In this hobby, nothing's for nothing. To get that gorgeous midrange, with its harmonic depth and inner detail, tube-amp enthusiasts are willing to give up some things in the bass. Tube folks put up with heat and occasional maintenance—routine or otherwise. To get the ideal middle, fans of single-ended triodes are even willing to shave off considerable dynamic range and settle for ultra-efficient speakers that often have limited response at the frequency extremes. Those who say nothing is lost by preferring tubes are in denial.
The VK-150SE stands tall at the top of Balanced Audio Technology's range. It and its smaller brother, the identical-looking VK-75SE stereo amplifier (or, sans the Special Edition mods, the plain VK-75, footnote 1), are related to BAT's first amplifier design, the VK-60. The company's partners, Victor Khomenko and Steve Bednarski, eventually realized that they'd made enough upgrades to the VK-60 to warrant a new model designation, and in 2000 they discontinued the VK-60. Bednarski explained that while the VK-60 accepted the upgrades with good results, the BATboys felt that, in order to fully realize the full potential of the 6H30 SuperTube, a new platform would be required. Enter the VK-75SE and VK-150SE.
It's been 10 years since Balanced Audio Technology (BAT) introduced their first products: the VK-5 line-stage preamplifier and the VK-60 power amplifier. (I reviewed both in the December 1995 Stereophile, Vol.18 No.12.) The success of these and other BAT products has allowed designer Victor Khomenko (the "VK" of the model designations) and partner Steve Bednarski to quit their day jobs at Hewlett-Packard; they were joined by Geoff Poor as a partner to handle the sales end of the enterprise. BAT's current lineup includes several preamps, phono stages, a CD player, and tube as well as solid-state amplifiers. The top of BAT's preamp range is the VK-51SE, which costs $9000; their top tube power amp is the VK-150SE monoblock ($17,000/pair); if you want their best phono stage, the VK-P10 will set you back $8000.
How important is the use of balanced circuit typology in the design of preamplifiers and power amplifiers? Ask the top audio designers (I didn't, but just play along, okay?) and you'll get a wide variety of opinions. Some reject the balanced approach outright, arguing that it represents a needless duplication of circuit components, and that better results can be achieved if the same attention and resources are devoted to perfecting a single-ended circuit. In his provocatively titled article "Balance: Benefit or Bluff?" (Stereophile, November 1994, p.77), Martin Colloms questioned the advantages of balanced designs, suggesting that while the results may be better in certain respects (eg, noise level), the reproduced sound may suffer in other, perhaps more important ways (eg, rhythm and dynamics).
I hate audio shows. All those manufacturers and retailers desperately demonstrating their products, knowing how impossible it is to do them justice in a hotel room. They might be saying, "It has gold-plated circuit boards and unobtainium binding posts," but all I hear is Please love it, please love it, oh puhleeze . . .
Although I retain a firm hold on the established audio world, and recognize and value all that it has achieved, I feel inexorably driven to make some space in my life for single-ended amplifiers—more especially, those that eschew negative feedback (footnote 1). A classic if costly example of the art is the Cary CAD-805C, which, to my ears, has earned the right to teach audiophiles what negative feedback really sounds like, and what damage it can do to the musical message when poorly handled. This shouldn't be taken as an out-of-hand dismissal of those many great pieces of electronics and amplification that use negative feedback—it is simply an acknowledgment, or even an assertion that negative feedback generates a sound of its own.
It was back in the mid-'70s that David Berning made a name for himself in the Baltimore-Washington area as an avant-garde designer—someone with a truckload of fresh ideas about tubes. At the time, though Audio Research was starting to crank out pretty decent amplifiers, tube design was pretty much reduced to a rehash of the Williamson circuit and the Dynaco mod of the month.
Many tube aficionados hold that amplifiers built with the venerable 300B tube hold the aces when it comes to sonic purity and beauty of harmonic line. Cary Audio Design's Dennis Had succeeded in producing what many believe is the definitive moderately sized single-ended triode (SET) amplifier: the CAD 300SE. This monoblock, powered by classic 300B Western Electric or derivative tubes, could provide 8–10Wpc, requiring the adoption of relatively moderate volume settings and/or sensitive, easy-to-drive loudspeakers. Cary also produced a lower-priced "integrated" stereo chassis, the CAD 300SEI.
In conversation with Cary founder Dennis Had at a recent audio convention breakfast, I learned that he had a long career in electronics, specializing in military/industrial high-power radio-frequency amplification and transmitters. However, his dream was always the re-creation of single-ended tube amplifiers, especially zero-feedback designs.
Lee de Forest filed for a US patent on his "Audion"—the first triode—on October 25, 1906, but never could explain why it worked (footnote 1). It was up to Armstrong and Langmuir, in their pioneering work, to place the hard-vacuum triode on firm scientific ground. When the US entered World War I in April 1917, the Army had to rely on French tubes. Six months later, Western Electric was mass-producing the VT-1 receiving tube and the VT-2 transmitting tube. However, it was only in the decade following World War I, as designers became conversant with the triode amplifier, that many of the crucial elements of tube amplification were nailed down. Technical issues such as coupling two gain stages and selection of optimal coupling impedance were already resolved by the mid-1920s. The triode ruled supreme until the tetrode came along in 1926, followed in 1929 by the pentode from Philips's research laboratories in Holland.
Although I'll be spending most of my time at Stereophile reviewing affordable gear, I will from time to time examine so-called "trickle-down" designs from high-end designers who have made their mark in the upper-price echelons. More and more, such designers are taking what they've learned and applying it to less-expensive products in order to broaden their customer base. Cary Audio Design, for example, of single-ended triode fame, has entered the ring with the SLM-100 pentode monoblocks.
At the last few audio shows, whenever I heard a pair of the big Cary CAD-1610-SEs, I fair licked my chops. The two-tiered monoblock looked positively stunning in black and polished aluminum, exotic tubes bristling from the top "floor" of its two-story edifice. The Cary always induced pelvic tilt in me—you know, when your lizard brain takes over and tube lust is in the air.
According to Cary Audio designer Dennis Had in this amplifier's documentation, "Countless hours were spent designing and voicing the CAD-280SA V12 stereo amplifier...It delivers high performance in a combination of class-A single-ended triode and true balanced push-pull technology."
For anyone who's been around the audiophile block a few times, Conrad-Johnson Design is a brand that needs no introduction. My first acquaintance with Conrad-Johnson was before I began writing for Stereophile (more than two decades agotime sure flies fast when you're having fun!). I was in the market for a new preamp, having become convinced that my Dayton Wright SPS Mk.II was the weak link in my system, and had narrowed my choices to two similarly priced products: a solid-state model made by PS Audio (I'm not sure of the model number), and the tubed Conrad-Johnson PV-2ar. They were carried by different dealers, who allowed me to take their preamps home over the same weekend for a direct comparison. I was impressed by both preamps, and was sure that either would represent an improvement over the Dayton Wright, but in the end decided to go for the PV-2ar. I later traded it in on a dealer's demo unit of another Conrad-Johnson preamp, the PV-5. And, as it turned out, one of my first reviews for Stereophile was of Conrad-Johnson's PV-11 preamp.