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NAD Masters Series M51

Stereo DAC/digital preamp (Silver)

19 Reviews | 5 questions - 15 answers

Item # 745M51

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Our take on the NAD Masters Series M51

Sure, NAD's M51 is an exceptionally musical-sounding digital-to-analog converter, but it's much more than that. It's also a versatile digital preamp with enough inputs to handle all of your digital music sources: disc players, network music players, and even your computer. What puts this DAC in a class by itself is NAD's acclaimed Direct Digital technology, which uses immense processing power to transform digital bits into music that's warm, involving, and lifelike.

A boxful of digital audio innovation

Sure, NAD's M51 is an exceptionally musical-sounding digital-to-analog converter, but it's much more than that. It's also a versatile digital preamp with enough inputs to handle all of your digital music sources: disc players, network music players, and even your computer. What puts this DAC in a class by itself is NAD's acclaimed Direct Digital technology, which uses immense processing power to transform digital bits into music that's warm, involving, and lifelike.

How NAD's Direct Digital technology works

NAD's powerful processing engine has exceptional speed and accuracy compared to typical DACs. To get technical for just a moment, the M51 re-samples the incoming pulse code modulated (PCM) signal and converts it to a pulse width modulated signal (PWM) with a sampling rate of 844kHz. One big benefit of converting PCM to PWM is that it completely eliminates any timing errors, known as "jitter," in the incoming signal. That's reflected in the M51's vanishingly low numbers for noise and distortion.

Sound that expresses the spirit and soul of your music

Specifications matter, but they can't describe the energy, presence, and life that the M51 restores to your music. Thanks to this DAC's extremely high clock speed, sophisticated filters can be used to remove nasty digital artifacts like ringing, while maintaining the nuanced dynamics and tonal purity that will make even familiar recordings sound fresh.

All the right connections — including HDMI


The M51 offers an array of digital inputs, plus high-quality analog outputs including balanced XLR.

The M51 is uniquely equipped to dramatically improve the sound quality of all your stereo digital music sources. It has a coaxial digital input, which is great for connecting a CD or DVD player, or a Sonos® Connect player. And an optical digital input is the ideal hookup for your HDTV, Apple TV®, or game console. In addition to these common inputs there's an uncommon balanced digital XLR input that provides an ultra-low-noise connection when used with a compatible high-end CD transport.

High-res audio

A Type B USB port makes it easy to feed the output from your computer into the M51's superb DAC, bypassing your computer's sound card to yield much higher quality sound with stored or streaming music files, including high-res files with sample rates up to 192kHz. (Free USB driver download required for Windows® PC playback.)

Plus, the M51 is the first unit of its kind that we've seen to offer HDMI connections: two inputs and one output with video pass-through. This gives you access to the high-quality 2-channel soundtracks found on nearly all Blu-rays and DVDs. Many symphony orchestras and some specialty music labels are also releasing high-res audio recordings on Blu-ray or DVD.

Praise for the NAD M51 from Stereophile

"The M51 projected a rich, lovely sound that wasn't too forgiving, which was to its credit. I like to hear a recording's technical warts, if any."

"I prefer DACs that reveal as much as possible about what was captured on the tape or in the digits, and couldn't care less about adding a rose-colored tint to dodgy digital sound. In this regard, the NAD M51 succeeds with a wonderfully detailed and revealing sound best described as honest, with a friendly smile. And it was a pleasure to listen to. "

— From Jon Iverson's review in Stereophile, July 6, 2012
Read the full review

It's a versatile digital preamp, too

The M51 is a fully functional digital preamp with one of the world's best volume controls. NAD's 35-bit architecture makes it possible to have a DSP-based volume control that does not reduce resolution — even with 24-bit high resolution signals. In fact, all switching and volume control is done in the digital domain. The only analog circuit is the Class A buffer at the output of the DAC.

Note: input selection is available from the front panel, but volume can only be adjusted via the remote control.

