Whither Class D amplification?

It’s been a bumper few years at Audiophilia on the integrated amplifier front. There have always been outstanding examples mating a preamplifier and power amplifier in one chassis and playing nicely together, but more and more high end companies are designing and manufacturing expensive integrated boxes with varying topologies.

In fact, my reference power/pre is the Jeff Rowland Continuum S2 Integrated Amplifier ($10,000) which has served me spectacularly well—it’s a Capri II preamp ($5,500) on top of a 400W Class D power section. It is not only much improved Class D—as seen and heard over the past decade—but Class D as sanctified by Jeff Rowland. Which means it’s a gorgeously transparent, sweet, very powerful solid state component.

On the island’s horizon are tube integrateds from Vinnie Rossi and Allnic Audio, and, presently in house, the gorgeous subject of this review, the MBL N51 Integrated Amplifier. Like the Rowland, the MBL amplification is Class D. This one sanctified, modified and conceptualized by MBL’s chief designer for over 35 years, Jürgen Reis.

Learn more about how Class D amplifiers work (also known as ‘switching amplifiers’) here.

The N51 is from MBL’s ‘Noble Line’, midrange between the ‘Corona Line’ and the ‘Reference Line’. Designed and manufactured in Berlin, Germany, the N51’s MSRP is $17,600.

Setup

The N51 box arrived from Germany on a skip with the equally imposing N31 CD/DAC box atop (review forthcoming). Unpacking is a two person affair—meticulous tendencies, please (MBL provides the linen gloves). The delivery fellow, much like every Victoria, BC example, was very charming and helpful, but full of woe about something or other. And happy to relay the woe. This fellow? His back. Oh boy, is he in the wrong business. Anyway, with the help of an electric pallet truck, he maneuvered the MBLs up the four outside stairs then into the house.

My wife and I took great care unpacking both, placed them on the foyer carpet, then sat back and admired their exquisite workmanship. I think her one word was ‘wow!’. My review models are in piano black with gold accents but they look equally luxurious in black with chrome accents or gloss white with either gold or chrome accents. You can’t go wrong with any combination. Stunning!

After we lifted both pieces into my Target rack (the N51 weighs in at a shade below 60 pounds) we setup following the very detailed manual.

Dimensions of the N51 are Width: 17.7” Depth; 17.7” Height: 5.5”.

Jeremy and Tara Bryan of MBL North America (who were instrumental in facilitating the review) answered my myriad of questions and offered support to get the very best out of the beast.

I assumed zero hours on the electronics other than MBL bench testing so readied the N51 with casual listening and overnight break in for about fifty hours.

Popping in and out of the music room during those first break in hours, I could adjust volume and inputs via the magnificent backlit remote control. Easily, the best I’ve used in high end audio. It’s functional with superb design, fit & finish. The chrome volume ring is very responsive. Many N51 functions (and those of the N31) are mirrored on the remote.

My Use

To power the N51, I used an Allnic Audio ZL-5000 Power Cable ($2,000). The cord is superb and I thought it would do justice to the N51’s equally refined design. I used reference level interconnects (single-ended and balanced) from Antipodes Audio, Anticables, and Allnic Audio. Speaker cables used during the review period were outstanding examples from Transparent, Antipodes or Allnic. Power cords used for other components in my reference system were from Anticables (Level 3 Reference Series Power Cord—$330/metre), Allnic Audio (ZL-3000—$1400/metre) and the $1300/metre Waveform Fidelity GS Mk III High-Current Power Cable from the pen of the great Paul Kaplan (sadly, Paul died recently after a valiant battle with cancer, but Waveform Fidelity is continuing to operate under the auspices of Paul’s friends).

All components were plugged into an Audioquest Niagara 1200 AC Power Conditioner (review forthcoming), the N51 into one of the 1200’s ‘high current’ outlets.

As suggested by MBL, I deactivated any unused inputs which they said could help eliminate interference. As such, I used inputs CD 1 for the N31 CD/DAC and Aux 1 for my Allnic Audio H-7000 LCR Phono Stage ($16,500). I did not have the MBL N51’s optional phono card installed for the review ($1,844).

The large, circular ID on top of the machine is a backlit touchpad—tap or press to lower screen brightness or turn off completely (if the screen is off, the 5” TFT screen has a proximity sensor and will turn on when approaching the unit). When the ID is set to off, the standby button on the front plate indicates a beautiful blue hue. The touchpad ‘off’ setting was also recommended to me by MBL.

