S/PDIF, USB and HDMI DAC with balanced preamp output Made by: NAD Electronics International, Canada Supplied by: Armour Home Electronics Telephone: 01279 501111 Web: http://nadelectronics.com; www.armourhome.co.uk OUTBOARD DAC NAD Masters M51 (£1500) Not only the ﬁrst stereo DAC to feature an HDMI input but another of NAD’s ‘Masters’ to employ the Zetex DDFA processor. It’s mathematics made into music Review: John Bamford Lab: Paul Miller I t’s not every day that NAD introduces a new product into its Masters Series line-up. This intriguing M51 DAC was previewed to the hi-ﬁ trade in January at CES and it boasts a wealth of features that tick pretty much all the boxes required by a 21st century audiophile. Yes, it has an asynchronous USB input that accommodates data up to 24-bit/ 192kHz to take advantage of 99.99% of all available hi-res downloads. It also has an AES/EBU (XLR) and two S/PDIF inputs (one RCA coaxial, one Toslink optical); it comes with a remote control handset and features built-in volume control allowing it to be used as a preamp in an all-digital system; and it even sports balanced analogue outputs. NAD’s M51 really looks the business. HDMI – NOT JUST FOR AV With its classy brushed aluminium front panel and high quality VFD display it might have come from the Scandinavian school of design. The face the NAD presents to the world is the epitome of minimalist understatement. But as our photograph of the NAD’s rear panel on p33 reveals, the M51 goes a step beyond any specialist audiophile DAC so far produced by adding a couple of HDMI inputs to its feature set. You might want a high quality DAC to improve the sound quality of an ageing CD player, of course. Most likely you’ll be interested in getting the best sound quality possible from a ‘digital library’ these days as well (this accounts for the resurgence in popularity of standalone DACs). But here’s an audiophile DAC that can also be hooked up to the HDMI output of a DVD and/or Blu-ray disc player to improve its sound quality through a hi-ﬁ enthusiast’s two channel system. You might well ask, ‘Why on earth hasn’t a hi-ﬁ manufacturer made a DAC like this before?’ And therein lies a story… While chipsets and ‘kits of parts’ for HDMI inputs/outputs are just as readily available as those for S/PDIF and USB interfaces, there’s a fundamental difference with HDMI in that it doesn’t transmit data in the clear. Developed to replace the (analogue) SCART connector, it allows data transfer of copy-protected material. As a consequence, a manufacturer must join the ‘HDMI club’ and become a licensee – an ‘adopter’ – privy to conﬁdential decryption keys. HDMI adopters pay an annual fee of $10k, plus (admittedly small) royalties to the HDMI licensing organisation of four cents per product sold, for so long as the manufacturer implements the ever-sonecessary High-bandwidth Digital Content Protection [HDCP] and uses the HDMI logo on its product and promotional materials. Adopters must license HDCP separately from Digital Content Protection LLC, a subsidiary of Intel. This costs a further $15,000 per annum, on top of which manufacturers then purchase quantities of ‘Device Set Keys’: $1000 for 10,000 sets; $2500 for 100,000; and $5000 for 1 million sets. It’s all geared towards largescale consumer electronics manufacturers whose highly automated production lines RIGHT: Plenty of processor power under the hood – Analog Devices DSP for HDMI, XMOS for USB and the core Zetex DDFA silicon that converts all LPCM to PWM [see boxout] REPRODUCED FROM HI-FI NEWS | www.hifinews.co.uk will deliver more products in a morning before a factory’s tea break than a boutique company – the type of specialist ﬁrm that makes niche products for audio enthusiasts, such as standalone DACs – might build in an entire year. MINEFIELD AHEAD… Full marks, then, to NAD for deciding to include HDMI on a DAC aimed at audiophiles. The company can afford to implement it, after all. Just consider all its DVD/BD players and AV receivers produced over the years. But don’t get