Product Highlights:

  • 35-bit/844kHz up-sampling digital-to-analog converter operating in differential mode for precise sound
  • asynchronous USB technology for reduced jitter and better sound with computer-based audio
  • front-panel vacuum fluorescent display shows sampling rate to verify source quality
  • preamp function with selectable inputs and remote volume control
  • 35-bit DSP-based volume control maintains full 24-bit resolution sound
  • phase-inversion (polarity) switch to compensate for out-of-phase recordings or phase-inverting amplifiers
  • HDMI connections with video pass through to allow two-channel home theater with a Blu-ray or DVD player source
  • remote control
  • two digital audio inputs: one optical (Toslink) and one RCA coaxial
  • USB (Type B) input for connecting a computer
  • two HDMI inputs for stereo-only audio and 3D-compatible video pass through
  • balanced digital XLR audio (AES/EBU)
  • one pair RCA audio
  • one pair balanced XLR audio
  • one HDMI video
Other info & specs:
  • supported sample rates: 32kHz to 192kHz (USB and digital S/PDIF inputs)
  • dedicated NAD USB Audio 2.0 Windows driver required for playback on a PC (free USB driver download available from NAD's website)
  • Mac OSX 10.6 or later includes NAD USB Audio driver, so no download is required
  • frequency response: 20Hz to 96kHz @ 192kHz sampling rate(±0.5 dB)
  • THD: <0.001%
  • signal-to-noise ratio: less than -123 dB
  • channel separation: greater than 115 dB
  • output level: 2V
  • RS-232 port for automated control systems
  • 12-volt trigger and IR input
  • detachable power cord
  • 17-1/8"W x 3"H x 13-1/16"D
  • weight: 12.8 lbs.
  • warranty: 3 years
  • Our 60-day money-back guarantee
  • If connecting to a TV, please make sure you can select "PCM" output in its audio menu. This DAC is not compatible with multi-channel Dolby® Digital signals.

What's in the Box:

  • Direct digital DAC
  • Two 6' AC power cords (US/EU)
  • Remote control (M50)
  • 2 "AA" batteries
  • Quick Start Guide
  • Warranty Card

I have systems in two different homes and own two of these units. A great dac and digital preamp. The sound is superb and the unit provides a wide array of hookups. It has multiple digital inputs and analog outputs. Particularly pleased with balanced outputs for my main amp and RCA's for my sub.

Mark, Wayzata, MN


NAD Masters Series M51 Reviews

Average Customer Review(s):

(19 Reviews)
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Hands-on research

Product Research



Direct Digital DAC/Preamp: The NAD M51 Direct Digital DAC introduces many "firsts" for the DAC product category: first to support HDMI, first to support USB Audio Class 2 with support for 192kHz, the first to use digital error correction, and the first 35-bit architecture to be found in a DAC. The M51 is also a fully functional digital preamp with seven digital inputs and one of the world's best volume controls. As a "preamp" it is totally noise and distortion free, because all switching and volume control is done in the digital domain. There are no analog circuits except for the Class A buffer at the output of the DAC. Whether you want to get into computer audio, Home Cinema 2.0, or just want to upgrade your CD player; the M51 Direct Digital DAC will get the best possible performance from your digital formats. All this innovation, performance, and flexibility come with NAD's legendary sound quality and performance.

Direct Digital Technology: NAD's Direct Digital technology is unique in both its extreme precision and in its speed. Direct Digital technology uses a very powerful processing engine that operates at much higher speed and with much greater accuracy than typical Digital-to-Analog converters. Running at 108MHz, the M51 resamples the incoming pulse code modulated (PCM) signal and converts it to a pulse width modulation signal (PWM) with a sampling rate of 844kHz. Operating in a differential mode with double precision, the M51 has state-of-the-art specifications for low noise and distortion free sound. The extreme headroom afforded by the 35-bit architecture allows for a DSP-based volume control that does not reduce resolution. Even with 24-bit high definition signals, the output can be attenuated by 66dB (very quiet) before bit truncation begins.

Precision Processing Engine: The incredible precision of the M51's processing engine gives music a vibrancy and transient accuracy that must be heard to be appreciated. The conversion process from PCM to PWM completely eliminates any jitter present on the incoming signal; again, offering state-of-the-art performance in this most important parameter. Due to the very high clock speed and mathematical precision of our reconstruction filters, the resulting audio signal is totally free of digital artifacts like ringing.

