Zesto Audio Bia 120 Stereo Power Amplifier


Equipment report
Tubed power amplifiers
Zesto Audio Bia 120
Zesto Audio Bia 120 Stereo Power Amplifier

When I first met George Counnas, President of Zesto Audio, the company had only one product, a splendid phonostage called the Andros (Issue 222). At the time, he told me a high-level preamplifier was on the way, but, when asked about a power amplifier, added he had neither interest nor plans for one. But when the Leto linestage turned out to be as splendid as the Andros, I figured it was only a matter of time before an amp came along. Counnas was refreshingly candid about his change of mind: “I needed it to round out the line.” For all their pretentions to mixing and matching components, quite a number of audiophiles seem to like their electronics from the same manufacturer, preferably consistent in visual style. So here is the Bia 120 to make the Zesto duo a trio. I’ll not indulge any suspense: Counnas is plainly a gifted designer who knows his way around circuits and sonics, and here hits the trifecta with this drop-dead gorgeous sounding amplifier.

Gorgeous looking, too. George’s wife Carolyn carries over her signature styling from the Andros and Leto, and the Bia 120 features the same split-level chassis found throughout the line.

With a graceful, wavelike pattern set in light silver aluminum bas-relief against black on the base, and the grand-piano-shaped (viewed from the top) upper chassis (housing the large toroidal transformer) with a curved polished-chrome fascia that reflects the softly glowing tubes, the amp makes a stunning impression. An elegant touch of visual rhythm is the repetition of the front-panel wave in the side vents on the upper chassis. As with its siblings, you’ll want to keep the Bia 120 out in the open for all to see, which is mandated anyhow by how much heat it generates, which is considerable because it’s 60Wpc in a push-pull output stage that completely eschews negative feedback and is operated in pure Class A.

Why Class A in a tube amp, which, after all, is not supposed to exhibit the typical solid-state notch when the signal crosses from positive to negative? “Unlike Class AB, where the A part is small and the B part happens only when the signal ‘turns on’ the tubes,” says Counnas, “in Class A, the current is going through the output tubes and not waiting for the signal, which gives you a more dynamic sound because the tube is constantly charged; it’s on all the time.” Doesn’t this shorten tube life? “Theoretically yes,” he answered, “but not by all that much in the Bia because the tubes aren’t being run that hard.” As for the absence of negative feedback, this is a prejudice from the early years of solid-state, when negative feedback got a bad rap because ridiculously large amounts were applied to transistor amplifiers to achieve distortion figures with four and five zeroes to the right of the decimal point. Trouble was, while this led to impressively low measured figures of steady-state distortion, it didn’t necessarily translate into good sound, especially when it was used in substandard circuits to overcome the severe limitations of the transistors themselves. Negative feedback is effective mostly when the basic circuit and parts are already of good or better quality, whereupon judiciously applied in small amounts it can improve performance. By the time Counnas finished designing the Bia’s circuit, he decided, based on measurements and listening evaluations, that he didn’t need any. “All it did was reduce dynamic range while adding nothing sonically.”

The Bia is a dual-mono design, with auto-bias and a large toroidal transformer. It features fully balanced and single-ended jacks and has heavy-duty binding posts with 4-, 8-, and 16-ohm taps. Owners of original Quads and very early LS3/5as (16 and 15 ohms, respectively) should take note: This is one of the lonely few modern tube amps that will match them optimally. Like all Zesto products, every Bia is broken in 50 hours before being boxed up, and is totally hand-made in the USA.

Counnas’ goal was identical to that for his phono and linestages: a component that approached the neutrality of solid-state with the attractive “tonality of tubes.” He succeeded spectacularly with the preamps and does so again here, though “approached” is the operative word, about which I’ll have more to say anon. Cut from the same sonic cloth as previous Zesto products, the Bia’s personality consists in a completely seductive musicality, free from the usual sorts of electronic colorations and artifacts, for a presentation that never, ever sounds electromechanical, instead drawing all attention to the music, which is reproduced in a wholly natural-sounding way. I simply never found myself thinking of reproduction as such or any of the typical audiophile categories—scintillating highs, slamming lows, liquid midrange, yak, yak, yak—rather about the music and music-making. Right now I’m listening to Valentina Lisitsa playing Liszt’s Totentanz and wallowing in the waves of sheer sonority, the way her generous use of pedal never seems to obscure the lines and textures, the control of the dynamics from delicate whisper to barnstorming roar, and bass that is exceptionally solid, extended, articulate, and powerful, with no need—thank you very much—to append the usual “for a tube amp” qualification. No wonder Counnas, who seems to love Greek names, christened this after Bia, daughter of Zeus and Styx, and the personification of force and raw energy.

Counnas told me that one of his goals was that if critical listeners didn’t know what they were listening to, they wouldn’t know whether it was solid-state or tubes. There’s certainly no hint of anything that some dyed-in-the-wool tube fanciers still don’t like about solid-state (even though almost no modern transistor amps suggest any of the nasties of the early ones). At the same time, however, they just might be a little disappointed that the Bia equally betrays so little of old-fashioned tube character either. There is something so completely natural about this reproduction that I really do find myself at a loss for words to evoke it. To be sure, it’s tactile, rounded, gloriously dimensional, and “continuous”; there’s nothing edgy, sharp, or overly articulate about it; it’s not “liquid” as such or excessively smoothed over (though it is extremely smooth); textures sound to me like the textures of real voices and instruments; there is zero impression of grain (I mean no evidence at all); transparency is not a concern; and detail is as detail should be, to be noticed but not zeroed in on. And it’s got by far lower perceived distortion than any tube amplifier past or present with which I’ve got more than casual acquaintance. In fact, the only tube amps in my experience that may trump this one for overall neutrality are McIntosh’s MC275, though take that “may” for all its worth, as it has been more than a few years since I reviewed those amps and my system was somewhat differently constituted then.

When it comes to dynamic range, the thing is wowie-zowie with a vengeance. I am gobsmacked by the prodigious levels Counnas gets out of these sixty watts, even Class A tube watts: I wish I could take all the audiophile cowboys who say Quad ESLs cannot play loud enough and force them to listen to the clear, clean, completely unstrained levels I’ve been enjoying daily with this combination. I played some piano recordings louder than they would be if the pianos were heard in real recitals, and certainly than I could listen to them comfortably, and neither the (very inefficient) 2805s nor the Bia evinced any strain that I could detect. The same is true for orchestral recordings, while voices have to be heard to believe (how refreshing not to hear sibilants unduly accentuated).

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