NAD C 390DD Direct Digital Integrated Amplifier (TAS 224)

Chip Off the Old Block

Equipment report
Integrated amplifiers
NAD C 390DD Direct Digital Integrated Amplifier
NAD C 390DD Direct Digital Integrated Amplifier (TAS 224)

It was only a matter of time before NAD brought the groundbreaking technology and architecture of its M2 Direct Digital Amplifier to a lower-priced product. The $6000 M2, which I reviewed in Issue 198, is unique in part because it converts standard-resolution or high-res digital bitstreams directly into signals that can drive loudspeakers. This approach eliminates from the signal path all the circuitry of a digital-to-analog converter, preamplifier, and most of a power amplifier, not to mention the interconnects, jacks, and wiring of separate components. Moreover, the M2 upended the traditional system configuration of a digital source feeding a preamplifier that then drove a power amplifier. With the M2, you simply connect a digital source to one of its inputs and loudspeakers to the output terminals. The unit’s functions mimic a DAC and integrated amplifier, with source-switching and volume control.

NAD’s new C 390DD brings the M2’s technology and features to a unit costing less than half that of the M2. Significantly, the $2600 C 390DD adds some new capabilities beyond those of the M2, including extensive room-equalization functions as well as modular construction that allows you to tailor the C 390DD to your particular connectivity needs as well as update the C 390DD’s hardware and software to accommodate technology advances. NAD calls this MDC for Modular Design Construction. In this era of rapidly evolving technology, it seems a no-brainer to provide an upgrade path through user-replaceable digital-interface circuitry.

In practice, the C 390DD has three rear-panel slots that will accept an optional input module (DD AP-1 Analog Line/Phono Module) or the module containing three HDMI inputs and one HDMI output (DD HDMI-1). Each optional module is $300. The analog-input board offers one stereo balanced input on XLR jacks, one unbalanced input on RCA jacks, and one phono input, also on RCA jacks. The phono input will accept moving-magnet or moving-coil signals. Because the C 390DD operates entirely in the digital domain, the analog input board performs analog-to-digital conversion. The sampling rate and word length are user-selectable, up to 192kHz/24-bit. The HDMI inputs are useful when using the C 390DD as part of a “2.0” or “2.1” theater system in which the soundtrack is reproduced by the left and right loudspeakers, foregoing a center channel and surround loudspeakers. Note that the rear-panel USB inputs (marked “Computer,” on a USB Type B connector and a USB Type A jack for connecting a FAT 32 storage device) are also on a removable board (included as standard) to accommodate possible hardware changes in the USB format (or entirely new digital interfaces). A second USB input on the front panel will play music from memory sticks. All three USB inputs are asynchronous, and can accommodate resolutions up to 96kHz/24-bit.

A stock C 390DD provides eight inputs; a fully loaded unit sports a whopping 14 inputs. The fixed inputs (those integral to the C 390DD rather than being on replaceable boards) include two digital coaxial on RCA jacks, one AES/EBU, and two TosLink optical. These inputs can accept resolutions up to 192kHz/24-bit. Digital outputs are also provided on RCA and TosLink optical jacks. To keep this input flexibility from becoming overwhelming, unused inputs can be removed from the front-panel display and input-scroll function, allowing you to more quickly and easily select between sources. Each input can also be named by the user. In addition to this wide array of inputs, the C 390DD offers a line-level output as well as a line-level stereo (or mono) subwoofer output. An onboard crossover can be engaged to split the frequency spectrum appearing at these outputs; the C 390DD thus functions as the crossover between the subwoofer and main speakers in a 2.1-channel system.

The C 390DD is rated to deliver 150Wpc into 8 ohms. As with other NAD amplifiers, this continuous power rating doesn’t adequately reflect the C 390DD’s real-world power delivery when reproducing music. Part of the C 390DD’s generous dynamic headroom is owed to NAD’s Digital PowerDrive circuitry, which automatically senses the loudspeaker’s impedance and adjusts the amplifier’s characteristics to more efficiently drive that particular loudspeaker load. The C 390DD also features NAD’s Soft Clipping circuit, which gently compresses peaks that would otherwise clip. If you overdrive the amplifier, Soft Clipping compresses the dynamic range rather than allowing the output stage to flatten the waveform tops (heard as a crunching sound on peaks). Soft Clipping can be engaged via the front-panel display.

The C 390DD’s on-board DSP provides extensive equalization possibilities. In addition to bass and treble controls, the C 390DD allows you to boost or cut six selectable frequencies below 240Hz to reduce room-induced peaks and dips. Each filter has adjustable bandwidth. As with the C 390DD’s other features, the room equalization is accessed via the unit’s large front-panel display. The manual makes reference to an integral test tone useful in setting the equalization, but that feature had not yet been implemented in the review sample. NAD says that the test tone will be available as a software update.

