Zesto Audio Bia 200 Select Stereo AmplifierZesto Audio Bia 200 Select Stereo Amplifier: World Premier Review

The brilliant late audiophile, J. Gordon Holt, once wrote that if the purchaser of a fine system was torn between buying a great pair of speakers or a great amp, one should choose a great amp and a good pair of speakers that fit your basic needs. He commented that he had heard numerous systems with expensive extraordinary speakers sound very ordinary with an ordinary amplifier. He had also heard many average or less-expensive speakers sound extraordinary with an extraordinary amplifier. I, too, have witnessed the same phenomenon often, sitting in front of mega-speakers and vin ordinaire amplifiers, and often exiting quickly. The moral: acquire very good speakers and break the bank on your amplifier choice.

Enter the Zesto Audio Bia 200 Select Stereo Amplifier, the one on which to break the bank! This Zesto Audio third-generation all-tube Bia 200 Select in my highly revealing primary reference system is so neutral, artifact-free, powerful, nimble, delicate, elegant, revealing, and jet-black quiet that your speakers will disappear and present to your ears the performance as recorded. I have never heard such glorious truthful amplification from a 100-watt stereo amplifier in my entire audiophile life, now spanning 60 years. And this with only two output tubes per channel!

With the KT150 tube choice, as provided in the stock configuration, this is the amp that will sonically bridge tube and solid-state performance and control. It took two years of R&D by George Counnas, Zesto Audio's designer and CEO, testing every component for its sonic performance and improving on all his previous designs to achieve this outcome. Made in Los Angeles, this nearly unique tetrode push-pull amplifier runs in Class A 100% of the time. I know of only one other amplifier in the world with this topology. The secret sauce is the output tube selector, activated on the fly by the user, choosing three bias positions and maximizing four different vacuum tube types: KT88, KT120, KT150, and KT170. A fantastic, original, and brilliant design—not to mention the fact that this approach is extremely hard to do well.

Detailed Specs

Dual Mono
Auto bias
No negative feedback
Frequency response 20Hz to 30kHz ~ 3dB
Total Harmonic Distortion ~ 0.22% at 1W into 8 Ohms
Gain of 24dB
Noise level > 2mV -RMS into 8 Ohms with input shorted
1% metal film resistors throughout
Polypropylene capacitors throughout the signal path

Active Components

Matched quad set of four (4) KT150 vacuum tubes
Four (4) Gold pin ECC82 (12AU7) vacuum tubes
High-quality gold-plated ceramic sockets

Other Features

Each unit is made by hand
50-hour factory burn in on all circuits and vacuum tubes
Dimensions 17" W x 20" D x 10" H
Weight 64 lbs. (29Kg)
Shipping box = 27" x 27" x 13" (68.5 cm x 68.5 cm x 33 cm)
Shipping weight: 80 pounds (36 kg)
16- and 14-gauge Zinc plated steel enclosure
Two-year limited warranty
Six months warranty on Vacuum Tubes

Inputs

Transformer floating ground differential balanced XLR inputs
Left and right balanced inputs (pin 2 hot), impedance 10K Ohms
RCA single ended inputs Left and Right with impedance of 47K Ohms
Independent ground lift switches on left and right balanced inputs
2.5 Volts RMS input to reach rated output

Output: Class A

KT150 = 100 Watts per channel into 8 Ohms
4 Ohm, 8 Ohm and 16 Ohm output taps
10A, 7A and 5 Amp 6mm x 32mm Slow-blow speaker fuses for outputs
Eight 5-way binding posts
Non-inverting output polarity
Push-Pull Ultra-Linear design

Power rating for Auto Bias Select Switch Settings

Left Switch Position

KT88 = 60 Watts per channel,
KT120 = 60 Watts per channel
KT150 = 60 Watts per channel
KT170 = 60 Watts per channel

Middle switch position

KT120 = 85 Watts per channel
KT150 = 85 Watts per channel
KT170 = 85 Watts per channel

Right switch position

KT150 = 100 Watts per channel
KT170 = 100 Watts per channel

Reference system

Speakers: Marten Bird Speakers
Preamp: E.A.R. Tube 912
Digital: E.A.R. Tube DAC 4 and matching Transport
Analog: E.A.R. Tube 88PB and Zesto Audio Andros Deluxe II
Turntable: E.A.R. DiscMaster Magnetic Drive
FM Tuner: Marantz 10B
Cables: Cardas Beyond PC, RSX Beyond Phono Cables and Power Cords, Kubala-Sosna Elation and Emotion Power Cords, UITaudio Interconnects, UITaudio USB, Jorma Origo Speaker Cables, Bybee Speaker Bullets, Stein Power Conditioner
Phono Cartridges: Grado Epoch III MI and Stein Music Aventurin V6 MK.2 MC (modified Benz LPS)
Sources: Records, CDs, SACDs, FM tuner, and Qobuz

The very cool thing about this amplifier is there will always be tubes available for this amp, even if they are just KT88s. 6550s and KT90s will not work in this amplifier and should not be tried. I heard all tube types at all bias choices, and will now give you my preferences. The designer delivers the amp with his favorite tube selection which turns out to be spot on. I only found one combination that was clearly superior, and possibly another combination perfect for speakers that are very inefficient. Tube rolling is my passion and this was great fun. Once you settle on your choice or use as supplied, you will most likely never touch the Bias control again.

