Reviews of Attainable Hi-Fi & Home-Theater Equipment

Reviews of Attainable Hi-Fi & Home-Theater Equipment

Note: for the full suite of measurements from the SoundStage! Audio-Electronics Lab, click this link.

Reviewers' ChoiceNAD’s new C 399 (with or without its BluOS-D expansion module) is a fascinating integrated amp straight out of the box. Fascinating because, despite claiming the top spot in the company’s Classic Series lineup and sharing that family’s aesthetic and naming conventions, it is in a lot of ways a bridge between the Classic and Masters Series, employing as it does the Ncore amplifier technology previously used in the latter, as well as the same 32-bit/384kHz ESS Sabre DAC chip used in the Masters M10 and M33.

There’s a lot of jargon to unpack in that last sentence, and to be frank, I’m not sure I have my head completely wrapped around NAD’s Hybrid Digital (sometimes spelled HybridDigital) signal path, or the company’s modifications to Hypex’s Ncore amplifier technology, at least not well enough to defend the merits of either in a rigorous and technical debate. But the incredibly truncated bottom line is that the C 399 combines a differential signal path coming off the DAC chip with a highly specialized self-oscillating class-D amp, all engineered to deliver output with low noise, low intermodulation distortion, clean clipping behavior, oodles of output, and linearity even with very difficult loads.


And that barely scratches the surface of what makes this such an intriguing product. The C 399 is also the first amp to feature NAD’s new MDC2 (second-gen Modular Design Construction), and it can be purchased either with or without the MDC2 BluOS-D module installed. The price for the base C 399 is $1999 (all prices USD), or $2549 as reviewed with the module pre-installed.

The MDC2 BluOS-D module takes what’s already an incredibly full-featured integrated amp and adds Wi-Fi and ethernet connectivity, advanced bass management, MQA decoding and rendering, Apple AirPlay 2 support, Spotify Connect, and Tidal Connect. It also—as its name implies—brings the C 399 into Lenbrook’s BluOS streaming ecosystem, which is effectively a slicker, more intuitive, and all-around better version of Sonos. But perhaps most importantly—and I’ll admit my biases are showing here—the module adds Dirac Live room-correction capabilities to the C 399.

Even without the MDC2 BluOS-D module installed, though, the C 399 is still quite a feature-rich piece of kit, with dual coaxial and optical digital ins, dual stereo line-level ins (RCA), a phono input (MM), an HDMI ARC port (PCM audio only), and dual subwoofer outputs (with a fixed 80Hz crossover unless you have the BluOS-D installed).


In terms of power, the C 399 is rated to deliver >180Wpc continuous power (measured full range, <0.02% THD, both channels driven) into 8 ohms or 4 ohms, with IHF dynamic power (a rather esoteric standard used by few companies other than NAD) rated at 217Wpc into 8 ohms, 400Wpc into 4 ohms, or 506.4Wpc into 2 ohms.

Setting up, tweaking, and calibrating the NAD C 399

Speaking of biases, it’s odd to me that NAD has delivered such an I/O-packed integrated amp that lacks a USB DAC input. I tend to do most of my listening via a USB connection from my Maingear Vybe media and gaming PC, so I’d be lying if I said the lack of such didn’t irk me a bit at first.

Key words there: “at first.” Once I got my head fully wrapped around the BluOS ecosystem, I adapted pretty quickly to using the BluOS Controller app on my PC and iPhone to control and stream all of my music, both locally stored and subscription-based. I did add my Oppo BDP-105 as a source (testing both analog and digital connectivity), but found that I used it less and less once the BluOS bug bit me.

For speakers, I started my critical listening through Monitor Audio’s new Silver 300 7G towers and then swapped in my Paradigm Studio 100 v.5 towers when the Monitors had to make the long trip up to Canada for measurements and photography. I relied on Elac Sensible speaker cables for speaker-level connections, and I used a variety of Straight Wire interconnects for the Oppo disc player and an SVS PB-1000 Pro subwoofer that I briefly added to the system to evaluate the NAD’s bass-management capabilities.


My review unit came with the MDC2 BluOS-D module pre-installed, so I didn’t have to worry about that. But after looking over the installation guide, I have to think that if you’re comfortable adding a PCI card to your desktop computer, you should have no trouble with it. I did have to update the firmware of the C 399 before I could access the amp with the BluOS Controller app, but that was no real surprise given that this was still a pre-release product at the time of writing.

Getting the BluOS app set up for my purposes was simple and straightforward. I added my login and password for Qobuz and added my local music libraries to the app. There was no need to add Spotify login info, since the ecosystem supports Spotify Connect.

Getting the most out of the C 399 BluOS-D’s Dirac Live room-correction capabilities took a bit more fiddling, although it didn’t have to. I decided to spend my first few weeks with the amp getting used to its sound without the benefit of DSP, and almost all of my listening via Silver 300 towers was done as such. Once I moved to my Paradigm towers and removed the SVS sub from the equation, I started tinkering around with correction curves.

According to the C 399 manual, “The MDC2 BluOS-D comes with Dirac Live Limited Bandwidth (20Hz–500Hz) installed with the option for advanced users to upgrade to the Dirac Live Full Frequency version.” But upon firing up the Dirac Live 3 desktop software and locating the C 399, I noticed that I had access to full-frequency correction, which I suppose is an extra perk of being a gear reviewer. That’s normally a $99 upgrade.


I didn’t make use of the full-bandwidth room-correction capabilities of Dirac Live (at least not for the bulk of my listening), but I did set filters higher than the 500Hz limit of the free version, so I guess I got somebody’s money’s worth out of the upgrade. If you want to get a sense of my overall philosophy on room-correction systems like Dirac Live, check out my older article titled “This One Room-Correction Trick Could Breathe New Life into Your A/V Receiver.” (It’s a clickbaity headline, I know, and it ignores stereo, but writing headlines has never been my strong suit.)

Long story short for those of you who don’t want to click away just yet: I typically prefer to apply room correction only up to the transition between the “resonant” region and the “ray” region of a room, two-ish octaves above the Schroeder frequency. And I feel even more strongly about that approach in a room like my two-channel listening room, which has a good amount of absorptive and diffusive acoustical wall treatments but no bass traps.

After running the nine measurements for Dirac Live with the included microphone and USB adapter, I eyeballed my Schroeder frequency at right around 200Hz (no surprise there), two octaves up from which would be 800Hz. As I also detailed in the article referenced above, I generally put my max filter frequency slightly higher than that just to smooth over the transition between filtered and unfiltered output. In this case, I ended up with a max filter frequency of 966Hz.


I’m not saying that’s the only right way to do it; I’m saying that’s the way I do it, and if you have a different philosophy on room correction, take that into consideration when reading my subjective listening impressions below.

The NAD C 399 allows you to store and easily access up to five different Dirac Live filters, although I only used four of them. The software defaults to the Dirac target slope, which is a bit of a shallow ramp that’s +2.2dB at 28Hz and +1.8dB at 54Hz. NAD also has its own target curve, available on its download page, which introduces a bit more of a bass boost and has a shape that will be familiar to anyone who’s aware of Floyd Toole’s research. I won’t detail all of the break points of the NAD target curve, but compared with Dirac’s target slope, it’s up 6.6dB at 30Hz and 6dB at 49Hz, and it then flattens out around 200Hz, with no high-frequency roll-off.

NAD Target Curve NAD target curve

I also designed my own target curve using the NAD curve as a starting point, but with a slight (~1 to 2dB) reduction of bass, and with the same 966Hz max filter frequency employed on the curves detailed above. Lastly, I saved a full-bandwidth filter using the unmodified NAD curve.

How does the NAD C 399 perform?

Before we talk about the effects of Dirac Live on the performance of the C 399, let’s discuss the amp on its own terms, since some unknown number of customers will undoubtedly opt for the model without the MDC2 BluOS-D.

The first thing that one can’t help noticing about the C 399 is just how little noise it generates. I had to turn the volume up to 0dB and shove my ear right next to the tweeter to even begin to hear the faintest, almost imperceptible hiss coming from my speakers. To put that into perspective, there’s absolutely no way I would be able to sit in the same room as this amp playing music at anything louder than -20dB. And even that’s only sustainable for a song or two at most. My normal “I need it loud!” listening level in my 12′ 4″ × 10′ 1″ two-channel listening room ended up being closer to -24dB, and comfortable, long-session listening normally occurred with the volume dialed down to around -27dB.


