Hands-On Review:
Gallien–Krueger MB Heads
Compact heads deliver high performance at affordable prices

By Terry Buddingh, International Music Gear Journalist

Gallien-Krueger has consistently been on the leading edge of bass amp design and technology for more than forty years, and that decades-long tradition continues with the ultra-compact, ultra-lightweight, full-featured and super affordable MB series heads. Featuring state-of-the-art Class-D power amps, these surprisingly powerful micro-size heads offer effortless portability and a full complement of essential features — all at amazingly affordable prices.
The MB200 and MB500 boast GK’s time-tested and gig-proven solid-state preamp and tone control circuitry, while the MB Fusion borrows its all tube preamp from GK’s heavyweight hybrid Fusion 550 (but without the Fusion 550’s programmable motorized tone controls). Built to endure the rigors of the road, these serious tone machines fully embody Bob Gallien’s ‘Tools, not Toys’ design philosophy and all three heads are loaded with essential modern day, real world gigging accouterments like balanced XLR direct outputs and Speakon speaker output jacks.


MB200
The MB200 is amazingly small; it’s smaller than many D.I. boxes, stand alone preamps and pedals, and it’s thin enough to easily slip into most gig bag pockets. Weighing a mere 2 pounds, it’s difficult to imagine a more travel friendly bass head. Despite its small size, GK still managed to include everything that a gigging bass player needs: there’s a -10 dB pad switch to accommodate high output active basses, an on/off switch for GK’s classic contour pre-shape circuit, plus GK’s legendary 4 band active EQ. The MB200 also has a balanced D.I. output with Pre/Post EQ selector button, an 1/8” auxiliary Input for CD, MP3 or other players, and a switchable line out/chain out/headphones jack. The MB200 has a single Speakon output jack.
It may look tiny, but the MB200 is indeed a serious and versatile tone tool. Conservatively rated at 200 watts @ 4 ohms, the MB200 is surprisingly loud, with amazingly strong and weighty low end response. It looks small, but it sounds massive. The MB200 is bound to find its way into to a wide range of applications. You could use it as a full featured D.I. box, enhancing your sound with GK’s excellent sounding contour and tone controls, or you could use the line out to drive a large power amp when extra volume might be required. I’m sure these pint size powerhouses will find their way into guitar, keyboard and other applications as well. Considering its effortless portability, gig worthy power, potential for adaptability, and affordable price, the MB200 will surely find a place in even the most extensive bass gear arsenals. This is a real no brainer — everybody should have an MB200.

MB 500
With its mute button, effects loop, tuner output, defeatable limiter, master volume control, and footswitchable boost with secondary master volume control, the MB500 offers a boatload of additional features to go along with its extra power. With an honest 500 watts @ 4 ohms, the MB500 kicks like a mule with an authoritative and forceful punch. This head likes to rock and rock hard; it really comes to life when you crank it up, and it seems to dare you to do so. Weighing in at 3.75 pounds, and breaking the buck-a-watt price barrier, the MB500 packs a lot of value into an incredibly portable high powered package.
The footswitchable boost feature greatly expands the MB500’s range of tonal options. Increasing the boost knob setting increases the trademark GK growl, and this added texture provides some colorful contrast when switching from a cleaner non-boosted setting. It’s useful for more rock flavored tone, soloing, or contrasting mid-song section and textural changes.
The post EQ, pre-boost effects loop works great with a wide range of devices, and greatly expands the MB500’s range of options. The MB500 has two Speakon speaker output jacks, so it can easily power two speaker cabinets.

MB Fusion
The MB Fusion grafts an all tube preamp onto the same power amp section used in the MB500, so the power is the same: 500 watts @ 4 ohms. Using three 12AX7 tubes running at high voltage, the MB Fusion’s preamp is essentially a tube driven adaptation of GK’s classic solid state preamp circuit design. The feature set is similar to the MB500, except the MB Fusion has selectable contour control mid dip center frequencies (500 or 800 Hz), and separate switches labeled presence and deep (for a 4 dB boost @ 10k Hz and 30 Hz, respectively).
The MB Fusion has two footswitchable gain and master volume controls. This allows you to instantly switch between two flavors of tube overdrive (or clean tones) with the tap of a switch. Like the MB500, the MB Fusion is capable of a wide range of tones and textures. The MB Fusion’s cleaner tones impart a delectable sense of hi-fi sweetness, texture, dimension and dynamic nuance that tube lovers will surely recognize and enjoy. Using a pick and cranking up the Gain knob elicits wicked grind and growl that clearly evokes the textures of far less portable all tube bass icons.

GK’s compact yet featured-packed MB heads offer gig worthy power and tone in surprisingly lightweight and exceptionally high value packages.

  • MB Series Heads, General Features & Specs
  • Passive and Active switch
  • Preamp Gain control
  • Contour control (on/off button on MB200)
  • Active 4 band EQ
  • Balanced XLR DI output jack
  • State of the art Class D power amp
  • Weight reducing switch-mode power supply
  • Speakon speaker output jacks