynamics the way the amp itself does. Delicious Audio's buying guide notes that a lo/hi switch kicks the pedal into hot-rodded high-gain territory8.
Catalinbread positions it as a "foundation" overdrive: a pedal you leave on as your core tone, setting dirt with the Volume control and overall loudness with Master, rather than a boost you stomp for solos. It joined the Foundation Overdrive range in 2017 alongside the company's other amp-voiced drives23.
The controls: Volume, Tone, Presence, Master and Hi/Lo
The control layout is simple: Master, Presence, Tone and Volume knobs plus the Hi/Lo switch3. How Catalinbread describes each one7:
| Control | What it does |
|---|---|
| Volume | The gain control. Works with the Hi/Lo switch to set your maximum dirt, from clean to fully saturated. |
| Tone | Behaves like the tone control on an actual Deluxe: its influence becomes more subtle as Volume is maxed out. |
| Presence | Governs frequencies around the 5 kHz range, letting you tune the top end to your pickups and amplifier. |
| Master | The output volume, with plenty of level on tap for a fat clean tone or for pushing your amp into overdrive on its own. |
| Hi/Lo switch | Two discrete gain modes, described below. |
The Hi/Lo modes: red and green
The two positions of the Hi/Lo switch are color-coded and voiced like different preamp tubes7:
- LO/GREEN: lower gain overall, which Catalinbread describes as being "as if your amp were now sporting 12AY7 preamp tubes." The maker describes the starting point as a nice mild cleanish overdrive, with a fatness in the low mids that it says is inherent to the design regardless of Tone setting, and notes that lower-output pickups may call for the Volume control to be turned up a little more.
- HI/RED: what Catalinbread calls "the raging, hot-rodded 12AX7 mode with more gain and saturation." The maker describes the signal as feeling more hyped, hotter, with stored potential at your pick, and with Volume maxed, an elastic sag when you dig in that blooms bigger than the initial attack.
Power: 9 to 18V DC, and what voltage does to the sound
The Formula 55 runs on a 9V battery or any good quality filtered and regulated 9 to 18V DC power supply with a center-negative plug7. To change the battery, remove the four screws on the bottom plate; there are no other user controls under the hood7.
The supply voltage changes the character of the pedal, and Catalinbread is explicit about it7:
- At 9V DC: a slightly softer sound that saturates more easily. The maker compares the difference to a 50-watt versus a 100-watt amp.
- At 18V DC: more volume, headroom and percussive attack.
- Drained battery: Catalinbread suggests trying a battery drained down to as little as 3 to 4 volts for an even softer sound, which the maker recommends for late-night jam sessions when you don't want to wake anyone up.
The 9 to 18V DC range means the pedal works on a standard pedalboard supply, but the maker specifies a filtered and regulated supply with a center-negative plug, so a cheap unregulated wall wart is not what Catalinbread calls for7.
History and versions
Catalinbread introduced the Formula No. 55 at NAMM 2017, with availability from the end of January3. Delicious Audio called it "certainly one of the distortion pedals that made ear turns at the latest NAMM show"2. Aion FX's project documentation says the Formula 55 was the third update in the line, releasing in 2017 as a near-complete redesign9.
In January 2023, alongside the launch of the Formula 51, Catalinbread gave the Formula 55 (and the Formula 5F6) a new look to match the new pedal45. Guitar World reported the new-look Formula 55 at $189 and the 5F6 at $179 at that time5. A December 2024 review listed the Formula 55 at £160/$1616.
The Aion FX Asteria connection
The circuit is also available as a DIY project from Aion FX. The Asteria Mk. I corresponds to the earlier version, and Aion FX describes the current Formula 55 as "a full redesign of the circuit from 2017," offered from Aion FX as the Asteria Mk. III910. So if you see an Aion FX Asteria Mk. III build, it is the same redesigned circuit as the Formula 55 you can buy boxed from Catalinbread.
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Questions
Does the Catalinbread Formula 55 take a battery?
Yes. Catalinbread says you can power the Formula No. 55 with a 9V battery, and to change it you remove the four screws on the bottom plate. The maker also suggests trying a battery drained down to as little as 3 to 4 volts for an even softer sound suited to quiet late-night playing.
Can I run the Formula 55 at 18V?
Yes. The pedal takes any good quality filtered and regulated 9 to 18V DC power supply with a center-negative plug. Catalinbread says 9V gives a slightly softer sound that saturates more easily, while 18V gives more volume, headroom and percussive attack.
What is the difference between the red and green modes on the Formula 55?
The HI/LO switch offers two discrete gain modes. LO/GREEN is lower gain overall, which Catalinbread compares to running 12AY7 preamp tubes, and gives a mild cleanish overdrive with fat low mids. HI/RED is a hotter, hot-rodded 12AX7 mode with more gain and saturation.
What is the Aion FX Asteria based on?
The Aion FX Asteria Mk. III is the same circuit as the Catalinbread Formula 55, offered as a DIY project. Aion FX describes the Formula 55 as a full redesign of the circuit from 2017, and the Asteria Mk. III is that redesigned version.
Sources (10)
- Lazy J x ThorpyFX The J review: a superb tweed amp emulation, Guitar.com, 2026-01-14
- Catalinbread Formula No. 55 Overdrive, Delicious Audio, 2017-02-08
- NAMM 2017: Catalinbread Formula No. 55 Overdrive pedal offers some heavy tweed, gearnews.com, 2017-01-18
- Catalinbread Formula 51: Neil Young style Tweed Champ tones in a stompbox, gearnews.com, 2023-01-04
- Catalinbread launches the Formula 51, an overdrive pedal inspired by the Fender Tweed Champ, Guitar World, 2023-01-05
- Origin Effects Deluxe55 review: the ultimate ‘tweed in a box’ pedal?, guitar.com, 2024-12-16
- Formula 55, Catalinbread Effects
- Best Tweed-Style Overdrives & Fender-in-a-Box Pedals In 2024, Delicious Audio, 2024-11-13
- Asteria Preamp Drive Mk. I, Aion FX, 2020-11-23
- Asteria Preamp Drive Mk. II, Aion FX, 2020-11-23
