September 1999 Art Audio Jota Amplifier by Srajan Ebaen

"...a major-league statement piece to be considered in the context of  the best currently available."

Review at a Glance Sound "Speed, dynamics and transparency"; emotionally gripping and supremely resolving; does string quartet as well as slamming dance-hall music. Features Auto-bias, zero-feedback single-ended design with high current delivery; honest 20 watts output; can be ordered with or without volume control; dazzling looks. Use Transformer’s single output tap is factory-matched to desired loudspeaker impedance; will work with speakers of more normal sensitivities and relatively benign load behaviors. Value Stunning sound and broader applicability than most SET amps but without a stratospheric price.

Art Audio’s Rhode Island importer, principal owner and contributing designer Joe Fratus is adamant about the importance and quality of his output transformers. Numerous fellow manufacturers -- most of them undoubtedly direct competitors -- have repeatedly pestered him for access to his proprietary design. Fratus always and without hesitation declines, unswayed by the inherent flattery or harder-to-resist financial compensation that could certainly prove very lucrative to a small niche maker of expensive SE amps.

What’s so important about output transformers? "Bandwidth," says Joe, "bandwidth and dynamics." In order to ensure big-league performance from his on-the-face-of-it under-endowed 20Wpc Jota, Art Audio’s output transformers are slow custom hand jobs -- hand wound, that is, precisely and painstakingly one at a time by a solitary Old World craftsman. Fratus made our anonymous gentleman sign non-disclosure and non-compete agreements to keep the secret safe from prying audio spies. All I’m allowed to disclose is that it’s an enhanced split-core transformer not usually associated with single-ended designs.

I’ve been privy to prototype-amplifier-voicing sessions comparing transformers of identical electrical specs. They nonetheless sounded nothing alike, affected by different winding geometries and other variables that frankly went over my head. All the old-timers readily admitted that output-transformer design is only partially science. The other and greater part is art, a kind of voodoo crystallized and eventually glorified through countless years of experimentation, experience and the occasional bout of good fortune -- or dumb luck. When a design for a particular application becomes finalized and passes muster in critical listening evaluations, there are very good reasons to keep one’s cards close to the chest. A future project for Art Audio, an EL34-based SE amp under $4000 retail, is currently on the drawing board. Even for this lower-priced brother of the Diavolo, Jota, Symphony and Carissa monoblocks, Fratus and British chief designer Tom Willis will continue to employ the expensive services of their master winder. "It’s more than half of what makes us sound the way we do," Fratus explains.

Power

Let’s briefly back up to my calling a 20Wpc single-ended amp under-endowed. Unless you refer to a 211- or 845- or heavily goosed KR 52BX-based amp, 20 honest watts from a 300B amplifier -- measured +/- 0.5dB from 20-20K at full output -- are monstrous. I know of other makes where an equivalent per-channel rating only amounts to 7-8 watts at 20Hz, performing in a rather different-from-advertised league when reality hits. The Jota’ s smaller brother, the Diavolo, outputs 13 real watts from the same KR32B tube that is a 300B derivative with a major wrinkle -- up to three amperes of current versus the 0.6 amperes delivery of the venerable Western Electric. This is a very significant increase of current delivery for what essentially is a pure voltage device.

In their quest for yet broader appeal, Art Audio’s designers wanted to increase the Diavolo’s maximum output by 50%, which for a 300B-type amp is already hefty. This would make it compatible with an even broader range of popular speakers, spreading the euphoria-inducing 300B virus amongst those still married to that most American of all beliefs -- that bigger is better. Seriously though, unless your speakers are deficient in the sensitivity department -- in other words, brawny he-man jobs sucking up juice like a V-10 -- most home listening takes place at output levels well below 10 watts. A robust 20Wpc amplifier with graceful overload and quick recovery behavior should be more than sufficient (and anyway, a 200Wpc amplifier will only play 10dB louder).

To this end, the Diavolo’s single GZ37 rectifier circuit was deemed insufficient to produce truly linear low bass at the Jota’s envisioned maximum power output. Faced with the option to add a second pair of GZ37s, Tom Willis produced a proprietary solid-state circuit instead that now precedes the tube rectifier stage. This hybrid marries the sonics of tube rectification with the low-end control of solid state. Additionally, transformers and voltage regulators were beefed up and power-supply capacitance substantially increased. The bias current was raised to 150 milli-amperes and plate voltage to 450 volts.

