Accuphase DP-85 SACD player Measurements part 2
Fig.6 Accuphase DP-85, departure from linearity, 16-bit PCM data (right channel dashed, 2dB/vertical div.).
Fig.7 Accuphase DP-85, waveform of undithered 1kHz sinewave at -90.31dBFS, 16-bit CD data.
Fig.8 Accuphase DP-85, waveform of undithered 1kHz sinewave at -90.31dBFS, 24-bit PCM data.
As is usual these days with digital source components, there was almost no harmonic distortion present in the DP-85's output. Playing back 24-bit digital data representing a full-scale 50Hz tone, the only harmonic present, even into the demanding 600 ohm load, was the third (fig.9), at -97dB (0.0014%). Intermodulation distortion (fig.10) was also vanishingly low in level.
Fig.9 Accuphase DP-85, spectrum of 50Hz sinewave, DC-1kHz, at 0dBFS into 600 ohms (linear frequency scale).
Fig.10 Accuphase DP-85, HF intermodulation spectrum, DC-25kHz, 19+20kHz at 0dBFS into 100k ohms (linear frequency scale).
Michael Fremer was disappointed with the DP-85's playback of CD data, yet there was nothing in the measured data above that would indicate why. When I examined the player's susceptibility to word-clock jitter, however, it definitely stumbled on CD playback. Using the Miller Jitter Analyzer to search the Accuphase's analog output from jitter-related sidebands while it played back a CD-R containing the diagnostic test signal, I found an extremely high 4.26 nanoseconds of peak-peak jitter. This is more than 20 times higher than I have found in the best CD players and processors.
Fig.11 Accuphase DP-85, high-resolution jitter spectrum of analog output signal, source PC fitted with RME Digi96/8 Pro soundcard via 1m TosLink (11.025kHz at -6dBFS sampled at 44.1kHz with LSB toggled at 500Hz). Center frequency of trace, 11.025kHz; frequency range, ±3.5kHz. Red trace is similar analysis from internal CD playback.
The grayed-out trace in fig.11 shows the spectrum of this jitter. Data-related sidebands (red numeric markers) are very low in level, almost all the jitter coming from pairs of sidebands at ±42.5Hz and its harmonics (circled in magenta). This behavior was not affected by turning off the supply, nor by floating the player's AC supply ground. What I did find surprising was that when I fed the DP-85's S/PDIF data input with 16-bit data of the same signal, the measured jitter level dropped to a respectable 311 picoseconds (foreground trace in fig.11). I don't have an SACD with the diagnostic jitter signal on it, but the "tentative" Sony test SACD does include a high-level 11.025kHz signal. Spectral analysis of the Accuphase's analog output while it played this revealed behavior similar to the way it had performed with external PCM data.
Other than the high level of word-clock jitter for CD playback, the DP-85 offered a respectable set of measurements.—John Atkinson