Zesto Bia 200 Select power amplifier

Like many other industries, audio has its power couples: behind-the-scenes movers-and-shakers who shape the trajectory of the industry and who also happen to be, well, together. Angela Cardas and Josh Meredith of Cardas Audio come to mind, as do Dave and Carol Clark of Positive Feedback, Eli and Ofra Gershman of Gershman Acoustics, Luke Manley and Bea Lam of VTL, Carl and Marilyn Marchisotto of Nola Speakers, Edwin and Gabi van der Kley-Rynveld of Siltech and Crystal Cable. George and Carolyn Counnas of Zesto Audio are a hi-fi power couple I'm especially fond of; I'm always happy to see them at shows, catch up with them on the phone, or exchange emails with them. Their sweet demeanor and good vibrations always lift my spirits.

George designs Zesto's preamplifiers, power amplifiers, phono stages, and step-up transformers, while Carolyn, a talented fine-art painter, gives Zesto's products their unique organic curves, which differentiate Zesto from the straight lines and square boxes that dominate the hi-fi world. But industrial design is not the only distinguishing feature of the Zesto brand. There's also the sound of their products: resolving, neutral, quiet, with hair-raising dynamics and precise imaging. Exciting.

I reviewed the Zesto Leto Ultra II line preamplifier in the January 2021 issue, and I'm happy to now bring one of its big sisters, the Zesto Bia 200 Select stereo power amplifier ($15,900), to my NYC crib for examination. With any luck, the Bia 200 Select's power tubes will provide not only fine sounds but also some extra heat to my apartment during the winter months as the building's 1970s-era boiler struggles to push adequate heat up to my penthouse pad.

The Bia 200 Select is an Ultralinear, dual-mono, class-A design in push-pull configuration with no negative feedback. Out of the box, it employs four JJ 12AU7 and four Tung-Sol KT150 power tetrodes: one input buffer/splitter and one driver per channel, but tube-rolling is encouraged and supported.

Compatible with KT88, KT120, KT150, and KT170 output tubes, the Bia 200's three-position bias selector allows you to set the bias with a turn of a dial in real time—no power-down required. The left position selects 60Wpc, usable with all four tubes; the middle position selects 85Wpc, which excludes the KT88; the right position selects 100Wpc, which, in addition, excludes the KT120. I experimented with different output tubes and found that, for a given tube set, changing the setting resulted in a slightly altered sound. The Bia 200's user manual, which devotes two pages to the use of the bias selector, confirms this observation and advises, "You can change the bias on the 'FLY' while the unit is on so you can hear the difference. It will take a few minutes for the tubes to react, to either heat up or cool down, to hear the difference."

The Bia 200 represents a substantial remake of its predecessor, the Bia 120 Select, including a new power supply, new input and output circuits, and new output tubes. The adjustable bias control and opportunity to use a greater variety of output tubes are also new.

Stout and strong with feminine curves, the Bia 200 stands 10" high, 17" wide, and 20" deep. Its sides and top are formed from 14- and 16-gauge zinc-plated steel. Steel is also used in the front and back panels, while those undulating faceplate pieces are made from brushed aluminum.

Viewed from above, the Bia 200 is divided symmetrically into two curved sections. The covered section contains the transformers; the uncovered part displays the power and signal tubes. There's not much on the front panel: just a recessed power button and two LED lights. The power button felt rather clunky and stiff. In an email, George Counnas explained that the power button—chunky by design—energizes a relay that powers the amplifier up or down. Both LEDs—one green (for high-voltage), one amber (for low)—are lit when the unit is powered and operating correctly.

On the amplifier's back panel, ground switches accompany the left and right balanced (XLR) inputs, allowing them to be ungrounded if ground loop hum is audible. These are flanked by two sets of speaker binding posts with 4, 8, and 16 ohm transformer taps. Fuses for each speaker post, left and right gold-plated RCA inputs, and an IEC power jack complete the amp's connectivity.

The Bia 200 employs a custom toroidal power transformer manufactured by Toroid Corp. of Maryland, 1% metal film resistors, polypropylene capacitors throughout the signal path, and solid state rectification. Counnas used circuit boards under the tubes, point-to-point wiring everywhere else. "Designing a working circuit is fairly easy," Counnas wrote. Most of his time is spent "making it sound good," he said. George Counnas favors Ultralinear designs because of their low distortion.

I've had tube amps in the past that allowed you to choose between Ultralinear and triode modes with a toggle switch. Curious to learn more about Ultralinear design, I did some reading and found that it is a type of what is termed distributed loading, used to reduce harmonic distortion in the push-pull output stage of a pentode or a beam-tetrode audio amplifier (footnote 1). Theory and Operation of the Ultra-Linear Circuit (footnote 2) says that "of all the methods that have been devised to minimize distortion, the Ultralinear principle is the only one that attacks the problem at the source, in the non-linearity of the output tube itself." Then, after some math and diagrams, "Ultra Linear operation does not eliminate distortion altogether. However, measurements have shown that with proper adjustments of the grid bias and load, third harmonic distortion can be virtually eliminated, and the percentage of higher harmonics greatly reduced. Moderate amounts of feedback can then be introduced to reduce the higher harmonics to insignificance." George Counnas doesn't do that last part in the Bia 200, though; its output remains feedback-free.

I asked Counnas what equipment was used to evaluate the Bia 200, as I believe a manufacturer's choice of playback gear says something about the designer and the product. He said, "We use a Merrill Williams Audio REAL 101.2 Turntable with a 10" Tri-Planar Mk VII U2 tonearm and a Benz Micro Gullwing SLR MC cartridge. Then, my Zesto Audio Andros Téssera Reference phono stage into our Zesto Audio Leto Ultra II preamp; after the amp—after the Bia 200 monos—Marten Django L speakers. Cabling by Cardas." That's a system I'd love to hear.

