NAD Masters Series M33 streaming integrated amplifier

On the cold and sunny morning of February 19, 2020, a dozen or so audio critics and writers gathered at Gilmore's Sound Advice on New York's far West Side to see some new NAD and DALI products that had been unveiled the prior month at CES. It was a friendly group, and we kibitzed over coffee before clustering in the arranged seats for presentations and auditions. I doubt any of us realized that it would be the last time for the foreseeable future that we would experience this familiar rite.

I vividly recall walking back to Times Square with John Atkinson while talking about amplifiers and expressing how impressed I was with the NAD M33 from its specs and the demo. He had reviewed the M32, with its optional MDC DD BluOS module and "DirectDigital" topology, and more recently, the M10 with integrated BluOS and "Hybrid Digital" amplifier. Both of those amps were NAD developments, with the former accepting a digital signal at its input while the latter requires an analog input.

The new M33 seems like the culmination of this progression, with a fully integrated BluOS streaming platform, sophisticated control and input/output options, and new power amplifiers based on a patent-pending class-D technology developed by Bruno Putzeys, the mind behind today's almost ubiquitous nCore power amplifiers.

At Munich High End 2019 in May of last year, NAD "announced that it will be the first international brand to incorporate and launch Purifi's new patent-pending class-D technology into its product family. The amplifier circuit, known as Eigentakt (meaning "self-clocking"), is the result of years of research by Purifi into the self-oscillation behaviours in class-D amplifiers with algorithms that, when applied in control loops, improve existing designs by an order of magnitude or more. ... [T]he Eigentakt circuit is expected to outperform any audio amplifier known, regardless of technology or class, with THD and IMD quoted as below 0.00017% at all frequencies and power levels." In the audioband, the frequency response is claimed to stay "within ± 0.01dB under all load conditions." I will not say I got sweaty palms that cold morning in February, but I knew I had to get those palms on an M33.

What is it?
The M33 comes packaged like other NAD Masters Series products: in a double-insulated case with two trays of small parts and accessories. The single page of setup instructions is sufficient, with diagrams that show you how to connect the speakers, your LAN (wired and/or wireless), and your AC power and how to turn it on. Everything else can be done from the generous and clear touchscreen on the front of the M33 and the large, smooth volume control knob on the front panel.

That touchscreen is a delight for ongoing playback operations, but I find finger-poking horizontally through setup menus on a vertical screen tedious. Fortunately, there are other ways to set things up, such as the BluOS app I installed on my iPhone; you can also use an iPad or a laptop. Android devices work, too.


The back panel confirms that the M33 is much more than a streamer: It accepts input from virtually any type of device one might want to use in a modern stereo system. Digital inputs via optical, RCA, and XLR handle PCM up to 24/192, and the BluOS system will play PCM files from a USB drive plugged into the rear-panel USB port. RCA and XLR inputs accept analog audio, and there's a phono input for MM and MC cartridges, although they, like the other analog inputs, are digitized with 24-bit resolution and a sample rate of 48, 96, or 192kHz. The M33 even has an HDMI/ARC input that extracts the audio from the HDMI/ARC connection of your smart TV, so you can accompany your TV's video with the M33's high-quality sound.

The M33's heavy processing is handled by an NXP 1GHz ARM processor running in a Linux-based operating environment. Digital-to-analog conversion is performed by an ESS 9028PRO Sabre DAC. In addition to the main speaker outputs, the M33 has a headphone jack driven by a dedicated analog amplifier and line-level stereo RCA jacks as well as a pair of similar jacks for subwoofers. Wireless (Bluetooth aptX HD) streaming to speakers and headphones is also on tap. BluOS will control and synch other BluOS devices with the M33.

For the power-mad who can never get enough, there is a switch to bridge the two channels into a >700W mono monster, and the line outputs allow you to add an external matching amp or two. (Do you think that NAD has something like that in the works?) Why two subwoofer outputs? NAD says that they are there to support the "Bass Control" function in Dirac Live3, but, at the time of this review, that advanced feature had not yet been implemented. Speaking of the future: There are two empty MDC slots for expansion modules, although it is hard to think of anything the M33 lacks.

How does it work?
With BluOS as its default streaming platform, the M33 is virtually a plug-and-play music system. Once you point BluOS to your music files, or log in to your favorite streaming services, or both, you have a world of music at your fingertips. After I did that, BluOS scanned the files on my NAS and added them to its library in minutes. More than a dozen streaming services are supported; I signed in to my Qobuz and Idagio accounts with ease.

The Roon core elsewhere in my system sees the M33 as an endpoint; because I'm so familiar with its user interface, I usually found it easier to browse and play stereo PCM files with Roon. Another advantage to using Roon to access music is that Roon will play files BluOS ignores, multichannel PCM files with resolution greater than 24/96 (footnote 1), and all DSD files (footnote 2). I could not perceive any audible difference between playback from BluOS and playback from Roon.


With the M33 playing the source files on my NAS or on the cloud directly to the Revel Studio2 speakers, the sound was impressive. I did not notice any compromise in tonal balance, transparency, or dynamic performance compared to the streamer, DAC, preamplifier, and power amplifiers—that's five components for stereo—that it replaced. Even when I fed the M33's balanced analog inputs with the aforementioned streamer, DAC, and preamp, adding an unnecessary round of A/D/A conversions, I could discern no consistent degradation in the sound. Still, why would anyone do that?

