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NAD Readies Digital-Input Amplifier

NAD’s first fully digital amplifier is the industry’s first digital amp that performs as well or better than the “very best linear Class A or AB amplifiers” with Class D efficiency, product development director Greg Stidsen contended.

The amp is the Master series M2, due in the summer at a recently revised suggested retail of $5,999. It’s rated at 2×250 watts into 4 or 8 ohms with 2×500-watt peaks and 120dB dynamic range. It ships only to retailers authorized to sell NAD’s top-end Master series components.

The M2 directly accepts a digital PCM signal, uses pulse width modulation (PWM) to amplify the signal, and incorporates a new type of closed-loop direct digital feedback technology to deliver better-than-Class-A performance at all output levels with 89 percent efficiency at 2×250 watts, Stidsen said.

Compared to a handful of other truly digital component amplifiers, Stidsen continued, “our amplifier is one-third the price with higher power, less distortion and more dynamic power output.” At $4,999, it’s the most expensive amp in the NAD lineup, which previously topped out at about $2,000, but it nonetheless reflects NAD’s position as delivering audiophile performance with value, Stidsen said.

Truly digital amps promise high levels of performance but haven’t lived up to their potential, so they haven’t been embraced by the audiophile community, Stidsen said. Truly digital amps, he explained, accept a digital PCM signal, whereas other types of amps, including Class D amps, take in an analog audio signal. Direct digital inputs “eliminate analog conversion, cable issues and lots of analog stages where you can lose information and add distortion,” he explained.

NAD’s collaboration with Zetex takes digital amplification to audiophile levels by using closed-loop digital-domain error correction developed by U.K.-based Diodes Zetex Semiconductor. “All the previous drawbacks of digital amplifiers are simply removed by use of digital feedback,” said Franz Riedlberger, Diodes Zetex’s research and technology development director. “Power supply noise and output-stage distortion are rejected, and output impedance is very low.” As a result, he said, the M2 delivers “the lowest available distortion and noise coupled with outstanding linearity, leading to a detailed and natural sound.”

The feedback technology differs from traditional feedback technologies that loop the amplifier’s analog output to the amp’s input, NAD said. The company contends such methods are “too slow.” Diode Zetex’s Direct Digital Feedback Amplifier (DDFA) closed-loop technology, on the other hand, “corrects for the analog output in the digital domain” with a bandwidth wide enough to prevent any truncating of the original signal’s information, Stidsen said.

The M2’s chassis incorporates digital/analog converters to connect directly to a source’s digital PCM output, basic digital-domain preamp functions except for tone controls, and a PWM amplifier section. For connection to sources with analog outputs, the device features analog/digital converters, single-ended analog stereo inputs, and balanced XLR inputs. The digital inputs include coax, optical and balanced AES/EBU. Other features include dual-mono power-supply design and two analog outputs per channel to simplify speaker bi-wiring.

In the device itself, NAD married Diode Zetex’s technology with some of its own proprietary technologies to boost performance. NAD’s technologies include PowerDrive to deliver high-power transient peaks and drive difficult speaker loads without upping distortion levels. Other NAD technologies are digital soft-clipping and digital volume control.

In the future, the digital amplification technology could be incorporated in multichannel home-theater amps, and such products could include built-in decoding of Blu-ray surround formats because the amp would have DACs and a basic preamp already built in, Stidsen said. The technology could also appear in $2,000 to $3,000 A/V receivers (AVRs) and be price-competitive with AVRs rated at the same power.

“The M20 is an audiophile amp and a test bed for future development to bring the technology to more mainstream products,” he added.

Truly digital amplification based on a Texas Instrument chip amp appear in many low-power moderate performance home theater in a box systems, but they don’t incorporate closed-loop error correction, said Craig Bell, Diode Zetex marketing manager.