For disciples of the Fulltone OCD overdrive—and they are legion—there is little reason to even flirt with other crunch boxes. This venerable pedal is so dependable at pumping out the kind of gain that was once the exclusive province of cranked-to-the-max tube amps that OCD owners never have to deal with the anxiety of wondering whether they’ll have enough gain if they show up to a gig and there’s a rented Twin Reverb in the backline. With the Plimsoul pedal, Fulltone only upped its cred—adding a hard-clip-style gain stage for sounds akin to an old-school distortion pedal or the singing sting of a Marshall output tube section.

So where does the new Fulltone Secret Freq pedal fit into the company’s overdrive spectrum? If you’re a fan of big, classic-rock lead tones, you’ll be stoked to know that the main thrust of the Secret Freq is its emphasis on boosting midrange by as much as 20 dB. But with its dedicated knobs for mid boost (“freq.”), volume, treble (“highs”), and distortion, the Secret Freq provides ample options for tonal variation.

Tie This Mother Down!
Like the OCD and Plimsoul, there’s nothing flimsy about the Secret Freq’s tank-like steel housing. Cosmetically, it resembles the Plimsoul, with a forest-green finish and a silver plate around the knobs and LED indicator. The 9- to 18-volt DC input is located just forward of the left-side output jack, which helps keep your pedal board looking clean. Access to the battery requires removing the top steel plate by unscrewing each of the four bolts—not the quickest way, but certainly more rugged than an easy-to-break plastic flip compartment.

At its simplest, the Secret Freq offers a fairly transparent volume boost: You just set the volume at unity, distortion in the 9 o’clock zone, and the freq. knob and highs controls essentially off—freq. hard left, and highs hard right. There’s little, if any, frequency coloration at this setting, other than the basic character of the soft gain, which is quite comparable to the soft clipping you hear in the OCD. As suggested in the user’s guide, this is a great vehicle for navigating SRV-style blues rhythms—especially with a Stratocaster’s neck pickup—and is a reliable catchall setting for soul, vintage R&B, and garage rock. Ratchet the distortion up to 10 o’clock, while goosing the mids a pinch, and you’re deep into the SRV lead zone, with more than a hint of TS9 bite and warmth. As previously mentioned, the Secret Freq’s volume knob adds up to 20 dB of boost, so you have to use it with restraint unless you want the discrepancy between your pedal-on and pedal-off volumes to drive the soundman out of his mind (they’re sensitive, those guys.)

Another especially effective Secret Freq effect involves bringing volume down a hair, setting distortion between 11 and 12 o’clock, and turning freq. to around noon, while rolling off the highs to around 3 or 4 o’clock. This is the sweet spot where those mid-’70s Jimmy Page tones really come alive—think “Custard Pie” and “The Rover,” and while you’re at it, try bumping up the distortion a bit more and rocking out “Houses of the Holy.” Here you’ll find a tight, pointed midrange bark that responds beautifully to both your fretting-hand technique and picking-hand intensity, without losing the low-end heft that supports vintage boogie riffs. Pushing the distortion up to the 3 o’clock range and goosing the freq. a bit more ushers in the zingy, pleasantly nasal tones of Queen’s “Tie Your Mother Down” and Thin Lizzy’s “Jailbreak.”

Dialing the distortion up to its maximum yields an extremely musical-sounding saturation—a rich, harmonically drenched texture that really comes alive when you crank freq. to 5 o’clock and dial back the highs to roughly 10 o’clock. Try playing the big guitar break in “Bohemian Rhapsody” with this syrupy, creamy tone, and listen as those 14th-fret figures glisten and bloom. Less intense freq. settings get you into Tom Scholz/Boston territory, with a ripe, focused tone that’s perfect for riffs like “Smokin’” and the fat chordal hooks of “More Than a Feeling.” Roll freq. back to, say, 12 o’clock, and you’ll nail Sabbath’s “Children of the Grave.” Again, be wary of tipping the Secret Freq’s volume past mid-point if you’re working with more extreme distortion settings— they don’t call this thing a “Freq” for nothing! That said, the highs knob does a great job of taming excessive glassiness and can contribute to beautiful violin tones.

The Verdict
Though I enjoyed the Secret Freq’s ability to tap into the zeitgeist of ’70s rock gods like Page, Brian May, Scholz, and Rick Derringer, as well as its ability to deliver tones reminiscent of Thin Lizzy, U.F.O., Scorpions and others, it doesn’t quite match the OCD as an all-purpose, go-to overdrive pedal for working gigs—even though it’s capable of tackling that assignment if you’re judicious about using the freq. control.

However, the Seek Freq is especially good at nailing the midrange-boosted tones that define a lot of classic rock. If those tones, as well as the parked-wah sounds associated with Frank Zappa and Kim Thayil, are in your paint box, you’ll find the Secret Freq an especially cool tone-coloring companion.

One of the Secret Freq’s greatest strengths will ultimately be as a tracking-room workhorse, because it’s a deep and impressive tool for crafting a focused and chiseled guitar sound in the studio—it’ll spare a lot of engineers the hassle of cleaning up a harmonic mess after you get a take. Whether in the studio or on the gig, though, the Secret Freq is sure to help you make the most of your amp’s potential (and potentially, its capacity for chaos)—secrets you’ll almost certainly be psyched to reveal.

Watch our video demo: