Ursa Major

Stereophile September 2006

mbl Reference 9007 power amplifier

Michael Fremer, September, 2006  

Best known for its omnidirectional loudspeakers, the German manufacturer mbl also produces three complete lines of high-performance electronics that, despite being large and built to jewel-like perfection, are sometimes lost in the shadow cast by the dramatic-looking—and -sounding—Radialstrahler 101E, which I reviewed in October 2004(html).

While mbl's least expensive line, the Basic models, is limited to one each of a preamp, stereo amp, integrated amp, CD player, tuner, and loudspeaker, the Noble and Reference lines are crowded with products from which numerous complete systems (minus a turntable) can be assembled.

The top line, the Reference series, includes three fully balanced monoblock amplifiers capable of being configured as unbalanced for stereo use. The newest of the three is the Reference 9007 ($13,300 each), claimed to deliver 440W RMS into 8 ohms, 570W into 4 ohms, or 800W into 2 ohms. Stereo operation cuts the power outputs significantly, to 130Wpc, 200Wpc, and 290Wpc, respectively.

What prompted this review was my auditioning of McIntosh Laboratory's C1000 balanced preamp (the review was published in the August issue). While the three-box C1000 can run single-ended, I felt it deserved a hearing in balanced mode. In Las Vegas during CES, I was asked by mbl if I had any interest in reviewing their new Reference 9007 amp, also balanced. I took them up on the offer.

Designed from scratch  Founded in 1979 by engineer Wolfgang Meletsky to produce the original Radialstrahler loudspeaker, Berlin-based mbl has since grown into a fully integrated company. Everyone at mbl with whom I spoke emphasized that the company's electronics, inside and out, are designed and built in-house, as are the 9007's gleaming curved faceplate (in black/gold or Arctic Silver) and beefy, solid-copper speaker terminals.

In early June, when I sat down with Meletsky at Home Entertainment 2006 to get a rundown on the Reference 9007's design, he emphasized that the DC servo-coupled amp is built using all discrete components—there are no integrated circuits or microprocessors. Low-tolerance, low-induction resistors and megahertz-bandwidth capacitors are used throughout, as are multilayer FR4 glass-epoxy circuit boards featuring ultrashort signal paths, heavy copper planes in the output section, and galvanic gilding to prevent oxidation. Other premium parts include "superfast" ring-emitter (bipolar) transistors and custom-built toroidal transformers for the driver and power stages. Energy storage is via a bank of custom-built, 132,000µF capacitors from Sweden, while separate power supplies feed the driver and output stages. The power transformer is mounted on an epoxy-encased aluminum shield.

The circuitry includes mbl's exclusive Direct Push/Pull (DPP) design, which is claimed to minimize delay by shunting part of the signal directly to the output instead of routing it through various stages along the way; and mbl's Isolated Gain Cell (IGC) technology, which requires less current and lets the amp run cool while offering class-A–like sound, though it actually runs in class-A/B.

Wolfgang Meletsky described to me in great detail the care that goes into choosing and loading the power capacitors used in the 9007; he said they generate only 1% of the distortion found in "normal" caps. The power supply also uses "fast" rectifiers to match the charging current to the capacitor's capabilities. According to Meletsky, if the capacitor is charged too quickly, there's ringing on the supply rails; too slow, and there's ripple. The charge and discharge times must be the same, he told me, also to prevent ringing.

He also explained why the 9007's full sonic potential is available only in balanced monophonic mode, but his explanation couldn't jump the language barrier and the gaps in my technical knowledge. One thing that was clear is that the 9007's frequency response is claimed to extend to 320kHz in balanced mono mode but to only 200kHz in single-ended stereo mode.

The gleaming exterior's fine, watch-like detail and fit'n'finish are equally impressive, and despite the 9007's relative compactness, it weighs 75 lbs. Whether or not you appreciate the oversized, mbl logo of shiny gold on the front is a matter of taste. I think a bit more understatement is called for.

$26,600 is a lot to pay for a pair of 440W monophonic amplifiers—some might even think it an exorbitant amount—but in terms of design elegance, circuit topology, parts and build quality, and its lustrous, satin-smooth finish, it's clear that no expense was spared in designing and building the Reference 9007.

Setup and use  Because the Reference 9007 can be used as either a balanced monoblock or a single-ended stereo amplifier and has provisions for biwiring and biamping, its rear panel has six output terminals and a potentially confusing cable-routing schematic etched onto it. The written instructions tend to increase rather than reduce the confusion. Also on the rear is a balanced XLR connector, a stereo pair of RCA jacks, an IEC jack, and an illuminated power switch.

Speaking of confusion, below the large mbl logo on the front is a function-indicator light flanked by two switches, Sleep and Standby/On. I never did fully comprehend the difference. The instructions tell you to first press Sleep to put the amp in "warmup mode." Then you're told to push Standby to turn the amplifier on. Push again and the amp is in Standby mode, and ready to operate when you push Standby again.

