Wadia 861 CD player Measurements part 2

Fig.7 shows the spectrum of the Wadia player's balanced analog output driving a high (100k ohm) load. The highest-level harmonic is the third, at a still very low -85dB (0.006%), with the second evident at -90dB (0.003%). The third harmonic rose into the punishing 600 ohm load (spectrum not shown). However, at -72dB (0.025%), this will still be negligible, though the fifth harmonic does now make an appearance, at -90dB. Intermodulation into either load was very low, the 1kHz difference component remaining close to -90dB, even into 600 ohms (fig.8). This spectrum was taken with Filter A: I extended the plot up to 25kHz to show the leakage of the aliased component at 24.1kHz (44.1kHz minus 20kHz), due to the filter's poorer-than-usual stop-band attenuation.

Fig.7 Wadia 861, spectrum of 50Hz sinewave, DC-1kHz, at 0dBFS into 100k ohms (linear frequency scale).

Fig.8 Wadia 861, Filter A, HF intermodulation spectrum, DC-25kHz, 19+20kHz at 0dBFS into 600 ohms (linear frequency scale).

Finally, I examined the Wadia 861's rejection of word-clock jitter using the Miller Audio Research Jitter Analyzer and a CD-R carrying the analytical signal, this a high-level Fs/4 (11.025kHz) sinewave over which is overlaid the LSB toggling on and off at a low frequency (229Hz). (It is important to note that, contrary to what you may have read on the Usenet newsgroups, this signal must be undithered to maximally excite wordclock jitter in the DAC under test.)

The solid trace in fig.9 shows a high-resolution spectrum of the Wadia's unbalanced analog output while it decodes data fed to its digital input by a PS Audio Lambda CD transport via a 6' electrical S/PDIF link. (ClockLink was turned off for this measurement.) The absolute jitter level is a very low 190 picoseconds, and the main jitter components are the pairs of sidebands at ±229Hz—clearly data-related and indicated with red "4" numerical markers—and ±16Hz (purple "1," circled in magenta).

Fig.9 Wadia 861, high-resolution jitter spectrum of analog output signal, PS Audio Lambda 2 transport via 6' Apature S/PDIF link (11.025kHz at -6dBFS with LSB toggled at 229Hz). Center frequency of trace, 11.025kHz; frequency range, ±3.5kHz. Grayed-out trace is similar analysis for internal CD playback.

Repeating the test using the 861's own drive actually increased the jitter to 191.6ps, which is still low in absolute terms. This surprised me, considering that the internal transport benefits from Wadia's ClockLink topology, which should reduce the DAC's susceptibility to word-clock jitter. I turned the front-panel display off and the measured jitter level dropped to 176.4ps. It appears that there is some interference between the display and the D/A circuitry with the internal CD transport but not with external digital sources; while the measured jitter levels are low in absolute terms, there is still some noise-floor contamination, as can be seen from the red-circled spikes in the grayed-out trace in fig.9.—John Atkinson

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