Conrad-Johnson ART Preamplifier
"We realized that Conrad-Johnson is coming up on its 20th anniversary," he said. "So we thought we might produce something special to celebrate. This is a version of the preamplifier we use in our listening room at the factory---we never even thought about producing it because it would be god-awful expensive. But it really is our last thought on what a preamp should be, so we figured we'd produce a limited edition, say 250 total, as a way of commemorating our 20 years in the business."
Looking at the blueprint, all I could think of was Frank Lloyd Wright's Falling Water: off to the right-hand side of each chassis was a cantilevered series of five black metal plates surrounding five 6922 dual triodes, while the faceplates, such as they were, were elegantly uncluttered by controls. The design seemed to look back to Art Deco while remaining as contemporary as possible.
"What are you going to call it?" I asked.
"Anniversary Reference Triode," Lew said. "ART, as in state-of-the-. And it will cost $15,000."
In art, economy is always beauty
Less than eight weeks later, I got my first glimpse of a production prototype at HI-FI '96, and it was just as timelessly elegant in the aluminum. The two champagne-and-black chassis---one per channel---were both simple, but one possessed two rows of input-indicating LEDs flanking two circular displays that gave the levels for each channel. The other had a single circular window concealing the receiver for the remote, a flat rocker panel that controlled volume, and four discreet buttons: one for choosing source, one for engaging the external processor loops, a mute switch, and on/off. All were replicated on the remote, which also allowed for changes in channel balance.
There were five single-ended RCA line-level inputs, two processor loops, and two main outputs per chassis. Each chassis had its own power cord permanently attached, as is C-J's custom. There was also a data interlink that connected the two chassis, allowing the microprocessor housed in the right channel to relay commands to the left-channel circuitry.
When I received the preamp in Santa Fe, I found that its outer simplicity is mirrored within. In principle, it's a single triode circuit. In order to keep output impedance low, conventional tube preamps usually mate a voltage gain stage to a buffer stage (usually a cathode follower; see the sidebar interview with Lew Johnson for a discussion of this). In the ART, Bill Conrad and Lew Johnson neatly sidestep the need for a buffer, fabricating the equivalent of a single high-transconductance triode by linking five dual-triode 6922s in parallel. Running 10 triode sections in this manner lowers the output impedance of the ART to about 500 ohms---at the high end of the range, but within the range nonetheless, of tube preamps utilizing cathode followers.
An additional benefit that accrues from running the triodes in parallel is an overall lowering of the thermal noise floor: each time you double the number of parallel devices you gain a theoretical 3dB in noise reduction. Among the other things Messrs. Conrad and Johnson left out of the ART was feedback: There is no global (loop) feedback, and no local feedback either.
The ART's control side involves a microprocessor whose only function is to switch relays on and off. When changing volume or balance, when choosing an input, or when muting, you can hear the relays switching inside the unit. (I found this somehow reassuring.) The microprocessor runs off a transformer separate from the audio circuitry.ÊEverything about the ART is solid and seems in keeping with its considerable price. Construction quality is superb---when I opened the unit, the quality of the individual components was obvious, as is only fitting. All of the capacitors---even in the power supplies---were polystyrene types, and the resistors were Vishays. All chassis work is substantial---overly so, if anything. Even the remote is carved out of a solid block of aluminum. No one who buys an ART is going to feel as though Conrad-Johnson skimped on anything.