too excited (as I did on ﬁrst hearing about the M51), as unfortunately its HDMI inputs cannot be used to transform the sound quality of that legacy DVD-Audio or SACD player that you might be using in your system, via line-level analogue connections. The Content Protection for Pre-recorded Media [CPPM] encryption employed on most DVD-A recordings ensures that a player’s digital outputs are downsampled to 48kHz and with SACDs the digital output is completely muted. This is a mineﬁeld, however – it varies not only from player to player but also from disc to disc – so if your local dealer is a NAD stockist you might want to ﬁrst try the M51 with your hi-res disc player if you consider this an important factor in your purchasing decision. Nor should you be overly wooed by the numbers bandied about in NAD’s marketing literature for the M51. A ‘35-bit/844kHz DAC’ sounds terribly exciting on paper. However, the numbers relate to the core Zetex PWM processor employed in the DAC, the same device that NAD ﬁrst used in its Master Series M2 digital ampliﬁer [see the Ed’s boxout]. Several years ago NAD partnered with the UK design team of Zetex plc, based in Oldham, Lancs, who had developed a novel switching ampliﬁer technology employing feedback around its output stage. By the time NAD’s M2 digital ampliﬁer came to market, Zetex was in fact acquired by the Texas-based semiconductor company Diodes Incorporated, whose website [www.diodes.com] refers to it still having an engineering centre in ‘Manchester, England’. NAD has furthermore trickled down this Diodes Zetex ‘engine’ to a more affordable 2x150W integrated ampliﬁer dubbed C 390DD (priced at €2500) that should be available here by the time you read this. Via the partnering remote control handset, a set-up menu conﬁgures the DAC for ﬁxed or variable output (including its output level in ‘ﬁxed’ mode), while buttons also control ﬁve levels of display brightness and absolute phase inversion. Don’t lose the handset if you’re using the DAC as a preamp as there’s no volume control on the front panel, only an ‘input’ button to scroll through its six digital inputs. ‘The rhythm section was served up with a vigorous power’ NEVER UNCOUTH Resisting temptation to dive straight in to the ‘novelty’ feature of the M51 – its HDMI inputs – and with the sound of various D-to-A converters fresh in my head following our June ’12 Group Test, I ﬁrst installed NAD’s USB Audio Class 2.0 CALCULATORS ON STANDBY The big Zetex processor at the heart of the M51 DAC is the same PWM (Pulse Width Modulation) device we saw in NAD’s M2 ‘digital’ ampliﬁer [see HFN Jun ’10]. Zetex calls this DDFA or Direct Digital Feedback, but instead of driving a high power Class D output stage, here it’s servicing a thoroughly audiophile analogue preamp. Volume is also handled digitally, but as Zetex employs 35-bit processing it offers a full 66dB of attenuation (that’s the top 11-bits) before squeezing the dynamic range of even the highest resolution 24-bit digital inputs. You’ll see some other numbers in NAD’s blurb, doubtless repeated verbatim in the red tops, that at ﬁrst sight make less sense. Converting incoming LPCM to a PWM bitstream at a ﬁnal 844kHz sample rate seems plain wrong – after all, why pick a number that’s not an integer multiple of the common 44.1kHz or 48kHz base rates? The answer, according to my maths, lies in the choice of commercially available crystal clocks and the 108MHz chip chosen by NAD and Zetex (it’s commonly used in ﬂat panel TVs). Because all incoming digital data, whether natively 16-bit or 24-bit, is truncated down to a 7-bit PWM bitstream, this yields a total of 128 discrete pulse ‘widths’ to describe the audio signal per sample (27 equals 128). Each of these 128 pulse widths is an integer multiple of the minimum ‘width’ which, to ensure accurate resolution or ‘timing’ of its cycle, demands a minimum sample rate of 108MHz divided by 128, or 844kHz. Mystery solved! PM ABOVE: Large vacuum ﬂuorescent display shows input, volume setting and sampling frequency of