The N51 has the following very high quality Inputs/Outputs:

6 analog inputs (2 x CD RCA, 2 x Aux RCA, 1 x Processor in RCA, 1 x Balanced In XLR)

2 analogue outputs (1 x preamp output RCA, 1 x record out RCA)

2 MBL ‘SmartLink’ connectors—these allow data exchange to other MBL components via Ethernet (MBL supplies an Audioquest Cinnamon Ethernet cable—impressive) allowing for single remote operation when using more than one MBL component. It worked a treat when I combined the N51 and the N31 CD/DAC.

Binding posts TDF! High-quality, vibration-damped full copper loudspeaker connections by the German manufacturer WBT. Inputs & Outputs are laid out perfectly. I’ve not seen better quality on a rear panel.

Specifications & Features

Jürgen Reis designs all MBL components and the famous Radialstrahler loudspeakers (MBL Radialstrahler 120 review forthcoming). If you have watched the MBL How It’s Made episodes on YouTube, you’ll observe the care taken building Reis’ brilliant designs. Think of Reis, with his litany of ground-breaking designs, among the pantheon of the legacy high end audio designers such as Dave Wilson, Dan D’Agostino, Bill Johnson, Nelson Pass, Jeff Rowland, John Curl and others.

The N51 uses ‘LASA 2.0’ (Linear Audio Switching Amplifier)—an MBL proprietary technology that combines the advantages of different amplifier concepts. In this respect, consider the N51 as a highly modified Class D design. MBL says ‘ …the resultant amplifier is perfectly suited to drive complex loads such as loudspeakers, ensuring that the frequency response remains stable even at varying loads and has a homogeneous tonal balance throughout frequency range’.

Agreed.

The N51 has 380 watts (4Ω). My reference Alta Audio FRM-2 Celesta Loudspeakers ($15,000) are 4 Ohms and 87.5 dB efficiency, so, not the most efficient load but a nothing burger for the N51. The integrated has soft clipping, but I could never demand enough to unsettle the musical information. As MBL describes it: ‘380 watts (4Ω) power with 28 Amp peak output current, values that ensure a sovereign and unconstrained performance even at higher volume levels.‘

Its power supply is built around an analog toroidal transformer with protective shield technology in an MU-metal enclosure and uses a rectifier with low recovery losses.

I always used the fabulous remote control, but the N51 has an analogue volume control via stepping motor and potentiometer.

The menu settings from the 5” TFT colour screen are very simple and intuitive to use with large input messages and volume control numbers. From the screen, you can set maximum volume, input selection, disable inputs, etc. An SD-card slot is provided on the rear panel for easy firmware updates.

‘Unity Gain’ is a setting developed by Reis for his preamplifiers. The feature ‘allows for higher dynamics, higher resolution, exceptionally low noise and vanishing distortion—factors that provide significant sound advantages over conventional amplifiers—the input signal is controlled so that exactly the maximum 2 volts are provided at the power amplifier’s inputs. As a result, the entire dynamic range of the D/A converter is completely retained and no dB in the signal-to-noise ratio is wasted. This is clearly audible and measurable.’

Unity Gain is the default setting on the N51. It is said to improve transparency and resolution of music through a lower noise floor and greater dynamic range. I heard nothing in the lengthy review period that disputes this. I used the default setting for the duration of the review.

Read more about MBL’s proprietary technology here.

The N51 comes with chrome accents as well as gold. It also has a 5” TFT colour screen with 6 ‘smart buttons’ to access the multitude of functions. It’s all very intuitive. You’ll notice the ‘Unity Gain’ default setting is displayed.

Sound

Using this gorgeous art piece was an aesthetic and musical joy from initial power up ‘till review’s end. I’ve not seen a more beautiful high end component in my music room.

Equal to its visual beauty are the multi functions, ease of use, and, above all, the beautiful sound it enables. Yet, like all great components, the N51 doesn’t have a sound signature per se. What it does brilliantly and beautifully is prepare and amplify digital and vinyl signals so they always sound their very best. Many components desire plenty of refined power—no nonsense energy from which music can flow and energize the listener and the room. Hand in hand down a musical lane—two against the world. The MBL N51 worked perfectly with my components. It endowed each to their musical fullest. As such, I’ve never heard them sound better or as cohesively from an integrated source. I dare say, you could place the N51 in any components’ company and it would accept the musical challenges and surpass your expectations.