The next observation is that—perhaps more so than any amp I’ve auditioned since the Marantz PM-KI Ruby—the NAD is a deliciously dynamic amp that delivers rich and full-bodied sound even at very low listening levels. I cued up “Scarlet Begonias” from the Grateful Dead’s Cornell 5/8/77, included in the May 1977: Get Shown the Light Limited Edition box set (Rhino Records R2 557479), and let it play for a bit at -32dB, just to serve as background music while I was finishing the write-up for my Monitor Audio Silver 300 7G review. The NAD was having none of it, though. It kept pulling me in, demanding my attention with its appropriately punchy reproduction of Bill and Mickey’s percussion and Phil’s meandering but boisterous bass.

I spun my chair to the left and faced the system to listen more intently, and even before I nudged up the volume, I got lost in the excellent soundstage and imaging, with Keith’s keyboards coming from way off to the left of my listening space and Jerry’s vocals locked dead in the center. As I upped the volume to really dig into the tune, I have to admit that not much changed about the presentation of the song, aside from the bass becoming more tactile and some of the intricacies of the percussion penetrating deeper into the room, as well as the tonal balance subtly changing shape consistent with ISO 226:2003.

Look, we audio writers are prone to leaning on magical language to describe experiences of this sort—because they do indeed feel magical—but the truth of the matter is that there’s nothing spooky going on here. This is simply what it sounds like when you listen via a well-engineered amp with low distortion, low noise, good tonal balance, and a beefy/responsive-enough power supply. And the C 399 has all of those qualities in spades, maybe more so than just about anything else I’ve heard in its class in quite some time. If there’s anything funky going on with the way the amp measures—and I’m not saying there is—I suspect it’ll be beyond the bounds of my hearing acuity, which nopes out at around 15.8kHz. But we’ll have to wait for Diego to get his paws on the unit to find out.


Shortly after my extended Dead session, I had to ship the Monitor Audio speakers up to Canada and replace them with my tried-and-true Paradigm Studio 100 v.5 towers. And once again, I immediately noticed something quite striking about the C 399. I had, in the course of my review, compared the Monitors with the Paradigms using a variety of amps, and their impedance swings in the low frequencies resulted in some perceptible—but inconsistent—differences in their bass performance. Nothing dramatic, for the most part, but still noticeable. With the NAD, though, I was immediately struck by how similar the Silver 300s and Studio 100 v.5s sounded at the bottom end.

It was also around this time that I switched over to BluOS for most of my listening. And I wish I had the space here to do justice to Lenbrook’s streaming ecosystem, because I quite love it, but we still have a lot to discuss about Dirac Live, so I’ll point you in the direction of Doug’s review of the Bluesound Powernode and Gordon’s interview with Lenbrook’s Andrew Haines for more insight into what makes BluOS such a groovy platform for both online streaming and local library management.

After a few days of listening to the Paradigms without the benefit of room correction, just to get a sense of how the NAD performed with these speakers I know so well, I started the process of filter-tinkering detailed above in the setup section.


Let’s go ahead and get my single non-glowing observation out of the way: I didn’t particularly care for the full-range filter based on NAD’s target slope. But again, I think that’s largely a consequence of the fact that my room is pretty well fitted with diffusive and absorptive wall treatments.

All of the filters limited to 966Hz, though, made substantial differences in the sound of my system, to differing degrees, since I don’t have any mechanical treatments in my room to deal with standing waves. And I think the differences between the filters I either chose or designed myself largely come down to a matter of preference.

One track in particular that really allowed me to parse the differences the filters made was “Sun King (2019 Mix)” from the Beatles’ Abbey Road: Super Deluxe Edition (24-bit/96kHz FLAC, Universal Music Catalogue/Qobuz). Without the benefit of Dirac Live, the bass in particular—especially starting at around the 0:20 mark—sounded a bit chubby and a little wobbly. Not so significantly that I couldn’t “listen through it,” for lack of a better way of putting it. But once I started A/B/C/D testing back and forth, the bass problems inherent to almost any normal room really started to stand out.

By contrast, the bog-standard Dirac target slope sounded fitter, to be sure, better controlled, more consistent—i.e., less distracting—but a bit too lean for my liking. Some of that pulsing, room-filling quality to Paul’s bass in this song was somewhat diminished.


