Bg audio electronics 2012 by Max Com

EQUIPMENT review - NAD C 390DD Direct Digital Integrated Amplifier

Pulse-Width Modulation How can a series of pulses represent the continuous waveform of music? In exactly the same way that Direct Stream Digital (DSD), the encoding format behind SACD, produces music from a bitstream. In fact, PWM and DSD are conceptually identical. Fig.1 shows the relationship between a DSD bitstream and the analog waveform that bitstream represents. The bitstream is a series of pulses of varying lengths, with the pulse length encoding the analog signal’s amplitude. The pulse-train generated by DSD encoding looks remarkably “analog-like.” That is, you can look at the pulse train and get an idea of what the analog waveform looks like. The relationship between the analog signal and the

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.

bitstream is so close that in theory, a DSD signal can be converted to analog with a single capacitor (DSD-to-analog conversion is more complex in practice). The bit rate of DSD as used in SACD is 2.8224 million bits per second. In a switching amplifier, the output transistors are turned fully “on” or fully “off” by Encoding is sometimes called Pulse Width Modulation (PWM). the pulse-width modulated signal.

“The NAD C 390DD is an extremely sophisticated, forward-looking product whose feature set perfectly matches the needs of today’s music listener.”

The analog signal’s amplitude is encoded as the “area under the pulses”; longer pulses (longer “on” times for the output transistors) represent a higher analog-signal amplitude. This is contrasted with traditional “linear” amplifiers in which the output transistors are 1010110111011110111110111101110110101010101010010001000010000100010010101010

in a continuously variable state of conduction.

The output of the PWM stage is a series of high-level pulses that must be smoothed into a continuous waveform. Every amplifier with a switching output stage employs a large filter (an inductor and a capacitor) between the output transistors and loudspeaker terminals to perform this smoothing function and to remove switching noise. In the DDFA system, the pulses are quantized with a master clock frequency of 108MHz. This frequency determines the number of discrete pulse widths available to represent the audio waveform. That number is 128, which appears at first glance to be too low to encode a complex musical signal. But even at 20kHz, there are many modulation cycles available within the period of a 20kHz waveform.

49 Guide to Audio Electronics

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 brokenin 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 iron-fisted 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-the-earth” 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 signalto-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 www.theabsolutesound.com