Balanced Audio Technology VK-5 preamplifier & VK-60/75 power amplifiers The VK-5i, April 1997
If Sue Grafton, author of the Kinsey Millhone series of mysteries (I've just finished "M" is for Malice) were writing this review, the title would have to be "I" is for Improved. But there's no mystery here: the folks at Balanced Audio Technology (BAT) have simply taken what was already an excellent design and applied some refinements to it while incorporating a highly convenient remote control. Case closed; Kinsey can go back to her peanut-butter-and-pickle sandwiches, and we can continue to wonder what's going to happen in her relationship with the enigmatic Dietz.
There's no denying that remote control, long established in video and mid-fi, is becoming a hot feature in high-end audio. An interesting White Paper on the BAT website describes the various ways of implementing remote control, including the use of digital IC gain attenuators and MDACs (Multiplying Digital-to-Analog Converters), as well as simple motor-driven potentiometers. All were deemed undesirable for sonic reasons, or because of problems in reliability.
The solution developed by BAT designer Victor Khomenko and his partner Steve Bednarski was to retain the shunt volume control topology of the VK-5, with the same Vishay resistors used as series-pass elements, but to substitute a microprocessor-controlled, discrete, film-resistor network for the VK-5's Noble potentiometer. Four individual circuit boards are used, two per channel in a balanced configuration. The microprocessor then switches-in different sets of resistors to shunt part of the signal to ground, the choice of resistors depending on the desired volume level, which is available from the remote control. Left/right trim continues to be controlled by potentiometers, and is not remote-controllable.
As well as incorporating this new method of implementing the shunt volume control, the "i" revision features three other significant changes. Probably the most important is an auto-balance circuit that stabilizes the positive and negative legs of the circuit, providing independence from variations in tube performance or aging (at least within certain limits). Balanced circuits must have each leg of the circuit functioning the same way; any differences introduced by the circuit result in nonlinearities.
The BAT design gets around this potential problem. The second change in the "i" version is a passive component upgrade: the resistors in the gain stage are now metal-film types. Finally, the AC shunt regulation has been changed to an auto-bias circuit, eliminating an adjustment that was previously required when changing tubes. One feature missing from the VK-5i is the VK-5's "Sleep" mode. According to Steve Bednarski, continued testing found this feature to be of no real benefit, so they decided to eliminate it.
The original VK-5 has been one of my favorite preamps (see my review in the December 1995 Stereophile, Vol.18 No.12, p.136), and is listed in Class A of "Recommended Components." I've been using the review sample of the VK-5—along with some other high-end preamplifiers—since the review, so I was able to compare it directly with a sample of the new VK-5i.
Associated equipment included Dunlavy SC-IV loudspeakers, Sonic Frontiers SFD-2 Mk.II processor, and Audio Research D130 or Sonic Frontiers Power 2 amplifiers; balanced connections (TARA Labs Decade) were used throughout.
Given what I knew of the sound quality available from the VK-5, I expected any differences to be relatively minor.
Boy, was I wrong! Every aspect of performance—transparency, detail, bass extension/quality, air, soundstaging, you name it—was better, making the older unit sound veiled, closed-in, and mushy by comparison. The slight sibilant emphasis that I had described as a characteristic of the VK-5 was now essentially gone (except for Varèse Sarabande's show-music albums, and they're recorded that way). Bass was tighter, more extended, and apparently better integrated with the rest of the spectrum. The midrange magic of the original VK-5 was present in full force, voices retaining the "rounded" quality that seems to be the particular provenance of tube designs, but with even better focus.
Noise level had not really been a problem with the VK-5, but the VK-5i, at matched levels, was significantly quieter. A possibly related difference was the emergence of detail that had been previously obscured. With the VK-5i in the system, the analog tape pre-echo at the beginning of each track of Center Stage (Wilson Audio WCD-8824) was very clearly audible (and, frankly, annoying). With the VK-5, it was there, but I had to make more of an effort to hear it.
The VK-5i's remote control is very well-thought-out, and has some unique features. Volume is adjustable in 0.5dB increments within the normal range of listening levels, which gives the feeling of a continuous control; I found the rate of change just right. There's provision for storing five specific levels (eg, background, normal listening, impress-your-audiophile-friends, etc.). In addition to Mute, there's a Fade button, which ramps volume down to zero (and back when it's depressed again) in a gradual manner. Very refined.
There's also a Unity Gain position, for use in home-theater systems where volume is controlled by a surround processor/preamp. To activate Unity Gain, the button has to be pressed twice, making inadvertent activation less likely. As the manual warns, you do not want to activate Unity Gain unless gain is reduced elsewhere in the signal path, so this option should be used with great care.
By requiring the double key-press, BAT may have succeeded in make the Unity Gain feature idiot-proof, but they haven't quite succeeded in making it reviewer-proof. You guessed it: I pressed Unity Gain twice while playing music, and was promptly blasted out of my listening chair. Fortunately this was during a relatively quiet passage, so there was no damage to the speakers, but since Unity Gain in my setup represents about 15dB above a fairly loud listening level, I figured I'd had a close call. BAT might consider making Unity Gain even more difficult to access.
Of course, volume can also be set on the preamp itself, via a large knob of the freewheeling variety. The numerical display, big enough to be legible from across the room, can be turned off from the remote. Some people have suggested that an illuminated display has some effect on the sound; I listened to the VK-5i with the display on and off and found the effect to be elusive, the sound being perhaps slightly cleaner with the display off. In any case, I find illuminated displays generally distracting, so I'd be inclined to turn it off. (Pressing the Volume Up or Down buttons restores the display.)
The good news for VK-5 owners is that their units are fully upgradeable, some of the changes having already been made before the formal "i" designation. The factory update of the VK-5 to remote-controlled VK-5i varies from $500 to $750, depending on the age of the unit. At a level of sonic performance where improvements tend to be very costly, this is undoubtedly a bargain. The price of the VK-5i without remote—but incorporating all other improvements—remains $4000, remote control adding $500 to the price.
The current VK-5i is a tour de force of technical sophistication, providing sound quality of the highest order and a user-friendly interface. I love it!—Robert Deutsch