Here's why: The M33 also offers Dirac Live 3 LE. Because the analog inputs—including the phono inputs—are digitized, Dirac Live's optimization features can be used even with an analog source.

Footnote 1: BluOS will play multichannel PCM files up to 24/96, ignoring all but the left and right channels; Roon downmixes all the channels in a multichannel file for a more pleasing stereo presentation.

Footnote 2: BluOS ignored all DSD files. The BluOS support website has an entry entitled "PLAYING DSD FILES IN BLUOS," but what it describes is an option for BluOS to copy all your DSD files and to convert the copies to FLAC/PCM. It will not alter your original DSD files, but it does not say how it deals with anything other than standard stereo DSD64. I declined to do this with my more than 20Tb of various DSD files; anyway, the M33 can play your DSD music, albeit as PCM.

NAD Electronics International
633 Granite Ct.
Pickering, Ontario L1W 3K1
(905) 831-6555

a.wayne's picture

Hello John ,

I still Can’t wrap my head around how badly Class D amplifiers measure on square-waves , Thinking this must lead to why most hear odd timbre from them especially on difficult to drive loudspeakers ..

MZKM's picture

A square wave mostly shows frequency range. This amp reaches the bottom of the graph at 50kHz, so naturally the square wave won’t look as good as an amp that is flat to 100kHz. A square wave is made up by adding harmonics of sine waves, so naturally if the harmonics are lower in level, it’ll look less like a square wave. A square wave doesn’t tell us anything that can’t be obtained from other graphs.

Go back to last measurements and you’ll see the same thing, the amps that can get close to a square wave have an extended frequency response. So, you have to believe that we can hear >20kHz in order to believe a difference in quality can be obtained by having a better looking square wave.

As for difficult to drive speakers, that is based on their impedance/phase. Two amps could have identical wattage using 4ohm load test, but the actual wattage available could be drastic if the speaker has say -45° phase and 4ohm and 100Hz. The tonal balance can also be altered by having low output impedance (low damping factor).

modern audio lovers's picture

Great review as always Kal!

Question for John: Is there a reason for using the analog input for the THD+Noise tests on integrated amplifiers that digitize their inputs?

These new breed of devices are obviously designed with playback of digital sources at the forefront. I think that publishing the end-to-end measurements for digital audio input -> amplifier output would serve the best educational interests for the readership-at-large.

This isn't to say that the analog input -> amplifier output measurement isn't useful... would be great to have both!

stereophileuser2020's picture

Looks fantastic, but I'm really disappointed that the M33 doesn't have a USB-B input for hooking up a computer. That's almost a dealbreaker for me.

mtrot's picture

Same here, deal breaker for me.

tonykaz's picture

High-End performance for everyman annnndddddd at everyman's price, egads, this device drove your Revels to convince even you, phew!

I'm wondering, what reward comes from spending 10x or 20x this kind of money for electronics?

I recall when the NAD 3020 marked the beginning ( 1978ish ) of an exciting Audiophile world, is this M33 guiding us safely/pleasantly/joyfully into the 21st Century? I wish it was made in Toronto. ( or Valencia, Ca. )

Thank you for another adventure , your writing never seems like a 'paint by numbers' review as is so common today.

Tony in Venice

Kal Rubinson's picture

Regarding Roon:

I have heard reports that the M33 does not support Roon and that I must have reviewed a "special" version not available to the public. I do not believe that is true.

The time I had the M33 was prior to 9/21. It was on that date that Roon cut off working with non-certified devices although Roon asserts that those already registered in use will have continued support. Only new ones will not be recognized until the device is certified. See:

When I learned of this change, I asked NAD about support for the M33 and the response they sent is as follows: "
“As Roon explain themselves, any device that has been used prior to Sep 21st, even in an uncertified way, will continue to work. The NAD M33 is with Roon for final certification approval and both companies are working together to have this completed as soon as possible.”

I did note, in the review, that the M33 was not yet certified but that it worked. That is true and, I believe, true for all M33s put into Roon use prior to 9/21. However, any newly purchased M33, although identical in all ways to the one I had, is likely to be ignored by Roon if the user attempts to register it with Roon after 9/21 and before Roon/NAD work out the certification.

I hope that this makes the current situation clear and that the certification issues will be completed soon.

MikeP's picture
sonictomb's picture

Thanks for this review, Kal.

I'm really loving the idea of this amp and minimizing my setup, but I'm also into vinyl.

Did you experience any vinyl using the digitized RCA inputs?

That would be the crux for me pulling the trigger on this, as I love all the convenience it offers for digital but I need a competent phono stage as well.

Wildcoach's picture


Enjoyed your review even though I didn't quite understand all of the test results (all? Hardly! But a few, hopefully, LOL).

In reading page 2 where you discuss the amplifier component of the M33, and the testing page, I was hoping you could comment on the M33's ability to dirve low loads. I have a pair of Infinity Kappa 8's which present very low (1.3) and varying loads throughout the range.

How does this new-style class-D amplifier section handle low loads like that? Is it stable or should I just stay clear of it and buy a McIntosh?



Just FYI, the M33 is now considered (officially) Roon Ready and Roon Tested:

I did it with my M33 recently... no problems whatsoever.