Gallien-Krueger MB Fusion 800 Head & CX-Series Cabinets (Review)

Gallien-Krueger president Bob Gallien is an especially deft engineer, and his designs almost always exhibit a fine attention to detail, tour-worthy durability, and enough sly twists to definitively stick out from the crowd.
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Gallien-Krueger president Bob Gallien is an especially deft engineer, and his designs almost always exhibit a fine attention to detail, tour-worthy durability, and enough sly twists to definitively stick out from the crowd. Known exclusively as builders of solid-state amps for most of its existence, G-K made a big move into the tube world with its Fusion 500 head several years ago. Pairing an all-tube preamp with a Class D power amp and switch-mode power supply (SMPS), the hybrid MB Fusion 500 sought to combine the plush feel, pillowy warmth, and pleasing overdrive character of a tube circuit with the authoritative slam of a well-designed Class D power amp. The MB Fusion 800 is essentially a higher-powered version of the 500, with an array of cool new features that confirm G-K is as groundbreaking as ever.

Unlike some so-called “hybrid” bass heads that pair a token tube for input buffering in the preamp with a solid-state power amp, the Fusion 800 is all-tube through the preamp. Taking a peek at the Fusion’s guts revealed only a handful of op-amps on the preamp board, but these aren’t in the audio path. With three 12AX7s onboard, there are essentially six tube stages to play with (12AX7s are “dual triodes,” meaning each tube actually contains two discrete triode circuits). One indication that the 12AX7s in the Fusion are doing something meaningful is their high plate (or anode) voltage. The high DC plate voltages are one indication that the preamp tubes are receiving the current necessary to function.

The rest of the G-K’s interior construction is serious stuff. The blue-masked through-hole circuit boards are tidy as can be, as are the abundant interconnects between boards. As with many other manufacturers of Class D/SMPS heads, Gallien-Krueger employs a power amp/power supply module from Denmark’s ICEpower, specifically the 250ASX2. Given the inherent complexity of Class D amps with integrated power supplies, almost every bass amp maker utilizes a third-party power amp and power supply. Kudos to G-K for sourcing a particularly good one in the 250ASX2, which here is wired in bridged-mono mode rated at a stable 800 watts into a 4Ω minimum load—a clever bit of engineering trickery, given the ICEpower modules aren’t technically rated for that impedance load.

The Fusion’s basic layout is easy to grok on first use, and the clever implementation of status-indicating LEDs is a cool feature. The preamp’s basic topology consists of two separately managed gain/volume pairings, indicated as A and B on the front panel. A player can set up a gain-staging setting on the A path and then use the front-panel button or the included footswitch to access an entirely different gain/volume setting in the B path. The result in practice could mean something as simple as a volume boost for a solo passage or a more saturated tone available via footswitch when needed. A word about the buttons is in order, too: They’re basically switches subtly engaged by pressing on one of the knobs. When you press a knob that does double-duty as a switch, the strip of color that shows position changes. In fact, all of the front-panel knobs and switches are illuminated. Not only does it look super cool, it also helps visibility when making quick changes on the fly, especially given the front panel’s relatively cramped confines.

The Fusion has all the I/O the average player will ever need, including an effect loop, full-featured balanced output, a tuner output, and a headphone output that doubles as an additional line-out for sending the preamp signal to another amp or mixer that requires an unbalanced output. Two side-mounted fans keep things cool, but they never switched on during testing.

The G-K’s tone shaping is straightforward and exceptionally flexible. Two shelving filters handle the bass and treble duties with peaking hi-mid and lo-mid filters governing the midrange. Additionally, G-K includes a contour control that employs a variable gain bass/treble boost and midrange cut as it’s turned up. It’s the insta-scoop sound on a knob, and it happens to be my least-favorite commonly included EQ feature on any amp, mostly because it’s responsible for so much bad tone when set inappropriately. But hey, that’s just me.


I tested the MB Fusion 800 with a variety of cabs, ranging from the sort of one-trip 1x12 gig boxes we all love to heartier affairs, like G-K’s own CX cabs (see sidebar), an Epifani 4x10, and an Ampeg SVT 8x10. The Fusion 800 packs a major wallop. It’s not only capable of exceptionally loud volumes, but it has a fast transient response and never tires, even when repetitively cranking out low notes on a 5-string. The tubes make themselves apparent when the gain is cranked to mid-way and up, with an oh-so-subtle bloom to the front edge of my bass’ attack that’s stereo-typically tube-like. The intrinsic tone of the amp is slightly dry and aggressive, but with healthy fur available when the input is judiciously cranked. Low-frequency output is stunning, and highs sizzle with all the treble you’d ever want. This can be expanded even further with the presence button depressed, but I never found it necessary. The EQ is well voiced and remarkably flexible, although its layout might be counterintuitive to some, with treble being the leftmost control. Gallien-Krueger has always laid out its EQ this way, in an effort to reduce the amp’s noise.

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The old ding on Class D/SMPS amps that they were grainy in the high frequencies or faltered under heavy duty is no longer true. The SMPS in the Fusion 800 is more than capable of delivering immediacy and thwack akin to that of linear supplies weighing many times more. With the controls set at noon, the amp seemed to have a fairly flat frequency response, with perhaps a small bit of midrange cut audible when I A/B’d its recorded signal with a straight-wire+ gain preamp.

The MB Fusion 800 is one of the slickest, most massive-sounding lightweight heads on the market. If you like modern-sounding transient response with the option to add harmonic richness courtesy of a real tube preamp, there isn’t any competition, really. It’s an impressive piece and well deserving of a Bass Player Editors’ Award.


On the heels of the Fusion 800 release comes the debut of G-K’s latest line of cabinets, the affordable CX series. Their design shows the same fastidious attention to detail that characterizes G-K’s amps. When I first picked up the CX410 4x10 ($500 street), I assumed it was equipped with neodymium drivers, given its remarkably light weight. Imagine my surprise when I discovered that it actually features G-K’s proprietary ceramic woofers, manufactured in its U.S. factory. The weight savings, then, really comes from the cabinets’ compact design and use of lightweight plywood. Yet the light weight doesn’t come at durability’s expense. G-K sourced a tough vinyl covering, interlocking metal corners, and tough spring-loaded handles. Interior construction is robust, with extensive bracing and chambered (but not completely sealed) cavities for each woofer to prevent undesirable acoustic interference. Tweeter control comes courtesy of a simple 3-position switch, and both Speakon and ¼" jacks are on offer.

My tester 4x10 sounded way too good for its price. It was punchy as all heck, sparkly when I needed it to be, and resilient. The overall impression was balanced, with a slight upper-midrange edge that can be a blessing when you’re trying to cut through a dense band. Given their great sound, low cost, and excellent construction, the CX cabinets are a superb value.



MB Fusion 800

Street $900
Pros The color and character of a tube head with the seemingly limitless power of a solid-state amp; exceptionally clever engineering; brimming with useful features
Cons None
Bottom Line G-K has created another modern classic in the Fusion 800, managing to pack the kitchen sink into an ultraportable head with more power than you’ll ever need.


Power rating 560 watts @ 8Ω; 800 watts @ 4Ω minimum load
Preamp All-tube; 3 x 12AX7
Power amp topology Class D
Power supply Switchmode
Outputs Two Speakon, XLR balanced line out (pre/pos-EQ), ¼" send out, ¼" tuner out
Tone controls bass ±14dB @ 40Hz; lo-mid +6dB, –9dB @ 250Hz; hi-mid +5dB, –8dB @ 1kHz; treble +10dB, –19dB @ 7kHz; bass +4dB @ 30Hz; bright +4dB @ 10kHz
Weight 5.5 lbs

Made in U.S. & China


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