However, Fratus is quite adamant that any owner of his amps deserves tubes that won’t give up their ghost after a brief and tempestuous honeymoon due to too much -- ahem, hot action. Injudiciously raising a tube’s grid voltage simply to rev up its output will drastically shorten the tube’s life expectancy. Fratus performed his own long-term tests to determine precisely where within the vendor’s specified bias window the Jota was to be calibrated. Also, KR Enterprise makes the 32B tube available with a blue-colored true thermal glass that reduces heat build-up by a stunning 50% -- that’s how the review amp was outfitted, and the tubes, even after 24 hours of continued use, remained unusually cool. To further enhance longevity, the Jota features a labor-intensive sub assembly suspended by sorbothane bushings that mechanically isolate the output tube ceramic sockets from the main chassis. When you insert the power tubes, don’t let the concomitant give scare you. The tube sockets are suspended just as with a turntable. As an aside, Fratus has 2.5-year-old units in the field running on their original sets of output tubes.

Owners and other liabilities

While we’re on the subject of tube rolling, let it be stated that the Jota was specifically voiced in concert with the KR32B. Unlike other 300B amplifiers that are designed around the Western Electric or Svetlana versions, the Jota's power supply and voltage regulators are geared towards the much higher current capabilities of the Czech valves. Hence substituting American or Russian or Chinese Valve Art versions will affect sonics but not cause any screen or grid resistor failures as could the reverse -- plugging a KR32B into a standard 300B amp. What will happen of course is a short-changed life expectancy for non-KR 300Bs -- the Jota drives them harder than they are spec’d for. If, on the other hand, some intrepid but ill-advised thermionic huckster were to gung-ho it with KR Enterprise’s own KR52BX in the Jota, the amp’s Motorola-processor-controlled, externally heat-sinked voltage regulators would slowly saturate and then shut down the output tubes. With its outputs muted but the driver and rectifier tubes still glowing brightly, the Jota would alert its capricious owner that Art Audio’s designers wisely anticipated such foolishness and protected the amplifier from its -- potentially dangerous -- owner.

The KRs of course aren’t the only valves in the Jota. Twin 6922s/6DJ8s power the gain stage while two additional 12BH7s provide further preamplification and act as cathode followers. The choke-filtered power supply is a dual-pi-filter solid-state design that uses two Mullard CV378/GZ37 as rectifiers, which double as soft start gates for the output tubes. The Jota features automatic bias and accurately tracks tube response through the aging cycle without needing readjustments as regular self-bias schemes require. Absolutely no feedback is employed, and the circuitry is true dual mono in a single chassis, with interior componentry and exterior socketry of the highest pedigree.

The Jota weighs in at 70 pounds, something its compact dimensions of 18.5"W x 10"H x 14"D don’t forewarn about. A high input sensitivity of 400mV and input impedance of 180/380k ohms mean it’s easily driven even from a digital front end’s output. The optional chassis-mounted potentiometer is evidence that such a possible single-source-direct application is actively encouraged. For consumers with preamp-based systems -- probably most of you - the Jota is shipped with the input impedance set to 180k ohms. This eliminates any possibility of potential interface problems with noisier preamplifiers. The review unit, to be used direct as single-source "integrated," was set at 380k.

A word on output taps. Art Audio’s own listening convinced the designers that a given output transformer’s maximum performance is reliant upon employing all of its windings to drive the speaker. Hence the Jota eschews multiple taps. Rather, Art Audio sets up the output transformer’s impedance based on the customer’s speakers. For example, quite a few Diavolos and a Jota in the field are driving old 15-ohm Quad 57s. They were accordingly custom outfitted with matching 15-ohm output transformers. A number of dynamic speakers that might appear counter-intuitive, such as Aerial 10t, Audio Physics Virgo and Avanti II, and the EgglestonWorks Andra, are known to be simpatico. On the subject of electrostats, traditionally said to be impossible loads for SET amps, the Jota has been routinely used with various models, including those from Soundlab, Quad, InnerSound and, in smaller rooms, MartinLogan.

Outerwear

What the Jota -- pronounced "hoe-ta" -- has in common with Gayle Sanders’ famous curvilinear speakers is stunning industrial design. This piece is a magnificent gleaming two-tone affair of high-luster polished, non-magnetic stainless steel and gold-plated name decal and tranny caps tastefully contrasted against satin transformer black. Softly rounded corners invite caresses if you don’t mind fingerprints, and except for the gold-plated cap nuts, there’s zero evidence of fixtures or mounting hardware in sight. The optional volume control, a substantial gold-plated and contoured cylinder, is centrally mounted to the front. Even the font created for the Art Audio logo exudes elegance. Two raised pilot lights on either side of the top-mounted nameplate confirm power status. From a distance, the emissions of these LEDs reflect from inside their miniature glass bubbles onto the stainless steel mirror. Their pale lavender is a perfect and tasty complement to the tubes’ orange glow. This Jota is one seriously addictive and chromilicious class act!

With the rear-mounted power switch engaged and the volume control opened to the stops, I park my ear next to the 93dB efficient Triangle Lyrr XS’s tweeter. Only the very faintest of white noise whispers emerges. Following up with a Van Gogh smack onto the transformer covers, there is no hum whatsoever, none. Ditto for mechanical noise from the tubes. Without signal, the Jota is as dead as a doornail.

