Digital Source Reviews

The BAT offered superb error correction, playing without skipping through the Pierre Verany test CD's track 33, which has a deliberate 2mm gap in the data. The BAT's output was noninverting from both single-ended and balanced jacks with the blue Invert LED off. (Pin 2 on the XLRs is wired to be "hot.") At 2.175V, the output level from the single-ended RCAs was 0.7dB higher than the CD-standard 2V. From the balanced jacks, the output level doubled to 4.36V. The single-ended output impedance was a moderate 882-908 ohms at middle and high frequencies, but rose to a very high 8475 ohms in the low bass. Similarly, the balanced output impedance varied between 986 ohms and 1203 ohms, but was much higher—17k ohms—at 17Hz.

While both the YBA 6-chassis preamplifier preferred by Jonathan Scull and Balanced Audio Technology's own preamps have input impedances well above 100k ohms, this high LF source impedance will give a rolled-off bass when the VK-D5 is used with preamplifiers having low input impedances. This can be seen in fig.1. The top pair of traces is the VK-D5's response into a 100k ohms load. (This was from the unbalanced output; the balanced output was almost identical, with very slightly greater extension at the two frequency extremes.) Reducing the loading to 10k ohms (a load typical of many solid-state preamplifiers) gave fig.1's middle trace, which rolls off by 2.3dB at 20Hz. This will be audible as a slight thinning of the sound, but also as an improvement in low-frequency definition. And note that with his YBA preamp, which offeres almost a 200k ohm loading, J-10 felt that there was a slight bloom in the low bass.

Fig.1 BAT VK-D5, unbalanced frequency response at 0dBFS into 100k ohms (top), into 10k ohms (middle), and de-emphasis response (bottom). (Right channel dashed, 0.5dB/vertical div.)

The bottom pair of traces in fig.1 is the BAT's response with de-emphasis engaged (offset by -1dB for clarity). The reasonably large (0.7dB) negative response error will make pre-emphasized CDs sound slightly mellow; fortunately, almost no CDs are pre-emphasized. The VK-D5's channel separation was superb, at better than 90dB in either direction below 1kHz. A small degree of capacitive coupling decreased the separation above that frequency with a L-R figure of 68dB and a R-L figure of 80dB at 20kHz, both of which are still good.

Fig.2 shows a 1/3-octave spectrum of the BAT's balanced output while the player decodes data representing a dithered 1kHz tone at -90dBFS. The plot is clean and free from spurious noises, though a slight power-supply component can be seen in both channels at 120Hz. There is also a peak at 60Hz present in the left-channel output. Repeating this spectral analysis with a wider, 200kHz bandwidth and digital silence gave the trace in fig.3. Again, the very small amount of power-supply noise can be seen, but the plot is free from idle tones and other digital nasties.

Fig.2 BAT VK-D5, spectrum of dithered 1kHz tone at -90.31dBFS, with noise and spuriae. (16-bit data, 1/3-octave analysis, right channel dashed.)

Fig.3 BAT VK-D5, spectrum of digital silence, with noise and spuriae. (16-bit data, 1/3-octave analysis, right channel dashed.)

Though a slight negative error is apparent in the BAT's linearity (fig.4), the machine offered good performance down to below -110dBFS. The waveform of an undithered 1kHz sinewave at -90.31dBFS (fig.5) was reproduced with a correspondingly accurate shape, the three levels easily apparent but with slightly more noise overlaying the plot than with the ultraquiet Meridian 508.24 (reviewed elsewhere in this issue).

Fig.4 BAT VK-D5, left channel, departure from linearity (2dB/vertical div.).

Fig.5 BAT VK-D5, waveform of undithered 1kHz sinewave at -90.31dBFS (16-bit data).