A heading in the manual labeled "Sleep Mode" reads: "When the amp is in 'sleep mode' only the sleep function is operating." Say what? To clarify, below that is a three-column grid labeled "Sleep Switch," "Standby Switch," and "Mode." When the Sleep and Standby switches are both off, you're in Sleep mode. When Sleep is on and Standby is off, you're in Standby mode. When Sleep is off and Standby is on, you're also in Sleep mode. When Sleep is on and Standby is on, you're in Operating mode.

Understand all that? I didn't—not for the entire time I had the 9007s for review. I just left them on all the time and paid the electric bill.

The Reference 9007 grips the road  For the McIntosh C1000 review, I ran the preamp balanced into the mbls and single-ended into my reference Musical Fidelity kW monoblocks—balanced because that's how most owners of the C1000 will probably use it, and single-ended for the benefit of unbalanced owners—er, I mean, owners of unbalanced gear.

Simultaneously inserting two new components into an audio system makes reviewing either tricky, but I'm confident I understood the personalities of the McIntosh C1000 and mbl Reference 9007, as well as the contributions each made to the exceptionally fine sound they together produced during the two months I had them in my system.

I also ran my reference Musical Fidelity kWP single-ended preamp into a single 9007 configured for stereo, though mbl of America's Jeremy Bryan made clear that the stereo configuration was intended more as a convenience for those who couldn't afford to buy two 9007s at once, and that it wouldn't sound nearly as good that way.

He was right. You don't want to buy a $13,300 Reference 9007 and use it as a single-ended stereo amp unless you plan on adding a second one some time soon. The 9007's performance in stereo mode, while competent, was not particularly distinguished for a $13k amplifier. In fact, it sounded spatially flat, anemic, and somewhat bright. Run as balanced monoblocks, two 9007s took on a considerably different personality.

The 9007 produced an appealing sense of continuous, liquid musical flow, combined with exceptional transparency and taut, rhythmic assertiveness. The amps presented a sonic picture that was coherent and whole—a prerequisite for $26,600/pair. While never bright, hard, or brittle, the overall presentation was nevertheless oriented more toward rhythmic drive, transient speed, and clarity than toward harmonic richness or textural suppleness. These qualities made the 9007 a perfect complement to the Mac C1000's moderate tendency toward delicacy, richness, and midband bloom.

Compared to the presentation of my reference Musical Fidelity kW amplifiers, the mbls sounded faster, somewhat more effervescent, and more "together," notes appearing instantaneously out of a black background and disappearing into the ether with equal speed—perhaps a result of the amplifier's ultra-low noise floor.

The 9007's fast attack and decay were especially well suited to reproducing music with heavy rhythmic drive. I recently acquired a copy of the vinyl edition of Give Up (Sub Pop SP595), by The Postal Service, the synth-heavy side project of Death Cab for Cutie's Benjamin Gibbard. The music—built from the sounds of drum machines, electronic blips, and occasional electric guitar and piano—sounded absolutely pristine, each carefully chosen element hovering and shimmering, tightly focused in three dimensions against the blackness.

When I hear a component excel with surgical precision at a particular musical task, as the 9007 did with percussion, I pick through my record collection looking for more such challenges. After Give Up, I pulled out an original LP (New World 319) and Classic's reissue of Pulse! , and reveled in John Cage's Third Construction, written for four percussionists playing everything from 20 tin cans of various sizes to tom-toms, claves, gongs, ratchets, cowbells, maracas, and even a conch shell. At one point a rubbed bass drum creates an explosion of low-frequency energy. The mbl 9007 delivered this stupendously recorded piece the way it was meant to be heard: with razor-sharp clarity, equally nuanced rich textures, and full-throttle dynamic authority.

I then moved on to an original pressing of Philip Glass's Einstein On the Beach (LPs, Tomato 4-2901), which is a genius, a genius piece, a genius piece to, a genius piece to, to, too, two, three, four, actually, to actually bring, to actually bring to, to actually bring to a crowded, to actually bring to a crowded beach, to a crowded beach, and play and play on a boom, on a boom box. After five minutes of it, the people around you will run screaming and you'll have a clear patch of sand to yourself. Anyway, I like Einstein; a while back, I sat through all four hours of it at the Brooklyn Academy of Music. This time, I sat through only one side. The 9007s reproduced the synthesizer parts and the male and female voices with bell-like clarity, offering sharply focused three-dimensional images, taut transients, and total freedom from smear, while decisively carving out and plumbing the depths of the low-bass synth notes.

