Balanced Audio Technology VK-40 preamplifier:
Page 2 The amplification devices are MOSFETs, which many audiophiles think of as the solid-state equivalent of tubes. Khomenko considers this an oversimplification, but agrees that MOSFETs and tubes are similar in one important respect: both need to be driven by a source that has lots of current. He points out that there are many types of MOSFETs, just as there are many types of tubes. The MOSFETs used in the VK-40 were selected for their "soft" linear characteristics.

The VK-40's gain stage is biased at a very high 250mA, which, according to Khomenko, eliminates the need for a buffer and allows a super-short signal path. The gain stage uses high-quality Caddock resistors as its load, the signal passing through only a single paper-in-oil capacitor on its way to the output terminals. The size of the output capacitor can be tripled with the Six-Pack option (included in the review sample), which improves the unit's ability to drive a low-impedance load.

Setting up the VK-40 was a snap—the programmable control functions worked in a highly intuitive manner. The only idiosyncrasy I noted in my initial experience was that pressing Mute or any of the input selector buttons resulted in a distinct pop coming through the speakers. Plugging the preamp into the same or a different AC line as the amplifier and/or the source component had no effect on the pop, nor did bypassing the PS Audio P300 I'd been using. I was prepared to live with it. Then, after I'd used the VK-40 for a couple of weeks, the pop disappeared and did not return.

I discovered another quirky problem when I was well into my serious listening to the VK-40. In checking out its various features, I happened to press the Mono button while playing a recording, and the result was badly distorted sound. Pressing the button again, thus switching back to stereo, restored the sound's clarity. I turned the unit off and on again, but the distortion-producing effect of the Mono function persisted. Something was amiss.

I reported the problem to the BAT people, who were suitably aghast and dispatched a second sample, this one (because of the need for haste) lacking a phono stage. The Mono function of the new sample worked perfectly. In stereo, the two samples sounded quite similar. (The pop was never present with the second sample.)

Some time later, I changed over from the PS Audio Lambda II transport/Perpetual Technologies P-1A/P-3A digital source to the BAT VK-D5SE player, which has XLR outputs. I checked the new VK-40 sample's Mono function again, and it worked fine. I then switched back to the original VK-40 sample and connected the VK-5DSE. With this combination, pressing the Mono button did not result in distorted sound.

Finally, to confirm my earlier observations, I kept the same preamp but changed the source back to the PS/Perpetual combo, and the mono problem was still there. It seems that, whatever the cause of the problem—it was obviously a sample fault, not a problem with the design—it affected only single-ended, not balanced inputs.

Sound
Getting a handle on the VK-40's sound was fairly tricky. Several times, after I thought I had a good sense of the BAT's sound quality, I would change or tweak something in the system and the sound would correspondingly change. While this can be taken as an indication of the VK-40's ability to resolve sonic differences, it meant that I had to repeatedly revise my assessment of the preamp's contribution to the system's sound. Interconnects, speaker cables, component supports—each made a difference.

I played around with a variety of cables, and found the best combination to be Nordost Quattro Fil interconnect between the digital source and the VK-40, Nirvana S-X between the VK-40 and the VK-75/75SE, and Nordost Valhalla speaker cables. (The Valhalla is priced in the if-you-have-to-ask range; at a more sensible price, the Nirvana S-L is a good alternative that falls just short of the last bit of definition and detail, and may even be preferred in systems that can use a bit of extra warmth.) Although the VK-40 is built with resonance control in mind, it nonetheless benefited from the use of suitable component supports. I got good results with Aurios MIBs (see the May 2001 issue) and with Symposium Rollerblocks. Nordost Pulsar Points were not as effective, but they were superior to the standard rubbery feet.

The VK-40 worked well with the Perpetual Technologies P-1A/P-3A as the source, and sounded even better—more lively and better-defined bass—with the BAT VK-D5SE, in what then became a fully balanced system. (The Perpetual Technologies components are single-ended.) The VK-D5SE, which uses the same 6H30 tube as the VK-50SE and the VK-75SE, struck me as an altogether superb product, confirming its reputation as one of the best one-box CD players on the market.

When I look back at the totality of my experience with the VK-40, the word that for me captures its most salient sonic characteristic is "dynamic." In fact, I think of this characteristic as a major part of the BAT "sound": starting with the original VK-5/VK-60 and including the VK-5DSE, VK-75, and VK-75SE, all BAT products have this characteristic.

This tradition was upheld by the VK-40. With the Avantgarde Uno horn hybrids (whose own long suit is dynamics) at the end of the chain, the sound had power, tautness, and the type of quickness that makes listening to music a compelling experience. (I think it's indicative of BAT's sonic priorities that BAT director of marketing Steve Bednarski, director of sales Geoff Poor, and Victor Khomenko himself all own Avantgarde speakers.) Large-scale transients, like the opening chord of the Grieg Piano Concerto (Bolet/Chailly/Radio-Symphonie-Orchester Berlin, London 417 112-2), had startling impact and presence, and there was a strong sense of the music's rhythm and pace. My guess is that this dynamic quality is due to BAT's attention to the power supply, those extra Six-Pack capacitors undoubtedly playing a major role.