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Classic-to-Wacky Trem Sounds, Easy ‘n’ Breezy

The PG Korora Merlo review.



Superb versatility yields a near-infinite variety of lush-sounding tremolos.

Experienced some noise in use, and the rate knob would benefit from a more gradual taper.


Korora Audio Merlo Harmonic Tremolo


Ease of Use:



The new Merlo harmonic tremolo pedal comes to us from Korora Audio, a small company in Seattle, Washington, that builds creative stomps like the Spira modulating filter (which won a Premier Gear Award in 2019). The Merlo isn’t inspired by brown-panel Fender or Magnatone tremolo, specifically. But it captures the spirit of the delicious tremolo on those amps while adding versatility, bountiful control, and textures spanning vintage classics and more radical modulations.

Like most harmonic tremolos, Merlo splits the guitar signal and uses LFOs to generate modulation. But in typical Korora style, that’s just the beginning. The EQ control is powerful, and the high- and low-pass filters modulate broader-than-usual frequency bands, emphasizing formant peaks that move with the modulation and create particularly rich, weird, and fine-tuned tremolo effects.

Shape Shifter
Two 3-way toggle switches are key to fine-tuning the Merlo’s voice. The upper toggle is a tone mode switch offering three settings: flat/transparent, mid peak, and warm, high-end roll off. Beneath that, an LFO selector switches between sine, triangle, and square waves. The LFO can be blended between wave shapes by using the, duh, shape knob. The EQ emphasis in a given wave peak can be enhanced with use of the color knob. It shifts the formant peaks, highlighting warmer or brighter tremolo tones and adding phase-like effects depending on the frequency shifts. It’s a powerful tool for shaping precise modulations, and can help achieve interesting blends of soft and hard-pulse textures. The rate and depth controls function as they do on a traditional tremolo, though, as we’ll see, the rate control is pretty range-y.

Dual status LEDs are a nifty visual touch. They pulse alternately in time with the split strands of the signal. If it gets a bit busy for your eyes, there are internal DIP switches to select whether you want the pulsing LEDs on or off. There’s also a DIP switch that determines whether the unit defaults to effect-on or -off on power-up.

Even in extra-choppy square and triangle wave modes, you can use the shape and color knobs to blunt the sharpest peaks.

Yet another, probably more useful, DIP switch activates a boost that can be set up to 3 dB in 1 dB increments. There are independent soft-relay footswitches for bypass and tap tempo. Input and output jacks are on the crown of the pedal, and Korora Audio recommends an external 9V DC power supply rated for at least 180 mA of current—which they thoughtfully supply in the box.

Pulse by Numbers
Needless to say, the Merlo can make a lot of sounds and bridges the gap between familiar vintage modulations and wilder fare beautifully. But, for me, the most appealing facet of the Merlo is the watery softness of the pulses you can achieve at many settings. Even in extra-choppy square and triangle wave modes, you can use the shape and color knobs to blunt the sharpest peaks while retaining the undulating feel of the more extreme wave shapes. That capability makes the unit feel more musical and flexible. The Merlo is also very responsive. Unlike some trems, it can be tuned to diminish pick attack less—even at extreme settings—and it feels incredibly dynamic at most settings.

The rate knob’s most conventional sounds live almost entirely within the first half of its rotation. Beyond that it tends to accelerate into hyper-speed warble. I’d guess that most players won’t use these speeds much, but the fast pulses are great for designing attention-grabbing passing phrases and solos. Personally, I’d prefer a pot with a more gradual taper and more precise control of traditional sounds. More experimental players might disagree. And, of course, the tap tempo is a very capable tool when you’re matching modulation rate to song tempo. At times, the extra color at many settings also seems to translate to a little extra noise from the pedal. (I used both the supplied adaptor and a Voodoo Lab Pedal Power ISO with isolated outputs.) Here again, though, the less noise-floor-obsessed may consider a little hiss fair trade for a wider range of sounds and EQ options.

The Verdict
The Merlo is a very hip effect and, in my humble opinion, a must-try for tremolo addicts. The harmonic tremolo sounds are complex and easy to tailor in precise ways (though the rate control might be an exception for some). The Merlo also gets a lot of great sounds out of a relatively simple control set. All that flexibility and modulation massaging potential will set you back a fair bit, at almost $250. But Merlo’s impressive performance often justifies the price.

Watch our demo: