NAD’s Masters M33 integrated amplifier-DAC, announced last January in Las Vegas at the 2020 Consumer Electronics Show, is the first commercially available product to implement NAD’s Hybrid Digital Purifi Eigentakt technology. This consists of Purifi Audio’s 1ET400A monaural, class-D power-amplifier technology, about which SoundStage! Network founder and publisher Doug Schneider wrote in June. Purifi Audio, founded in Denmark by entrepreneur Peter Lyngdorf and electronics designers Bruno Putzeys and Lars Risbo, was at first devoted to pure research. Later, after it had become a commercial enterprise, Purifi sent Doug an “engineering evaluation” version of the first Eigentakt amp. This comprised two 1ET400A modules, a Purifi-designed gain board, and a Hypex power supply, all housed in a DIY-style case. Doug was enthusiastic: “I was bowled over by the Purifi Eigentakt’s sound and operation. It turned on silently, made almost no noise, provided more than enough power while generating hardly any heat, and passed music through so transparently, at volume levels from low to high, that it left me in near disbelief that so small a box could accomplish so much.”
The Masters M33 ($4999, all prices USD) is more than just a power amp based on Purifi’s 1ET400A modules. It has a moving-magnet/moving-coil phono stage, subwoofer outputs, a headphone amp, and a host of other features (see below). The result is one of the most forward-thinking and versatile integrated amplifier-DACs around.
What doesn’t it do?
Rather than describe each of the Masters M33’s many features, it would be far easier, if not as informative, to list the handful of things it doesn’t do. Too bad that’s not part of my job description . . .
NAD describes the Masters M33 as a BluOS streaming DAC-amplifier. It supports multiroom systems and streaming via its BluOS app, which can be installed on Windows, macOS, iOS, and Android devices. Excellent descriptions of how BluOS works can be found on SoundStage! Simplifi, in Gordon Brockhouse’s reviews of NAD’s Masters M10 streaming integrated amplifier and C 658 streaming DAC. In addition to BluOS, the M33 includes Dirac Live room-correction software (more about this later).
All of the M33’s digital inputs are capable of accepting signals up to 24-bit/192kHz, the maximum resolution of BluOS. There are two coaxial (RCA) inputs, two optical (TosLink), and one AES/EBU (XLR). The USB Type-A input is for connecting a USB storage device, with files accessible through the BluOS app, and there’s an HDMI eARC input for connection to similarly equipped A/V devices. Wireless connectivity consists of Wi-Fi 5, Apple’s AirPlay 2, and two-way Bluetooth aptX HD. The M33 also supports Amazon Alexa and Google Assistant voice control, and Apple’s Siri via AirPlay 2. The M33’s full suite of analog inputs comprises line-level unbalanced (RCA), balanced (XLR), and switchable MM/MC phono (RCA). There are also a preamp output (RCA) and two subwoofer outputs (RCA), with a crossover adjustable from 40 to 200Hz in increments of 10Hz. Finally, there are two of NAD’s Modular Design Construction (MDC) expansion slots. There is currently one optional MDC module available for the M33. It has three 4K-capable HDMI inputs, one output, and the ability to play two-channel PCM audio from any of the inputs. Additional MDC modules are planned.
As impressive as the M33’s connectivity is, it lacks a USB Type-B input -- understandable, given its plethora of other digital and streaming connection options. But many of today’s digital components offer support for resolutions higher than 24/192 via their USB inputs, as well as support for DSD -- two of the few things the M33 doesn’t do but that some audiophiles would appreciate. The M33 does offer a workaround: it can convert DSD files to PCM-based FLAC files and save them for later playback.
Also found on the rear panel are two sets of high-quality speaker binding posts, a 12V trigger input and output, an IR input, an RS232 port, a USB Micro-B port for servicing, connectors for the Wi-Fi and Bluetooth antennas, an IEC power inlet and main Power rocker, and a switch to put the M33 in monaural Bridge mode. According to NAD, setting the M33 to Bridge mode provides about 640W of power into 8 ohms. In stereo, the M33 puts out 200Wpc into 8 ohms.
The front panel is dominated by a large (7”) color TFT touch display that provides access to all of the M33’s many functions; in streaming mode, it displays track and album information. Although I mostly used the BluOS app to control the M33, I found its onscreen menu system intuitive and easy to use. To the right of the display is a large volume knob, and to the left an illuminated NAD logo that changes color to indicate power status. The capacitive-touch power button is at the top of the front panel.
NAD also provides their excellent HTRM 2, macro-capable, learning remote. This long, slim wand of brushed aluminum with angled sides fit nicely in my hand and worked well. Its backlit buttons, though a bit small, are logically placed and of various shapes, for different functions -- it’s one of the better remotes I’ve seen.
The Masters M33 weighs 21.4 pounds and measures 17.1”W x 5.25"H x 15.6”D. Its case consists of thick panels of brushed aluminum with attractively contrasting matte-black front and top panels, and the build quality is very good. The eight large vents in the top plate are each covered with fine mesh, and the four spiked feet come with metal discs to place under them, to protect whatever surface the M33 sits on. Like the other models in NAD’s Masters series, the M33 has a two-year parts and labor warranty.
Guts and Glory
Purifi Audio’s Eigentakt class-D amplifier technology is claimed to produce ultra-low distortion regardless of frequency or load. Greg Stidsen, director of technology and product planning for the Lenbrook Group -- which owns Bluesound, NAD, and PSB -- explained to me that, instead of buying 1ET400A amp modules directly from Purifi, NAD has licensed the technology and, working closely with Purifi, builds their own circuit boards to ensure that the result is at least equal in performance to the reference design. Because the Eigentakt -- its German name means “self-clocking” -- is quite low in gain, NAD has added a gain stage to increase its headroom so that it works better with the DSP circuits of its room-correction software and tone controls. NAD concedes that this slightly decreases the M33’s signal/noise ratio, but with careful design and premium parts, and because the Eigentakt’s S/N is so low to begin with, the noise is still inaudible. NAD specifies the S/N of the M33’s amplifier section as >100dB (A-weighted, ref. 1W out in 8 ohms) and >125dB (A-weighted, ref. 200W out in 8 ohms), with total harmonic distortion of <0.002%, 20Hz-20kHz (250mW-200W, 8 and 4 ohms).
NAD also uses a high-quality, active power supply of their own design that, they claim, maintains the correct DC output voltage over a range of AC input voltages while remaining free of noise. The left and right channels are run internally out of phase, to maximize the power available from the supply, monitor the rail voltage/current, and cleanly clip the input to prevent severe output-stage distortion.
The other important technology licensed by NAD for the M33 is Dirac Live room-correction software. The standard version of Dirac Live (included) calculates corrections up to 500Hz; the full-frequency version, which can correct up to 20kHz, is available for download for an additional $99. NAD also makes available their own target curve for Dirac Live, based on work done at Canada’s National Research Council, in Ottawa, by many researchers, including Paul Barton, chief designer for sister brand PSB. Dirac Live’s Bass Control add-on, which includes such features as phase correction for speakers and multiple subwoofers, to smooth their low-frequency response throughout a room, is currently available for use in some Dirac-compatible products, but not yet for the M33. (The multiple-subwoofer version of Bass Control for those other products goes for $499.)
Like many high-end components, the M33 uses ESS Technology DAC chips -- one Sabre ES9028 chip per channel, with differential output to the amplifier stage. All incoming analog signals are converted to digital with high-quality A/D conversion that NAD says is very transparent. This also makes possible multiroom streaming of the analog inputs. For A/D conversion, the final sampling rate for each input can be set to 48, 96, or 192kHz. DSP functions are performed by a 1GHz ARM Cortex A9 processor, and the volume is set using the ES9028 chip’s built-in, high-quality, 32-bit volume control.
BluOS supports playback of many file formats -- AAC (M4A, MP4), AIFF (AIF, AIFC), ALAC (M4A), FLAC, MP3, MQA, OGG, WAV, WMA, and WMA-L -- as well as many popular high-resolution music-streaming services: Amazon, Neil Young Archives, Qobuz, and Tidal, among others. Finally, I didn’t try BluOS’s multiroom features -- I had no other BluOS devices in my system.
Islands in the Stream
When the Masters M33 arrived, I connected it to my home network with an Ethernet link, updated its firmware, and from that point on it worked without incident for the entire review process. After moving it back and forth between my two systems a few times, I found it easier to access my network with the Wi-Fi connection. I had no problem setting up and using the Masters M33, so intuitive and simple is its interface.
I used the M33 mainly with Qobuz as a streaming service, with either Roon or BluOS to manage playback. I also used its digital and analog inputs: the MM phono input with my Pro-Ject X1 turntable, and my Oppo Digital UDP-205 4K UHD universal BD player through its balanced (XLR) analog outputs. Although I primarily used a MacBook Pro computer to control the M33, I also installed and used the BluOS app on my Apple iPhone 6S and Samsung Galaxy S9 smartphones.
Speakers were my reference MartinLogan Masterpiece Classic ESL 9 hybrid electrostatics, a pair of PSB Alpha T20 floorstanders, and two JL Audio E-Sub e112 subwoofers. All were connected with Clarus Aqua speaker cables and power cords, Nordost Quattro Fil interconnects, and an AudioQuest Carbon USB link; power conditioning was by Zero Surge and Blue Circle Audio.
I was provided the full-frequency version of Dirac Live, which I used in conjunction with NAD’s target curve to set up profiles with and without subwoofers. I limited Dirac Live’s correction of higher frequencies to a ceiling of 1kHz -- I found that setting it higher, using the NAD target curve, slightly dulled the sound of my MartinLogans. This was similar to my experience with the Anthem Room Correction Genesis software built into my reference preamplifier, an Anthem STR.
I first used the Masters M33 with my MacBook by streaming Qobuz, via BluOS, to the PSB Alpha T20 speakers. Like other multi-kilobuck integrated amps I’ve recently reviewed, the M33 sounded excellent with these relatively efficient and overperforming budget floorstanders ($649/pair), the sound easily better than what I hear with this system’s usual electronics: an Oppo BDP-105 universal BD player ($1199, discontinued) used as a preamplifier-DAC to drive a five-channel Axiom ADA 1000 power amp ($1530).
The title track of Gaslighter (24-bit/44.1kHz FLAC, Columbia/Qobuz), the latest album from the former Dixie Chicks and the first released under their new name, the Chicks, began by sounding a bit thin -- a characteristic of this recording. But when the bass kicks in at 0:43, the M33 grabbed hold of the little Alpha T20s to slam out some serious lows. The PSBs don’t go extremely low, but low enough for most music, including the Chicks’ country pop. The M33’s articulation and speed in controlling these speakers fully reproduced the fast attack of each drum beat and its brief, precise decay -- something I hadn’t thought possible with so inexpensive a pair of small floorstanders, regardless of amp. Other integrateds, such as Naim’s Supernait 3 ($4990) and Musical Fidelity’s M8xi ($6499), have exerted similar control over the PSBs, but the M33 seemed just a bit more able to communicate different low-bass pitches. The NAD also produced a bigger soundstage with more space between voices and instruments, even with the clearly artificial reverb used in the multitracked “Gaslighter.”
The Fast and the Furious
The sound of the Masters M33 through my MartinLogan ESL 9 speakers with Dirac Live switched off was involving without sounding unnatural or forced -- perfectly balanced and neutral, everything in the mix at exactly the right level, which allowed instruments, voices, and other sounds to be easily distinguished from each other while highlighting none of them. “Desert Rose,” from Sting’s My Songs: Deluxe (24/44.1 FLAC, A&M/Qobuz), opened up to sound much bigger than it has through other integrateds I’ve had in my system. There was now clearly more space between voices and instruments, as was most apparent with Cheb Mami’s backing vocal. Throughout this track, Mami’s voice seems to emanate from various positions relative to Sting’s stationary lead vocal at center stage, producing a swirling effect that’s exhilarating when accurately reproduced. The M33 did that.
One thing the M33 did not do was present hyper-sharp outlines of aural images -- which, while certainly impressive, can sound a little artificial. The amazingly crystalline sound of Musical Fidelity’s powerful M8xi did produce super-sharp image outlines, but its soundstages were shallower than the M33’s. Although Sting’s and Cheb Mami’s voices in “Desert Rose” were a bit more transparent through the M8xi, the Musical Fidelity didn’t produce the sense of space between them that I got with the M33 -- the sound was less three dimensional, the swirling effect less pronounced.
In addition to its many streaming options, I also verified that the M33 could accept audio signals through its HDMI eARC input from my Vizio TV, Bluetooth from my Galaxy S9 smartphone, and balanced analog and coaxial digital inputs from my Oppo UDP-205. All worked well, including the balanced analog input. In fact, I found the A/D conversion at the analog input very transparent -- its sound was essentially indistinguishable from that of the coaxial digital input. I also plugged my Sennheiser HD 580 headphones into the M33’s headphone jack -- the sound was clear and detailed, but lacked a bit of the bass weight of the Oppo, my reference for a headphone amp included in a larger component primarily designed to perform other duties.
The NAD Masters M33 sounded great even without room correction -- but when I configured Dirac Live to compensate for the interaction of my MartinLogan ESL 9 speakers with my listening room, I was rewarded with some of the best sound I’ve ever heard from this system. Nor was this unexpected -- other integrateds I’ve reviewed, such as Anthem’s STR ($4499) and Lyngdorf Audio’s TDAI-3400 ($6499), have greatly benefited from their high-quality built-in room correction. The result with the NAD and Dirac Live was tighter, more articulate bass, as well as a clearer midrange and thus less-obscured microdynamics, which can affect imaging. The overall sense of space and depth of soundstage was most pronounced -- my speakers and my room’s walls seemed to disappear, leaving only the musicians singing and playing as they gave me an intimately private performance.
With the M33, the crowd noise in “Love Shack,” from the B-52s’ Cosmic Thing (24/96 FLAC, Rhino/Warner Bros./Qobuz), sounded more uncannily realistic than I’d ever heard it in my system, every hoot ’n’ holler captured as a discrete event rather than as an undifferentiated part of a continuous roar. Kate Pierson’s and Cindy Wilson’s voices were now more distinct from each other, Pierson to the left and more forward than Wilson, who was to the right. When they sing together in the chorus, I could more easily identify each voice, even though, in the chorus, they converge at center stage. In the bridge, not only were the backing voices extremely intelligible, but the bass, though recorded at a low level, was very articulate and expressive. This provided a funky, grooving rhythm which perfectly suited this fun and well-recorded track.
I hooked up my JL Audio E-Sub e112s to the M33’s subwoofer outputs. As mentioned, the M33 with Dirac Live provides limited bass management -- unlike my Anthem STR preamp, whose automatic bass management includes phase alignment of the speakers and subwoofers. But I’ve got a pretty good idea of how the JLA subs interact with my room and speakers, so I had no trouble inserting them in the system and then reconfiguring the sound with Dirac Live. The opening timpani and gong in Aaron Copland’s Fanfare for the Common Man, with Eiji Oue conducting the Minnesota Orchestra (16/44.1 FLAC, Reference/Qobuz), were thunderous, their sounds slowly fading with exquisite delicacy into the acoustic of Minneapolis’s 2089-seat Orchestra Hall.
One thing that the M33 does do in the analog domain is RIAA equalization for its MM/MC phono stage. According to Greg Stidsen, using DSP to provide the great amount of headroom (40dB) required for this wouldn’t have allowed them to meet their signal/noise target with the digital technology currently available. He added that they were still able to achieve a precision of ±0.2dB by using high-quality resistors and capacitors in the analog circuits. Whatever NAD has done in the analog and digital domains, Dire Straits’ Dire Straits (LP, Vertigo) sounded fantastic. In “Six Blade Knife” there was plenty of separation and imaging of Mark Knopfler’s unique finger-picking style on electric guitar, and of John’s Illsey’s bass guitar. And even though my turntable’s analog signal had been digitized by the M33 and then further DSP applied to that signal, everything in “Sultans of Swing” sounded exactly right. The M33 situated Knopfler’s guitar more centrally and not as far forward as it appears in “Six Blade Knife” and “Down to the Waterline,” slightly differentiating the presentation of the guitar on these three tracks.
Overall, the M33 sounded even more neutral than what I remember of the sounds of the Anthem STR and Lyngdorf TDAI-3400 integrateds, neither of which was still on hand for direct comparison. However, I recall that the Lyngdorf sounded slightly richer, and that Anthem’s slightly leaner sound revealed more extremely fine detail. If you value a neutral sound, the M33 is the amp for you, but I can see how some people might prefer the sound of the Anthem or Lyngdorf. But despite the differences in their presentations, each of these integrateds sounds exceptional, has more than enough power to drive most speakers to room-filling volume levels, and includes room-correction software that can take its sound to a higher level.
The sound of the Masters M33 was even more neutral than that of my reference Anthem STR preamp ($3999) and M1 monoblocks ($7000/pair). Again, some might prefer the slightly warmer sound of the Anthem combo, but as I listened to the hi-rez version of “Thunder Road,” from Bruce Springsteen and the E Street Band: 1975/10/18 West Hollywood, CA (24/192 FLAC, nugs.net), I found the NAD impossible to fault. From the opening notes of Roy Bittan’s piano and Springsteen’s harmonica, surrounded by the dim, muggy atmosphere of the Roxy Theater, the sound was as precise and effortless as I’d ever heard. The Anthems might have been a little smoother when the Boss’s restless and youthfully exuberant singing hits its peaks, but the M33 didn’t sound objectionable, instead more like what I might expect from a live location recording. Danny Federici’s delightful glockenspiel, which can be overpowered by the piano and voices through some systems, was perfectly placed with a light touch at far left, while Bittan’s more demonstrative piano was at half-right and slightly farther back. With this track and the electrifying “Jungleland,” both the M33 and my reference Anthems could transport me to that emotional Roxy performance of fall 1975, in slightly different ways that were equally convincing and emotionally involving.
NAD’s Masters M33 is an incredible achievement for a leading-edge integrated amplifier. As Doug Schneider predicted, NAD’s implementation of their Hybrid Digital version of Purifi Audio’s Eigentakt amplifier has resulted in excellent sound -- and the M33 does so much more. It has nearly every option you could want in an integrated amp, including Dirac Live’s top-flight room correction and a highly capable streaming platform. Whether you prefer its neutral and confident sound over that of other integrateds of similar prices and features will be a matter of personal taste. I was never disappointed in the M33, even when I compared it to my far costlier separates, and I enjoyed the convenience of streaming and controlling it with its BluOS app. The Masters M33’s combination of sound quality and features makes it the current front-runner in the extremely competitive market of $5000 integrated amplifiers.
. . . Roger Kanno
- Speakers -- MartinLogan Masterpiece Classic ESL 9, PSB Alpha T20
- Subwoofers -- JL Audio E-Sub e112 (2)
- Preamplifier -- Anthem STR
- Power amplifiers -- Anthem M1 (monoblocks), Axiom ADA 1000
- Integrated amplifier-DAC -- Musical Fidelity M8xi
- Digital sources -- Apple MacBook Pro computer running Catalina 10.15.6, Roon, BluOS with Qobuz; AudioQuest JitterBug; Oppo Digital UDP-205 4K Ultra HD and BDP-105 universal BD players
- Turntable -- Pro-Ject Audio Systems X-1 with Pick it S2 cartridge
- USB link -- AudioQuest Carbon
- Speaker cables -- Clarus Aqua Mark II
- Interconnects -- Analysis Plus Super Sub, Clarus Aqua Mark II, Nordost Quattro Fil
- Power cords -- Clarus Aqua, Essential Sound Products MusicCord-Pro ES
- Power conditioners -- Blue Circle Audio PLC Thingee FX-2 with X0e low-frequency filter module, Zero Surge 1MOD15WI
NAD Masters M33 Integrated Amplifier-DAC
Price: $4999 USD.
Warranty: Two years parts and labor.
Lenbrook Industries Limited
633 Granite Court
Pickering, Ontario L1W 3K1
Phone: (905) 831-6333