incoming data. The only buttons on the spare fascia are standby and input select driver, in order to listen to the DAC with all manner of music tracks from my Dell PC’s digital library. The driver must be downloaded from NAD’s website, but of course this is not required for Macintosh users running MAC OSX v10.6 (Snow Leopard) or later, that natively supports audio up to 24-bit/192kHz. The sound of the M51 is not without character – I’m not entirely convinced that it’s wholly neutral and transparent to the source recordings one feeds into it – however it’s a charming sound that I warmed to within minutes of having it up and running in my system. (You can see the system and listening room by visiting www. hiﬁnews.co.uk/news/article.asp?a=9884.) The M51 sounds meaty and powerful in the bass, warm and almost ‘tubey’ through the midband, and sweetly balanced at the top end: making for a relaxed sonic presentation that’s particularly forgiving of harsh recordings and rarely grates. If you’re looking for a DAC that gives digital sources a degree of analogue warmth, this is it! The demeanour of the M51 was readily apparent when listening to modern, ‘hot’ tracks such as ‘Letters From The Sky’ from Civil Twilight’s eponymously-titled debut album [Wind-up 60150131522]. The piano sounded bold and immediate, the lead vocal was richly textured with plenty of ‘air’ around it, and the sound remained consistently controlled and intelligible. Where more explicit components tend to highlight the ingress of hard-edged sibilance in the recording’s production, the M51 remained couth and civilised. The M51 threw up countless delectable surprises. Vintage recordings such as Hendrix’s Band Of Gypsys recorded live at New York’s Fillmore East on New Year’s Eve of 1969 sounded wholesome, energetic and deliciously fresh. Remastered umpteen times over the decades, mine was a rip of a 1997 CD reissue [MCA, MCD 11607-2] www.hifinews.co.uk | REPRODUCED FROM HI-FI NEWS LAB REPORT OUTBOARD DAC NAD MASTERS M51 (£1500) ABOVE: A choice of single-ended (RCA) and balanced (XLR) preamp outputs are joined by AES/EBU (XLR), S/PDIF (coax and optical), USB and two HDMI inputs. There’s also an HDMI pass thru’, USB upgrade port and RS232 for system controllers. The M50 remote is essential for navigation and it sounded fabulous through the M51, the rhythm section of Buddy Miles and Billy Cox served up with vigorous weight and power. The DAC’s opulent sound was further demonstrated on Caravan’s epic ‘Nine Feet Underground’ from In The Land Of Grey And Pink [Decca 8829832], showcasing the rounded, throaty texture of Richard Sinclair’s Fender Jazz bass guitar and the primal growl of David Sinclair’s Hammond organ redolent of yesteryear. DISASTER STRIKES! I then tried the free 44.1, 96 and 192kHz downloads of an excerpt from Stravinsky’s Firebird Suite performed by the Budapest Festival Orchestra, from Channel Classics. Again, the sound was luxurious when playing the 44.1 ﬁle and even more splendid at 96kHz… but imagine my chagrin when the audio stuttered to a halt and my PC (running Windows 7) completely froze once I selected the 192kHz ﬁle. NAD’s perfunctory M51 user manual gives no clue as to what might have been amiss, but on revisiting the company’s website I clocked the notice that advises: ‘Any drivers previously loaded must be uninstalled prior to installing this driver’. With a heavy heart I set about purging my PC of myriad drivers installed for auditioning USB DACs in recent years. Our editor experienced no such problem when testing the M51 using Windows XP, by the way. Nevertheless, you have been warned! As already mentioned, not all DVD-As are downsampled by legacy hi-res disc players, and the M51’s smooth and reﬁned sound remained evident via HDMI when playing one of Mark Waldrep’s excellent 24-bit/96kHz recordings on his AIX Records label. I was listening to Dorian Michael – Acoustic Blues [AIX 80016] featuring guest performances by guitarists Albert Lee and Laurence Juber, an exemplar of modern media’s ability to describe