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User Review: M51 Direct Digital DAC - M51 punches well out of its weight class

December 28, 2011

Products: M51 Direct Digital DAC

First, it’s a standalone DAC utilizing the Direct Digital architecture developed in cooperation with Zetex to convert from PCM digital to a PWM output with a clock frequency of about 850 kHz. Previous test results on the M2 Amplifier incorporating this chipset show a very wide dynamic range, with a true 20-21 bits of resolution versus noise, and essentially unmeasurable jitter.  However, I’ve never had a chance to hear the M2.  And frankly, being familiar with some of the SRC approaches used in other DACs and the chipsets on which they’re based, and their shortfalls in audible performance, this excellent specification still left me skeptical.


A second reason for interest in the M51 was that it’s architecture with wide dynamic range calculation supports a built in high resolution volume control- I’m pretty keen on DAC’s that can manage this well (not all do), as it simplifies the system configuration and lowers cost to not need an external preamp in all situations. 

Finally, the HDMI input with pass through was quite intriguing and especially useful in the secondary system I planned to use the M51 in, which is a mix of audio and video, and for which HT 2.0 with a high res DAC handling audio was absolutely perfect for me, if totally unlike what the rest of the industry is offering. This can be used for both the few music disks, but also for video pass through and two channel audio decoding.  Hurrah!

However, to date I haven’t tested it in that mode. You see, my first desire was to put it in my main audio system and check out the basic audio quality, to understand what I was getting in comparison to my Metric Halo LIO-8, and also see how it stacks up against the Berkeley Alpha DAC currently in the secondary system.  At face value, that’s not a fair comparison, considering the over 2:1 disparity in price, but you have to use some kind of benchmarks to see how things stand. 

I have a very wide range of musical interests, and while some of them fall within the domain of typical “audiophile” music, a fair amount of it doesn’t, and these disks are often the acid test for listenability.  In my experience, a really good DAC will not make disks sound the same, but reveal faithfully what was put on them; an excellent DAC will deliver that without any additional edge, detail, or loss of coherency on complex material, preserving harmonic relationships and tonality even in the presence of very complex dynamics.  Being an old school kind of guy, with recording experience in the 70’s, the biggest compliment I can probably pay a DAC is to say the playback sounds more like a pro reel to reel that’s properly setup, than like a DAC.  Or, taking it to the final extreme, more like the mic feeds. 


Disks that are described as audiophile material, very cleanly recorded pop (Jennifer Warnes, for example) or ECM jazz, (Keith Jarret, Changes), jazz fusion (many Stanley Clarke albums, particularly the latest electric one, and the “Bass-ic” collection Japanese import), and more eclectic music such as Curandero’s “Arás” reveal everything you could hope for in terms of dynamics, tonal integrity and imaging.  What’s more impressive to me are the results with some of my old favorites that are not exactly audiophile grade sources- but dear to me musically, like the old Mastersound SBM of Pink Floyd’s “Wish you were here”, Boston’s Mastersound SBM version of “Boston”, or the remaster of the Alan Parson produced “Ambrosia”, by Ambrosia.  These are clearer and more natural sounding (i.e., like a master tape) than I’ve ever heard these albums before.  These CD’s were played back via a Tascam CD 01U CD transport over AES/EBU. 

Other  material I’ve had only a small opportunity to listen to includes high resolution material played back over my Macbook Pro through the Fidelia player.  This includes downloads from various sources, and my own extractions of SACD’s at 24/176.4, from disks as diverse as The Who’s “Tommy” to  releases from Water Lily Acoustics like “Tabula Rasa”, “Mumatz Mahal” and “The Philadelphia Orchestra — Nature's Realm”, plus pop titles from Dire Straits, Steely Dan, and others. The results indicate that the USB interface of the M51 works quite well also, including at high sample rates. 

The only real caveat or concern I can come up with about this unit is the remote and lack of front panel controls.  Now, the remote functionality is fine, and it seems to be well made and I hope quite reliable.  I mention that only because unlike some other DAC/preamp combos, like my Berkeley Alpha DAC, there are no front panel controls other than an on/off switch.  If the remote goes down, you lose control of the unit.  Now, hopefuflly this is unlikely.  On the other hand, an acquaintance’s remote for his Berkeley DAC did go down over the recent Thanksgiving holiday- not a major problem for him as all controls are replicated on the front panel.  But, the Berkeley remote is clearly of a smaller, cheaper construction than the one NAD supplies with the M51.  Nevertheless, getting a back up remote for the M51 is on my to-do list for 2012. 


In conclusion, I have to say the M51 offers very high value, and punches well over the weight class that it’s purchase price puts it in.  Anyone considering a DAC, especially one with preamp capabilities in the $2K to $7K region should give it a close listen before making their purchase decision.   As for me, I’ll be doing some more listening comparisons and carefully pondering whether I need to pick up a second one for my main system.  

Jon Mark Hancock - Livermore, CA; USA

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