Positive Feedback Logo

Zesto Audio EROS 300 Class A Monaural Power Amp Premier Review

12-18-2015 | By Robert H. Levi | Issue 83


(Image courtesy of Zesto Audio)

Introduced at RMAF in October by Zesto Audio, these new powerhouse mono-blocks have the Zesto signature house sound, which is nearly nothing at all. It also has enough power from tubes to be an amplifier solution to any and all speakers I know of, with extraordinary results. If you loved the Bia 120, you will adore these improved, impactful big brothers. Triple the tubes, triple the fun I say!

Bob Levi's Reference System

  • E.A.R. Disk Master Turntable with two Helius Omega Tonearms
  • Kiseki Purple Heart MC Cartridge
  • Grado 2 Reference Statement Mono MM Cartridge
  • E.A.R. 88PB Tube Phono Stage
  • E.A.R. DAC 4, Acute 4 Digital Player
  • E.A.R. 912 Preamp
  • Kubala-Sosna Elation Cables, Jorma Origo Cables, Merrill Audio ANAP Cables
  • Dynamic Design Heritage Series Challenger Power Cord
  • Marten Bird Speakers, REL Stadium 3 Sub-woofer
  • All connected balanced from all sources.



  • Pure Class A
  • 150 Watts per amp
  • 4 and 8 Ohm output taps
  • 8 and 5 Amp Slow blow fuses for outputs
  • Three 5 way binding post
  • One SpeakOn connector
  • Non inverting output phase polarity
  • Push-Pull and Ultra-Linear design


  • Transformer floating XLR input
  • Balanced inputs with pin 2 hot, impedance of 12K Ohms
  • Single Ended input, impedance of 100K Ohms
  • XLR ground lift switch on balanced input
  • 1.8 Volts RMS input to reach rated output

Detailed Specs

  • Monaural
  • Auto bias
  • No negative feedback
  • Frequency response 20Hz to 50Khz ~ 2dB
  • Total Harmonic Distortion ~ 0.43% at 1W output into 8 Ohms
  • Gain of 26dB
  • Noise level > 5 mV RMS into 8 Ohms with input shorted
  • 1% metal film resisters throughout
  • Polypropylene capacitors throughout the audio path


  • Custom Toroidal power transformer with global mains
  • Choke based power supply design
  • 120 Volts AC mains
  • Optional factory installed 220V, 230V, 240V 50/60Hz
  • Power consumption at rated output 360 Watts
  • Power consumption at idol 348 Watts
  • On/Off switch conveniently located on front panel
  • 3 pin IEC power connector with fuse

Active Components

  • Matched sextet, set of six (6) KT88's vacuum tubes
  • Two (2) Gold pin ECC82s (12AU7) vacuum tubes
  • High quality gold pin 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. (29.03 kg)
  • Shipping weight 80 lbs. (36.28 kg)
  • 14 and 16 gauge Zinc plated steel enclosure
  • Two year limited warranty
  • Six month warranty on vacuum tubes


(Image courtesy of Zesto Audio)

Overall Sound Quality

With a carefully tuned circuit that has pretty much unlimited Class A power from six KT88's per channel, this is a truly garbage-in-garbage-out amplifier. Based on my experience with my well-known front-end gear, as I listened via the EROS 300, I heard textures that abounded, while definition was outstanding. This amp does warmth in spades, and marvelous imaging galore. This is 2016 sophistication at its best, and a true second-generation effort by Zesto Audio. With width, depth, imaging, textural cues all showing themselves to be exceptional, your investment in the EROS 300 is a safe one for the long term. 

The EROS are neutral to the max, and Class A 100% of the time. No tube amp I know of today is more neutral. And when it comes to power, I tried hard to get them to clip. Even at volumes over 100 dB continuous output at five meters, I heard no clipping, thickening, or distortion with 89 dB efficient loudspeakers. The house shook, but the music was unshakable! 


The EROS is ultra-capable to communicate an enormous envelope of air and ambiance. I hear mountains of definition without any etch at all! Lots of sparkle and extended imaging permeates high frequencies. If you are a Zesto Audio Bia fan, you will love the enhanced smoothness and sophistication in this design. The amount of definition is very nearly the state-of-the-art.


Once integrated into a highly revealing system, the EROS will perform. This is reach-out-and-touch-it sound. The EROS pops with attitude and realism. Soundstaging and imaging is as good as it gets. Plus, dynamics appear unlimited. There is no blurring or homogenizing at any volume with the most complex material. When the music is warm and emotional, you will hear it. When it is exciting and explosive, you will hear that, too. This is an amp with control, composure, and sophistication.


The EROS delivers some of the deepest bass with the most definition for tube or solid state that I am aware of. I can count on one hand amps that are this good on the bottom octaves. The bass is as detailed as any other sonic range. I suspect there are very few woofers that will not be well controlled by the EROS. My Birds were at their peak in their bass range with the EROS, and I could not have asked for more.

How to love the EROS

This is not a forgiving amplifier that covers your system's sonic pimples with sweet loving kisses. I needed to tune the EROS and my DAC to bring out all of its gorgeous qualities. I kept all cables the same as with my reference E.A.R. amps, to give me a clear picture of the EROS' performance. 

