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MBL Noble Line N11 Preamplifier and N15 Monoblock Amplifier

MBL Noble Line N11 Preamplifier and N15 Monoblock Amplifier

MBL’s Noble Line electronics sit midway between its ultra-expensive Reference Line offerings and its least costly Corona gear. Though the Noble N11 preamp and N15 monoblock amps   aren’t stripped down compared to their Reference counterparts, they do differ in price, size, power, and mode of operation. The enormous $106k/pr. Reference Line 9011 monoblocks, for example, one of the world’s great amps, generate 840W/50A/100V into a 4-ohm load, have a signal-to-noise ratio of 118dB and distortion of under 0.001%, and run in Class AB. The far lighter, more compact, $35k/pr. Noble Line N15 monoblocks still generate a hefty 560W/36A into a 4-ohm load, also have low noise, but run in Class D.

Now, it’s been better than a decade-and-a-half since yours truly reviewed Class D amplifiers in TAS. (Loved them in the bass, not so much in the upper midrange and treble.) Since then Class D has gained a firmer foothold in the high end, particularly in products like self-powered loudspeakers and active subwoofers where Class D’s exceptional efficiency, small size, low generation of heat, and relative affordability are obvious plusses.

Often erroneously called “digital” amplifiers, Class D (or “switching”) amplifiers do not work like linear amps, in which the input is sent directly to the amplifier’s various gain stages for boosting. In a Class D amp the input is first converted/encoded by a modulator into a pulse train (using pulse width, pulse density, or related modulatory techniques) that represents the amplitude variations of the audio signal. This pulse train is then fed to the amplifying devices (usually MOSFETs), which operate like electronic on-off switches. Working alternately, these transistors switch back and forth between the supply rails, generating positive and negative boosted signals that are subsequently low-pass filtered (to get rid of the very high frequencies used by the modulator to encode the input signal), sometimes high-pass filtered (to reduce residual distortion), and fed as a higher-gain analog (sinusoidal) signal to the loudspeakers. Theoretically, a switching amplifier (which dissipates virtually no power as heat) has an efficiency of 100%, while Class B amps have a theoretical maximum efficiency of 78% and Class A amps 20–50%.

Unlike its predecessors and much of its current competition, the Noble Line N15 monoblocks under review are said to guarantee a linear signal independent of load, level, or frequency. This is a bold claim, considering (as MBL itself points out in its LASA 2.0 white paper) that Class D amplifiers inherently distort the music signal depending on frequency. (Natively they have low THD in the bass and very high THD in the treble.) Moreover, Class D amplifiers are always designed for a particular resistance value (e.g., 4  ohms), but a loudspeaker does not have a constant resistance—it is a “complex  load” with impedances varying with frequency. Thus, in addition to their native non-homogeneous distortion profile, Class D amplifiers change their power delivery (and hence their frequency response) with changes in load. On top of this, the louder a typical Class D amp plays, the lower its overall distortion, and (paradoxically) the quieter it plays, the higher its distortion.

MBL claims to have solved these myriad problems with its LASA (Linear Analog Switching Amplifier) 2.0 technology, which, instead of the typical and economical switch-mode power supplies of most Class D amplifiers, uses a massive analog toroidal power supply. The LASA circuitry is also symmetrical in layout for better common mode rejection, employs low-drop fast-recovery rectifiers to create a low-noise supply voltage, and has a “soft-clipping” provision to eliminate aggressiveness and distortion at very high output levels. Whether or not these strategies result in an amp that (as MBL claims) is closer to Class A or Class AB in linearity, noise, and stability than it is to typical Class D, there is no question that the N15 differs sonically from the switching amplifiers I auditioned lo these many years ago.

During most of the review period I used the N15 with its companion Noble Line linestage preamp—the single-gain-stage, high-bandwidth, Class AB N11, often run in “unity gain mode” (about which I will have more to say in a moment)—driving a cone loudspeaker that presents a moderately difficult load (the Magico M3) and sourced by Walker and TW Acustic analog and MSB digital. To be honest I didn’t expect the world from this combination, especially since I’m used to listening to the Magicos with much higher priced Class A/AB electronics from Soulution and Constellation. And, to be honest, I didn’t get the world—or all of it. But what I did get was good enough and surprising enough to make me re-think what Class D (or at least MBL’s LASA 2.0 version of it) has to offer.

For one (perhaps most important) thing, the N11/N15 combo did not have all of the treble-range eccentricities that I remembered from earlier-gen Class D. Where Class D’s top octaves used to sound as if they were roughened in the low-to-mid treble and abruptly rolled off above that, the MBLs’ high frequencies did not. (They were just a bit on the soft, sweet, dark side with a relatively insignificant reduction of “air.”) For another, the N11/N15 did not have the almost-digital flatness of aspect in the midrange that I also remembered from early Class D. No, the MBL gear had three-dimensional imaging in the mids (and in the treble and bass, too). And in the area where Class D was always at its best, the bottom octaves, the N11/N15 did not lose a step, sounding just as powerful, tightly controlled, and deeply extended as earlier Class D, with (as noted) the added bonus of three-dimensional bloom.