All listening was done with the 4 ohms output. The amplifier was already well exercised when it was delivered. My Marten Bird speakers are 89dB efficient, bass reflex/point source radiators, Accuton ceramic bass and mid drivers, and diamond tweeter.

Tube rolling

KT88

There is a single Bias position on the selector for this tube and it is precisely perfect. Every KT88 I tried performed quite differently, which was really a learning experience.

The JJ KT88 was a bit thin sounding, had very good clarity, big soundstage, rather cool and mechanical, and not overly organic. I was not impressed.

The Gold Lion Re-issue had soul. More organic and natural than the JJ, it has tons of definition and slam. The bottom end was a bit thick, but acceptable. Mids and top end were very beautiful. Lots of air and space. Background was somewhat dark gray and not as black as the amp is capable of delivering. There were fairly high grain levels around the instruments, with too much haze. I could live with this tube if nothing else was around.

The NOS Genelex KT88 tubes circa 1969 matched quartet: approximate cost, $2000+. Best tetrode power tube ever produced and that is exactly how they sounded in the Bia. These made the reissue from Russia sound broken; the originals were utterly perfect. No quibbles. The background was jet black, the definition was extreme and organic, pinpoint imaging, outstanding control and drive at all frequencies, and the most realistic presentation of all tubes tried. Their powerful sound was without limitation, and the headroom during crescendos was awesome. I became lost in the music, and I was very sorry to return them to their owner. If you acquire this amplifier, do not hesitate to spend the extra bucks if a quartet of these beauties comes to your attention. What an experience!

KT120

The KT120 was not bad, but it had a mechanical and grainy texture that was off-putting to me. I like the KT120 in the original Bia 120, but less so here. It did not do anything very well except play dynamically loud. The other Bias choice did not improve it. The low setting made it sound muddy and vague. The middle setting was the best of the bunch but not nearly as good as the KT150 supplied.

KT150

The manufacturer-supplied KT150 in the middle setting is a joy to hear. A very massive and handsome tube, it is a musical treasure. It does nothing wrong. There is not a parameter to criticize. It does bombast and delicacy, depth and width, clarity minus all grain, an extremely black background, headroom galore, and a sense of realism to die for. While a bit less full and alive sounding than the NOS Genelex, it equals it in all other parameters. The low bias muddies the KT150's sound and ruins it. The high bias makes the sound more bombastic, mechanical, and uninteresting. The middle position is just exactly right for the pickiest audiophile. Highly recommended.

KT170

The huge KT170 is quite a tube. It also heats up to 350 degrees, so tube swapping is an adventure. I found the middle position with this tube retained much of the musicality of the KT150 with some added slam and attack. As it turned out, there was too much attack for my Marten Birds, but it may be just right for less efficient speakers or speakers without ceramic drivers. They are quite fun to listen to, but I noticed some fatigue sneaking into my listening session. You like these more when you first hear them. Later, you just want to move on. Too much attack and not enough delicacy for my ears. The low bias setting makes them muddy and warm, shrinking the soundstage. The high setting adds even more edge and bombast. The middle setting will bring your more inefficient speakers to new heights.

12AU7

I tube rolled the small signal tubes with Mullards. They added a muddy quality to the amplifier in the output stage, and an old-fashioned kind of texture to the inputs. Neutral was restored with the selected gold pin JJs, and I suggest you leave them alone. This amp has been modified and tweaked to use modern, available tubes and make a glorious realistic sound.

Summary

In my experience, the Bia 200 Select is the most mellifluous and realistic-sounding amplifier, tube or solid-state, currently produced anywhere within its power rating, and with only two output tubes per channel. It is an absolutely breakthrough design, fabulously flexible, and capable of maximizing current and NOS tubes for decades to come. As a Class A tetrode design, it never runs out of gas, and never disappoints the listener. It is more neutral and quieter than any amplifier with tubes made by anyone I've heard, and that would hold true for most solid-state designs that I know, too.

The Bia 200 Select is a wonder. It is well worth its not inconsiderable price. Most highly recommended by me, regardless of your predilection for tubes or solid-state. The Zesto Audio Bia 200 Select Stereo Amplifier is state of the art.