Tube Power Amp Reviews

Zesto Bia 200 Select power amplifier Manufacturer's Comment

Manufacturer's Comment

Thank you everyone at Stereophile for all their support. We are so pleased with Ken Micallef 's review and all his comments on the musical performance of our amp.

I would like to point out to your readers important conditions regarding John Atkinson's technical measurements on this amp. Tubes are the only active component in a tube amplifier, so all tube amplifier measurements are sensitive to the condition of the tubes. Tubes need to be tested separately before testing the unit. In this case, the amplifier was used to test the tubes, so the measurement results show the performance of the tubes, not the amplifier.

Zesto's technical specs are based on new matched tubes with 50 hours of burn-in. The Bia 200 tubes in the review have approximately 500 hours of use and are exhibiting normal tube decay, which will affect the measurements and overall power rating.

The tubes may not be optimal for measurements but certainly are optimal for listening. It was important to Zesto to give Ken the very best listening experience for his review with a well burnt-in amplifier.

We feel it was misleading to compare the measurements between our Leto preamp and the Bia 200 amp because while 500 or 1000 hours on a small-signal tube has very little effect on its condition, similar hours on an output power tube will result in significantly more decay because it is working so much harder. The nature of tubes is always changing, which only matures and enhances the musical experience.

Barring any component failure, Zesto Audio makes no apologies for any measurement differences due to tube decay from 50 hours to 500 hours of use. It is clear from Ken's review he thinks the amp sounds great!—George Counnas, President Zesto Audio

COMMENTS
bhkat's picture
Submitted by bhkat on March 4, 2023 - 8:50am

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

Bacheaudio's picture
Submitted by Bacheaudio on March 5, 2023 - 4:17am

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

bhkat's picture
Submitted by bhkat on March 5, 2023 - 7:26am

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

JD85's picture
Submitted by JD85 on March 5, 2023 - 9:14am

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
Submitted by georgehifi on March 5, 2023 - 12:08pm

"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
Submitted by ok on March 7, 2023 - 10:14pm

..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
Submitted by JHL on March 8, 2023 - 4:16am

...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
Submitted by JRT on March 11, 2023 - 6:41pm

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
Submitted by JRT on March 11, 2023 - 11:46am

Western Electric 300B direct heated triode vacuum tubes, matched pair:
https://www.westernelectric.com/300b

Bottlehead BeePre2 300B two channel stereo preamplifier kit:
https://bottlehead.com/product/beepre2-300b-preamplifier-kit/

Bee2Quiet Stepped Attenuator / Constant Current Source upgrade for the BeePre2:
https://bottlehead.com/product/beequiet2-stepped-attenuator-upgrade-for-beepre2/

Hybrid Shunt Regulator and Low Impedance Balanced Output, upgrade for the BeePre2:
https://bottlehead.com/product/beepre2-output-upgrade/

Benchmark Media AHB2 power amplifier:
https://benchmarkmedia.com/collections/all-products/products/benchmark-ahb2-power-amplifier

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