By Jonathan Herrera
Since the 1994 debut of its “ Simul State” MOSFET power-amp technology, Mesa Engineering has made hay with the design, featuring it in a trio of cool bass heads: the Walkabout and M-Pulse 360 and 600. To add a pit bull to its kennel, Mesa dreamed up the Big Block 750, which compared to its siblings offers more aggressive midrange voicing, tube distortion, a bigger power amp, and a more straightforward control layout. Though Mesa admits that the Big Block was designed for a strong rock voice, the company also boasts of the Big Block’s style-spanning tone.
The Big Block’s EQ is a sort of hybrid descendant of several oftseen tone-shaping circuits. Its shelving BASS and TREBLE controls, based on the famed Baxandall design, provide broad-spectrum boost and cut with a gentle slope at each end of the audible frequency range. The cut-only PASSIVE - MID is derived from the classic Fender tone-stack circuit, and it’s interactive with the other controls. In general, the subtle circuit works well for delicately sprucing up a barky sound. A semi-parametric ACTIVE - MID control beefs up the Big Block’s EQ potency. Though the manual clearly states the circuit’s frequency range, gain, and flat knob setting, Mesa should have provided more informative front-panel text and used a pot with a center detent. Since the Big Block utilizes an all-tube front end, the GAIN control has a significant impact on tone. Increasing GAIN pushes the 12AX7 input tube harder, changing the signal’s harmonic structure from scoopy and bright at low settings to richer and woollier at higher positions. The Mesa doesn’t have an input pad, so high-output active basses require a judicious touch on GAIN . With a hot Bartolini pickup and preamp-equipped Modulus Guitars Quantum 5, the Big Block clipped at GAIN settings past 12 o’clock.
The Mesa’s tubalicious tone extends to its 12AX7-driven OVERDRIVE circuit. Derived from Mesa’s V-1 Bottle Rocket pedal, the circuit runs parallel to the clean tone. The OVERDRIVE knob controls gain, while O. D. MASTER governs the overall volume of the overdriven sound, controlling its ratio to the clean tone. Unfortunately, the overdrive is accessible only via footswitch— I would prefer a redundant front-panel switch.
Big Bottom Mesa definitely nailed the Big Block’s look. Its spartan, chromed-out appearance screams rock like a studded leather jacket. Our test head’s construction was excellent, each part exuding a rugged, luxurious feel. The deeply knurled knobs turned smoothly, thanks in part to a plastic washer placed under each knob to prevent metal-to-metal contact. The big baseball- bat power switch felt reassuring, and the accompanying purple jewel lamp is a nice vintage- style touch. The front-panel TUNER jack is redundant with its rear-panel equivalent, enhancing routing flexibility. I appreciated the MUTE function, but like the overdrive, muting is available only with the footswitch, a slightly maddening design that would have been easily resolved by including a front-panel button. Particularly delicious rear-panel goodies include a full-featured DIRECT OUTPUT and a SLAVE output with LEVEL control for driving additional power amps. Ventilation comes by way of two rearmounted fans and rear-panel vents.
Popping off the Big Block’s chassis cover revealed rugged interior construction. The four 12AX7 tubes were easily accessed and firmly supported, and each preamp IC chip was socket-mounted for easy replacement. Mesa prefers the “flying lead” design for its pot mounting, which limits the pots’ physical connection to the preamp to connecting wires, not the pot itself. Some believe this is a more rugged design, and there’s no doubt it makes for a less painful pot replacement. The Big Block’s large toroidal power transformer is surrounded by shielding plates—a nice idea that can help reduce noise due to irradiated interference. The Mesa’s power comes by way of a “Dual MOSFET Block” output section: Two symmetrical rows of 20 total MOSFETs are attached to large finned aluminum heatsinks that terminate at the rearpanel fans.
Block Rockin’ I used a gaggle of groovy cabs and basses with the Big Block. Test speakers included the Mesa Powerhouse 1000 (see sidebar), Bergantino NV425 and HT-322, Ampeg SVT Classic, and an Eden D-410XST. In the Soundroom and out in the wild I thwacked several Sadowsky Metro basses, a Mike Lull Vintage J, a Fender Precision, an F-Bass BN5, and an Epiphone Vinnie Hornsby Signature Les Paul through the Big Block.
With as close to a flat setting as possible, the Mesa’s strong midrange voice and rich, dynamically sensitive attack seemed ideally suited to rock or any style that requires big punch. The Big Block preamp’s plush, tubey feel is anchored by a quick power section that provides a palpable feeling of headroom. The shelving BASS and TREBLE EQ filters were powerful and musical, resulting in an intuitive tweaking experience that paid big sonic dividends. The two midrange controls work well together; I barely used the subtle PASSIVE - MID , preferring to notch out honk with the ACTIVE - MID , but the lack of frequency information around the knob sometimes made it a bit hard to find a previous setting.
Frankly, the Big Block’s overdrive kicks ass. It’s obvious Mesa knows distortion for guitar—just look for that “Triple Rectifier” logo behind many of metal’s heaviest bands—but with the Big Block, Mesa’s engineers prove themselves bass overdrive experts as well. The circuit is phenomenally tight, controlled, precise, and vicious. It can provide a demonically bleating belch or a furry tinge that recalls bygone vintage amps. One staffer praised its “total wall of buzzsaw attack” and “distinct color.” The separate gain and O . D . MASTER controls are great aids in dialing in the desired degree of dirt.
Despite the simple EQ, the Big Block offered a wide variety of onstage tones. It provided the hi-fi clarity I needed for a fusion trio gig, but it also doled out seriously greasy funk at a big outdoor festival. It doesn’t provide ultra-crisp tone, but it makes up for it with personality-rich gooeyness. The robust balanced output worked flawlessly on gigs, and the LEVEL control was a welcome feature, allowing me to retain a bit of audio autonomy while onstage.
If Mesa addresses the fact that the footswitch is necessary for both the MUTE and OVERDRIVE to work and provides an input pad for active basses, the company will have itself one hard-to-fault amp, especially for those who don’t need tons of EQ. Rockers might be drawn to the overdrive, but savvy tonehounds of all stripes would be wise to give the Big Block a look-see.
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Bass Player Editor's Award for Outstanding Tone |
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