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Introduction to the NAD C 390DD Direct Digital Integrated Amplifier

NAD launched its first direct digital amplifier, the M2, almost three years ago. As we have come to expect in audio and technology generally, however, it is never long before the state of the art trickles down to more modestly-priced products. Such is the case here, as NAD claims the $2600 C 390DD is a direct descendent of the $6000 M2 and even includes some advanced features, such as room equalization (available by the time you read this), not available on the M2.


  • Design: Integrated Stereo Amplifier
  • Output Power: 150W @ 4 or 8 Ohms
  • Frequency Response 45 Hz – 40 kHz (-3dB)
  • Dimensions: 5.2″ H x 17.1″ W x 15.3″ D
  • Weight: 17 Pounds
  • MSRP: $2,600 USD
  • NAD
  • SECRETS TAGS: NAD, Digital, Integrated, Amplifier, Audio

While digital amplification itself has been quite common for a number of years, direct digital goes one step further, eliminating all analog stages in the signal path, including the preamplifier functions, which allows the signal to stay in the digital domain all the way to the speaker. In this way, direct digital amplifiers such as the C 390DD, function more like powered DACs. This technology has interested me for several years and I was an early adopter of pure digital amplifier designs, having owned products from Tact, Lyngdorf, and even two budget receivers from Panasonic (XR45 and XR70). I owned the Tact almost ten years ago, but even today, pure digital is still considered somewhat esoteric and only a handful of manufacturers offer such products.

Design of the NAD C 390DD Direct Digital Integrated Amplifier

Aside from its Master series, of which the M2 is part and the C 390DD is not, NAD’s casework is pretty nondescript—basic shapes in basic black. And so it is with the C 390DD, looking much more mass-market receiver than audiophile centerpiece. Probably because the C 390DD is tall, much taller than a typical integrated amplifier, you notice its aesthetics when it is in your system. It is especially large compared to my reference, the Naim Nait XS-2 integrated amplifier. While not exactly pretty, the NAD’s front panel controls are both easy to understand and use and kept to a minimum—a large vacuum fluorescent informational display, volume knob, USB port, and power, source, and navigation buttons. Given the dimensions, the amplifier’s 17 pounds are lighter than you might expect, but such is usually the case with digital amplifiers.

Another point of evolution over NAD’s own M2 is the C 390DD’s modular architecture, which means in addition to the eight digital inputs it has in stock form, it is designed to accommodate expansion cards, which add to its rear-panel connectivity. It features three such rear-panel slots, one of which is filled from the factory by a direct digital USB module, which includes both USB type A and type B inputs. The C 390DD’s other rear panel inputs include two coaxial, two optical, and one AES/EBU input. As mentioned above, an additional USB input is located on the front panel. All three USB inputs are asynchronous. The USB type B terminal supports 24/96 resolution, while the type A terminals support up to 24/48.

NAD offers two additional modules (MSRP $300/each) and if you have any analog sources, you will need at least one, the direct digital analog-phono module. The analog-phono module includes balanced and unbalanced line level inputs and perhaps surprisingly, a phono input, which accommodates both MM and MC cartridges. Because the C 390DD operates exclusively in the digital domain, the analog input signals are converted to digital. The line-level analog inputs thus feature user-selectable settings for sample rate (48, 96, or 192 kHz). Of note, the phono input also features an infrasonic filter, which, when activated, filters out frequencies below 10Hz. If you have ever experienced excessive woofer motion that does not correspond to audible sound, you have experienced infrasonic distortion. Such distortion can be caused by a variety of factors, including imperfections in the vinyl, tone arm resonance, and turntable vibration. The other module, the direct digital HDMI module, includes three HDMI inputs and an HDMI output with video pass through. The direct digital HDMI inputs allow the reproduction of the three front channels through the left and right channels in a stereo set-up. The review sample included both the HDMI and Analog-Phono modules. Also of note, the C 390DD includes a stereo preamplifier/subwoofer output.

The C 390DD is fully remote-controlled and its remote can also operate other NAD devices. The remote allows direct access to each of the C 390DD’s eight digital inputs and the source selection button allows you to scroll through all the device’s inputs. Unused inputs can be deactivated (and thus skipped during input scroll), and all the inputs can be named, which makes the remote interface very user-friendly.

Setup of the NAD C 390DD Direct Digital Integrated Amplifier

I connected the NAD using my reference cables, which include DH Labs signal cables and Synergistic Research signal and power cables. My current system is built around a pair of Focal Electra 1008 BEs, a JL Audio F112 subwoofer, and various source components, the details of which are listed at the end of this review.

The initial sound, like the looks of the C 390DD itself, was rather blah. It wasn’t all bad, however, and even moments after powering on, there was an astonishing amount of bass, and I’m talking kick-your-front-door-in bass. This was both a positive and a negative, however, as my subwoofer no longer blended seamlessly with my main speakers. I found it initially difficult to find a mix I liked, despite playing with both the NAD’s and the F112’s settings to the point of annoyance. I figured I would address the subwoofer issue later and so for the time being, I shut it down completely. The bass output of the Focal’s was much stronger than what I was used to, to say the least.

Encouraged by what I heard, I played a few Radiohead albums on vinyl. The results were not altogether satisfying. Most noticeably, the mid-range sounded flat and distant. With some patience dialed into my brain, I switched to Redbook CD through the coaxial output of the Oppo DVD player, listened a bit more, and a second positive trait began to stand out, which was confirmed switching to Apple TV—no matter which input, the NAD was dead silent. Painting its sonic pictures on a canvas utterly devoid of background noise, the NAD is easily one of the quietest amplifiers in my memory. Despite greatly piquing my interest in its abilities though, the NAD wasn’t altogether ready for critical listening. I pulled up Apple TV’s classic hip-hop radio station through one of the NAD’s optical inputs, lowered the volume a bit and let it play. A particularly busy period at work allowed me to do this over the next several weeks every day before leaving for the office.

