dCS Puccini SACD playback system Page 2

But there was trouble in paradise. The Philips transport mechanism used in the P8i proved, over the long haul, to be as unreliable in the dCS player as it was in contemporaneous SACD players from Krell and Musical Fidelity. The Puccini, therefore, uses a high-quality transport mechanism from Japanese company Esoteric, the UMK5. Though an expensive part, it has so far proved bombproof in use.

Discs are loaded on an elegant, slim drawer mounted on the right of the player's gracefully carved front panel. The central blue LCD display is, thankfully, large enough to see from my listening chair, while an array of 10 pushbuttons to the left of the display (these arranged in two subtly converging rows of five each) control the Puccini's functions, which include, as well as the usual transport functions, Volume and Menu. These are duplicated on the remote (a rather cheesy plastic thing, since replaced by a more substantial metal unit), along with direct access to the Balance and Mute controls, the reconstruction Filter choice for CD and SACD playback (four are provided, with increasing degrees of ultrasonic rolloff), and digital input selection, all of which can be selected only on the front panel, via the Menu tree. The Menu, however, also offers a wealth of secondary functions, such as polarity inversion, Channel ID and polarity check tones, display options, layer selection for hybrid SACDs, and setting the maximum output level to 2V or 6V RMS. There's also a Factory Reset function!

One small operational niggle: The front-panel Open/Stop button acts as a Mute when a digital input is selected. I kept finding myself walking over to the player to play a disc after I'd been playing audio from my computer, only to remember that, to select disc playback before I could load the disc, I needed either to navigate the Menu tree, or go back to my chair to fetch the remote.

Like its predecessor, the Puccini uses dCS's Ring DAC, clocked either by a high-precision, voltage-controlled crystal oscillator, or by an external word-clock signal fed to the appropriate 75 ohm BNC input jack. For SACD playback, the DSD datastream is fed directly to the DAC; when a CD is played, the "Red Book" data can be played as straight PCM or upsampled to DSD, this selectable with the Menu button. External PCM data are not upsampled, however. A choice of four reconstruction filters is provided for CD playback, these again selected by the Menu button. With the firmware upgrade, the Puccini will also upsample PCM data fed to the external inputs. As mandated by the Sony-Philips SACD license, the player's digital outputs are deactivated when an SACD is playing; they are also disabled when one of the external data inputs is being used. When one of the external inputs is in use and lock has been achieved, the Puccini's display helpfully shows the bit depth and sample rate.

Internally, the Puccini is dominated by two large printed circuit boards. The Ring DAC board, with its power-supply regulators and class-A analog output circuitry, is immediately behind the front panel. Behind it is the Control board, with the power supply, the microcontroller, the digital input/output circuitry and its associated phase-locked loop and crystal-controlled clocks, and the DSP section.

The Puccini is available in silver or black. I found it visually stunning, and considerably more elegant than the rather industrial-looking Scarlatti.

Asynchrony
Visually, the slim U-Clock echoes the Puccini's asymmetrically bowed front panel. Like the earlier dCS Verona, which I reviewed in March 2005, it provides the Puccini, via one of four BNC jacks, with a very stable word-clock signal switchable between 44.1 and 48kHz.1 The master clock can be switched between dithered and undithered operation—undithered clock operation might be thought theoretically better, but, as I wrote in my Verona review, the use of a small amount of random dither avoids the "dead zone" that receivers using a phase-locked loop with a very narrow acceptance window can suffer from (footnote 1). The dither is said to ensure that the receiving PLL remains locked to the U-Clock's output with the minimum of jitter. (The dither itself is filtered out by the PLL.)

The U-Clock's rear panel also offers two S/PDIF digital audio outputs that echo the audio data fed to the USB input. Like the Ayre and Wavelength DACs (footnote 2), the U-Clock's USB port uses a Texas Instruments TAS1020B USB receiver chip operating in what's called "asynchronous" mode. (This is not to be confused with the asynchronous sample-rate conversion used by digital processors like the Musical Fidelity V-DAC, which I write about elsewhere in this issue, or the Benchmark DAC 1.) Almost all USB DACs operate in what's called adaptive isochronous USB mode, which means they have to adjust the frequency of their master-clock oscillator every millisecond to match the rate of the data being streamed from the host PC. This inevitably leads to increased jitter that potentially degrades ultimate sound quality. By contrast, the asynchronous mode slaves the PC to a high-precision, fixed-frequency master clock in the DAC (Ayre, Wavelength) or the U-Clock. In theory, this eliminates jitter entirely.



Footnote 1: In general, the tighter the PLL's acceptance window, the lower the jitter, but the longer the PLL will take to lock to an incoming datastream. Courtesy of Mark Gurvey of Esoteric USA, I experimented with the ultra-high-precision, rubidium-based Esoteric G-0Rb "atomic" master clock. The measured results were unpredictable—whether or not the external clock made the result better depended entirely on the design of any particular DAC's word-clock input circuit. It can't be taken as a general rule, therefore, that an external clock generator will result in lower jitter.

Footnote 2: For the TAS1020B's embedded microcontroller Ayre uses the Streamlength code, developed by Wavelength's Gordon Rankin. dCS's Andy McHarg wrote his own code for the U-Clock's TI chip.

COMPANY INFO
dCS (Data Conversion Systems), Ltd.
US distributor: dCS America
PO Box 544, 3057 Nutley Street
Fairfax, VA 22031
(617) 314-9296
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