Sony Discman (D-50 MkII) Lab Repor

Lab Report

About 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 moniker 'Discman' was firmly established. Despite superficial similarities, and a very similar analogue stage (with the same source impedance trend – 425ohm increasing down through the bass to 2315ohm/20Hz), the performance of the D-50 MkII is markedly improved. This Sony achieved while also further reducing power consumption from 8W to a mere 2W, facilitating the use of its compact 1350mAh BP-200 battery pack.

Sony's DAC was replaced by the lower-consumption PCM55 from Burr-Brown, a 16-bit monolithic chip time-shared between channels and, once again, free of any oversampling or digital filtering. This is clear from the impulse response [inset, Graph 2 below] which shows none of the pre-ringing associated with standard FIR digital filters – the 0.0113msec offset between left (black) and right (red) a function of the sequential left sample-by-right sample conversion performed in this 'mono' DAC. The reconstructed response is subtly improved at HF over the D-50 but still shows a slightly depressed presence/treble [Graph 2].

The PCM55 achieved a sub-16-bit A-wtd S/N ratio of 88.9dB in the D-50 MkII (a few dB behind the D-50) but low-level resolution is improved with errors of just –1.5dB over a 100dB dynamic range. The output level is also reduced from 1.8V to 1.5V but distortion, especially over the top 10dB of its range [see Graph 1], is significantly lower than measured from the D-50. So, at 0dBFs, 0.0023-0.0035% readily bests 0.0045-0.020%. Finally, even jitter is reduced: from 825psec to just 130psec! PM


Distortion versus 16-bit CD digital signal level over a 120dB range (black, 1kHz; blue, 20kHz)


Frequency and time domain responses (left, black; right, red) and output impedance (green). No digital filter – no pre-ringing on the impulse response!

Maximum output level / Impedance 1.48Vrms / 420-2315ohm
A-wtd S/N ratio 88.9dB
Distortion (1kHz, 0dBFs/–30dBFs) 0.0023% / 0.0035%
Distortion & Noise (20kHz, 0dBFs/–30dBFs) 0.0088% / 0.0024%
Frequency response (20Hz-20kHz) –0.36 to –1.60 dB
Digital jitter 130psec
Resolution @ –90dB/–100dB –1.5dB / –0.7dB
Power consumption 2W
Dimensions (WHD, inc. battery) / Weight 125x43x127mm / 1.2kg