The EROS is supplied with select JJ 12AU7 tubes in the front end. These are as neutral as neutral can be, and may be just right for your speakers. Drivers made of materials that are complex and a bit thicker and slower than ceramics, planar and ribbon drivers, and other unusual materials, may work just fine with the EROS as supplied. For speakers like mine, with super-fast ceramic, diamond, or electrostats, Zesto will supply a warmer driver tube from JJ, the 803s, at no added cost for you to use. I tried this tube with excellent success on my Birds with their ceramic and diamond drivers.

You can also tube roll the inputs of each amp with one or two NOS Mullard 12AU7s, at $95 each from Upscale Audio in Upland, and get even more textural nuance and sophistication. Your system's front end must provide that increased definition and resolution, or you can replace tubes all day with no benefit. I did not change anything in the DAC or phono section, as all mated perfectly with the EROS. My Kubala-Sosna Elation! power cords brought out maximum performance from the amps. The new Dynamic Design Heritage Series Challenger Power Cord was exceptional with the DAC.

Reference LPs and SACDs


(Cover photograph courtesy of Yarlung Records)

The brand new Dialoghi from Yarlung Records, in 45 RPM LP, has just arrived from Europe and is available now. The CD hit (also available in Quad DSD, where it is stunning), featuring classical cello and piano pieces, is outstanding and alive on the new LP, YARO9262-876V, with the EROS. I was astounded by the air, textural nuance, power, and truthfulness of the instruments. Clearly outclassing the CD, the LP is a shocker. Each note thrills and entertains the listener. Try this one with the lights turned low for ultimate fun. This is the best cello instrument sound on LP or CD I own, period. This recording should be in every audiophile's collection.


(Cover photograph courtesy of Deutsche Grammophon)

Also just arrived, released in 2015 from DG, Hillary Hahn plays Mozart 5th Violin concerto and Vieuxtemps Violin Concerto, Paavo Järvi, Kammerphilharmonie, Bremen, CD B0022698-02. This is one sweet beauty. The violin is perfectly imaged and sweet as sugar. Wonderful soundstaging and smooth textural nuances. This is a truly mellifluous CD, showing that DG is doing great work currently. The EROS amps propel Hahn's artistry with energy and naturalness.


(Cover image courtesy of Acoustic Sounds)

With upfront dynamics and ultimate swing, the Duke Ellington Nutcracker Suite from Pure Pleasure Records, CS8341, is a winner on the EROS. The EROS digs amazing definition and heart pounding richness from the Duke that no solid state amp on this planet I know of can match. The EROS swings with the greatest tube amps ever made, making its price tag smaller than you might believe in comparison. 


(Cover image courtesy of Acoustic Sounds)

Check out My Foolish Heart, Eddie Higgins Quartet, Master LP, MVLP 1001, new to the marketplace. This is stunning jazz with great old timers playing with great love and sophistication. The instruments are in the room and a joy to hear. Almost the real thing! The EROS is shown to be a real charmer to the last note. This reference disk made a lasting impression on all who heard it and enjoyed it.


(Cover image courtesy of Deutsche Grammophon)

Also on DG, I auditioned the new two LP set of Schubert's The Great Symphony, 4795087, conducted by Claudio Abbado with the Orchestra Mozart. This one is a tremendous tour de force recording, with perfect surfaces. Another LP that transports you to the hall, I was stunned by how well the EROS supported this great soundstage.

The EROS was exceptional at reinforcing the nuances and delicacy of the quiet passages, just as it propelled the drama of the loudest ones. The combo of low distortion and high tube power is addictive.

I dug out an old favorite, a genuine EMI LP of Rachmaninoff's first symphony, Andre Previn, LSO, ASD3137. The Fourth Movement is a stunner on the EROS, but the slightly shrill violins in the loudest passages are apparent. This is in the EMI recording, and there is no way to fix it, but ignore it. If you want a sense of reality, the EROS is king.

If you want fiction to cover up poor source material, look elsewhere.


The Zesto Audio EROS 300 Class A Monaural Power Amp takes the next sonic step toward perfection and huge power in the Zesto Audio line-up. Now the equal of the most powerful tube amps in the world, it is phenomenally neutral and revealing of source material. Laden with features, it is ultra-quiet and flexible. Best with the finest loudspeakers and source material, you must be prepared to tune your system to bring out its luscious realism. Once you have tweaked your system, you will enjoy these powerhouse beauties to the maximum. I am mightily impressed by their overall performance, as they left little to aspire to. You are only bound by your ancillaries and speaker capabilities as far as I can tell.

Another clear winner from the soldering pen of brilliant designer, George Counnas.

Bravo George!

MSRP USD $19,900

Engineering & Tech Support
George Email: [email protected]
Phone: 805-807-1840

Sales and Marketing
Carolyn Email: [email protected]
Phone: 805-807-1841

Zesto Audio
3138 Calle Estepa
Thousand Oaks, California, 91360 USA.