For the record: my listening room is 18'W x 30'L x 15'H with plenty of adjoining open space. The CD player’s output would be a standard 2 volts. If the Jota could drive average speakers to satisfying output levels in such a space without the assistance of additional preamp gain (usually about 18dB), whatever preconceptions you might have about real-world power requirements can be safely set aside, forgotten and buried. In audio, less is usually more.

Down and dirty -- the short version

To be blunt, the Jota makes everything else I’ve listened to of late -- TacT Millenium excepted -- sound flat and less than fully inspired. In my eight years in high-end audio, the Jota has provided me with the very best sound I’ve ever had in my system, the revolutionary Millenium following the parade a bit further downhill. That in itself is worthy of note, to compare, in the same breath, so decidedly yesteryear a technology as triode valves with an entirely novel execution of digital-domain amplification via pulse-code to pulse-width modulation requiring massive, state-of-the-art computational powers. My preference for the older technology might make me an antediluvian fossil but, like the recent upsurge of alligators in Florida, we’ve been around for ages, we’re multiplying and we’re here to stay.

The Jota is the complete antithesis of what popular lore suggests single-ended 300B tube amps to be: euphonic, midrange-only amps. Or, as some would put it more plainly, toys unfit for a real man’s job. The Jota, while looking as though it might be nothing but a spit-shined boulevard cruiser, will tear a hole into such preconceptions the size of Mike Tyson’s fist. It’s as full-range and muscular as any solid-state bruiser far in excess of its own power rating. But more, it’s a dynamically turbo-charged speed demon, tracking the output swings of minute to massive crescendos with a precision that hits you as possible only afterwards. Translation: raw, naked, immediate.

Thus when an instrumental soloist emphasizes certain notes in a passage, the notes literally jump out at you while those following recede rapidly, creating movement and color in the artist’s delivery that distinguishes the real from the piped. That’s microdynamics. When an intermediate orchestral climax approaches, you can literally feel the forces beginning to gather much earlier. When they finally erupt, they do so more violently than before, louder, more massively, while the pianissimos remain intelligible much further down into the noise floor before decay trails fade into oblivion. That’s macrodynamics. Both small- and large-scale dynamics were real ear-openers on all speakers used, but especially explosive on the lightning-fast Triangle Lyrr XSes.

The longer version -- up and up and freshly showered

The Art Audio Jota is not a golden-colored lens through which things are editorialized to create images of a bygone area when a certain patina rendered black-and-white prints more yellowish, softening contrasts and prettifying even a bleak downtown ghetto shot with a certain romantic aura. Movie directors nowadays are pursuing a similar effect when they go soft-focus during a close up on the female lead. Those listeners "into" the romanticizing effect of traditionally voiced low-power SETs won’t find the Jota their cup of tea. This is well enough. There already are many amplifiers available that cater to that particular sonic school. The Jota does maintain -- and elaborate on -- the traditional tube virtues of superior, finely layered soundstaging of epic proportions, but it emphatically does not shelf off the upper treble nor round off, bloat, restrict or otherwise handicap the lower bass.

If you add up the qualities already mentioned -- speed, dynamics and transparency -- you would be right assuming that the Jota also is a resolution machine. It very much is, but not in the same way the Tact Millenium struck me. I’m inclined to call the Millenium a veritable resolution monster because resolution presented itself as the amp’s overriding attribute; the unraveling and laying bare of unheard details in recordings I knew best -- as though it was an electron microscope. But whenever a characteristic attracts what eventually seems like undue attention, it’s fair to suspect a slight misbalance as its cause -- something stands out over against everything else. The Jota’s detail retrieval is outstanding, but not in a "I’m here, so pay attention" kind of way.

To give you an example: I played classical clarinet for more than 15 years. The length, slope, fiber density and thickness of a reed all contribute to not just the sound but also influence playing technique. Listening through the Jota, I spontaneously had a very clear image of a sax player’s reed and how I would file it down differently. Rather than becoming an important event to ponder, dissect and analyze, this simply became a part of the listening experience, breaking down yet another barrier between me and the musician. The same held true for the element of air around performers. The Jota’s presentation includes cubits of air for sure -- you’d expect that after what I told you about top-end extension -- but it doesn’t stand out, just as tasting a complex, well-blended soup doesn’t give away its ingredients. And that’s really the crux of the matter: when a component is right, something in you responds but you can’t necessarily put your finger on it. It’s how you know that a string quartet in the distance is for real -- sitting there inside a restaurant -- and not some audiophile system going off. But obviously a review seems flawed when you merely read "it felt right end of story period." You want to know why it sounded right.

