Catalinbread Formula 5

The Formula ppppppppppo5 was inspired by old tweed amps, most notably the 5E3 circuit. The character of the 5E3 is very unique. It has very minimal power filtering, low plate voltages, elemental tone stack, and does next to nothing to control the low end between gain stages, not to mention the under-rated output transformer and speaker. The entire system runs inefficiently resulting in a loose bass, greasy mids, cutting treble, and incredible grit -- none of these qualities were ideal or intentional back in the day. In spite of this, over the past five decades the amp inspired some of the coolest, most sought after guitar tones ever recorded.

We've captured the unique qualities of these amps in the Formula 5. For this circuit we felt cascaded JFET gainstages yielded the best result. They have a softer sound than MOSFETs. JFETs also have much more natural attack/decay than diode clipped rigs which are pingy on the attack and fizzy on the decay. We chose capacitor types that enhanced the midrange and burnished the treble.

We've recorded some clips that highlight the qualities of the Formula ¹ 5. For an amp we used a Quad Reverb (basically a 4x12 Twin) VOL=3.5, TRE=6, MID=6, BASS=3, REV=2, MAST=10. The microphone is a Royer 121 placed 3" from one of the cones.

Like the 5E3 the Formula 5 GAIN and TONE are highly interactive. The tone circuit is such that it functions as a bright cap or treble rolloff depending on where the GAIN is set. The higher the gain the TONE becomes nullified and less effective. Conversely, the lower the gain the more effective the tone sweep becomes. We felt this behavior was crucial to reproduce for an accurate tweed-in-a-box.

The Formula 5 can run at 9V or 18V. At moderate gain settings you will find an increased bass tightness and volume @ 18V.

The difference between a great dirt box and the average run of the mill distortion pedal is how well it respects your pickup position. Here is a showcase of a humbucker equipped LP: First, is a little boogie, starting off clean and a bit sterile, but when the Formula 5 is engaged you can hear how well it encourages the playing attitude. Next, is the LP in the bridge position, demonstrating how well it retains the bridge pickup character. The final humbucker clip is the LP neck position. Listen to how sweet and singing the Formula 5 is while maintaining articulation and detail.

In addition to pickup position a great dirt box respects your pickup type. The following set of clips showcase the Strat.

The bridge position has a vocal quality that can cut through a mix.
The middle position is a tad fuller than the bridge with every bit as much detail.
The neck position is noted for its fullness yet glassy character, the Formula 5 does not obscure this