 

Though the big, robust bass range of Class D was always its strong suit, it was also a weakness in that in combination with the perceived roll in the top octaves it tended to make older-gen switching amps sound quite dark or “bottom-up” in balance. While the MBL N15 was not as strongly colored in this way as Class D amps of yore, it was still a bit on the dark side with the somewhat-tricky-to-drive Magico M3s, though, oddly, I didn’t hear any of this same darkness with the near purely resistive load of the Maggie 30.7s. Indeed, with the Maggies the MBL electronics sounded quite neutral, if not a little lean and bright (which, to be fair, is precisely the way the Maggies sound when their ribbon tweeters aren’t damped down via resistors, as they were not when I originally auditioned the MBL/Maggie combo). You could argue that this difference in presentation reflects the difference in the sonic balance of the two speakers, supporting MBL’s claim of load insensitivity. But given that the Magico M3 does not sound darkish with the Constellation amp, you could also argue that the difference reflects a slight tendency (far slighter than in the past, as it is not accompanied by treble-range roughness and roll-off) to change sound with changes in load. (The N15’s darker palette is undoubtedly also a reflection of MBL’s “house voicing,” which has always been bottom-up and is accentuated when the N11 preamp is not used in its unity gain mode.)

This said, what the N11/N15 did have with both the Magicos and the Maggies—and Class D, as I remember it, never had before with any speaker—was surprisingly high-resolution top to bottom, lifelike three-dimensional presence, and superb transient response, particularly in the midband and lower treble. On a recording like the fine Analogue Productions 200-gram LP reissue of Son House: Father of Folk Blues, you’d simply have to hear the “in-the-room-with-you” realism with which MBL gear (in combination with the Maggie 30.7s) reproduced the sting and snap of Son House’s hard-plucked National steel guitar and his weathered voice on “Death Letter” to appreciate how realistic MBL’s Noble Line electronics (in combination with a first-rate analog front end and a congenial load) are capable of sounding. This is nothing like Class D of old, as I remember it.

With the Magicos I tried an experiment, comparing the sound of the M3s driven directly by the MSB Reference DAC’s excellent analog volume control (i.e., with no outboard preamp) into Constellation’s superb Hercules II Stereo amplifier to the sound of the M3s also driven directly by the MSB DAC into the Noble Line N15 amps, and then with the signal sent from the DAC through MBL’s N11 preamp into the N15s. To minimize the difference that I knew the MBL preamplifier was going to make, I used it in what MBL calls “unity gain” mode, which is said to lower the noise floor, increase transparency, and improve dynamic range.


How unity gain does these things involves an interesting bit of thinking. In a typical playback system, the power amplifier expects the preamplifier to relay a signal at a maximum of 2V RMS (which happens to be the standardized fixed output of a DAC). However, today’s preamps typically amplify the input signal by 12dB (a gain factor of 4) before delivering it to the amplifier input. With a source device that has a voltage of 0.75 volts (such as certain analog phono- stages), the preamplified voltage would be 3V, which means the volume level would have to be reduced by at least 33% in order not to exceed the maximum level that the amplifier is looking for. With a 2V digital source, the preamplified voltage would be 8V, which means the volume level would have to be reduced by at least 75% not to exceed the maximum level the amplifier is expecting.

If drastically reducing volume levels via your preamp’s volume pot were a harmless procedure, there would be no problems. But it is MBL’s contention (proven by measurements—for which see the LASA 2.0 white paper) that such massive reductions in volume are not made without a cost. In fact, such changes dramatically constrict dynamic range, reduce resolution, and raise distortion.

When used in user-selectable unity gain mode (actually a misnomer—it should be called “low-gain” mode, one of the two volume-control strategies available in the preamp, the other being a conventional “high-gain” mode), the N11 adds considerably less boost to and subtracts considerably less boost from the signal it is being fed than a typical linestage preamp. Though what MBL is calling unity gain isn’t, technically, a true pass-through (in which nothing at all is added to or subtracted from the source signal), the circuit does reduce the preamp’s maximum gain factor to something on the order of 1.8, making the price you pay in dynamic range, distortion, and resolution for reducing levels less deleterious, audibly and measurably. 

