Naim NA CDS CD player Page 2
Overall, the CDS's massive and elaborate power supply is impressive. Further, the execution is superb, with a high level of craftsmanship. At Naim Audio, assemblers build an entire component themselves rather than repeating the same operation on an assembly line. This is a more expensive way to build electronics, but the CDS's beautiful, meticulous build seems to exude a sense of pride.
The transport, based on a custom version of the Philips CDM-4 mechanism, is implemented in a unique way. The mechanism is mounted on an aluminum subchassis and suspended on three leaf springs. Three small pins protrude from the subchassis bottom and fit into three tiny cups mounted at the ends of the leaf springs. The suspension's "Q" and resonant frequencies in each axis were chosen to avoid multiples of servo frequencies. This technique reportedly reduces servo current demands, transmits less vibration to the disc, and eases stress on the power supply. According to Naim, servo current draw feeds vibration to the disc and degrades the HF signal recovered from the disc. The mechanism was thus tuned for minimum servo current draw. Additionally, the subchassis is painted flat black to absorb any stray light.
Because the subchassis is not secured to the leaf springs, the player must not be transported or tilted more than 15° from horizontal without first locking the transit screws.
Conventional wisdom says that adding mass to a spinning CD is a good thing: the disc is rendered less prone to resonant vibrations, thus decreasing servo current demands. This is the rationale behind CD mats, heavy clamps, and stabilizing discs. Naim, however, has taken the opposite approach; the CDS's clamp weighs virtually nothing. Here's how it works.
After putting a CD on the spindle, the clamp, looking like a tiny top hat, secures the disc to the transport. The clamp uses magnetism rather than weight to hold the disc down. A very tiny rare-earth magnet inside the clampa magnet so powerful that it takes a firm pull to remove it from the spindle when changing discsmeets the metal spindle. The idea was to get solid clamping action without adding mass to the spinning disc. According to Naim, heavy clamps tend to couple motor vibration to the disc, degrading the sound and taxing the power supply. Additionally, a heavy clamp forces the motor to draw more current, further adding to the vibration imparted to the disc. The CDS's clamp is the smallest, lightest design possible. The clamp also has a tiny loop of rubberlike material on the bottom that makes contact with the disc at only one point. According to Naim, the size, shape, and material of this tiny loop had an extraordinarily large influence on the CDS's sound.
The single printed circuit board that contains the local power-supply regulation, decoding chips, DAC, and analog output stage is mounted on a 5mm-thick plate that floats on a suspension. This isolates the chips from mechanical vibrationprimarily acoustic energy from loudspeakersand reportedly improves the sound.
The processor section is based on Philips's SAA7220 4x-oversampling digital filter and TDA1541 S1 "Crown" 16-bit DACnothing esoteric here. The "Crown" version of the 1541 is the highest grade, selected for best low-level linearity. A pair of OP42 op-amps (one per channel) serve as current-to-voltage converters. The direct-coupled analog output stage is also based on the OP42, with two of these devices cascaded per channel. De-emphasis is active, formed around a 711 op-amp and switched in with relays. Another pair of relays mutes the output until the circuit has stabilized. Polycarbonate and polystyrene capacitors are used throughout, and components are matched between left and right channels. The DAC, I/V converter, and output-stage circuits are very close together for the shortest pcb traces. As previously mentioned, all power-supply rails are re-regulated on the player's pcb.
A huge benefit of this designintegrated CD player with outboard power supplyover the more conventional transport/processor configuration is the absence of the S/PDIF interface and its associated problems. Rather than trying to recover a clock in the processor (and introducing jitter in the process), the CDS's single-box approach puts the clock right there on the pcb. No muss, no fuss. Naim believes that the problems inherent in the S/PDIF interface make it impossible to design an outboard converter to equal the sonic performance of a single-box design. In my review of the Linn Karik/Numerik, I was able to audition the unit with high or low levels of jitter in the S/PDIF interface. The sonic improvement obtained from lower jitter levels was dramatic (footnote 3).
Overall, I found the CDS attractive and very well built. I especially liked the player's ease of use: the large, back-lit transport control buttons were readily accessible and intuitive. Further, I was intrigued by the level of mechanical design that went into the CDS, especially the clamp, transport subchassis suspension, and floating pcb.
But let's find out how the Naim CDS sounds.
To its credit, the CDS had no salient sonic characteristics that called attention to the player. Many digital products have a certain interpretation of the music that makes them immediately identifiablea lightweight bass, overly bright treble, or forward midrange, for example. The CDS was remarkably free of such departures from neutrality.
Footnote 2: Adding these regulators reduced noise on the digital supply rails from 110dB to 130dB. This may seem academic, but the effects were certainly audible. Naim will announce an upgrade program for owners who bought the original CDS without this additional regulation.
Footnote 3: See the sidebar on pp.166167 of Vol.15 No.1 for a more complete description of problems inherent in the S/PDIF interface.