Wadia 27ix & Wadia 270 transport Measurements part 5

This can be seen graphically in fig.14. Without the clock link (grayed-out trace), the first three lower, data-related sidebands (red markers "2," "3," and "4") are higher in level than the upper sidebands. Adding the clock link drops these sidebands in level to match the lower ones. It also eliminates pairs of sidebands at ±15.6Hz and ±340Hz. However, it does not appear to affect the higher-harmonic sidebands (red markers "5" through "11"), and a pair of low-level sidebands at ±174Hz can now be seen (purple marker "1").

Fig.14 Wadia 270 & 27ix via ST-optical connection with clock link, high-resolution jitter spectrum of analog output signal (11kHz at -6dBFS with LSB toggled at 229Hz). Center frequency of trace, 11kHz; frequency range, ±3.5kHz. Grayed-out trace was taken under identical test conditions but without clock link.

I then replaced the Wadia 270 with the PS Audio Lambda Stereophile uses as a test-bench reference. (The volume control was set to "92" in both cases to avoid clipping the National Instruments PC card.) To my astonishment, the measured jitter level dropped to 162.5ps using an ST-optical link, with a similarly low level when this was replaced by an Apature S/PDIF electrical link. Fig.15 compares the high-resolution spectral analysis of the Wadia 27ix's analog noise floor when driven by the clock-linked, ST-optical Wadia 270 (grayed-out trace) and the S/PDIF Lambda. The latter has the upper data-related fundamental sideband higher in level. It also has some very-low-level sidebands, at ±60Hz and ±120Hz, that must be power-supply-related—but all the other data-related sidebands are lower in level than with the 270.

Fig.15 Wadia 27ix & PS Audio Lambda via S/PDIF electrical connection, high-resolution jitter spectrum of analog output signal (11kHz at -6dBFS with LSB toggled at 229Hz). Center frequency of trace, 11kHz; frequency range, ±3.5kHz. Grayed-out trace is of the 27ix driven by the Wadia 270 and clock-linked.

What is also surprising from this graph is that the overall noise floor is around 3dB lower with the PS Lambda. I then remembered that I had the Wadia 270's resolution-enhancement function set to mode "B." This adds dither, which will raise the noise floor slightly when the 27ix is driven from the 270 transport, but not from other digital sources. The Miller Audio Research program searches through the FFT-derived spectral data for symmetrical sidebands on either side of the fundamental tone, calculates their frequencies, then estimates a peak-peak jitter level in picoseconds from their weighted sum. The difference in noise floor between the 27's performance with the Wadia 270 and PS Lambda transports should not affect the measured jitter level.

Finally, the Wadia 270 coped well with data dropouts. It played through track 32 on the Pierre Verany Test CD without a glitch, and only occasionally muted on track 33, which has 1.5mm gaps in the data spiral.—John Atkinson

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