Simaudio Moon Eclipse CD player Measurements

Sidebar 3: Measurements

I hadn't seen Brian Damkroger's review text when I measured the Moon Eclipse, and so hadn't noted that he preferred to use the unit with its digital output linked to its digital input. Nevertheless, I did collect a full set of measured data via the unit's digital input, which will be representative of its performance as auditioned by Brian.

The Eclipse's error correction was excellent; it played up through track 34 (which has 2mm gaps in its data spiral) of the Pierre Verany Test CD without dropouts. The Eclipse proved to be non-inverting from all outputs (with the XLRs wired with pin 2 "hot"), as long as the red Phase LED was illuminated. The source impedance was a low 44 ohms unbalanced and 88 ohms balanced.

Playing CDs via the HDCD filter, the unit's unbalanced maximum output level (MOL) was 1.93V, this doubling from the balanced outputs, as expected. With the Moon fed from an external digital source, I expected a 6dB rise in level; the external input bypasses the PMD100 filter, which drops the level of non-HDCD-encoded discs by the same 6dB. However, the maximum output level actually rose by 7dB for external sources, to a high 8.644V from the balanced output jacks. (This could prove problematic for some older preamps with switched-transistor volume controls.)

The frequency response (fig.1, upper traces) rolled off slightly early, reaching -0.5dB at 19kHz, which should be subjectively inconsequential. However, repeating the measurement with a pre-emphasized signal (fig.1, lower traces) depressed the mid- and upper treble to an extent that will be audible. (Interestingly, the Naim CD5, reviewed elsewhere in this issue by Michael Fremer, features an almost identical de-emphasis error.) Fortunately, there are almost no pre-emphasized CDs available, so this error will be largely irrelevant. Channel separation (not shown) was superb at better than 100dB across the band.

Fig.1 Simaudio Moon Eclipse, frequency response at -12dBFS, without emphasis (top) and with emphasis (bottom). (Right channel dashed, 0.5dB/vertical div.)

Fig.2 shows spectral analyses of the Moon's output playing a dithered 1kHz tone under two conditions: the top traces were taken with the unit playing 16-bit data from a CD via the HDCD filter, the lower traces with a 24-bit external signal, which will be decoded via the Burr-Brown filter. There is a 21dB difference in the levels of the noise floor, which will be due not only to the increase in word depth, but also to the 6dB gain reduction applied by the Pacific Microsonics filter and the 7dB increase in MOL for external digital sources. A similar difference can be seen in the spectra of digital black taken under the same conditions (fig.3). In both of these graphs, however, spurious tones creep in in the lower mids and bass to spoil the player's otherwise excellent dynamic range in this region. These spuriae are definitely not power-supply-related; I have no idea what they are due to. (For these measurements, I turned off my computer monitor, which can otherwise be an excellent source of RF-induced nasties.)

Fig.2 Simaudio Moon Eclipse, 1/3-octave spectrum of dithered 1kHz tone at -90dBFS, with noise and spuriae, 16-bit internal CD data (top) and external 24-bit data (bottom). (Right channel dashed.)

Fig.3 Simaudio Moon Eclipse, 1/3-octave spectrum of "digital black" with noise and spuriae, 16-bit internal CD data (top) and external 24-bit data (bottom). (Right channel dashed.)

Linearity error (fig.4) was assessed through the external input using 16-bit data. It was very low down to below -112dBFS, which is excellent. As a result of both this and the large dynamic range, the waveform of an undithered 1kHz tone at -90.31dBFS (fig.5) clearly showed the three discrete voltage levels. Reproduction of this waveform via the HDCD filter (not shown) was also excellent, but a little noisier.

Fig.4 Simaudio Moon Eclipse, departure from linearity, external 16-bit data (2dB/vertical div., right channel dashed).

Fig.5 Simaudio Moon Eclipse, waveform of undithered 1kHz sinewave at -90.31dBFS, external 16-bit data.

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