Here’s my answer for you. As a musician, I respond foremost to musical energy, the very element that is born from the performer’s passion and inspiration. It miraculously survives both the recording process and the subsequent mathematical, electrical and mechanical transfer back into sound. It then can trigger and stimulate the tuned-in listener. But this is something very fragile and thus easily stifled and killed. Most components, for whatever reason, interfere with that emotional communion between the music and me. Of course, besides suitable components, this also requires great music well performed, much more so than audiophile recording quality. Now, anyone who’s athletic or works out regularly knows the sensation of being on, fully functioning, alert, vital, vibrant, when energy is coursing freely through the body, unimpeded by emotional, mental or physical blocks. It’s the polar opposite of sleepy, groggy or achy. Listening to the Jota had that kind of kinesthetic effect, as though the music was supremely sharp, in focus, crystal clear, playing fast ball with my psyche, all cobwebs removed. But there was no effort involved as you may read into the ball-playing bit. It happened spontaneously, as easily as the "aaahhh" response after seeing a tremendous sunset. And yes, it does require to bring oneself to the event in an alert state.

One cannot expect an amp, any amp -- or speaker, cable or any component for that matter -- to be solely responsible for one’s musical turn-on. Just like with good sex, it requires two. That out of the way, the Jota did its job better than any other amp I’ve heard, conveying an unfiltered sense of the music’s life. If you insist on adjectives, the foremost words are immediacy and energy. It’s a striptease that reveals music in her naked, most intimate glory hitherto never glimpsed. This makes for absolutely thrilling encounters, the colorful language here fully deliberate. The Triangle Lyrr XS speakers I recently reviewed have a very similar set of attributes, designed, it seems to me, like the Jota by dyed-in-the-wool music enthusiasts who routinely attend live performances as a matter of course. It should come as no surprise that this combination proved extremely fortuitous, a match made in heaven -- Europe to be more precise -- gifting me with that unmistakable sense of I’m there as opposed to they are here or they are there. This is not an attempt to sound like Gertrude Stein but an accurate description of the various perspectives different equipment creates on the recording venue and its performers. The Jota seems to transport you into the original space rather than teleporting it into your living room -- if that makes any sense to you.

That’s what 300B tubes are supposed to do well, you say? Harmonic purity coupled to an absolutely liquid, riveting directness? True, but what they’re not supposed to do is killer bass and dynamics, or have an utter disregard for the kind of music you feed them. The Jota thrives on Cassandra Wilson, grooves to the Neville Brothers, slams to trip-hop, swells with Holst’s "Mars" movement in The Planets, hypnotizes to trance music and probably does rap and country equally well if I was more open-minded towards those genres. This in itself ought to be a revelation to those who believed otherwise based on listening to less accomplished SE designs.

The 300B magic -- and magic it is! - can now be tapped and enjoyed by so many more who own regular, not special-application, speakers of medium efficiencies. The Art Audio Jota’s asking price, while not insubstantial, makes its effect seem downright reasonable. Its appearance being in an altogether different class should prove yet further inducement. Proper SE etiquette still demands a narrow impedance window, hence a nominal 4-ohm speaker with an impedance swing from 3.5 to 6 ohms is suitable, while a so-called 8-ohm speaker that swings from 4 ohms to 26 ohms is not. This opens untold doors previously shut or assumed shut, through which the single-ended, zero feedback 300B experience can now be approached. I used a variety of speakers throughout the review, and the Jota proved supremely adept and assured with all of them, never once running out of steam or gain, its volume control opened past 12 o’clock only with a few audiophile CDs recorded at extremely low levels. That’s without preamp in a large space, remember? The Gallos were even faster than described in my June Standout Systems article. The elegant and full-range Gershman Acoustics GAP 520-X sounded at least as impressive as during trade shows when driven by powerful Plinius or SimAudio Moon gear, and the entry-level Soliloquy 5.0 and 5.3, with and without subwoofer, were equally impressive.

Wrapping up

To appropriate a famous slogan, the Art Audio Jota gets my vote as the ultimate driving machine. It transports me into the music in a way that’s intrinsically emotional, like a direct injection of adrenaline that instantly enhances one’s sense of energy and well-being. Yet the Jota appeals equally to my occasional fascination with counting the violins, sensing a reed’s rating, absorbing a complex fugue’s voices all at once, visiting the subterranean air conditioning units the recording engineers didn’t think audible, or indulging in dance-hall music at levels that are ultimately not good for you.

Joe Fratus, Art Audio’s passionate ambassador, didn’t know this, but my wife, having spent years with campesinos in Ecuador, pointed out that the word "jota" there is used also to denote an exclamation mark! That, my friends, hits the nail on the head with a gold-plated sledgehammer. The Jota is a major-league statement piece to be considered in the context of the best currently available.

...Srajan Ebaen
srajan@soundstage.com

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