beautifully the subtle variations in tonality and timbre of instruments. The sound lacked a little sparkle and pizzaz, but it wasn’t so creamy that it robbed the recording of vibrant detail and dynamics. And while I could criticise the M51 for softening images and sometimes proving too syrupy, it certainly transformed the lacklustre, anaemic sound of the analogue outputs of an inexpensive three-yearold Pioneer BDP-320 Blu-ray player. With the Pioneer set to output LPCM via HDMI the 24/96 Dolby TrueHD audio track of Dave Matthews and Tim Reynolds concert performance Live at Radio City Music Hall was enthralling via the M51 DAC, as was the sound from Jeff Beck: Performing This Week... Live at Ronnie Scott’s, albeit encoded only in 16-bit/48kHz for the Blu-ray release. While Beck’s guitar variously sang and cried throughout, the combined power of Vinnie Colaiuta’s drumming alongside the bass playing of the terrifyingly talented Tal Wilkenfeld made a compelling argument for employing the M51 as a digital hub in a high-end two-channel system. Aside from the advantage of managing volume in the digital domain, this ‘preamp’ version of the Zetex DDFA [see boxout, p31] also brings with it a unique technical ‘ﬁngerprint’. Premature digital clipping is evident at the nominal 0dB volume position and so all testing was performed at –1dB, at which point the M51 delivers a full 4.13V (phase-inverted) balanced output from a low 90ohm source impedance. In a parallel with most Class D ampliﬁers, output impedance increases at HF as does its response, reaching +0.08dB/20kHz (44.1/48kFs), +0.37dB/45kHz (96kFs) and +2.8dB/85kHz (192kFs). Distortion also increases very markedly indeed at high frequencies, from a vanishingly low 0.00025% through the midrange to 0.06% at 20kHz and 0.6% at 40kHz (all re. 0dBFs). Once again, this is the behaviour of a typical Class D amp than a typical outboard DAC. Low-level linearity is spot on, true to within ±0.5dB over a full 120dB dynamic range, but the pattern of distortion versus digital level is less uniform than usual [see Graph 1, below, and compare with DACs in previous issues of HFN]. Importantly, the M51 locks ﬂawlessly onto all 44.1-192kHz sample rates via S/PDIF, USB and HDMI interfaces and its performance, including the 115dB S/N, is remarkably unvarying (further suggesting that all this ‘character’ is determined by the central onboard processor). Jitter is low but also low rate and decorrelated, from 200psec (S/PDIF) to 300psec (USB) [see Graph 2], this noise-like pattern often linked to a not unwelcome softening of ‘edgy’ material but also a softening of sharp stereo imaging. Readers can download full QC Suite test reports for the NAD M51 DAC’s S/PDIF, USB and HDMI performance by navigating to www. hiﬁnews.co.uk and clicking on the red ‘download’ button. PM ABOVE: Distortion vs. 24-bit digital signal level over a 120dB range at 1kHz (black) and 20kHz (blue) HI-FI NEWS VERDICT Keenly priced given its feature set and refined sound quality, NAD’s M51 is a fabulous DAC that can also be used as a preamp in an all-digital system. It sounds sophisticated and sumptuous, never edgy or mechanical. I’ve heard DACs that are sharper focused and more transparent with hi-res sources; nevertheless it is sure to find favour among many audiophiles, thanks to its sound being notably free of grain. Sound Quality: 82% 0 - - - - - - - - 100 ABOVE: Zoomed, high res. jitter spectrum (±500Hz) comparing low-rate jitter with 24-bit/48kHz data over S/PDIF (black), HDMI (green) and USB (red) HI-FI NEWS SPECIFICATIONS Maximum output level (Balanced) 4.13Vrms at 91ohm A-wtd S/N ratio (S/PDIF / USB) 115.3dB / 114.9dB Distortion (1kHz, 0dBFs/–30dBFs) 0.00025% / 0.024% Dist. & Noise (20kHz, 0dBFs/–30dBFs) 0.06% / 0.11% Freq. resp. (20Hz-20kHz/45kHz/90kHz) –0.0dB to +0.1dB/+0.4dB/–3.6dB Digital jitter (48kHz/96kHz/HDMI/USB) 222ps / 200ps / 265ps / 300psec Resolution @ –100dB ±0.1dB Power consumption 12W (1W standby) Dimensions (WHD) 435x78x296mm www.hifinews.co.uk | REPRODUCED FROM HI-FI NEWS