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Zesto Eros 300 Monoblock Amplifier

Zesto Eros 300 Monoblock Amplifier

The new Eros monoblock amplifier is the most ambitious offering yet from Zesto Audio, a relatively new company on the audio scene. All its products are designed by music-fanatic-engineer George Counnas and built by hand in-house in Zesto’s Thousand Oaks, California, location. I did some basic research on the word “Zesto” and was surprised to discover it isn’t a valid Scrabble word. Who knew? But a little deeper digging did reveal a Greek derivation of “Zestos,” meaning “boiling hot.” Since George is of Greek derivation himself, I figured this must have been what he was going for. With “zest” coming in as “an enjoyably exciting quality,” and “Eros” being the Greek mythological god of love and desire, I became concerned I might need fireproof gloves just to install the amps.

I shouldn’t have worried. The installation chores were handled entirely by George and his lovely wife Carolyn, who deserves a raise as she not only schleps all equipment with her husband and helps set up shows, but is also responsible for the stunning visual design of the Eros and all Zesto products—part retro, part industrial, and (literally) new wave.

Although Zesto is a relatively new company as I said, George is no newcomer to designing circuits based around vacuum tubes. As a young(er) guy in England, he designed vacuum tube amplifiers when he was in college. He was also part of a design team working on navigational systems for the Royal Air Force. Smitten by the warmth and tonality tubes offer, he researched early tube designs as far back as the original RCA circuits of the 1930s. George’s goal was to start with the classics of the past, but to proceed with the use of modern computer simulation techniques and the best components currently available. In other words, he wanted to design amplifiers that offer the benefits of classic tubes but that also reflect the more modern state of the art.

I had heard nice buzz about Zesto products at shows and was looking forward to auditioning the Eros 300. But before describing the amplifier’s sound, it is helpful to briefly outline its circuit design. George eschews the use of negative feedback, so none is to be found in the 300. Probably the amp’s most defining design characteristic is that it runs in pure Class A at all times. Counnas explains that such operation has the benefit of no crossover distortion, and he believes Class A is more musical-sounding than Class AB, and I have no reason to doubt him.

I quickly discovered an easy way to confirm these amps are pure Class A—they run seriously hot (zesty?). Your free-range pets should roam elsewhere, and you will definitely save on heating bills in the winter. The Eros 300s feature six KT88 output tubes per monoblock and deliver 150 watts per channel. If my time with the 300s is any indication, it appears that a Class A watt packs more punch than its AB counterpart; the 300s sound far more powerful than their rated power would indicate.

There was an element of nostalgia in seeing the KT88s light up for the first time. It reminded me of my first tube amps: a pair of Dyna Mk. IIIs that used two KT88s each to generate 60 watts. I loved those amplifiers and I have enjoyed the sound of subsequent amps that used these tubes. Nevertheless, I have not had KT88s in my system for many years and was looking forward to hearing how they would sound in a truly modern design.

So, are these amplifiers all show and no go, or do they deliver the goods? Setup was simple (especially because I didn’t have to do it), and there are sufficient connectors on the back panel to work in any system. In addition to an RCA input jack and a true floating balanced input, the rear panel offers the convenience of a ground lift switch for the balanced input, making it easy to set up the amps for minimum hum. I experienced no hum whatsoever from the amplifiers. Speakers may be hooked up either by separate 4-ohm and 8-ohm binding posts or by a 4-pin SpeakOn connector.

My biggest concern (voiced to George long before he set up the amps) was whether or not a 150-watt amplifier could even drive my power-hungry Maggie 20.7s, let alone whip up the sonic magic which they are capable of. In the past, amplifiers in this power range have not been a great match for these speakers.


Once the amplifiers were warmed up, my concerns about their capabilities were put to rest in fairly short order. So long as I was not trying to blast the speakers at larger-than-life volume levels, the Zestos drove the Maggies with surprising ease. I have written in the past that the 20.7s will certainly sound good with quality amplifiers in the 200-watt range, but really come alive with more powerful amps. I still believe this to be true. Nevertheless, the Eros 300s’ performance belied their nominal rating of 150 watts a side—they powered the Maggies with the ease of 300–400Wpc amplifiers. I cannot say if this prowess is a product of its Class A design, but I am guessing this gain strategy has a lot to do with it.

Moreover, the 300s deliver in spades the full musical magic of which tubes are capable. Voices and virtually all musical instruments reproduced by the 300s possess a richness of tonal color that, to these ears, solid-state has yet to deliver. This is not intended to imply that these are throwback tube amps, slow and syrupy. They are not. They are modern state-of-the-art-sounding amplifiers across every important criterion—fast, transparent, and fully extended at both frequency extremes. In fact, their tight control of the bass might lead one to (erroneously) believe that some transistors are hidden inside. But this lower-octave control and slam is combined with a bull-bodied roundness—especially on double bass and drums—that eludes many solid-state amps.

