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NAD run their new M51 DAC at an enormous sample rate, way higher than rivals. Rafael Todes listens to the result.

My first experience of the NAD brand came as a spotty schoolboy, drooling outside my local hi-fi shop, ogling the now celebrated 3020 amplifier. I eventually persuaded my father to buy one, and still remember the moment when I hooked it up to some Acoustic Research AR18 'speakers. It gave a level of reproduction hitherto unknown in my house. Now, years later, I found the new NAD M51 DAC (£1500) a polished performer too.
    NAD's new DAC sports many useful features. It has a remote control with volume control, as it has a fully-fledged digital preamp on board. It shows the precise sampling frequency it has been locked onto, and it also has HDMI inputs, to convert the output of a DVD or Blu-ray player into two channel stereo. An HDMI output enables video content to be sent to a screen, a nice touch to be sure, necessary to show disc menus on a TV.
    An innovation NAD bring to the party is the way this DAC re-samples all material into a pulse-width-modulation signal at a sample rate of 844kHz, controlled by a clock running at 108MHz. The theory behind this is that it eliminates the jitter arising from the conversion stage, and digital ringing is eliminated.
    The unit has a sleek elegance to it.  A full-width but half-height brushed aluminium case surrounds a generous blue vacuum fluorescent screen. There are only two buttons on the front panel; standby and input selector. To control volume, you must use the remote control.
    On the rear panel there is the usual set of inputs:  AES/EBU, Coax, Optical, USB (Audio Class 2) and as already mentioned HDMI. The inputs are all capable of handling up to 24 bit/192kHz. There are both single-ended as well as balanced outputs.
Due to the 35bit architecture employed, the preamp is capable of 66dB of attenuation before there is any loss of resolution. The remote gives the ability to change from fixed to variable output, change the screen brightness, as well as absolute phase inversion.
    So all-in-all, the M51 has a lot of well-thought out features, with a particularly effective digital preamp thrown in. I had no difficulty downloading the necessary drivers from the NAD website to use on my Toshiba laptop.

Using my reference Bel Canto CD2 as a transport, feeding the NAD with a Chord Indigo Plus Digital cable, I listened to some of my reference CDs. The Solti/Decca ‘Tombeau de Couperin’ exhibited a very sweet-sounding treble. An exceptionally beautiful, smooth silky violin section lacked any hint of the harsh graininess that makes analogue worshippers run a mile. This alone would make the DAC a number of friends on first hearing. The sound had a refinement to it, often found in DACs selling at several times the price. The sound stage had a fair amount of left-to-right information, and a little less by way of the front-to-back placement of an orchestra. Reasonable staging, but not outstanding.
    In the bass department, timing was average, but not outstanding. In particular, cello pizzicato was more bloated than some of the cheaper DACs I’ve heard recently, such as the Rega DAC, reviewed a couple of months ago. Not terrible, just not up there with the best. I had a feeling listening to one of the more dance-like movements, that some of the micro dynamics were being understated a bit too much, and that the lilt of the musical line was being ever-so-slightly eroded.

    The Beaux Arts Trio playing Mozart Trios can cause DACs great problems - particularly with the sound of a piano. Very often the percussive nature of the piano and the rapid transients yields a nasty ‘ringing’ sound, just after the initial moment when the hammer has hit the strings. The NAD does quite well on this test, slightly better in fact than my reference Weiss DAC 202. The sound is wholesome, Isidore Cohen’s Stradivarius violin sounds utterly believable. NAD effortlessly captures the silky shine of the violin, a sound not unlike a really fine wine - full of complexity and tonal depth, rounded and smooth with no brittleness to it. Listening to my reference Weiss DAC202, the string sound is a touch less rich, but it separates the three instruments more convincingly, spatially as well as the different textures of the violin and the cello.
    Listening to ‘Ray Gelato’ skillfully recorded on the Linn label, yields a vibrant interpretation by the NAD, particularly outstanding is the realism of Ray Gelato’s voice. There is an accuracy and naturalness which is up there with the best I’ve heard. The plucked double bass isn’t the tightest I’ve heard, but the overall effect is glorious, real quality, especially when Claire Martin joins the proceedings. The NAD particularly captures her presence and the sense of fun the two singers are having.
    Turning to some High-Res material, Charles Mackerras conducting the Scottish Chamber Orchestra, again the NAD triumphed with a really sparklingly clean treble, which really suited this excellent Linn recording of Mozart’s Jupiter Symphony. I have a strong suspicion that the USB/SPDIF bit of the DAC is doing a fine job. I had more difficulty in following the counterpoint when the basses and cellos were playing, as compared to the violins and violas.

This DAC has many special qualities to it. It has a rare beauty of sound to it that so many others lack, it has a superb preamplifier built-in, and may be the instrument of choice for those people who value these qualities above all others. It does, like all hi-fi products, have areas of lesser strengths, principally in the bass and timing departments, as well as a less-than-holographic sound stage, and in these areas, the most discerning punters may be disappointed. I think the decision to buy will come down to individual preferences, but for its ability to beguile and seduce tonally, and in particular its ability to capture the human voice, it is well worth an audition.

A new technology DAC with great flexibility and impressive sound. A top performer, if with minor weaknesses.

-  super smooth treble
-  wide range of inputs
-  remote volume control

-  large
-  no ARC with HDMI
-  bass timing

NAD M51 DAC  £1500
Armour Home Electronics
       (+44) 01279 501111

Measurement by Rohde & Schwarz UPV audio analyser



Frequency response measured flat to 21kHz with a 44.1kHz sample rate CD signal; there is no roll off or peaking. The same result was obtained with 96kHz sample rate. With a 192kHz sample rate test signal anti-alias filters imposed a peak above 50kHz, seen in our analysis, but subjectively this is unlikely to be consequential. The M51 will have an even tonal balance in use, or may have some sheen.

    Distortion levels were on the high side with CD (16bit/44.1kHz sample rate) measuring 0.4% at -60dB with a 997Hz tone, where 0.2% is possible. With 24bit resolution the M51 was incredibly linear, distortion measuring just 0.012% at -60dB (96kHz sample rate). Similarly, EIAJ Dynamic Range was mediocre with CD, measuring 100.5dB where 102dB is expected, but 110dB with 24/96.
    Noise was low at -123dB at 0dB, quantisation noise raising the figure to -100dB with 16bit and -111dB with 24bit, when using a -60dB test tone, notched out to lift digital-zero muting. These levels are inaudible of course.
    Output was a high 4.8V from the balanced XLR sockets and  2.4V from unbalanced phono outputs.
    The M51 produces a good set of results, interestingly different from other DACs. It is unusually linear, as linear as DSD from SACD,  and should give a silky sound. NK

Frequency response (-1dB)
    1Hz - 96kHz

Distortion (16/24bit)    %
0dB                           0.01
-60dB                       0.4 / 0.012
Separation (1kHz)      112dB
Noise (IEC A)            -123dB
Dynamic range (16 / 24bit)    100/110dB
Output                     4.8 / 2.4V




DISTORTION  (16bit, 44.1kHz)


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