Tube Preamps

Considered on its own, the Balanced Audio Technology VK-40 was a very fine-sounding preamplifier, but how did it compare sonically with competing products? I put it up against my reference preamp, the Convergent Audio Technology (CAT) SL-1 Ultimate (see the August 1999 Stereophile). At $5995, the CAT costs about $500 more than the "loaded" VK-40, and lacks a remote control; if you omitted the VK-40's remote option, the difference in price would be $1000. The CAT is a single-ended design, so combining it with a BAT amp meant using the supplied RCA/XLR adapters.

This setup worked well, noise levels being just a bit higher than with the VK-40. To keep potentially confounding variables constant, I used the Perpetual Technologies combo as the source for both preamps, and Nordost Quattro Fil interconnect (single-ended RCA for the CAT, balanced XLR for the VK-40) to connect each preamp to the power amp (VK-75SE). Each preamp was placed on Aurios MIB component supports and was given an hour's warmup. The lack of continuous level controls meant that levels could not be matched to within the ideal 0.1dB, so I used the "bracketing" method: listening to the VK-40 with the volume set slightly higher and lower than what I had set for the CAT.

Both preamps excelled at communicating the music's dynamics, and both had superb bass definition—not much to choose here. Tube equipment has a reputation for being noisy, and the higher noise level from the CAT/VK-75SE seemed to confirm this; however, the difference in noise levels with the preamp muted vs unmuted was less for this combination than for the VK-40/VK-75SE. (The higher overall noise level for the CAT/VK-75SE combo could reflect greater RFI pickup by the single-ended than by the balanced cables, or a less-than-optimal match between the two components.)

If I told you that one of these preamps had a softer, more forgiving sound, you'd probably say, "That's tubes for you!" You'd be wrong. It was the VK-40 that had the softer sound, the CAT having what seemed like a brighter, more extended top. The CAT had greater top-end clarity; the VK-40 sounded very slightly veiled in comparison. Both preamps provided a soundstage that was wide and deep, but with the CAT, images within the soundstage were a bit cleaner, more precisely delineated.

Finally, to check whether the VK-40 was being handicapped by the use of a single-ended source, I changed its input over to the fully balanced VK-5DSE. This improved the precision of the soundstage imaging, and the sound acquired a greater sense of bass power, but there was still a bit of top-end veiling in comparison to the CAT.—Robert Deutsch