Vintage

Less than 12 months separated the launch of Sony’s first portable CD player, the D-50 [HFN Mar ’85 and Jan ’13], and the MkII version [HFN Apr ’86] during which time the ‘Discman’ brand had taken hold. Three years of evolution later and the dual-DAC/8x oversampling D-Z555 [HFN Sep ’90 and Jul ’23] is reckoned by many Discman aficionados to be the apex of the genre. Another three years saw Sony’s Discman players almost universally adopt a bitstream DAC technology, rather erroneously referred to as ‘1-bit’, and spearheaded by the SM5853BF PWM converter. The fully ‘gasketed’ Discman (ESP) Sports models like the D-421SP had other strings to their bow, but the PWM DAC certainly brought an improvement in low level resolution – accurate to ±1dB over a 100dB dynamic range, or a 10x improvement over the 16-bit DACs used earlier. Distortion is low too, falling to a minimum of 0.002-0.017% (20Hz-20kHz) over the top 20dB of its dynamic range [see Graph 1], though the maximum (line) output is just 880mV and from a rather high 831ohm source impedance, rising to 1.41kohm at 20Hz.

Even with DSP and ESP turned off, our sample suffered a repetitive pattern based on a spurious signal at 516Hz and odd harmonics thereafter at ~100dB below full signal. This dragged the achievable A-wtd S/N ratio down to a sub-15-bit 88.4dB (re. 0dBFs) even though the signal linearity, as mentioned earlier, was superior. The digital filter is a linear phase type offering a 54dB stopband rejection and a response – with some visible ripple – extending out to –0.77dB/20kHz. Jitter is very high indeed at 5570psec (some 20x higher than seen in the D-Z555) and primarily data-induced in nature [see Graph 2, below]. This result was not improved by the ESP function’s data buffering. PM