The Catalinbread Formula 5F6 is an overdrive pedal built around the preamp and tone stack of a tweed Fender Bassman. Catalinbread says its controls reproduce the Bassman's tone circuit, part for part, and the circuit uses JFET transistors in place of tubes, in what Delicious Audio's buying guide calls "the classic layout of the Bassman circuitry, in a compact pedal format"12. It belongs to the same Formula family as the Formula No. 5 and the Formula 51, and it is one of the pedals players usually mean when they talk about "amp in a box" designs: a pedal intended to behave like the front end of a specific amp rather than a generic dirt box.
A tweed Bassman preamp in a pedal
The Formula 5F6 was released in the summer of 2013 as a variant of the Formula No. 5. Aion FX, which documents Catalinbread circuits, describes it as "the same circuit with several tweaks in part values," retuned for the Bassman rather than the smaller amps behind the No. 54. Pedal of the Day's reviewer, Mike B, came to it the same way, calling it the No. 5's "big brother"3.
Like several Catalinbread pedals, the Formula line sits between overdrive and preamp. Aion FX notes of the related Formula No. 5 that the circuit "blurs the line between a preamp and an overdrive," reacting strongly to what feeds it and working both as a standalone drive and placed after other drive pedals but before modulation6. The 5F6 carries that same family character into Bassman territory, and Catalinbread's own setup guidance treats it like an amp: the pedal should be set slightly louder when on than when bypassed1.
The current version is the new-look edition. In January 2023, alongside the launch of the Formula 51, Guitar World reported that the Formula 5F6 was available in a new look, priced at $17957, and gearnews noted that the Formula 55 and 5F6 "have also been given a new look to match" the 517. By November 2024, Delicious Audio's guide to tweed-style overdrives listed it at $1492.
The controls and the internal mode switch
Catalinbread's product page describes a Gain and Volume layout where the two interact like an amp's channels: lower Gain settings call for higher Volume settings, and full Volume with Gain at minimum gives the best clean and edge-of-breakup response. The Volume knob is the master volume controlling the pedal's output1.
The tone controls are the heart of the design. Catalinbread states that they reproduce "exactly, part-for-part, the tone circuit ('tone stack') of the tweed Bassman," the interactive bass and treble network that gives the original amp its midrange character1.
There is also a mode switch, and it is not on the outside1:
"There's a switch inside that switches between Stock Bassman (S. Bass) and Secret Lead (S. Lead) mode!"
- S. Bass (Stock Bassman): the vintage low-gain Bassman voicing1
- S. Lead (Secret Lead): pushes gain way up and reconfigures the tone stack to a new bright, full voicing while staying "American," in Catalinbread's words; the maker says it transforms the pedal "from vintage low-gain goodness into a re-breathing monster from California"1
Because the switch is internal, changing modes means removing the back plate, which is worth knowing before setting up a board around one voicing1.
Power: 9V to 18V, negative tip
The Formula 5F6 takes a negative tip DC supply from 9 to 18 volts1. The voltage choice is a voicing control in itself:
| Supply | What Catalinbread says it does |
|---|---|
| 9V | A slightly softer sound that saturates more easily1 |
| 18V | More volume, headroom and percussive attack, with attack and clarity to cut through the mix1 |
Catalinbread compares the choice to a 50 watt versus 100 watt amp, so players after the most authentic Bassman feel have a reason to try 18 volts, while players wanting easier breakup can stay at 91.
What reviewers said
Pedal of the Day's review by Mike B summed the pedal up as having a "Great EQ section, great Gain tones, great overall power AND it plays nice with other pedals"3. Delicious Audio's Griffin Jennings included it in a buying guide to Fender-in-a-box tweed overdrives, crediting the JFET design with carrying the Bassman circuit layout into pedal form2.
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Questions
What is the difference between the Formula 5F6 and the Formula No. 5?
The Formula No. 5 came first and is modeled after old low-power Fender amps such as the Harvard 5F10. The Formula 5F6, released in the summer of 2013, is the same circuit with several tweaks in part values, aimed at the tweed Bassman preamp and tone stack instead. Pedal of the Day's reviewer called the 5F6 the No. 5's big brother.
Does the Formula 5F6 use tubes?
No. According to Delicious Audio's buying guide, the Formula 5F6 uses JFETs in place of tubes, reproducing the classic layout of the Bassman circuitry in a compact pedal format. JFET transistors are used to approximate how tube stages clip and respond.
Where is the Secret Lead switch on the Formula 5F6?
It is inside the pedal. Catalinbread says there is a switch inside that switches between Stock Bassman (S. Bass) and Secret Lead (S. Lead) mode, so you need to take the back plate off to reach it.
Does the Formula 5F6 sound better at 18 volts?
It depends on what you want. Catalinbread says running an 18 volt supply gives more volume, headroom and percussive attack, with clarity to cut through a mix, while 9 volts gives a slightly softer sound that saturates more easily, which the maker compares to a 50 watt versus 100 watt amp.
Can the Formula 5F6 be used as an amp in a box?
Yes. The pedal reproduces the tweed Bassman preamp and tone stack part for part, and Catalinbread describes it as blurring the line between a preamp and an overdrive. It can be run into a clean amp or power amp as a standalone rig, or used as a conventional overdrive pedal.
Sources (7)
- Formula 5F6, Catalinbread Effects
- Best Tweed-Style Overdrives & Fender-in-a-Box Pedals In 2024, Delicious Audio, 2024-11-13
- Catalinbread Formula 5F6 Overdrive, Pedal of the Day, 2014-12-17
- Triton Preamp Drive Mk. III / Catalinbread DLS V3, Aion FX, 2020-11-27
- Catalinbread launches the Formula 51, an overdrive pedal inspired by the Fender Tweed Champ, Guitar World, 2023-01-05
- Asteria Preamp Drive Mk. I, Aion FX, 2020-11-23
- Catalinbread Formula 51: Neil Young style Tweed Champ tones in a stompbox, gearnews.com, 2023-01-04