The Bia 200's manual says the Bia and its tubes receive "50-hour factory burn-in," but it also notes that it can take 200 hours of break-in for best performance. I commenced the break-in process using Roon, Tidal, and Qobuz. I stationed the Bia 200 on a large bamboo Ikea Aptitlig chopping board atop a rug on my suspended hardwood floor. I connected it to power with a Triode Wire Labs Obsession NCF power cable and to my Shindo Allegro preamplifier with a pair of Neutrik cables. Loudspeaker connections were made with the Analysis Plus Silver Apex. For phono playback, I used the Shindo's internal MC/MM phono stage.

Footnote 1: See the article in r-type.org/articles/art-115.htm.

Footnote 2: This booklet from about 1952, by Herb Keroes, is available for download at tubebooks.org/file_downloads/ultralinear.pdf.

bhkat's picture

Measurements that askew could indicate something happened during shipping. Zesto should send another amp to be measured.

Bacheaudio's picture

I dont see terrible measurement, listen this amp a lot of times, good sound and design , good job Ken

bhkat's picture

Seriously, you don't see that the right channel has 20dB more distortion than the left?

JD85's picture

I heard some bigger Zesto amps at the Toronto audio show and found them wonderful - some of the best tube amps I've ever heard. I had to sit down and stay a while. In a show filled with bad sound, Zesto made great music.

georgehifi's picture

"I dont see terrible measurement"

If you can't hear + - 8db!!! (or even half that) of frequency variations from flat, your either deaf or not an audiophile.

Cheers George

ok's picture

..measure significantly different, something is obviously broken. It could be tube wear, loose logistics, poor quality control; some people might hear it, some others might not; it doesn't matter. This is not what the manufacturer intended and must be fixed asap. That's what measurements is all about - hardware failure alert, not subjective experience prediction.

JHL's picture

...as you put it, ironically becomes just that when people seize on an artifact without correlation in the actual sound of the device.

When data biases us we've lost perspective. Then we have *subjective prediction of experience* without known correlation and even without the suggestion of what that sound would be. That's subjective.

Yes, ideally the amp should be adjusted or the tubes replaced, but in any meaningful perspective this is another example of how data serves unconnected assumptions and does not serve sound, even if, in cases like this, apparently its purported benefits are virtually imperceptible.

No? The review itself describes real sound as it's altered by the aspects of the same product that actually influence it. Tube type, output circuit type, and so on, as it commonly is when evaluating these sorts of devices. Why? Because people consistently hear their objective sound and have for years. I suspect it's why makers include them.

These comments push that aside. I think we have it backwards.

JRT's picture

An alternative to this amplifier under review would be to use neutral sounding, low noise, low distortion, load invariant amplifiers to drive the loudspeakers, in combination with a tube-audio preamplifier providing tube-audio sonic qualities while driving the resistive (non-reactive) high impedance inputs of those amplifiers.

It was mentioned that this Zesto Bia 200 Select two channel stereo power amplifier has an MSRP of $15.9k, which is a budget that could accomodate some interesting alternatives.

For example, the "Bottlehead BeePre2 300B" stereo preamplifier kit is priced at $1529. There are some worthwhile optional upgrades, including the "Bee2Quiet Stepped Attenuator / Constant Current Source" for $349, and the "BeePre2 Output Upgrade – Hybrid Shunt Regulator and Low Impedance Balanced Output" for $249. Including those upgrades brings the kit subtotal to $2127. The aforementioned $15.9k budget could afford some very high quality tubes, including new Western Electric 300B direct heated triodes, which are available at $1.5k for a matched pair, sold direct from Western Electric. Complete with other items and consumables needed to finish the kit, end cost could be under $5k, or not much more than that if you include the costs of an inexpensive temperature controlled soldering iron and some basic hand tools.

Early hifi audio had at least some of its roots in DIY and in kit assembly. Some of the contributing writers at Stereophile have sometimes embraced, or at least have not completely eschewed DIY and kit assembly efforts, though the magazine articles and website content have not included more than a very little of that.

That "Bottlehead BeePre2 300B" is a preamplifier kit, and is not a stereo power amplifier, however it leaves almost $11k in the budget for power amplifiers and XLR terminated balanced interconnect cables.

Benchmark Media's AHB2 bridgeable two channel stereo amplifier with balanced inputs is available through retailers, or is available direct for under $3.3k each. The AHB2 has received very positive review in Stereophile, exhibiting neutral, clean, load invariant output. There is enough room in the budget for two of those, at under $6.6k for the pair. Each could be bridged as mono block amplifiers, and located near the loudspeakers, using balanced interconnection cables (XLR terminated shielded twisted pair or shielded twisted starquad cable) and short loudspeaker cables.

That brings the total to approximately $5k+$6.6k= $11.6k, not including the cables. That leaves $15.9k-$11.6k= $4.5k remaining in the budget, unspent. And it includes a pair of Western Electric 300B direct heated triodes in the signal path.

There are many other alternative possibilities within this budget, and I wanted to highlight at least one of those.

JRT's picture

Western Electric 300B direct heated triode vacuum tubes, matched pair:

Bottlehead BeePre2 300B two channel stereo preamplifier kit:

Bee2Quiet Stepped Attenuator / Constant Current Source upgrade for the BeePre2:

Hybrid Shunt Regulator and Low Impedance Balanced Output, upgrade for the BeePre2:

Benchmark Media AHB2 power amplifier: