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Spaceman Mercury IV Review

Spaceman’s magical tone masseuse has a way of making everything sound just plain better.



Transformative tone-shaping power. Powerful boost. Sensitive, interactive EQ and harmonic controls.

Controls can be vague. Toggle functions are unclear.


Spaceman Mercury IV


Ease of Use:



If I had to pinpoint a single quality of Spacemen stompboxes that makes them worthy of the hype and sky-high resale prices, it’s a sense of feel. Of course, that doesn’t pinpoint much of anything, because the “feel” component of a Spacemen pedal experience typically transcends any one meaning of the word. Certainly there’s the physical heft and solidity of the pedals themselves, and the engraved panels and gem lamps that evoke ’60s outboard studio gear and aviation-spec instruments. There’s the immediacy and responsiveness that makes single notes and overtones feel startlingly alive. And the way the pedal’s controls interact with your tones and each other—a nebulous, drifting, exploratory feel that paradoxically enables super-precise tone sculpting.

Though the Mercury IV Harmonic Booster delivers satisfying experiences on each of these fronts, it’s the last two—those sensations of fluid, illuminated musical and mechanical interaction that distinguish this latest evolution of the Mercury line. Mercury IV enhances the sound of your guitar, amp, and other pedals in overt ways and barely perceptible ones too. And its capacity for exciting and enlivening guitar tones can make Mercury IV feel as powerful as an expensive outboard compressor or preamp.

Instrumentally Speaking
I’ve written at length about the quality and aesthetics that distinguish Spacemen pedals in other reviews. It’s more of the same with the Mercury IV. The engraved panel makes you feel like you’re dialing in a vintage Fairchild limiter aboard an X-15 cleaving the stratosphere. The switches and knobs respond with precision and smooth, perfect resistance. Inside, the circuit board is a feast for the eyes—all well ordered and immaculately seated components on a reflective foil surface that looks lifted from Warhol’s Factory circa ’66. The myriad components also hint at the depth and complexity of the tones within.

That the tactile pleasures of navigating the Mercury IV are numerous is a good thing, because the function of individual controls is not always clear. The “boost” knob, which enables access to as much as 35 dB of extra kick, is the easiest to grasp. The “harmonics” control, however, can be subtle, even vague, depending on the context. The “high” and “low” toggles, with positions marked by small hash marks of varying thickness, are ultimately easiest to sort through trial and error. The set of hash marks under each one indicate areas of EQ emphasis— with thicker hash marks corresponding to the bassiest sounds, and so forth. But there is little specific explanation of what you’re adding or subtracting with these switches. If you savor the experience of navigating controls intuitively and letting your ears be your guide, the Mercury IV is a joy. Players that prefer knowing what frequency they’re manipulating down to last megahertz may be less thrilled.

Even at settings least suited to a given guitar, the pedal adds air and dimension and animates overtones.

Bigger, Brighter, Full of Light
For all the Mercury IV’s nuances, countless potential tone colors, and sometimes perplexing functions, it’s a breeze to just plug in and get great sounds. Even at settings least suited to a given guitar, the pedal adds air and dimension and animates overtones. And it usually takes just a few exploratory flicks of the toggles and a little twist of the harmonics knob before you start to hear tone improvement and sense the range and sensitivity of the controls.

Much of the pedal’s magic hides in overtone details that are, yes, almost felt more than heard. In the case of the harmonics control, its nuances and sensitivity to the other controls are most apparent in big amps at high volumes. And my most satisfying experiences with the pedal transpired when I hooked it up to my Bassman piggyback blaring away at concert volume. The Bassman has hints of 50-watt Marshall plexi in its harmonic makeup. But typically, they’re overshadowed by the amp’s softer attack and substantial, contoured low end. Boosting high-mid content via the Mercury IV’s switch array and the harmonics control illuminated those facets of the Bassman’s harmonic spectrum brilliantly without sacrificing any of the amp’s low-end potency. And I wouldn’t be exaggerating if I called the effect transformative. Mercury IV gave the Fender a more aggressive, oxygenated and combustible voice that I’m not sure I’ve ever heard in quite that way.

Mercury IV’s effect on small amps can also be profound. You won’t necessarily hear all of the pedal’s full-spectrum overtone magic through an 8" speaker at apartment volume. But you can plainly perceive the sense of extra size and dimension that it lends. You can also still experience the Mercury IV’s capacity for reshaping effects and pedal chains. Mid-forward overdrives can be massaged into fatter, fuller versions of themselves. Fuzzes with high octave content or toppy tone signatures can take on smoother, more muscular voices or be driven to explosive teetering-at-edge-of-feedback extremes. Even delay and modulation effects with pronounced overtone colors can be manipulated to de-emphasize or highlight such quirks.

The Verdict
Mercury IV’s tone-sculpting potential is impressive and expansive. And its capacity to be both masseuse and provocateur to your guitar, effects, and amplifier with equal aplomb is uncommon. Exploring it’s refined voices and malleable, adaptive nature led me to imagine a much more streamlined pedalboard—and many fewer backline headaches. But a pedalboard maximalist could just as easily find a place for its rich, sublime boost and overdrive colors and thrill to its positive influence on other pedals. Indeed, there a few musical devices that Mercury IV can’t transform into a fuller, richer, more beautifully sculpted version of itself.

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