The Formula No. 5 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.
Catalinbread has captured the unique qualities of these amps in the Formula No. 5. For this circuit they 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. Catalinbread chose capacitor types that enhanced the midrange and burnished the treble.
The folks at Catalinbread have recorded some clips that highlight the qualities of the Formula No. 5. For an amp they 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.
If you click on the hyperlinks in the folowing text section, it will bring up the corresponding audio file referred to in the text.
This audio demo starts out by presenting a reference clean sound with a Tele. Big & clean all day! Keep coming back to this clip as necessary to clear your pallet! Next is a general gain sound of a Tele into the Formula No. 5 with the Gain @ 3 O’clock, Tone @ noon. This showcases the “loose bass, greasy mids, cutting treble, and incredible grit” mentioned above quite nicely. Listen to how chords decay – just like an amp. No pingy attack. No fizzy decay. Now the demonstration will include the amp-like clean up with a Tele into the Formula No. 5 with the Gain @ 3 O’clock, Tone @ noon. Usually a player can leave the Formula No. 5 on all the time and get a clean sound by rolling back the instrument’s volume knob. Like the 5E3, the Formula No. 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. Catalinbread felt this behavior was crucial to reproduce for an accurate tweed-in-a-box. The Formula No. 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 No. 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 No. 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 No. 5 does not obscure this!