t.r.a.n.c.e. said:

  I just bought a new M51 for 1 grand on clearance. I'm running newest FW 1.50. I'm about to try revert to FW 1.39. I'm scared schitless that I might brick my unit. For anyone that doesn't know, FW 1.39 has 1dB more gain than the newer firmwares, which is why many people found it to sound more dynamic and lively than newer firmwares. Nad reduced the gain by 1dB due to clipping when run at 0dB volume, but that was easily fixed by running at -1dB volume. So technically the newest firmwares are a better implementation of the hardware as 0dB is bit perfect for the dac and should not have clipping, but to achieve this the dynamics will have taken a hit due to the reduced gain.
 
Also on a technical level the SPDIF inputs of coaxial and optical should be the most pure representation of your source input, as it takes PCM from the input and gives it straight to the M51 Dac (Zetex DDFA) to convert to 844mhz PWM. While the other inputs go through another chip before going to the Dac,  the Usb input goes through an xmos chip, the Hdmi input goes through an Analog devices chip, the Aes/ebu input goes through an Akm chip. So all these chips introduce their own sound sig onto the input signal, not that its a bad thing as they are all high quality chips, but the SPDIF input will just have a sound that is truer to the source input, I also always favor coaxial over optical in any system.

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ellevoid said:

   
Thanks for the technical info on each input. I just bought a new music server and it has usb output only.
Is it gonna be a lot better in sound quality if I bought another usb/spdif converter to use with NAD M51?

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olor1n said:

  Pretty sure the clipping "issue" was solved in firmware prior to 1.39.

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t.r.a.n.c.e. said:

   
No there is no point getting a converter imo. The converter will be doing the same thing, using a chip inside to convert the usb signal to spdif, and the M51 chips are already as good as it gets for the most part, so a converter may even reduce sound quality compared to the M51, unless its a high end implementation that betters the M51's. The M51 usb implementation is using xmos, which is much better than your average spdif convertor will be using.
 
 
Ok, that may well be, I haven't looked into the previous firmwares. If that's the case then I suppose Nad just wanted a more neutral sound sig, as FW 1.39 and below were said to have noticeably more bass than the newer firmwares, but I'm already getting bucket loads of clean bass on the latest firmware so I can't complain there at all. I personally think a Dac should be as neutral as possible, and any coloration if wanted should be added by the amp and/or speakers, I usually prefer neutral speakers + neutral Dac, and the coloration left to the amp personally. Nad knows what they are doing, and they wouldn't have made their changes without good reason, and judging by what I'm hearing I am happy with what they've accomplished.

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kmanchu said:

   
The AES input is the superior input on the M51 in my experience (the owner's manual even hints at as much.) I (and several others) found the integrated USB input leaves a lot to be desired. I was not satisfied with its performance through that input. Introducing a power conditioner helps (such as Schiit wyred or iFi iUSB Power) but it's still not great. Introducing a good high quality source like Audiophilleo, NAD's own M50, Berkeley Alpha USB, Yellowtec Puc2, or even the humble iFi iLink provide superior performance to the built-in USB. In my opinion a very high quality source brings the performance level into another league.

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kmanchu said:

   
The AES input is the superior input on the M51 in my experience (the owner's manual even hints at as much.) I (and several others) found the integrated USB input leaves a lot to be desired. I was not satisfied with its performance through that input. Introducing a power conditioner helps (such as Schiit wyred or iFi iUSB Power) but it's still not great. Introducing a good high quality source like Audiophilleo, NAD's own M50, Berkeley Alpha USB, Yellowtec Puc2, or even the humble iFi iLink provide superior performance to the built-in USB. In my opinion a very high quality source brings the performance level into another league.

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lappy27 said:

  X100
 
My NAD M51 sound so much better with the Audiophilleo2 + PurePower than from his USB input that it's not even funny. 
 
Yeah it's not a cheap add on but if you have the chance to compare you will be convinced without a hint of a doubt. Put it simply the sonic difference is like if you are listening to two very distinct component. No jokes or exageration here.
 
A much cheaper alternative that make a buzz currently on the market of USB to SPDIF converters is the Gustard U12. China made but apparently extremely surprising performance for it's price.

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olor1n said:

"Lean" is the last word I'd associate with the M51.

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karmanfamily said:

  Here are my 2 cents about the NAD M51...
 
Last week I received my new (used) M51 and connected it to both my setups with several different inputs and file qualities.
 
the first setup is my test setup, it has good gear except for the speakers. The used gear is as follows:
PC with files from MP3 to 24/192 FLAC connected with USB
Decware CSP2+ tube pre amp
Bel Canto S300 power amp
Mission 'something something' cd player connected with digital RCA
Pioneer SP-BS22 speakers
PS Audio UPC200 power conditioner
The cables are generic or basic cables, nothing fancy
 
The inputs I used were USB and Digital RCA.
Ouputs used were RCA to the Decware pre amp and XLR directly feeding the S300 power amp.
 
Songs used:
Eagles, Hotel California 24/192 FLAC
Norah Jones, Come Away with me 24/192 FLAC
Metallica, Nothing Else Matters 24/96 FLAC
Lenny Kravitz, Are you gonna go my way, crappy MP3
Red Hot Chili Peppers, Under the Bridge CD
Smashing Pumpkins, Siamese Dreams entire CD
 
I compared the M51 with a Musical Fidelity M1DAC (MF). The MF M1DAC is one of the most neutral DACs I have ever heard and will be a good base line.
 
After playing my test songs on the MF M1DAC and getting used to that sound I connected the M51 and played the same songs and what I heard was both surprising and I was a little disappointed... (the disappointment has more to do with my taste as you'll read later)
 
The pre-review info will be longer than the actual review...
 
Biggest surprise was how it handled the crappy MP3, there was a HUGE improvement over the detail heard compared to the MF and it sounded less 'digital'.
 
The low end sounded good, it was there, it sounded nice and tight, but it was missing some 'oomph'.
Mid range was great, voices sounded clean and very separated from the instruments, which is a weak point of many DACs that I have heard.
High range was crisp, but way too clean for my taste, crazy detailed. I heard more little things than I remember hearing with any other DAC.
 
From an audiophile point of view this DAC is the best I have heard, beating the MF, PS Audio PWD, Bryston BDA-1 and Rega DAC in detail, instrument separation and again.. DETAIL! You will hear little nuances hiding in the music that stayed hidden with most other DACs.
 
From a music lover point of view this DAC lacks some emotion, some character, warmth. You miss that little raspy sound in a voice, the sound of the fingers touching (plucking) the snares of the guitar. Qualities that the Bryston and Rega definitely have.
 
This DAC will divide the camp in 2 groups:
1. the lovers of detail and pure sound quality, that will rave about the M51.
2. the lovers of a more 'live music' sound that has more warmth and might not sound as perfect.
 
At that point I was still divided, until.....
 
I added the M51 to my main setup:
Oppo 103 as cd transport Optical
Sonos ZP90 with W4S 96kHz mod Digital RCA
Primaluna Dialogue 2 with KT120 tubes
Goldenear Aon 3 speakers
All audio cables are Anti-Cables
All Power cables are Wireworld Silver Electra
API power conditioner
 
I played the same songs, but all at 16/44.1 (cd) quality.
 
To compare I used my faithful Bryston BDA-1.
 
First I played all the songs with the BDA-1 in place and it sounded like perfection (in my ears). Not the greatest detail, but when you close your eyes you are in that 'smokey bar' and the band is there playing in front of you.
 
Plugging in the M51, letting things warm up and playing the same songs I could not believe what I heard....
Compared with my other setup and test this sounded so lean, thin, uninteresting and bland... What!
I disconnected everything, checked again if everything was connected right and working as it should. Played the same songs again and crap.... well.. crap? not crap, but not what I heard in the other setup.
The bass was almost gone, mid range was still very good and the high end was real sharp. Don't get me wrong, the incredible amount of detail was still there. I was still hearing little details that I did not hear with the BDA-1.
 
I think that in this setup classical music will shine a whole lot more than what I prefer to listen to. Just from a detail and separation of the instruments point of view.
 
It may sound like that I am biased and will pick the BDA-1 over about anything, but I am looking for a serious replacement for the BDA-1 and was critically listening to both DACs.
 
I will keep on playing with the M51 over the next few days and see if things change after more time settling in and if anything changes I will let it know...
 
I hope it all made sense...

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karmanfamily said:

  Here are my 2 cents about the NAD M51...
 
Last week I received my new (used) M51 and connected it to both my setups with several different inputs and file qualities.
 
the first setup is my test setup, it has good gear except for the speakers. The used gear is as follows:
PC with files from MP3 to 24/192 FLAC connected with USB
Decware CSP2+ tube pre amp
Bel Canto S300 power amp
Mission 'something something' cd player connected with digital RCA
Pioneer SP-BS22 speakers
PS Audio UPC200 power conditioner
The cables are generic or basic cables, nothing fancy
 
The inputs I used were USB and Digital RCA.
Ouputs used were RCA to the Decware pre amp and XLR directly feeding the S300 power amp.
 
Songs used:
Eagles, Hotel California 24/192 FLAC
Norah Jones, Come Away with me 24/192 FLAC
Metallica, Nothing Else Matters 24/96 FLAC
Lenny Kravitz, Are you gonna go my way, crappy MP3
Red Hot Chili Peppers, Under the Bridge CD
Smashing Pumpkins, Siamese Dreams entire CD
 
I compared the M51 with a Musical Fidelity M1DAC (MF). The MF M1DAC is one of the most neutral DACs I have ever heard and will be a good base line.
 
After playing my test songs on the MF M1DAC and getting used to that sound I connected the M51 and played the same songs and what I heard was both surprising and I was a little disappointed... (the disappointment has more to do with my taste as you'll read later)
 
The pre-review info will be longer than the actual review...
 
Biggest surprise was how it handled the crappy MP3, there was a HUGE improvement over the detail heard compared to the MF and it sounded less 'digital'.
 
The low end sounded good, it was there, it sounded nice and tight, but it was missing some 'oomph'.
Mid range was great, voices sounded clean and very separated from the instruments, which is a weak point of many DACs that I have heard.
High range was crisp, but way too clean for my taste, crazy detailed. I heard more little things than I remember hearing with any other DAC.
 
From an audiophile point of view this DAC is the best I have heard, beating the MF, PS Audio PWD, Bryston BDA-1 and Rega DAC in detail, instrument separation and again.. DETAIL! You will hear little nuances hiding in the music that stayed hidden with most other DACs.
 
From a music lover point of view this DAC lacks some emotion, some character, warmth. You miss that little raspy sound in a voice, the sound of the fingers touching (plucking) the snares of the guitar. Qualities that the Bryston and Rega definitely have.
 
This DAC will divide the camp in 2 groups:
1. the lovers of detail and pure sound quality, that will rave about the M51.
2. the lovers of a more 'live music' sound that has more warmth and might not sound as perfect.
 
At that point I was still divided, until.....
 
I added the M51 to my main setup:
Oppo 103 as cd transport Optical
Sonos ZP90 with W4S 96kHz mod Digital RCA
Primaluna Dialogue 2 with KT120 tubes
Goldenear Aon 3 speakers
All audio cables are Anti-Cables
All Power cables are Wireworld Silver Electra
API power conditioner
 
I played the same songs, but all at 16/44.1 (cd) quality.
 
To compare I used my faithful Bryston BDA-1.
 
First I played all the songs with the BDA-1 in place and it sounded like perfection (in my ears). Not the greatest detail, but when you close your eyes you are in that 'smokey bar' and the band is there playing in front of you.
 
Plugging in the M51, letting things warm up and playing the same songs I could not believe what I heard....
Compared with my other setup and test this sounded so lean, thin, uninteresting and bland... What!
I disconnected everything, checked again if everything was connected right and working as it should. Played the same songs again and crap.... well.. crap? not crap, but not what I heard in the other setup.
The bass was almost gone, mid range was still very good and the high end was real sharp. Don't get me wrong, the incredible amount of detail was still there. I was still hearing little details that I did not hear with the BDA-1.
 
I think that in this setup classical music will shine a whole lot more than what I prefer to listen to. Just from a detail and separation of the instruments point of view.
 
It may sound like that I am biased and will pick the BDA-1 over about anything, but I am looking for a serious replacement for the BDA-1 and was critically listening to both DACs.
 
I will keep on playing with the M51 over the next few days and see if things change after more time settling in and if anything changes I will let it know...
 
I hope it all made sense...

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karmanfamily said:

  A little correction on my review above:
Last night I replaced the KT120 tubes in my amp with a set of Svetlana 6550C's and the bass improved a lot.
I guess the KT120's are not really working well for me in my amp. Later I read that the KT120's shine at higher volumes, so that might have been the issue.
The M51 is starting to look like a keeper.

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