Vintage

Rarely seen, or implemented, the PCM55 was Burr-Brown's ±5V 'low consumption' version of the full-sized ±12V PCM54 16-bit monolithic DAC used (as a dual-mono pair) in the huge Technics SL-P1200 [HFN Aug '13]. Just one PCM55 is used in the SL-XP5 but while the sequential left sample-by-right sample conversion would ordinarily result in a 0.0113msec offset between left (black) and right (red) channels, this is halved here (and the interchannel phase lag reduced from 90° to 45o) thanks to Technics' 2x oversampling. This is a simple linear phase digital filter, invoking both pre- and post-event ringing [see impulse, Graph 2], but in combination with the SL-XP5's analogue filter delivers a very creditable 84dB stopband rejection. The two filters also help define the player's frequency response [also Graph 2] with its very gentle ±0.02dB passband ripple and mild +0.3dB treble peak. The gently declining bass (–0.3dB/20Hz) ties-in with the increasing output impedance which reaches 1.2kohm/20Hz via the line outputs [green trace, Graph 2].

Technics achieved a maximum 1.7V line output and full 16-bit 95.7dB A-wtd S/N ratio from the SL-XP5 even though its compressive linearity trend – where signals at –80dBFs appear +2.5dB higher (and +4.9dB at –90dBFs) – suggest its low-level resolution is closer to 15 bits. Peak level distortion is moderate, reaching 0.007% at 1kHz and despite appearing initially higher at 0.035%/20kHz/0dBFs, the highest frequencies are ostensibly the least distorted as Technics' digital/analogue filters also remove any >20kHz harmonics [blue infill, Graph 1]. The player's jitter performance is also slightly higher at 890psec on the right channel, falling to 350psec on the left – all data-induced. PM