Sony SCD-1 Super Audio CD/CD player Page 2
The SCD-1's three footers are anything but ordinary. They've got an interior insulator with a stubby nipple on top which takes the weight of the player. A "gel damper" ring sits on the top surface of the inner insulator. According to Sony, this "pinpoint" contact eliminates resonance, prevents muddled sound in the mids and highs, and improves the bass. Even the base plate of the footer was given due consideration: it's made of high-carbon cast iron with "good attenuation characteristics."
Beginning at the laser and working our way back:
Sony reminds us that laser pickups are very susceptible to noise, especially from servo current flow. Particular attention was paid to creating what Sony calls "a quiet environment" within which the two lasers can operate undisturbed by the outside (or inside) world. There are two independent optical pickups: one operating at Super Audio CD's 650nm wavelength, one for CD's 780nm wavelength. The laser heads are fixed in place on a base unit that is in turn fixed to the chassis. The disc moves along a motorized spindle platform as it reads the data.
Even though separate laser pickups are used for SACD and CD, after the RF signals have been retrieved from disc, the same processor is used to demodulate the RF, correct data errors, and extract the clock and synchronization signals for both. If the data are being read from a CD or the rear CD layer of a SACD (see fig.1), this processor feeds the two-channel, 16-bit, 44.1kHz datastream to a new Sony IC, the CX8762, where it is oversampled, digitally filtered (see later), and noise-shaped. If the data are from a SACD, the datastream is first fed to a DSD decoder, then to the CX8762, where it processed by an "Accurate Complementary Pulse Density Modulator" which compensates for ringing at bit transitions.
Fig.1 In a two-layer, hybrid SACD, the CD data are encoded on the rear layer, the DSD data on a semi-transparent intermediate layer (after Sony).
Whether derived from CD or SACD, there is now a single stream of data pulses that is fed to an "STACT" IC (the CX8594). This generates the necessary system clock signals and improves the timing precision of the pulse data before feeding them to the actual D/A converter, this called by Sony a "Current Pulse" DAC. The reconstructed analog signal is fed to an I/V converter, a low-pass filter, and the output amplifier. The SCD-1 offers both single-ended outputs on RCAs and balanced connections via XLR connectors with pin 3 hot (in the Japanese fashion) (footnote 1).
An S/PDIF digital output is available on an RCA jack and an optical port but this yields a 16-bit/44.1kHz PCM output from CDs only. When the DSD layer on an SACD is playing, the digital output is disabled. In any case, there is no digital decimation filter to convert a DSD datastream to PCM.
Footnote 1: Running single-ended avoided absolute polarity problems, but balanced connection definitely sounded better and had to be compensated for elsewhere in the system, reversing the speaker leads, for example.