When I started my listening evaluation, the first pleasant surprise came with some material that was not terribly taxing for the amps: a very nice LP reissue of Boss Tenor with Gene Ammons on tenor sax [Alto]. Played at lifelike levels, Ammons’ sax was three-dimensional and golden in tone while the rhythm section (bass, drums, and conga) was swinging. Every instrument was crystal clear and the stand-up bass, unlike some of Rudy Van Gelder’s other recordings, remained taut and controlled without devolving into pluminess. Power-wise, there was no sense of the 300s straining or running at the limit. I was just hearing really great music playback.

Turning to more demanding material, I took an old favorite for a spin on my Kuzma Stabi M: Martinon and the Paris Conservatory Orchestra playing works of Ibert, Bizet, and Saint-Saens [London]. Those of you who have the LP know it to be one of London’s finest, with great dynamic range, sweet strings, and huge stage width and depth. The Zesto Eros 300s loved this recording. Sounding fast, delicate, and surprisingly powerful, the amps placed the orchestra in an enveloping, three-dimensional space that transformed most of my listening room into a hall. The jet-black background was in stark contrast to the sometimes startling appearance of whistles and horns in Ibert’s playful “Divertissement.” Even “Danse Macabre,” a piece I have heard so many times that I usually skip it on most recordings, had a new-found charm and excitement when heard through the Zestos. The strings were luscious and even the grave-dancing skeletons seemed more energetic than usual. The bass drum whacks were powerful and filled the room.

But, on this recording at least, the full beauty and capability of the Eros 300s were revealed in Bizet’s “Jeux d’Enfants,” a fanciful homage to the world of children’s toys. As noted, violins were lovely throughout this recording, sounding neither metallic nor screechy. Compared with the high energy of “Danse Macabre,” the lyrical passages of “Jeux d’Enfants” showcased the Zestos’ ability to change pace and mood at a moment’s notice, conveying all of the subtlety and joy of Bizet’s light-hearted fare.

At this point in the review process I became curious as to how the Zestos compared to higher-power amplifiers. I remember the wide-open sound of the Aavik Acoustics U-300 integrated amplifier that was recently in my system. That solid-state amplifier, rated at 600 watts per channel into 4 ohms, rocked the house and never sounded ruffled. Unfortunately, manufacturers want their review gear returned and that amp no longer resides chez moi. Based upon recent memory, I would say that the U-300 (retail price: $30,000) presented a slightly larger soundstage and somewhat more slam at higher volume levels than the Zestos. On the other hand, the Zestos offered a somewhat richer tonal palette and a more three-dimensional presentation.

I was also able to compare the 300s with my VTL 750s, admittedly amps engineered and built years ago and not representative of the latest in design or technology. (To my knowledge, VTL’s most recent offerings in this 600-plus-watt power range cost more than three times the price of the Zesto Eros 300s.) I was interested in determining if the VTL’s power advantage was beneficial. The same musical selections played through the 750s sounded very good, but immediately it was apparent that the Zesto Eros 300s displayed more transparency, quieter background, and a more three-dimensional presentation than the VTLs. On the other hand, at high to unnaturally high listening levels, the larger tube amps sounded slightly more relaxed and produced a fractionally larger soundstage. This is not a criticism of the Zestos; they conveyed a very convincing sense of space. But quadrupling the output power led to a slightly more spacious presentation (if the recording captured this)—not four times as large, of course, but still the increased sense of space was noticeable.

Putting all of this into perspective, the 300s were undeniably superior to the larger tube amplifiers in many important ways: greater transparency, more body to instruments and voices, very lively with no tendency to sound dark(ish), and blacker of background. The 300s gave up only a slight sense of ease at the highest volume levels and a small but noticeable sense of space on large orchestral recordings. To be fair to the Zestos, and figuratively putting the large Magneplanars aside for a moment, most real-world loudspeakers, regardless of size and cost, are more efficient and hence considerably easier to drive than my Maggies. I am making a (hopefully) well-educated guess that with most speakers owned by most music enthusiasts the Zesto Eros will be exemplary for all musical styles at all listening levels, with no shortage of power or slam.


I played many other types of music through the Eros 300s. At no time was I let down or disappointed. Whatever I threw at them, from Shostakovich string quartets to Ella Fitzgerald to The White Stripes to Metallica, the 300s provided a wonderful listening experience. They exhibited the best quality of sonically superior equipment: They encouraged me to play LPs and CDs I had not heard in quite some time. For example, I pulled out the LP Brazilian Soul with Laurindo Almeida and Charlie Byrd on guitars [Concord]. I figured that any record with a “Picante” catalog number should be right at home with the Zestos—was it ever! The dueling guitars were fast, fully fleshed out in tone and overtone, against a background so quiet that Almeida and Byrd sounded convincingly present in the room. Especially satisfying was the cut “For Jeff,” a tune written by Byrd that showcases both guitarists’ terrific talents. Very spicy!

