March 2000

Art Audio Jota Amplifier

by Srajan Ebaen

KR 52BX output tube

My September 1999 review of the Art Audio Jota amplifier generated enough reader e-mail to suggest two things: an overt disbelief at many of the statements made, and an underlying and implicit desire that passionately wanted to believe a single-ended-triode amplifier did exist that could do the things I described, but -- even though nobody blatantly accused me -- I was most likely deluded or worse, full of shit. And I couldn’t really blame such feelings. At one time, I did harbor very similar preconceptions about SETs that caused me to react condescendingly to any claims to the contrary.

When I realized that a second version of the Jota had been introduced, I jumped at the opportunity to revisit this amplifier and shed further light on its capabilities. Replacing the standard VV32B with the new KR 52BX tube, the amp’s power output has been increased to 25-30Wpc, a 50% increase over the version I had reviewed. The parallel raise of available current promised bass control and drive for even those loudspeaker loads that might still elude the potent 32B version. Since none of my resident speakers had caused the regular Jota a hiccup even in the absence of a preamp-induced gain boost, I suspected that I might have to look for more dastardly loads. Coasting a big-block engine down Main Street in first gear leaves you in the dark as to how it might behave with a horse trailer in tow. In such relaxed mode, you might actually prefer a more nimble, smaller-engine car. I would have to go and make an appointment with mule kickers like the big Hales Transcendence monsters. But before that, a showdown between both power tubes was planned in my own corral. Brawn versus finesse?

To follow up, a second Jota arrived a few weeks later. Would it merely share or actually steal the limelight from the original amp that I had subsequently purchased as my new reference? The optioned Jota differs not merely in the output tubes but sports larger output transformers, power supplies and voltage regulators. However, these enhancements are internal and not apparent to the eye. What is apparent is an increase in price -- from $7395 to $8695. Other than the upgraded Jota, I’m aware of only two amplifiers that use the KR 52BX direct-heated triodes. Gordon Rankin offers his 32Wpc interstage-transformer-coupled Wavelength Audio Kir and Kir Elite monoblocks at a retail of $10,000 to $15,000 per pair depending on trim. Precluding easy audition because of factory-direct only distribution, the Welborne Labs Apollo II monos are available as kit or assembled, spec’d at 22 watts each and sell fully assembled for $4650 per pair.

Riccardo Kron’s 52BX tubes are very stout and weighty glass bottles. They feature KR’s exclusive 32-cathode construction and 10 to the -3 Torr high vacuum and come with a one-year warranty. Filament voltage and amperage are 5V and 2A respectively. Even though spec’d for plate voltages up to 600 volts with an attainable output of 40 watts, a more realistic window for minimal distortion and noise plus superior longevity is 450-525 volts. The concomitant minor reduction in peak output is a smaller price to pay than yearly re-tubing. Max cathode current is 160mA and plate dissipation 100W, with peak currents of 5 amperes. That’s ten times the current delivery of the venerable Western Electric 300B. The dynamics of these tubes should be positively explosive. Raw drive could promise to be of the anything-goes variety -- within reason of course. We’re still talking single-ended-triode designs, but of decidedly modern iteration. I was ready whenever the tubes were.

Behind the iron mask

Joe Fratus of Art Audio had warned to be patient. I’m not, but I was. Good thing too. At first, my resident 32Bs sounded distinctly sweeter, more relaxed and puzzlingly, with seemingly more gain. If I didn’t know better, I would have pulled the bigger tubes out of the socket and concluded right then and there that this was yet another exercise in less-is-more philosophy. Or, as the battle cry of the micro-power crowd of 2A3 aficionados has it, power corrupts. Does it?

I had to leave on business for a week. While I usually wouldn’t be comfortable doing this with tube amps I don’t own, I left the freshly arrived Jota powered up and set the CD on endless loop. When I returned eight days later, neither the amp nor its tubes were any warmer than when I had left. My Bel Canto DAC1 had arrived in the meantime. It was inserted into the system for a second week of nonstop break-in while I had to split town again. Fourteen days or 336 hours of nonstop action later, I was ready to prick up my ears, turn into analytical Spock and take notes.