A number of other miscellaneous features are also included. For example, the unit has IR inputs and outputs, an RS232 input, and 12V triggers, all useful for integrating the C 390DD into an automated system.

The remote control is outstanding for its ease of use, volume control ballistics, and comfort. Although this is the same generic remote supplied with NAD’s AV receivers and disc players, the superfluous buttons didn’t interfere with operating the C 390DD. Incidentally, when I was using the NAD remote it struck me how much more functional and comfortable it is compared to many high-end remotes that are machined from aluminum and have tiny points for buttons, illogical layouts, and difficult-to-read legends.


The C 390DD replaced in my reference system the Berkeley Alpha USB USB-to-S/PDIF converter, Berkeley Alpha DAC Series 2, Hegel H30 linestage, and Hegel H30 power amplifier. With cables, this signal chain has a retail price of about $30,000, eleven times the C 390DD’s price. I fed the C 390DD with the USB output (AudioQuest Diamond USB) from an iMac running iTunes and Pure Music, as well as with analog signals from the Aesthetix Rhea Signature phonostage. As mentioned earlier the C 390DD operates only on digital signals, requiring that analog inputs be converted to digital. The review sample was fitted with the optional analog-input board that offers balanced and unbalanced line-level inputs as well as a phono input.

I controlled the iMac music server from my iPad with Apple’s free Remote app. With this app, your iTunes library interface appears on the iPad. My system was reduced to the iMac, the NAD C 390DD, a pair of Venture Ultimate Reference loudspeakers, and the iPad for remote-control music selection.

After living with NAD's M2, I was interested to hear how that unit’s impressive technology translated into a unit of half the cost. In addition, my friends Scott and Kerry have been asking me for some time how to upgrade the sound of their existing system and at the same time transition into a music-server. They have a Pioneer Elite AVR with a Pioneer CD changer driving GoldenEar Triton 2 loudspeakers. They want better sound quality for music than this setup delivers, and are ready to replace the CD changer with a computer-based digital source that can be controlled wirelessly. They primarily use their system for music (and they play lots of vinyl on a Pro-Ject turntable). I’ve had my eye on a number of products for them (mostly separate USB DACs and integrated amplifiers), but I advised them to hold off until just the right product came along. (Many readers are also exploring ways to get better sound and at the same time make the leap to computer audio.) The C 390DD, with its unique technology, functionality, and future upgrade potential via the modular construction, could be a highly appealing option if its sound quality was anything like that of the M2.

But out of the box the C 390DD sounded dark and closed-in through the upper treble, and bright and grainy in the upper midrange and lower treble. This character diminished over the first few days, and after four days, disappeared. The transformation was more dramatic than I have experienced with any other component. If you audition the C 390DD, but sure that it is fully broken-in and warmed up. In fact, I thought that the C 390DD continued to improve over about a ten-day period.

After the C 390DD was fully broken in, there was no mistaking its heritage; it sounded very much like the M2. The C 390DD’s greatest strength was undoubtedly its authoritative bass and startling bottom-end dynamics. This amplifier sounded like a powerhouse, with rock-solid solidity to bass guitar and tremendous impact to kick drum. The C 390DD took ironfisted control of the Venture Ultimate Reference loudspeakers’ four 9" woofers per side, serving up a visceral, body-involving experience on albums such as Talking Heads’ Speaking in Tongues (96kHz/24-bit). Even at high levels, the kick drum’s ability to cut through the bass guitar lines was phenomenal. The C 390DD’s terrific bass and wide dynamics were also on full display when I listened to large-scale orchestral music; I heard no strain on even the most demanding passages. In fact, I experienced a kind of disconnect when listening to an album like Jeff Beck’s Performing this Week...Live at Ronnie Scott’s; it seemed hard to believe that the massive kick-drum impact and rock-solid bass lines were being produced by this diminutive and lightweight (compared with the huge monoblocks flanking the C 390DD) integrated amplifier. A phrase came to mind when I was marveling at the C 390DD’s bass: “Krell-like.” Krell amplifiers have, since their introduction in the early 1980s, represented the pinnacle of “center-of-theearth” solidity and bottom-end dynamic impact. Improbably, the 17-pound C 390DD invited this prodigious comparison.