I’d have to say from listening tests that what unity gain is doing is largely, though not entirely, salubrious. While the MSB/MBL/Magico system (with or without the preamp in unity gain) did not have quite the astonishing neutrality and sensationally realistic “thereness” that the MSB/Constellation/Magico one did on, say, Harry Connick, Jr.’s, rendition of “A Nightingale Sang in Berkeley Square,” it came close, with slightly less treble detail and that darker palette I mentioned holding it back from unalloyed goosebump territory. On the other hand, the MBL preamp in so-called unity gain mode did have a wee bit more dimensionality on Connick’s voice (and Branford Marsalis’ sax) and about the same amount of dynamic energy (albeit with less detail) as the MSB volume control by itself. For a preamp priced a hair under $15k and a pair of monoblock amps about a third the price of the Constellation stereo amp, this was highly competitive performance.

 

The last speaker I tried with the Noble Line electronics was one of the Radialstrahlers it was designed with and for—the MBL 101 E Mk.II omnidirectional. Since the 101 Es are themselves dark in balance, the Noble Line’s tendency toward a bottom-up presentation was definitely more marked with them than it was with the Magicos and Maggies. However, this darker tonal balance isn’t what struck me first or foremost. No, it was the sheer joy I experienced listening to the system. Driven by the Noble Line electronics the 101 E Mk.IIs were and are nothing if not continual goosebump-raising fun.

Now I know that “fun” is not a usual critical superlative in our hobby. Indeed, a speaker or set of electronics that is a visceral joy to hear (at any level on any music) is almost automatically suspected of lacking accuracy or of compromising the absolute sound. Such suspicions may, in fact, have a bit of truth to them, but they are also an almost unbelievably narrow way of looking at what a hi-fi does (or should do). If we rule out deriving close to non-stop pleasure from our stereo systems—if we rule out the ways in which a great component is capable of turning off our critical faculties, rather than persistently turning them on (or off and on repeatedly)—then why in hell are we even bothering to purchase expensive toys that are bound to frustrate? Indeed, while they may not have quite the timbral linearity, accuracy, and realism of the standard-setting Magico M3s, the 101 E Mk.IIs are scarcely inaccurate or short on sonic lifelikeness when it comes to tone color, and are very close to the Magicos’ equal in dynamics, and their superior in dimensionality. Plus the Radialstrahlers do something else as well as, if not better than, the best cones in a box: Let’s face it—when we go to a concert in a recital hall we don’t ask ourselves whether the instruments we are hearing, a string quartet for example, sound like “real instruments in a real space.” They are real instruments in a real space—and they sound the way those particular instruments, the performance of the artists, the acoustics of the room, our seating position in that room, and a host of other factors permit them to sound. This does not mean that the “absolute standard” is invalid when it is applied to a recording of that same string quartet. What it does mean is that we never merely listen to sound. We listen to and are thrilled and moved by the gestures and feelings those sounds express. In short, we listen to and are moved by music. And while the Radialstrahlers may not capture the timbre of real instruments quite as neutrally and accurately as the Magico M3s do, they capture the toe-tapping, goosebump-raising thrill of hearing live music at least as well (which is why I once called Radialstrahlers the thrill rides of the high-end-audio amusement park).

The Noble Line N11 and N15 certainly bring out the 101s’ virtues without being hamstrung by their peculiarities. You might think that a speaker with a sensitivity of 81dB (or less), like the 101 E Mk.II, would be a challenge for any amp short of a behemoth, but the N15 (like the even more powerful MBL Reference 9011) never seemed fazed by the Radialstrahlers’ hunger for watts, volts, and amps. While I wouldn’t say that the N15s had quite the overall resolution or sensational treble snap and extension of the 9011s, they effortlessly reproduced hard-hitting bar-band rock ’n’ roll like Lake Street Dive’s “Shame, Shame, Shame” from Free Yourself Up [Nonesuch] at lifelike levels (ca. 95–96dB average SPLs), and they did this without sacrificing one of the very things that makes Radialstrahlers such a pleasure to listen to—their ability to play at very very high volumes without turning the slightest bit rough, bright, or annoying. (According to MBL’s literature, the N15 has a “soft-clipping” feature that, I assume, makes it sound even less rough and bright at very high levels, though this feature may also be partly responsible for the amp’s slight reduction in treble-range brilliance).

Another thing that the Noble electronics do not short-shrift is three dimensionality. Of course, an omnidirectional loudspeaker like the 101 E Mk.II, with 360-degree dispersion (and no enclosure), is a paragon of 3-D sound—to the extent that it is the one transducer I’m familiar with capable of making digital seem as if it’s got nearly as much bloom as analog. Already notably three-dimensional with the other speakers I used, the Noble amp and preamp made the Radialstrahlers sound, as I once said about their big brothers, the X-Tremes, like the sonic equivalent of going to a stage play rather than watching a movie. Indeed, the 101 omnis’ inherent ability to project musical energy in all directions rather than merely forward (or forward and back) is highly realistic—and a large part of the reason the Radialstrahlers sound so thrilling and real with the right sources and electronics. The Noble Line gear did them proud in this regard.

