Balanced Audio Technology VK-5 preamplifier & VK-60/75 power amplifiers Page 3
Because the BAT VK-5 is line-stage-only and I didn't have a balanced phono stage on hand, I used only digital sources: PS Audio Lambda Transport (a current production sample that has faster access time and sounds better), Sonic Frontiers UltraJitterbug, and either a Sonic Frontiers SFD-2 Mk.II or PS Audio Ultralink Mk.II (both HDCD-equipped) serving as a digital processor. Most of my listening was with the SFD-2 Mk.II. The sound of the SFD-2 Mk.II improved (less upper-end grain) with a Shakti stone placed on the top of the chassis above the transformer. Interconnects, digital links (AES/EBU), and speaker and power cables were latest-generation TARA Labs RSC. I have Original Cable Jackets, grounded to a single wire, on all the power cables, which are plugged into dedicated AC lines. Speakers were a pair of the revised-version Dunlavy Audio Lab SC-IVs (see Vol.17 No.4 and Vol.18 No.3). My listening room is fairly small (14' by 16' by 7.5'), but it's been liberally treated with assorted RoomTunes, CornerTunes, and Tube Traps.
Like most high-end audio equipment, the VK-5 and the VK-60 proved sensitive to setup details and tweaks. I listened to each piece of equipment exactly as delivered, then set about making those small changes that might yield significant improvements. The stock rubber feet were the first to go: Michael Green's AudioPoints (the screw-in type) under both the preamp and the power amp improved the sound's focus.
In the past, I've had mostly negative results using power-line conditioners with amplifiers, finding that they tend to suppress dynamics. While doing the BAT review, I got a chance to try the Chang Lightspeed CLS 9600 ISO, which is claimed to leave the speed and dynamics of high-powered amplifiers unimpaired. It was true: with the VK-60 plugged into the Chang, there was a decrease in noise, an improvement in overall clarity, and no damping of dynamics. I tried the Chang and the Tice Series II Power Block that is normally in my system in various combinations, and eventually settled on having the digital components and the VK-60 plugged into the Chang (which isolates digital from analog components), and the VK-5 directly into the wall. (The VK-5's design includes AC shunt regulation, which might account for the fact that it performed best with "raw" AC.)
A fairly simple tweak I've found useful with preamps is stopping the unused inputs with shorting plugs. I tried this with the VK-5 (BAT supplied me with XLRs that had all three pins connected to each other), but darned if I could hear a difference.
I wanted to compare the effects of balanced vs single-ended connections between the VK-5 and the VK-60. As it turned out, the comparison led to another tweak. The VK-60 was a bit noisy in balanced mode, but no more so than other tube amps that I've had experience with, and not to a bothersome degree. (Substituting the Rowland Model 2 showed that source of the noise was the VK-60, not the VK-5 or something else in the system.) However, changing to the single-ended connection resulted in a fairly serious case of buzz/hum. Lifting the AC ground on the VK-60 (I dismantled the plug of the TARA Labs power cord and disconnected the ground wire) got rid of most of this noise. I repeated my listening to the amp in the balanced mode with the AC ground lifted and—whaddaya know—the sound was a bit cleaner, with depth more precisely layered. To my surprise, I couldn't hear, or detect with a voltmeter at the amplifier terminals, any change in noise level when the ground was lifted with the amp in the balanced mode. Anyway, for the rest of my listening, the AC ground on the VK-60 stayed disconnected. (Try this tweak at your own risk; without a separate AC ground, if there's a malfunction that results in AC appearing on the chassis, you could end up being the ground path, a potentially painful—even lethal—experience. But then, no one ever said that being an audiophile was going to be easy.)
BAT's product literature stresses the importance of reliable operation: parts have been selected from sources known for their reliability, and all components are being operated well below their maximum ratings. The VK-5 functioned flawlessly throughout the review period, except for a bit of noise that developed in one channel—which cleared up when I replaced one of the tubes. However, the first pair of VK-60s, part of an early production run, had more than their share of difficulties. Both were fine when delivered, and I proceeded to use just one of them, in the stereo configuration, planning to later change over to the bridged monoblock setup. Before I could get around to doing that, however, the amp I was using started to blow its AC line fuse and trip the line's circuit breaker. Something was clearly amiss.
I shipped the amp back to BAT, and they sent me a replacement. The new amp had a revised chassis (more ventilation), a modified circuit-board layout, and a blue (rather than green) LED indicator. I thought the new amp actually sounded slightly better than the old one—for a few weeks, at least—and then its power transformer developed a noticeable mechanical buzz. BAT's Steve Bednarski admitted that they were having a problem with the transformers; the transformer in the amplifier that I shipped back to them turned out to have an internal short.
Plitron, the transformers' manufacturer, is only a 20-minute drive from where I live; they picked up the amplifier and returned it a few days later, having replaced the buzzing transformer with one that was much quieter. However, while the amplifier was away being repaired, the other amp developed an electrical hum. I was sent a new set of input tubes (the mil-spec 6H8Cs that are currently being fitted); substituting these fixed the problem. For the rest of the review period, both amplifiers were completely reliable, with no buzzes, snaps, crackles, or pops.