It wasn’t just that the bass had depth and impact; it also exhibited texture, definition, nuance, and dynamic flow. I love the sense of swing and movement that bassist Ray Brown brings to music, a swing that the C 390DD conveyed with aplomb. On the Kenny Burrell tune “Bass Face” from Bill Evans’ Quintessence [Analogue Productions 45-rpm LP], Brown locks the group into a deep groove that sets a foundation for solos from Burrell, Evans, and tenor player Harold Land. The C 390DD conveyed this aspect of the music so well largely because the amplifier was so dynamically agile and precise sounding, revealing both Brown’s perfect timing and the full measure of attack of each note. Moreover, the bass sounded like a large wooden body resonating with rich density of tone color and clear pitch definition.

The C 390DD shared another characteristic with the M2: a dead-quiet background. As described in the sidebar, the C 390DD’s architecture confers advantages in signal-to-noise ratio, advantages that are heard in the listening room as a blackness against which the music seems to hang in space, detached from the loudspeaker. The silent background also aided in low-level resolution, which was outstanding for an integrated amplifier of this price.

In overall tonal balance, the C 390DD had a somewhat subdued character through the upper-midrange and treble. This was not a forward or bright-sounding amplifier by any stretch. The upside of this tonal balance was a sense of ease and lack of fatigue during long listening sessions. I listened to music through the C 390DD exclusively for about two weeks and never found it aggressive, hard, or tiring. The downside is a slight diminution of palpability and presence in the midrange along with a minor reduction in treble air. Interestingly, the M2 sounded more forward and assertive through the midrange and treble than the C 390DD. Concomitantly, the C 390DD had greater liquidity and warmth than the M2. Midrange forwardness and a reduction in liquidity can be a jitter-induced artifact; it is perhaps no coincidence that the C 390DD has less jitter than the M2. Whatever the reason for this overall tonal balance, the C 390DD should mate well with mid-priced loudspeakers that often have a bit of midrange prominence and extra sparkle in the lower treble. The C 390DD’s tone controls can provide a treble boost to restore the top-end extension, but I found that even the smallest boost increment was too much for most recordings— which gives you an idea that the character I’m describing is not significant in magnitude.

The C 390DD was not identifiable as a Class D amplifier by its sound. That is, it lacked the characteristic “fingerprint” of most switching amplifiers. Although you wouldn’t mistake the C 390DD for a tubed amplifier, the NAD had an organic and natural rendering of timbre free from the “chalky” coloration of some switching amplifiers. I also found that the C 390DD’s sound quality didn’t vary as much with loudspeakers and cables as other Class D amplifiers (I drove a pair of GoldenEar Triton2s with Kimber speaker cables as well as the Ventures with Shunyata and FIM cables).


The NAD C 390DD is an extremely sophisticated, forward-looking product whose feature set perfectly matches the needs of today’s music listener. It is ideally suited as the core of a music-server-based system, yet will also accommodate those with multiple analog sources including vinyl playback. In addition to a wide range of connectivity options, the ability to replace the digital-interface boards and update the software assures that the C 390DD won’t be left behind in technology’s inexorable march forward.

All this great functionality wouldn’t mean much if the C 390DD didn’t deliver musically, but on this count the new NAD is a winner. The C 390DD’s sound quality is easily commensurate with conventional integrated amplifiers near its price. You might find a similarly-priced integrated with greater midrange presence and more treble air, but to equal the C 390DD’s bass quality— dynamic impact, muscularity, and texture—you’d have to spend four figures for massive monoblocks. The C 390DD’s bass is that good.

This combination of sound quality and features makes the C 390DD a very capable and compelling package. I can’t think of another integrated amp anywhere near the C 390DD’s price that I’d rather own.


Output power: 150Wpc into 8 ohms, 20Hz–20kHz, 0.005% %THD
IHF dynamic power: 165W into 8 ohms, 250W into 4 ohms
S/N ratio: >95dB referenced to 1W
Inputs: Two coaxial digital, two TosLink, one AES /EBU, one computer (USB Type B), two mass-storage input (USB Type A), IR, RS232
Optional I/Os: DD1 Analogue Phono Module with one balanced input on XLR jacks, one unbalanced input on RC A jacks, one phono input (mm or mc); DD HDMI-1 HDMI Module with three HDMI inputs and one HDMI output
Formats and resolutions supported: MP3/WMA/FLAC up to 48kHz (USB mass-storage inputs); USB output from Macintosh or PC up to 96kHz/24-bit (computer input); up to 192kHz/24-bit (TosLink, coaxial, AES /EBU)
Outputs: One coaxial digital, one TosLink digital, one line-level, one subwoofer
Dimensions: 17 1/8" x 5 3/16" x 15 5/16"
Weight: 17 lbs.

Price: $2600

NAD Electronics Intl
633 Granite Court
Pickering, Ontario
Canada, L1W3K1
(800) 263-4641