When separating the pre from the power (using an Allnic Audio MU-7R RCA Cable @ $2500/metre via the N51’s ‘Bypass’), the $16,500 Allnic Audio L-7000 Preamplifier was a lovely match to Reis’ amplification—the gorgeous transparency of this brilliant Korean preamplifier allowed me to adjudicate the N51’s power section with CD, streaming and vinyl. The L-7000, one of the world’s great tube line preamplifiers, in no way embarrassed the preamp section of the N51. The N51 is not a tube design, but Reis’ schematics and MBL’s manufacture, much like my Jeff Rowland Continuum S2, retain a sweetness and diaphanous transparency that is not always heard in expensive solid state designs. As this is an N51 review, I only allowed myself a short time separating the N51’s pre/power to test functionality. Thus, the N51 power and L-7000 time together was short, but very, very sweet.

I use the L-7000 daily as my reference coupled with the Rowland Continuum S2 power section bypassed. When choosing your integrated, always leave yourself a get out of jail free card by ensuring your purchase has a ‘Bypass’ feature. It may be invaluable.

Back to one box living.

In comparison, my 10K Rowland is suitable to all manner of high end systems—and lives with this audiophile very happily day in and day out. However, in the here and now, it is bettered by the MBL N51 by $7,800 AND ultimate refinement. Both have gobs of power and their delivery of it is done ingeniously, but the refulgent, tactile sound the N51 produces is ultimately more musical.

How is that achieved?

A deeper soundstage and even more detail than the already beautifully clinical Continuum S2. As an example, I heard the 2nd horn’s hand stopped position ‘whine’ with even more clarity at the start of ‘Gnomus’ from Reiner’s Pictures—it’s heard pianissimo way back in the mix after a hell of a bass drum/cymbal thwack floating in the resonance of Chicago’s Orchestra Hall. This needs very good component synergy to hear clearly, but most importantly the accurate and very beautiful rendition of instrumental and vocal timbres. This last quality is intoxicating from the N51.

Whether those (musically worthy) qualities and that last ounce of refulgence are worth $7,800 is between you and your musical maker. I know many audiophiles would play twice as much for less. The Law of Diminishing Returns, and all that.

What is pragmatically apparent in comparison is the N51’s screen (the Continuum S2’s small, monochrome screen is volume only), its audiophile-friendly functionality, the Unity Gain technology, SmartLink connectivity, and, wait for it, the remote. Readers of Audiophilia will know of my feelings about the Rowland remote.

The timbral accuracy of the N51 is uncanny, and across every octave, even subterranean bass. The tonal centre never implodes, no matter the volume set. I could even tell the 2nd horn’s stopped note mentioned above was not quite stable (I guess the old man didn’t have an N51 in the playback room back in 1956!). The power afforded the buyer will certainly be enough for most situations and room sizes—unless you have Apogee Scintillas and organizing a rave, and even then, just switch off the Unity Gain.

Listening to a $5 second hand record, Schumann’s gorgeous Novelletten played so beautifully on a Philips release by Chilean piano master, Claudio Arrau, was wonderfully instructive. The delicacy with which Arrau caresses the keys in all registers was laid out with gorgeous detail and then, when he thunders in some bass octaves, the N51 can switch on a dime and relay that power demand with complete ease. And with the same timbres. This is hugely important and is not always apparent from expensive kit.

I remember being shocked at the amount of very fine, low level detail afforded my musical choices by a $2000 power cord. With the N51/Allnic ZL-5000 combination, I tried the same source (The Constant Gardener soundtrack) from the same Qobuz HiRes Roon stream and was even more surprised at just how low and deep great gear can get you into the recording. With the MBL in the chain, information retrieval is a very deep dive.

I read a post on Facebook this week by a reviewer I admire about the fabulous Colgem’s original LP pressing of Casino Royale (1967). He loves the recording but does not like the repertoire. Poor man. I think it’s great—classic Burt Bacharach with Herb Alpert as trumpet soloist. Okay, it’s a paper thin score, but fun. Bacharach tells of his wife of the time, Angie Dickinson, convincing the McGill University music grad he had the talent to complete a full movie orchestral score. He was not so sure. In any case, the record is filled with lots of cute tunes and audiophile signposts, no more than Dusty singing ‘The Look of Love’. With my vinyl setup driven by the N51, Dusty’s phrasing and word painting was soft, sexy and tactile. Once heard in this combination, it’d be difficult to forget. Interestingly, my tenor-playing father worked a lot with Springfield in the 60s—the tales!

Summary

There’s nothing in the N51’s design chain that Reis has not figured out, solved and built upon to produce a component that looks and sounds fabulous. You need a one box solution? There are many from which to choose at all price levels, but this MBL box has a brilliant design, uses an extensive feature set and is chock-a-block with wonderful technology. Purchase one, and you are set for the foreseeable future. Very highly recommended.

Further Information: MBL