The Catalinbread Formula 51 is an analog overdrive pedal built to put a Fender Tweed Champ amp on your pedalboard. Guitar World described the stompbox as one that "promises to deliver the full touch-sensitive Tweed experience," and noted that the amp-in-a-box is also the latest addition to the brand's Foundation Overdrive collection1. It is part of Catalinbread's Foundation Overdrive collection of amp-in-a-box pedals1.
How the circuit works
Rather than a simple gain stage, the Catalinbread team built a circuit featuring a preamp, a discrete power amp simulator and an output transformer4. The idea is that the pedal behaves like the amp's signal path: the Gain knob works as the volume control on the original Tweed Champ, feeding the power amp and transformer, and the Sag knob lets you load that transformer down the way a struggling Champ does. The maker puts it plainly: "this is supposed to be a Tweed amp after all"2.
Controls
| Control | What it does |
|---|---|
| Gain | Works as the volume control on the original Tweed Champ; controls preamp gain, or how much juice hits the power amp and transformer, from slightly gritty cleans to heavy distortion at maximum2 |
| Tone | A mids control wired in reverse from a Framus Cobra amp mod; all the way down is Tweed, maxed is scooped "blackface"2 |
| Sag | Controls the degradation of the transformer; too much sounds farty or weird, and its useful range depends on the signal strength fed into the pedal2 |
| Volume | Overall output level; sounds great at any position other than zero2 |
The Sag control is the pedal's signature feature. RockBoard's listing describes it as loading down the transformer to your taste, "giving you some real-deal blown-out leads with the twist of a knob"3. Note that the Sag knob's useful range depends on how hot the signal hitting the pedal is, so where you put it changes with your guitar and any pedals in front2.
Tone range: Tweed to blackface
The Formula 51 covers more ground than its Champ inspiration alone. Guitar World reported that when Tone is all the way down, the Tweed Champ sounds are at the forefront, though when it is maxed out the pedal taps into later Blackface amp tones1. That comes from the reversed mids wiring: a burly, mids-focused Tweed amp gets its mids scooped as the knob turns up2.
Power and setup
The headroom and functionality of the Sag control is built for using 18V, so when you run at 9V it is very sensitive2. The pedal takes a center-negative DC supply between 9 and 18 volts and draws at least 2mA, so almost any supply will run it. Wrong polarity, voltage outside the recommended range, or AC power will damage the pedal and void the warranty2.
Catalinbread's suggested starting point: set everything fully counterclockwise except the Volume. That puts the gain at minimum with no sagging or mids adjustment, and you dial up from there2.
What reviewers said
The pedal arrived in early January 2023, available for $1791, with a UK price of £151.555. Delicious Audio's buying guide later listed it at $1796. gearnews.com's reviewer found that "Overall, this new overdrive pedal, on paper at least, offers a lot of nice features," singling out the Sag control as making a lot of sense and noting the Tone control does more than you might expect7.
Where it sits in Catalinbread's range
The Formula 51 is one of Catalinbread's amp-focused Foundation pedals. Players chasing other classic Fender voicings can look at the Formula No. 55 or the Formula 5F6, or the broader range of overdrive pedals on the site1.
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Questions
Should I run the Formula 51 at 9V or 18V?
Catalinbread says the pedal takes a center-negative DC supply between 9 and 18 volts, but the headroom and functionality of the Sag control is built for 18V, so at 9V it is very sensitive. The pedal draws at least 2mA, so almost any supply can handle it. Wrong polarity, voltage outside the recommended range, or AC power will damage the pedal and void the warranty.
What does the Sag knob do on the Formula 51?
The Sag knob controls the degradation of the output transformer, loading it down to your taste. Catalinbread says too much sounds farty or weird, and its useful range depends on how strong a signal the pedal is fed. Used well it delivers blown-out lead tones with the twist of a knob.
Can the Formula 51 get blackface tones?
Yes, through the Tone knob. The control is wired in reverse, based on a Framus Cobra amp mod: all the way down the Tweed Champ sounds are at the forefront, and maxed out it scoops the mids and taps into later Blackface amp tones.
What is a good starting setting for the Catalinbread Formula 51?
Catalinbread suggests starting with everything fully counterclockwise except the Volume. That sets the gain to minimum with no sagging or mids adjustment, and you bring the controls up from there.
Is the Catalinbread Formula 51 analog?
Yes. RockBoard lists the circuit type as analog, and the circuit is built around a preamp, a discrete power amp simulator and an output transformer rather than digital modeling.
Sources (7)
- Catalinbread launches the Formula 51, an overdrive pedal inspired by the Fender Tweed Champ, Guitar World, 2023-01-05
- Formula 51, Catalinbread Effects
- Formula 51 by Catalinbread, RockBoard (www.rockboard.de), 2026
- Catalinbread Formula 51 Tweed Drive, Delicious Audio, 2023-01-04
- The need for Tweed: Catalinbread's new Formula 51 overdrive pedal is inspired by Fender's classic Champ combo camp, MusicRadar, 2023-01-04
- Best Tweed-Style Overdrives & Fender-in-a-Box Pedals In 2024, Delicious Audio, 2024-11-13
- Catalinbread Formula 51: Neil Young style Tweed Champ tones in a stompbox, gearnews.com, 2023-01-04