Switching to CD, I wanted to hear a few recordings of Yuja Wang, a young pianist whose playing is simply electrifying. I was fortunate to hear her play live twice last year and am looking forward to her upcoming recital at the historic Granada Theater in Santa Barbara. (For anyone planning to travel to hear this concert, the trip would not be complete without at least one night at the fantastic Belmond El Encanto hotel—as close as we will get to the South of France in Southern California.) Yuja has a special relationship with the city as the University of California Santa Barbara has sponsored her since she was a teenager. It’s amazing to watch and hear this diminutive lady—usually clad in a runway dress and stilettos—take on the most difficult material in the piano repertoire and simply pulverize the Steinway. I am not attempting to compare her with other great pianists of the present or past—to me, such comparisons are interesting but not that meaningful. She is one of the world’s great musical talents right now, which is sufficient reason to seek out her live performances as well as her recordings.

To get an idea of Yuja’s musicianship, I highly recommend the CD of her live performances of Rachmaninov Piano Concerto No. 3 and Prokofiev Piano Concerto No. 2, with Gustavo Dudamel conducting the Simon Bolivar Symphony Orchestra of Venezuela [Deutsche Grammophon]. The sound quality of this recording is very good, if not quite reference quality. Wang’s playing is lyrical and sweet in the slower passages (although some critics, unfairly in my opinion, accuse her of losing some magic when her speed is below supersonic). She handles the most complex passages with an ease and fluidity that is simply stunning. Listening to both performances through the Zesto 300s was very gratifying, as they captured the full sweep, warmth, and majesty of the orchestra, while at the same time allowing Yuja’s piano to take center stage with unfettered speed and dynamic range. The enjoyment level in my listening room was very nearly what it had been at the live event, which is all we can ask our sound systems to do. Truth is, after a while I just forgot about the electronics and simply enjoyed the performance and the music.

The Zestos were as enticing with voice as with instruments. Eva Cassidy does not have a classically beautiful or powerful voice, but there is a raw honesty to her singing that is very engaging. I put on her Time After Time LP [Blix Street] mainly to see if the Zestos captured the shy yet heartfelt feeling of many of her songs. They did. I had only intended to listen to her rendition of the Bill Withers song “Ain’t No Sunshine,” but ended up playing both sides of the album. The great transparency and three-dimensional body of the 300s truly made it seem as if she, and her guitar, were in the room.

To sum up, the Zesto Eros 300s proved to be amiable listening partners. They were completely reliable and silent in operation. They look good too, though this is not a necessity. Through several months of living with the 300s, listening to music was always a pleasure and each session lasted longer than planned. My notes reflect my overriding perceptions that the 300s are extremely transparent, lush, warm in the way that live music is, and more powerful than their rating would suggest. Their only downsides, in my view, were heat output (par for the course with higher-powered tube amplifiers) and a slightly reduced soundstage compared with much higher power (and generally more expensive) amplifiers. Some may feel that the often cooler presentation of solid-state amplification is more accurate, but not to my ear. Moreover, I have not heard any other amplifiers in this power and price range reproduce the sense of orchestral space and three-dimensionality that are second nature to the Zestos.

Where this sonic mix will end up on a given user’s personal score card will vary, but it is undeniable that the Zesto Eros 300s offer an intriguing and inviting alternative to the army of solid-state amps out there. I can envision many music lovers being thrilled with these amps—indeed, even feeling that they have “arrived” musically. My review pair has been sold and must be returned to Zesto tomorrow. I will miss them.

Specs & Pricing

Type: Mono tube amplifier
Class of operation: Class A
Power output: 150 watts continuous
Total harmonic distortion: 0.8% at 1W into 8 ohms
Gain: 29dB
Input impedance: 100k ohms (single-ended); 12k ohms (balanced)
Tube complement: Matched sextet of six KT88s, two gold pin ECC82s (12AU7)
Output taps: 8 ohms, 4 ohms
Dimensions: 17″ x 10″ x 20″ 
Weight: 59 lbs.
Price: $20,000/pr.

3138 Calle Estepa
Thousand Oaks, CA 91360
(805) 807-1841

Associated Equipment
Magneplanar 20.7 loudspeakers, Kuzma Stabi M turntable with Kuzma 4Point tonearm, Lyra Etna and Koetsu Rosewood Platinum Signature cartridges, EMM Labs CD playback system, Aesthetix Eclipse Io phonostage with two power supplies, Aesthetix Eclipse Callisto linestage with two power supplies, Audio Research REF 10 Line Stage, Audio Research REF 10 Phono Stage, VTL 750 amplifiers, Purist Audio Design, Transparent, and AudioQuest cabling, Sain Line Systems power cables, Stillpoints Ultra 6 isolation feet


By Don Saltzman

My stock in trade for the past 45 years or so has been business litigation. If you are being sued for breach of contract or, better yet, you want to sue someone who has done you wrong, just give me a call. I love courtroom brawls.

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