Solid State Power Amp Reviews

As large as a small file cabinet and weighing 223 lbs, MBL's most powerful amplifier, the Reference 9011, is a tour de force of electronics design and implementation that will set you back $60,000 if you're a stereo enthusiast, or $120,000 if you like pure balanced mono.

Though it includes two separate amplifier modules per chassis and can be run as a lower-powered stereo amplifier, I've seen the 9011 used only in pairs, as monoblocks, at shows and in owners' homes. I guess if you can afford to spend $60,000 for a power amplifier, you can comfortably double up to get the most from this design. The instruction manual includes a diagram for hooking up four 9011s, which I'm sure some wealthy, power-hungry audiophiles actually do.

The instructions warn that, should you "wish to operate two or more amplifiers, never stack them." Right! Each 9011 requires two AC cords for maximum output, and is powered up by flipping as many as three illuminated rear-panel switches, one for each of its three main power transformers; the second and third switches, labeled Boost 2 and Boost 3, are used depending on the speaker load (Boost 3 is recommended for 2 ohm loads). A fourth shielded transformer supplies the voltage-amplification stage.

Used as a bridged monoblock, the 9011 can only be run from its balanced input. Because the amp can be used in multiple ways, the amp's rear panel sports six hefty copper binding posts fitted with large, finger-twist screw-down clamps. Unfortunately, if your speaker cables have angled spade lugs, the screw-downs will interfere with the spades, making it difficult to fully insert and tightly secure the spades. Where's a good standards committee when you need one?

Power to Spare?
The 9011 is rated at 440W into 8 ohms, 840 into 4 ohms, or 1390 into 2 ohms. Its "Peak Pulse Power" rating is 5000W into 2 ohms. But really, if you own 8 ohm speakers, all that physical heft gets you just 440W—still plenty, but somewhat surprising given the 9011's weight and size: 19" wide by 13" high by 34" deep. If you look at MBL's spec sheet, you might notice that the 9011's maximum output power into 8 ohms is identical to that of MBL's Reference 9007 amp, which I reviewed in September 2006 (Vol.29 No.9). Into 4 and 2 ohms, however, the differences become obvious between the 9007's single 400VA transformer, four 3300µF capacitors, and 12 output transistors and the 9011's three 400VA transformers, eleven 3300µF capacitors, and 24 output transistors.

The 9011 is capable of delivering three times the long-term power output and twice the short-term current delivery compared to the 9007 and that becomes important when you ask an amp to deliver power into a complex real world load, rather than into a simple constant-impedance test bench load. Of course, brute-force power isn't everything. The 9011's peak current output is 50 amps compared with the 9007's 30 amps, which is a significant increase.

The 9011's frequency response is claimed to be DC–200kHz! Its distortion is rated as an impressive <0.001% at 50W into 4 ohms at 1kHz. The signal/noise ratio of 118dB, A-weighted is also impressive.

Setup
When MBL North America's Jeremy Bryan and an assistant arrived to install the Reference 9011s, my system included the Wilson Audio MAXX 3 speakers and the Ypsilon PST-100 Mk.II preamplifier. Because the 9011 used as a monoblock must be driven by a balanced signal, I borrowed from Aaudio Imports a pair of Ypsilon BC1 single-ended-to-balanced transformers. When driven by a 100 ohm source, these have a claimed frequency response of 4Hz–250kHz, ±3dB. There was room for only the two MBLs between the Wilsons, so I lent a friend my Musical Fidelity Titan amp.

Although my stash of cables is big enough to build a suspension bridge, it included no long balanced cables. Bryan brought along a full set of Wireworld Platinum Eclipse balanced interconnects Eclipse ($16,400/2.5m), which I first used for my review of Music Reference's RM-200 Mk.II power amp (December 2011), along with double runs of Platinum Eclipse speaker cable, which I needed for next month's review of MBL's Radialstrahler 101E Mk.IIs. But because I've been using TARA Labs Zeros as reference interconnects for years, I asked TARA if I could borrow a long set of those (which probably would cost as much as that suspension bridge!).

After I installed the balanced TARA Labs Zero interconnects, I turned the amps on, and went upstairs to attend to something. I returned to the smell of burning electronics and an odd noise coming from the speakers. The 9011s felt hot. Fearing I'd fried at least one of them, I immediately turned them off and let them cool down. Then I removed the TARAs and reinstated the balanced Wireworlds. Much to my relief, both amps were functioning fine. Clearly, as John Cameron Swayze used to say, they can take a licking and keep on ticking.

The TARA cables, like the MBL amps, have a very wide bandwidth. TARA Labs also floats the shield, which returns to a star-grounded box containing nonferrite RFI/EMI shielding, but the cables apparently acted as antennas and picked up ultrasonic noise (perhaps from my WiFi network?)—and the MBLs, trying to amplify that high-frequency noise, went into oscillation. I hate when that happens. I had also requested and received a long pair of ZenSati #1 balanced interconnects, which are also ultrawide-bandwidth cables but also have no shielding. I hooked them up, and this time the dedicated line's circuit breaker blew almost immediately. [This was due to the combination of the Ypsilon preamplifier and transformers mandating the use of properly shielded cables; see the "Measurements" sidebar—Ed.]

This is not a "fault" of the amplifier, which, as it is intended to dp, protected itself. Rather, it indicates you or your dealer must choose appropriate cables for use with this amplifier. In the meantime, I used the Wireworlds with the Ypsilon preamplifier to get my listening underway.