Though the 9007 was a somewhat cool customer, less "ripe" than some other amplifiers I've encountered, it managed to effectively capture the harmonic structures of instruments on familiar recordings, reproducing with great clarity the texture and tonality of pianos, for instance. I pulled out Nat "King" Cole's 1956 trio recording After Midnight (LP, Capitol W782) one evening, and this mono recording's three-dimensionality and instrumental palpability were impressively revealed thanks to the 9007's musical grip. Rhythmically, the record had never sounded more assured, though it had less of its familiar tubey warmth and "golden glow" than I'm used to.

Andrew Litton and the Dallas Symphony Orchestra's recording of Mahler's Symphony 2 (CD, Delos DE 3237), which I picked up during a recent visit to Dallas, demonstrated the 9007s' impressive dynamic reserves and soundstaging prowess, as well as their harmonic capabilities. While the amps' midband was somewhat reticent compared to my reference kWs, and certainly when compared to what tube lovers might expect, I found that the cellos and basses on the right side of the orchestra sounded woody and full-bodied, and the brass had a proper velvet glow and sufficient bite to satisfy, though the 9007s were more "event-oriented" than emphasizing tonality and texture. When timpani mallets hit drumheads, the emphasis was more on the impact than on the ensuing reverberation.

Well-recorded female voices confirmed that while the 9007 was not the richest-sounding amplifier you'll ever hear, neither was it thin or bleached-out. Its tonal balance tilted only slightly to one side: it could tidy up and clarify a too-warm recording or ever so slightly lean out a neutral one. More important, its balance was consistent throughout the audioband, giving it the coherence and authority one expects at this price point.

The 9007s' imaging and soundstaging were up there with the best I've heard: tightly focused, not edgy, and presented with great solidity and three-dimensionality. The 9007s produced believable, palpable, properly sized images on stages whose width and depth were appropriate to the recording. The "black" backgrounds added drama to the picture.

Overall, what made the Reference 9007 an exciting, credible performer was that it spoke with a singular voice: It was as fast on top as it was on the bottom. It delivered sparkling, transparent, shimmering highs, and tight, well-damped bass. The 9007 never sounded mechanical or thin, nor did it show any grainy, bright, or etched seams. While it sacrificed a bit of bloom and suppleness to deliver the music with crystalline transparency, the tradeoff was more than worth it. The Reference 9007 was among the most exciting and engaging amplifiers I've heard.

Conclusion  I have come to appreciate what lots of power can bring to an audio system. An amp working at the lower end of its power limits always sounds more relaxed than one asked to perform at or near its upper limit (lovers of mini-watt single-ended-triode amps, start screaming now). Even though the mbl Reference 9007 used as a monoblock is rated at a prodigious 440W into 8 ohms and delivered authoritative, powerful musical experiences, it couldn't scale the dynamic peaks produced by my 1000W references, the Musical Fidelity kWs, or provide the kWs' weight and sense of ease. But in other, very significant ways I felt the 9007 outperformed the kW: in terms of rhythm'n'pace, overall coherence, and high-frequency transparency, where it set new standards in my listening experience.

Overall, the mbl 9007 struck me as delivering almost as much detail and resolve as the big Halcro dm68s, which I was fortunate to spend some time with—but with greater musical flesh on the bone and more intense emotional involvement. The 9007 offered sound about halfway between the sweetness of the far more powerful (and less than half as expensive) Musical Fidelity kW750 dual-mono amp and the resolution, ultralow distortion, and analytical prowess of the big Halcros. That's saying a lot.

While a single Reference 9007 can be configured as a single-ended stereo amplifier, I don't recommend this except as a temporary measure for buyers who can't afford to buy two at the same time. But as a pair of monoblocks, the mbl Reference 9007's exceptional qualities of sound, build, and appearance justify its high price. Here's hoping its measured performance backs me up. If you're comfortable spending $26,600 for a pair of solid-state monoblocks, add these to your list

Specifications

Description: Solid-state power amplifier capable of being used as a balanced monoblock or a single-ended stereo model. Rated power output: 440W into 8 ohms (26.4dBW), 570W into 4 ohms (24.6dBW), 800W into 2 ohms (23dBW), mono; 130W into 8 ohms (21.1dBW), 200W into 4 ohms (23dBW), 290W into 2 ohms (18.6dBW), stereo. Frequency range: DC–200kHz, mono; DC–320kHz, stereo. Distortion: <0.003%, 1kHz at 50W into 4 ohms. Output current: 30A peak maximum. Signal/noise ratio (no reference level given): 114dB unweighted, 118dB A-weighted, mono; 113dB unweighted, 123dB A-weighted, stereo. Damping factor: 300 at 1kHz. Input impedance: 20k ohms (XLR, mono), 10k ohms (RCA, stereo). Input sensitivity: 2.2V, 570W, 4 ohms. 

Dimensions: 19" (480mm) W by 9" (230mm) H by 17" (430mm) D. Weight: 75 lbs (34kg). 

Finishes: Black/gold, Arctic Silver *

* La finition Black & Chrome est une finition spéciale URSA MAJOR