I could go on about the 101 E Mk.IIs—about their incredibly lifelike power-range weight and impact, about their bottommost octaves (which are said to extend to 22Hz), about their uncannily natural reproduction of voices, brasses, and strings, about their boxless openness and vast soundstage—and even though some of these things would also be to the credit of the Noble Line electronics driving them, the Radialstrahlers are not the subject of this review. It is the N11 and N15 that I’m focusing on, and the bottom line here is plain. Neither the amp nor the preamp is the last word in high-end electronics (even in the MBL lines), but then they don’t cost anything close to what that last word costs. What they are, like the MBL Radialstrahlers they pair up with so beautifully, is thrilling to listen to—a little dark, a little soft and sweet on top, a little lower in top-end extension and resolution than their $100k+ competition, but always enjoyable, powerful, and musical, and, given the right source and pairing, fully capable of a realism that raises goosebumps and of a soundfield of head-slapping breadth, width, and depth. In sum, these are components I can recommend to every kind of listener, and particularly to those with Magneplanar or MBL loudspeakers.

Specs & Pricing

N11
Type: Linestage preamplifier
Inputs: Seven analog
Outputs: Five variable, two fixed
Dimensions: 17.7″ x 5.9″ x 17.7″
Price: $14,600

N15
Type: Class D monoblock amplifier
Power: 560W/36A into 4 ohms
Inputs: Two XLR, one XLR pass-through
Outputs: Two pairs WBT binding posts
Dimensions: 17.7″ x 5.9″ x 16.8″
Price: $35,200/pr.

N51
Type: Class D integrated amp
Power: 380Wpc/28A into 4 ohms
Inputs: Six analog (RCA and XLR)
Outputs: Two analog (RCA)
Dimensions: 17.7″ x 5.9″ x 17.7″
Price: $16,500

MBL NORTH AMERICA 
217 North Seacrest Blvd. #276
Boynton Beach, FL 33425
(561) 735-9300 (office)
(917) 306-7588 (mobile)
[email protected]
mbl-northamerica.com

JV’s Reference System
Loudspeakers: Magico M Project, Magico M3, Raidho D-1, Zellaton Reference Mk II, Avantgarde Zero 1, MartinLogan CLX, Magnepan .7, Magnepan 1.7, Magnepan 30.7
Subwoofers: JL Audio Gotham (pair), Magico QSub 15 (pair)
Linestage preamps: Soulution 725, Constellation Audio Altair II, Siltech SAGA System C1, Air Tight ATE-2001 Reference
Phonostage preamps: Soulution 755, Constellation Audio Perseus, Audio Consulting Silver Rock Toroidal, Innovative Cohesion Engineering Raptor
Power amplifiers: Soulution 711, Constellation Audio Hercules II Stereo, Air Tight 3211, Air Tight ATM-2001, Zanden Audio Systems Model 9600, Siltech SAGA System V1/P1, Odyssey Audio Stratos
Analog sources: Acoustic Signature Invictus/T-9000 tonearm, Walker Audio Proscenium Black Diamond Mk V, TW Acustic Black Knight/Raven 10.5, Continuum Audio Labs Obsidian with Viper tonearm, AMG Viella 12
Tape deck: United Home Audio Ultimate 1 OPS
Phono cartridges: Clearaudio Goldfinger Statement, Air Tight Opus 1, Ortofon MC Anna, Ortofon MC A90
Digital sources: Berkeley Alpha DAC 2, MSB The Reference DAC
Cables and interconnects: Crystal Cable Absolute Dream, Synergistic Research Galileo UEF, Ansuz Acoustics Diamond
Power cords: Crystal Cable Absolute Dream, Synergistic Research Galileo UEF, Ansuz Acoustics Diamond
Power conditioners: Synergistic Research Galileo UEF, Technical Brain, AudioQuest Niagara 5000
Support systems: Critical Mass Systems MAXXUM and QXK equipment racks and amp stands
Room treatments: Stein Music H2 Harmonizer system, Synergistic Research UEF Acoustic Panels/Atmosphere XL4/UEF Acoustic Dot system, Synergistic Research ART system, Shakti Hallographs (6), Zanden Acoustic panels, A/V Room Services Metu acoustic panels and traps, ASC Tube Traps
Accessories: Symposium Isis and Ultra equipment platforms, Symposium Rollerblocks and Fat Padz, Walker Prologue Reference equipment and amp stands, Walker Valid Points and Resonance Control discs, Clearaudio Double Matrix Professional Sonic record cleaner, Synergistic Research RED Quantum fuses, HiFi-Tuning silver/gold fuses

By Jonathan Valin

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