The Sound of Nothing Minus Something
Between the recently reviewed Soulution 710 ($45,000, August 2011), the VTL MB-450 Series III Signature ($18,000/pair, April 2011), the Music Reference RM-200 Mk.II ($4200, December 2011), and my reference Musical Fidelity Titan ($30,000, June 2009), you're talking about many different flavors of power amp—all of them mighty tasty!

The MBL Reference 9011 immediately impressed me with its essential lack of character, neatly threading the needle between the Soulution's cool speediness, the VTL's assertive top end, and the MF's warmer if less resolving sound.

Like the Titan, the 9011's huge power reserves meant that, at all times, it loafed while driving the relatively sensitive MAXX 3s, though even they require a good deal of current to be driven well. Not a problem for the 9011s, or even for the RM-200 Mk.II. But while the Music Reference produced an expansive, inviting, physically deep soundstage, the MBL was simply "there" in that whatever sonic character it had was not immediately obvious. The positive aspect of this plenty of nothing was a complete absence of "electronic." If the Soulution 710 immediately announced its presence as an amplifier that was hairpin-turn fast and tight, and paced to stimulate the secretion of adrenalin, the sound of the MBL 9011 at first simply appeared without having presented its calling card, though eventually one did emerge. Before it did, I confess to having never heard an amplifier that was so lacking in character as to be completely invisible. If there's higher praise you can heap on a piece of electronics, I don't know what that might be, but it makes writing about it difficult.

More time spent with the amp revealed that despite its physical heft, power rating, and low output impedance, though the 9011's bass response driving the MAXX 3s was complete in terms of extension, texture, and finesse, it was less than fully developed in punch and forward thrust.

I played a series of LPs and CDs with notably fine bass: Davey Spillane's Atlantic Bridge (LP, Tara 3019); Larry Young's Unity (LP, Blue Note/Music Matters 4221); and the single-sided, 45rpm reissue of Ernest Ansermet and the Royal Opera House Orchestra, Covent Garden's The Royal Ballet: Gala Performances (RCA Living Stereo/Classic LDS-6065), recorded at the justly famed Kingsway Hall—you can hear and feel the "room rumble" (not to mention the occasional subway train passing underneath!). The 9011 reproduced the low-frequency extension, but not the expected weight, muscle, and grip. In that regard, the Soulution 710 was superior.

Just as the Soulution's sound was all of a piece, with fast, sharp high-frequency transients to match its punchy bottom, the MBL was less crystalline on top. High-frequency extension and air were fully developed, but high-frequency transients were slightly soft compared to the Soulution—though they matched well with the 9011's bottom-end performance. It can easily be argued that this presentation is more natural and what you hear listening to live, not electronically reproduced music.

The 9011's midrange was perfectly suited to the extremes: rich, almost creamy-full, but, not surprisingly, no match for the vibrant, effusive mids produced by the tubed RM-200 Mk.II. However, it could be argued that this is actually a euphonic coloration.

Tonally, the 9011 produced a neutral full-range balance with top-to-bottom transient performance that could be heard as naturally developed or slightly soft, depending on your taste, just as the Soulution 710's transient performance could be heard as being as fast as live or unnaturally sharp and etched—and, of course, the associated equipment will play a key role in what you hear.

When, for my review of the 9007 in 2006, I interviewed one of MBL's three founders, Wolfgang Meletzky—Meletzky, Bienecke, and Lehnhardt; Meletzky has since sold his stake in the company and has no further affiliation with it—he described the amp as offering class-A–like sound, even though it actually ran cool in class-A/B. The 9011's overall sound was more like class-A, and it ran very cool, as it should, in class-A/B. The overall sound tended toward the rich and fleshy, and less toward the Soulution's lean, fast, tight, and (some would say) skeletal balance.

The description of the MBL Reference 9007 in my 2006 review conflicts in some ways with what I've so far written here about the 9011. In that review you'll find such language as "sparkling, transparent, shimmering highs, and tight, well-damped bass," and this sentence: "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."

How to account for the discrepancies? Perhaps while the 9007 and 9011 share circuit topologies and parts, the additional power somewhat changes the overall character? Maybe the different associated equipment had some influence (including the Wireworld Platinum balanced interconnects the importer delivered with the amplifiers and with which I had no previous experience). Or perhaps five more years of reviewing experiencing, and encountering in the meantime speed demons like the Soulution 710 and even the tubed VTL MB450, have changed my perspective. Whatever the cause or causes, the 9011 driving the MAXX 3s sounded as described.

I went back to a record I'd used for the 9007 review and had described in some detail: an original pressing of Pulse, by the percussionists of the New Music Consort (LP, New World 319)—a sonic spectacular written for six percussionists who play variously sized tin cans, tom-toms, maracas, and a conch shell, as well as a rubbed drum that produces shivers of low-frequency vibrations.

While the 9011, as I said of the 9007, delivered "nuanced[,] rich textures, and full-throttle dynamic authority," the cowbells, ratchets, gongs, and other metallic-sounding instruments sounded richer and warmer than the "razor-sharp clarity" I remember the 9007s producing (with different associated gear). Which one might prefer will be a matter of taste. Those who love the Soulution's sound might find the 9011 too smooth. No doubt those who like the 9011 might find the Soulution too crystalline, and missing some body and warmth.