With my resident Triangle Lyrr XS and Soliloquy 6.3 speakers, connected via the phenomenal Analysis Plus Oval 9 copper cables and matching Oval-In interconnects, fed from the very secret and sophisticated Sound Application CF-X RF filter and power-line conditioner, the 32B Jota gave me a distinctly superior sense of intimacy and magic. In Sam’s Telling words, there simply was more there there. The 52BX tubes sounded removed and distanced by comparison. The very tangible presence and immediacy of the 32Bs was significantly diminished, as though emotionally I had just taken a few steps backwards. The best simile to describe this effect is looking through an expensive Zeiss lens and missing perfect focus by perhaps just one click. Nothing is blurry or seemingly out of whack, but moving the lens further by just one more notch alerts you without a doubt that now things are spot-on. This impression was universal no matter what the music. I suspect that the 32Bs are more refined and superior in their ability to track minuscule microdynamic fluctuations, thereby enhancing their uncanny "live" quality.

What the 52BX tubes produced at elevated volume levels was a particular "Technicolor" effect of meatiness and robustness. It was very impressive but didn’t go under my skin. The 32Bs were more relaxed, didn’t miss any heft and communicated emotion like an exotic dancer exudes heated sensuality and captures your attention. Trying to delve into what exactly set both presentations apart, a suitable example stared at me from arm’s length. Interlock your fingers with deliberate pressure so that all the minimal air spaces between your fingers get eliminated and your clasp feels rock-solid. Then relax, withdraw volition and notice the sense of space between your fingers even though they are still touching. Without producing any actual air by relaxing, the feeling -- or in musical terms, the gestalt of the presentation -- is noticeably different. To my ears, this relaxation and appearance of space is preferable and more natural. Whatever impact on bass slam, extension or dynamics I had assumed the additional power would provide, it proved entirely imaginary. I can’t call it wishful thinking since the standard Jota is utterly beyond criticism, but it screwed up my preconceptions nonetheless.

To those like me who own speakers of average sensitivity, stable impedance behavior and modestly sized woofers, I would have to declare the less expensive, less powerful 32B tubes and the standard Jota the clear victor. Save yourself the expense; stay with 20Wpc and relish in the unmistakable magic that made me purchase this marvel.

Power does corrupt then?

For me to declare categorically the 52BX version inferior based on my own experiences so far would be like claiming that four-cylinder engines are better than six-cylinder versions. It depends on what you plan to use them for. Certain jobs absolutely necessitate more horsepower. Why complain like a duffer that you’ll use more gas or, as in this case, that the sound might be slightly less sweet? Better some sugar than none at all, ja? Do we care if the 52BXs can move the load in that uniquely single-ended fashion?

Don’t fence me in

To investigate how the increase in power and drive would translate into a load that, unlike my resident speakers, truly required it, I used a pair of Hales Design Group Transcendence Eight speaker. As a nominal 4-ohm load that drops significantly lower in the midrange, they are not the type of speaker one usually mates to a single-ended amplifier. Also, their dual 10" metal-cone woofers require substantial current for good control, which generally isn’t available from a single output tube. While the 32B Jota handled this challenge without obvious signs of distress, a reduction of width and depth in the soundstage and a loose and somewhat boomy bass made it transparent that the amp was at the very edge of its power band. The 52BX version not only corrected these shortcomings but ran head to head with a highly regarded solid-state amp of more than 10 times the power into the same load. This Jota excelled in all the areas one would expect -- soundstaging, immediacy, palpability, dynamics and speed -- while being bettered in bass slam and extension by the transistor amp.

Mission accomplished

My respect for the Jota had drastically increased despite my obliviousness to such a possibility or my contrary conclusions with the 52BX tubes in my personal system. In light of popular SET notions, I find it vital to stress that this 52BX-outfitted Art Audio amplifier -- without support from a suitable preamp but outfitted with an optional GoldPoint attenuator -- had no trouble whatsoever controlling the challenging load of the Hales Transcendence Eights. This seems shocking to say the least, but it is entirely in line with my earlier review of the unusual drive of the 32B version. What the advent of the 52BX tube and its employment in the Jota has done is move the fence post outward by a considerable margin. Its superior drive with counter-intuitive, "solid-state-only" loudspeaker loads is clear vindication and justification for Art Audio’s insistence that due to an increasing demand for the single-ended, zero-feedback triode experience, the motto can no longer be power to the people but must become more power for more people.

...Srajan Ebaen
srajan@soundstage.com

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