If there’s such thing as a cult modulation effect, the “harmonic tremolo” found in certain early-1960s Fender brownface amps certainly qualifies. Unlike most trems, which modulate the entire frequency of your signal, the circuit splits your sound into high and low bands, modulating one with an LFO, and the other with an inverted version of the LFO, alternately emphasizing treble and bass. The result isn’t pure tremolo, but a trippy trem/vibrato/phaser hybrid. Fender soon replaced this complex, three-tube circuit with the simpler (and cheaper) single-tube optical tremolo found in most Fender blackface amps. But for some players, the phasey brownface sound remains the definitive tremolo.

Brownface Reborn
The harmonic tremolo effect is often resurrected in the digital realm, where it’s easy to simulate the two-band effect without tricky, tube-intensive circuitry. But it’s rarely been realized as suavely as in Coldcraft’s Harmonic Tremolo stompbox, which combines an analog preamp stage with a DSP chip and some clever new controls. It’s the company’s second edition of the effect, replacing a discontinued all-analog version.

The effect is every bit as pretty, immersive, and swirly as it should be. It definitely sounds distinct from standard single-band tremolo effects.

Coldcraft has crammed so much circuitry into a standard 1590B enclosure that there’s no room for a battery—AC is required. In addition to the effect circuitry, there’s soft-touch relay switching. An oddball mix of ICs and both standard-sized and miniature analog components are laid out on two circuit boards linked by ribbon connector, with board-mounted pots and jacks. Construction seems solid, aside from soldering-iron scars on a couple of the box capacitors. High-quality metal knobs lend a classy touch.

The stompbox offers a convincing version of the original brownface effect. Naturally, you don’t get some of the subtle, random variation of the analog circuit, and you’ll never get the exact brownface sound from a stompbox positioned before the amp’s input. But there’s nothing overtly “digital-sounding” about the tones here, and the effect is every bit as pretty, immersive, and swirly as it should be. It definitely sounds distinct from standard single-band tremolo.

But the coolest things about Coldcraft’s pedal are the ways it goes beyond Fender’s original design. In addition to the expected speed and intensity controls, the pedal boasts three extra pots that unlock cool variations on the original concept.


A fine digital replica of a great analog effect. More versatile than the original.

No battery option.


Ease of Use:




Coldcraft Effects Harmonic Tremolo v2

A volume knob, which sets the amount of analog boost, is a big part of the equation. Some digital trems sound limp simply because the designers didn’t realize that tremolo effects require a bit of signal boost—otherwise, there’s an inevitable energy drop when the effect is engaged. Here you can fine-tune the level to taste. You might, for example, set the gain on the high side if you tend to use tremolo on quieter, clean-tones passages.

Equally useful is a treble-nixing tone cut knob. A darker setting might suit a bright single-coil pickup, for example, while you might want maximum brightness to cut through with an overdriven humbucker tone.

Phase for Days
But the coolest new feature is a balance control, which regulates the blend between the two frequency bands. With the knob centered, you get something close to the original Fender sound. Twisting it fully clockwise emphasizes treble trem, while the opposite direction puts the low-frequency effect front and center (and provides a darn good Uni-Vibe sound). There are many nice variations along the way. You can’t do that with a ’62 Fender Pro!

Another clever idea: A momentary mode, where the effect is enabled only when the footswitch is held down. (You enter the mode via a tap-tap-hold footswitch sequence. To exit this mode, repower the pedal.) It’s a nice option with many possible application, though because of the optical muting component of the bypass system, there’s a slight disruption when the effect is engaged—not a pop or a silence, but enough of a contrast that you probably wouldn’t activate the effect over a sustained chord. But it works great for applying the effect to a single phrase.

The Verdict
Coldcraft’s Harmonic Tremolo is a cool digital incarnation of a rare and revered two-band modulation effect. Core tones are warm and inviting, and thoughtful extras such as volume, tone, and balance controls unlock additional colors brownface Fenders can’t deliver. You get fine sounds and innovative design at an inviting price.

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