Pure Class A Analog Stage: A Pure Class A analog stage with very low output impedance provides the perfect interface to your favorite amplifier. Also, both balanced (XLR) and unbalanced (RCA) outputs are available.


Power On/Off Switch: The NAD M51 direct digital DAC's main power switch is located on the rear-panel. Once this main power switch is set to "On", you can switch the NAD M51 from "On" to "Standby" using the front-panel On/Off button.

Input Selection: There is an Input Selection button on the M51's front-panel which allows you to switch between connected sources (AES/EBU, Coaxial, Optical, USB, HDMI, & HDMI2).

Remote Control: The supplied IR remote provides wireless operation of the M51 and features controls for NAD's matching M50 Digital Music Player (745M50, sold separately).


USB (Type-B) Port: The NAD M51 direct digital DAC is ready for the world of computer audio with its rear-panel asynchronous USB (type-B) input that can directly stream 24-bit/192kHz content from your Windows PC, Mac computer, or  other network-attached storage device (NAS). Your computer will need to meet the following system requirements.

  • Windows PC Users: Microsoft Windows XP Service Pack 2 or higher, Microsoft Windows 7.
  • Mac Users: Minimum Mac OS X Snow Leopard (version 10.6) and later versions.
Note: Download the "NAD USB 2.0 Audio Driver" and install this driver to your Windows computer. Mac OS X Snow Leopard (version 10.6) and later versions already include USB Audio 2.0 drivers (no need to download NAD USB 2.0 Audio Driver).

Digital Audio Inputs: The NAD M51 Direct Digital DAC includes three digital audio inputs; optical (Toslink), one coaxial (RCA), and one AES/EBU (balanced XLR).

  • Digital AES/EBU (XLR) Input: The NAD M51 is fitted with a Digital AES/EBU (XLR) jack to connect high-end audio sources, such as SACD and DVD-Audio players. For high-end sources with higher sampling rates like 176kHz and 192kHz, it is highly recommended that such sources be interfaced with the AES/EBU (XLR) In connector.
  • Digital Coaxial/Optical Inputs: The M51 also features a rear-panel optical (toslink) digital input and coaxial (RCA) digital input to connect your digital audio components. Connect your CD, DVD, and Blu-ray disc players. You can also add NAD's innovative C 446 Digital Media Tuner (745C446, sold separately) to stream and manage your internet radio and NAS devices, as well as local AM/FM broadcasts. The Digital inputs support sampling rates of 32-192khz.
Note: If connecting to a television set's optical output, please make sure that you are able to select PCM as the default optical out audio format from your television's Audio menu. This DAC is not compatible with multi-channel audio signals and will not work with televisions that do not output PCM.

Analog Audio Outputs: The NAD M51 offers balanced (XLR) and unbalanced (RCA) analog audio outputs.

  • Balanced XLR Output: The M51 is fitted with a pair of balanced XLR outputs to connect your high-end or professional audio amplifier.
  • Unbalanced RCA Output: There is one set of unbalanced analog stereo RCA outputs to connect to your stereo amplifier.

HDMI Inputs/Output: The M51 offers two HDMI v1.4 inputs and one HDMI v1.4 output with video pass-through. This opens up the possibility of using the M51 Direct Digital DAC as the heart of a "Video 2.0" system using the mandatory two-channel linear PCM soundtrack from Blu-ray or DVD to make a compelling two-channel high definition theater presentation. Many symphony orchestras and some specialty music labels are also released in HD recordings on Blu-ray or DVD. The M51 is fully 3D video compatible, but there is no surround sound decoding or video processing.

USB (Type-A) Port: The M51's USB (type-A) port is only used to update the unit with future software/firmware upgrades from NAD.

12V Trigger Inputs: With this 3.5mm input triggered by a 12V DC supply, the M51 can be switched On remotely from standby mode by compatible devices; such as amplifiers, preamplifiers, receivers, etc. If the 12V DC supply is cut off, the M51 will return to standby mode.

IR Input: This 3.5mm input is connected to the output of an IR (infrared) repeater (Xantech or similar) or the IR output of another component to allow control of the M51 from a remote location.

RS-232 Port: The RS-232 port allows connection to a compatible PC or external whole-house control system from companies such as AMX or Crestron. NAD is a certified partner of AMX and Crestron and fully supports these external devices.

AC Power Cord: The M5  comes supplied with a detachable 6' AC power cord.

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Q & A

Customer Q&A

Crutchfield asked  
Why did you buy this?

Quality sound [ Gary  Jan 21, 2018 ]
high end DAC plus has HDMI in (2) and 1 out. Reviews are off the scale for DAC and Pre-amp. Looking forward to hearing just how quiet the Pre-amp is. Will be using both balanced and unbalanced outputs. [ melvin h.  Jan 02, 2018 ]
Looking to complement my NAD Master Series M22 amplifier with a balanced front end. [ L  Dec 27, 2017 ]
Just seemed like a can't refuse purchase price ! [ Jay  Nov 17, 2017 ]
Good Reviews, [ MELMOTH B  Apr 11, 2017 ]

5 questions already asked

I have the M51 and using the Oppo 205 4K player, I was able to pass though a 4K signal using a 4K disc through the M51 to my 4K television. Interesting since the M51 was designed before 4K was in wide use, I believe. [ Joel  Jan 10, 2018 ]
Not that I know of But you can control pro amps with iPad iPhone apps I have crown xti2 amps and this method works very well Set the dac to your liking and control the rest with the software in the amps Hope this helps [ William  Sep 28, 2015 ]
I use the Roomie IR blaster, app, and subscription service which syncs with all my old iPhones. Tip: if you are not good figuring out new stuff find an audio pro or techie to get it programmed for you. Then on every phone you have is a backlit, touchscreen remote. [ Bart  Sep 28, 2015 ]
Not that I know. [ James  Sep 28, 2015 ]
Hey Los I have not used the unbalanced connects so I sorry I can't help My setup is balanced to Crown XTI 2 amps that are daisy chained I can tell you this, the Nad DAC is a quality product and sounds great hooked up through USB if that's your intended use. Zero hum through balanced. Shoot an email to NAD and ask them [ William  May 27, 2015 ]
Both are active at the same time and I've used it in a similar configuration (driving two separate amplifiers) with no ill effects. [ Aaron  May 27, 2015 ]
Yes, they will have simultaneous output. I have the balanced outs connected to my loudspeaker amp and the unbalanced outs connected to my headphone amp - usually only one of those has power at any given time, but I just tested & confirmed there's output to both at the same time. [ Steven  May 27, 2015 ]
Yes. Both the balanced and unbalanced outputs send signal simultaneously. [ david  May 27, 2015 ]
Yes, but of course the gain levels are different. [ JARED  May 27, 2015 ]
The DAC doesn't play any files, by itself. You'll need another source to decode the AIFF file, then decide whether or not to use the NAD as the DAC. [ Kelly  Mar 15, 2016 ]
Hi John, A DAC doesn't actually play audio files - you'll need a media player for that. The DAC just takes a digital signal and converts it to analog for input into your amplifier. If your media player plays AIFF (or any other digital audio file) and outputs digital data over XLR, coax, optical or HDMI, you'll be able to connect it to this DAC to do the conversion to analog. Hope this helps, Steven [ Steven  Mar 15, 2016 ]
Hello Gib, I think it depends what inputs and outputs you use. Otherwise there is a conversion stage. I am going in AES/EBU and XLR out. This is the only DAC I have heard that sounds like a high quality reel to reel. Long break in is true on this unit. [ BRETT W  May 29, 2014 ]
And as Taylor C said, the unit is very quiet. With the volume set high and no sound playing, there is zero hiss or hum. It's hard to get that with a mixer. All of my muisic is stored on a desktop PC. I am not a DJ. This is a home installation. Any DAC will be a plus for you if your going to be using a PC to amp or receiver. Be sure to get a high quality stereo USB cable as short as possible. It does make a difference in sound quality. [ William  May 27, 2014 ]
I not sure I understand your question. The M51 does have balanced XLR stereo outputs if that is what your referring to. I'm using mine with two 6000 watt Crown pro amps. The sound I get now is phenomenal compared to my previous setup where I was using a DI box. Good Luck! [ William  May 27, 2014 ]
Yes. Unit is very quiet. [ T.J.  May 26, 2014 ]