The NAD target curve, by contrast, definitely controlled the bass every bit as well as Dirac Live’s slope, but especially in a room my size, I felt like it overemphasized the lower frequencies. Not egregiously so, but it seemed to change the bass characteristics of my Paradigms rather than smoothing out their response.

Again, I wouldn’t say that my own target curve split the difference between the Dirac Live and NAD defaults—it definitely hewed closer to the latter—but by tinkering with the highest break points, I was able to construct a filter that followed the shape of the natural response of my speakers in my room, just without the peaks and valleys caused by room geometry. And it was, without question, the single most substantial tweak I’ve made to my two-channel setup in ages.

Make no mistake about it: even without the benefit of the MDC2 BluOS-D add-on, the C 399 is a magnificent integrated amp with incredible tonal balance, exceptional neutrality and transparency, spot-on D-to-A conversion, and the ability to plow straight through substantial dips in speaker impedance without breaking a sweat. Take Dirac Live out of the equation, and I would still be a smitten kitten.


But the addition of room correction—plus the BluOS capabilities unlocked by the MDC2 BluOS-D—transform this into an integrated amp that fits my specific needs perhaps better than any I’ve auditioned in who knows how freaking long.

Add to that a fantastic headphone amplifier (seriously, I couldn’t find a pair of cans in my collection that didn’t sound mind-blowingly good plugged into the C 399), and there’s really next to nothing to grumble about here. NAD has hit it out of the park, in my opinion.

What other integrated amps might you consider in this class?

Well, it depends on what you need. If you have no interest in the integrated BluOS streaming or the Dirac Live room correction of the NAD, I quite like Parasound’s Hint 6 Halo integrated amplifier ($2999). The Parasound has a leg up on the NAD for analog audiophiles thanks to its MM/MC phono stage. The Hint 6 also has home-theater bypass capabilities, and that’s handy if your multichannel and stereo setups live in the same room. But I find the Parasound’s headphone amp output underwhelming with my larger and fussier cans, and once you go Dirac Live, it’s hard to go back.

I also dig the Rotel RA-1592 ($2499.99) quite a bit, and if you need more analog inputs, as well as more optical and coaxial digital ins, it’s quite well equipped. The RA-1592 sounds fantastic, although its BT connectivity is quirky and I’m not a fan of the 3.5mm headphone jack. But again, if you’re averse to room correction and have no interest in BluOS, it’s one to audition for sure.

TL;DR: Is the NAD C 399 worth the money?

It’s honestly a little hard for me to answer that question objectively, because I almost feel like NAD is pandering to me with this one. They’re not, of course; nobody at NAD has a clue who I am. But the simple fact of the matter is that the C 399, especially with the BluOS-D expansion module installed, very nearly represents my platonic ideal for everything I want in an integrated amp. Before I dug in, I bemoaned the lack of a USB DAC input, but I got over that real quick-like once I fully warmed up to the BluOS platform. My one little remaining nit to pick is that I wish its Bluetooth connection supported AAC, not just aptX HD, but that’s just my bias as an iPhone user showing.


In literally every other respect, though, there’s simply nothing about this product I would change. I think NAD could have easily squeezed another 500 bucks out of customers, and it still would have represented a hell of a value.

Again, I must admit that I don’t have all the particulars of the amp’s signal path or its amplifier architecture figured out well enough that I could explain it to my dad, and I won’t bullshit you by pretending that I do. But the proof of the pudding is in the listening—or something like that. And for everything else the C 399 BluOS-D does well, my favorite thing about it is that it sounds brilliant and is nearly infinitely tweakable to fit my preferences and my listening space.

. . . Dennis Burger

Note: for the full suite of measurements from the SoundStage! Audio-Electronics Lab, click this link.

Associated Equipment

  • Speakers: Paradigm Studio 100 v.5, Monitor Audio Silver 300 7G.
  • Speaker-level connections: ELAC Sensible speaker cables.
  • Sources: Oppo BDP-105 Blu-ray player, Maingear Vybe PC, iPhone 12 Pro Max.
  • Power protection: SurgeX XR115 power conditioner.

NAD C 399 Integrated Amplifier-DAC
Price: $1999; $2549 as reviewed with pre-installed MDC2 BluOS-D module.
Warranty: Two years, parts and labor.

The Lenbrook Group
633 Granite Court
Pickering, Ontario, Canada L1W 3K1
Phone: (905) 831-6555