Vintage

A year separated the launch of the D-50 [HFN Mar '85 and Jan '13], Sony's first portable CD player, and the D-50 MkII [HFN Apr '86] during which time the 'Discman' brand had taken hold, but the next three years saw a marked evolution in this portable technology, culminating in the D-Z555 [HFN Sep '90]. The single, time-shared PCM55 DAC with analogue filter used in the D-50 MkII was transformed into two PCM66P DACs driven via a Sony CXD2551 8x oversampling filter within the D-Z555. Both these Burr-Brown DACs were 16-bit monolithic types but, despite a pair of the superior PCM66Ps being employed with digital upsampling and filtering, the practical low-level resolution achieved by the D-Z555 was not an improvement over the 'analogue' D-50. Our lab tests, 34 years later, show digital signals dropping away below –80dBFs to –13dB below the anticipated level at –90dBFs. This, and the relatively poor 92dB A-wtd S/N ratio (0dBFs raised 0.8V from the 3.5mm line output) implies an effective resolution ~15-bits – just like its illustrious forebears.

Where the D-Z555 does have the upper hand is in the greatly reduced interchannel phase error of its synchronised L/R conversion. The pre/post ringing of the low-tap linear phase FIR digital filter is clear [see Graph 2], as is the phase-inverted output, realising a flat response (±0.02dB ripples) prior to a final +0.4dB HF peak. Again, this is an early 8x filter and so the stopband rejection is a mere 27.3dB. Peak level distortion is moderate at 0.008-0.045%, with a minimum of 0.007%/1kHz over the top 10dB of its dynamic range [see Graph 1, below] but at least improvements in the digital processing, and local clocking, manifest positively here in the 'low' 265psec jitter. PM