The NAD C 390DD Direct Digital Integrated Amplifier In Use

Finally ready to undertake the task of critically evaluating the C 390DD, I put on Otis Redding’s Otis Blue on vinyl. I found the midrange had pleasantly improved, but the record overall seemed less lively and involving than what I recalled from the Naim/Musical Surroundings combination. Indeed, I found this to be true on records ranging from Joan Armitrading’s self-titled debut to CSS’s La Liberacion to Nas’ Illmatic. As I gradually moved away from playing vinyl through the NAD, I thought perhaps the NAD’s phono stage was the weak link, so I tried the Musical Surroundings connected through the C 390DD’s line level input, but the results were substantially similar. The sound was just not as exciting or involving as I was used to. Of note, however, the NAD’s infrasonic phono filter was remarkably effective, eliminating the excessive woofer movement of the Focal’s that usually occurs on certain records at certain volumes.

Hooking up my MacBook Air to the USB type B terminal and digging into my iTunes library was a completely different story. Fifty-one seconds into “60 Feet Tall,” track one on The Dead Weather’s debut album, Horehound (AIFF), the bass drum just about overwhelms you. I start the track again because, well, it’s like playing with a new toy. I notice that before the drum becomes the thing, the NAD makes quick work of laying out the stage – a guitar in the background sounds like it’s being given a final tune and drumsticks crack against each other. Further into the track, Alison Mosshart shouts “You got my attention. You got it all. I can take the trouble. I’m sixty feet tall.” Indeed. The sound is exploding around me, a kaleidoscope of detail and drive. There is a scale and urgency to this song I don’t recall, a visceral quality that the NAD has suddenly unchained. The bass is propulsive, addictive. The C 390DD loves rock and roll and loves high-quality digital files.

Curious how the C 390DD would fare on other material. I switched gears to the quiet and delicate (Atlas Sound “Sheila,” Logos), then back to explosive and insistent (The Stooges “I Wanna Be Your Dog,” The Stooges). No matter what the digital file, the C 390DD displayed a firm grip on the music, a dead-quiet background, and colossal bass.

Comparison is almost a misnomer because in my system, the NAD accomplishes what I need three separate components to do—amplification, phono pre-amplification, and digital to analogue conversion. There really is no direct comparison. For example, if you use separates instead of an integrated amplifier, the NAD takes over duties from four separate components. Just on paper, both the value and space-saving propositions of the NAD rate very high. In my system, those three components retail for $4550, significantly more than the C 390DD’s $2600.

First up to compare was something that called for great clarity, Cat Power’s Moon Pix (Redbook CD through the coaxial output of the Oppo DVD player). The first thing I noticed was the wonderful way the NAD wove together Chan Marshall’s guitar and voice. There was, at once, both weight and separation of the guitar strings. Compared to the Naim/Wyred 4 Sound combination, however, the NAD seemed to leave out some of the breath Chan Marshal wraps around her vocals. My sense listening through the NAD was a somewhat diminished sense of that being-there quality, even though overall, it was extremely difficult to fault.

Turning to a compressed digital file of fairly raucous material, Sleigh Bells “Ring Ring” (192KB MP3), the NAD dazzled, revealing a tonal quality to the bass that I just marveled at. The Naim/Wyred 4 Sound combination could not match the tear-the-woofer-ferocity of the NAD’s bass, but did show a bit more nuance, drawing more attention to the cadence of the lyrics. Alexis Krauss sings “Have a heart, have a heart, have a heart” and then continues “sixteen six six six like the pentagon.” She sings the latter faster and while this would be obvious through any system, the qualities of the Naim/Wyred 4 Sound combination underscore the transition in pace, suggesting something the NAD seemed to gloss over. I listened to the song several times and while I came to no satisfying conclusion what to make of this, the Naim/Wyred 4 Sound combo had the edge simply because it invited the interaction and invited the question.

Conclusions about the NAD C 390DD Direct Digital Integrated Amplifier

The NAD’s arsenal of superlatives merits it serious consideration for any high-end system. Indeed, the overall impact and scale of the C 390DD’s presentation never ceased to amaze me, and for the price, astonished me. My one reservation involves what I found to be the superiority of my reference components’ handling of vocals. If I was deciding between the two, it must be said the NAD showed itself as the better overall value and is sure to flatter most speakers, but the extra money does buy you something. The slight, yet noticeable upper midrange and treble dryness of the NAD did not ultimately suit the Focal’s ultra-resolving Beryllium tweeters. These are tweeters capable of letting you hear things you have probably not heard before. I recall marveling at such things as how moist a singer’s lips are, which one listen to Nina Simone’s To Love Somebody on 180 gram LP puts well on display. Since I don’t get to listen to music nearly as much as I would like, qualities like this have become critical to me because they elevate the listening experience from something passive to something that engages both your audiophile brain and your music-loving soul and I just don’t know how to put a price on that.

Associated Equipment:
Focal JM Lab Electra 1008 Be, Wyred 4 Sound DAC-2, Oppo DV-980H, XBOX 360, Clearaudio Concept Turntable (Concept MM cartridge), Musical Surroundings Phonomena II Phono Pre-amplifier, signal cables by DH Labs and Synergistic Research, Power cables and conditioning by Synergistic Research.