Given all of this, why then am I reviewing an almost-$20,000 tube integrated amp? Curiosity, mostly. When I bought my Concentra, I only compared it to other solid-state integrateds and this review would give me an opportunity to compare and contrast, to determine what, if anything, Id given up in terms of tonal beauty and resolution. My previous experiences with tube integrated amps were a mixed bag; push-pull designs were generally enjoyable, but SETs were too euphonically rich for my tastes with a sound that made it seem that the notes themselves were covered in some sort of syrupy sonic goo.
The A-100 ($19,000 USD) is from Esoterics MSW Amplifier Series, a new product line from Esoterics Master Sound Works, which has the stated goal of reproducing the intricacies and sonic beauty contained on the master tape. The A-100 is rated at 45Wpc, has two 12AT7, four 12AU7 and four KT88 vacuum tubes, and uses a number of proprietary features to facilitate its stated goal, one of the most important being the variable self-bias system. This advanced active biasing circuit is stated to compensate in active fashion for the bias voltage supplied to the output stage, making the A-100 the ultimate in "set it and forget it" technology and your volt/ohm meter obsolete. Other features include a zero voltage control system that acts to stabilize the cathode follower DC output level, keeping stable the operation of the directly coupled circuit components. Additionally, the A-100 also has custom output transformers, and all stages, apart from the KT88 stages, are powered by fully stabilized power supplies. Frequency response is quoted as 20Hz-60kHz. The signal-to-noise ratio is said to be greater than 98dB.
The A-100 is one massive and robustly designed component. The outer panels are of thick, non-resonant aerospace-grade aluminum. The chassis is extremely rigid, with the power supply and the transformers residing in the center of the chassis, surrounded by the circuitry to ensure isolation from vibration and resonance. The three self-leveling isolation feet on the bottom panel of the amp further aid in control of vibration.
Monolithic yet handsome in a chunky sort of way, the A-100 takes up a lot of real estate. Although its footprint is similar to my Concentras, its almost twice as high and twice as heavy. Dimensionally, the A-100 measures 15 1/16"W x 9 7/8"H x 19 1/16"D and weighs in at 88 pounds. There are no rack-mounting handles, and although I was able to lift the A-100 out of its box with a quick clean and jerk, I wouldnt recommend it. Get a buddy to help you.
A centrally placed motorized volume knob dominates the subtly sculpted front panel. Above this are five buttons for choosing among three single-ended RCA inputs and one balanced XLR input, plus one button for muting. Below the volume knob is the power button, which initially glows red when the A-100 is powering up but then glows blue once the amplifier section is up to its proper operating temperature. The same pleasing blue color indicates which input button is in use and also if the muting is on.
The A-100 is equipped with a protection circuit that activates if its driven into overload. When the protection circuit has been activated, the power button glows red until the amp is switched off and allowed to recover. Despite driving the amp at high output levels, not once did the protection circuit activate for me. The last item on the front panel is a sensor for the supplied remote control, which allows for input selection, muting and volume control. The remote is illuminated and is also compatible with Esoterics digital integrated amplifiers and can control the functions of the company's disc players, with the exception of the P-01/D-01 transport and DAC.
The rear panel has three WBT RCA inputs and one XLR input for use with line-level sources. Theres one additional RCA input for use if the A-100 is paired with a preamplifier or a digital source with its own volume control. A switch below the inputs allows for switching between line in and direct in. Although my Wadia 830 CD player has a digital volume control, Ive never used it, and since I didnt have an audiophile-grade RCA-terminated interconnect handy, I wasnt able to assess this particular feature.
Connection to the speakers is via one of three pairs of vertically arrayed, gold-plated, plastic-shrouded WBT Nextgen binding posts, which are suitable for bare wire, spade lugs, and banana plugs. The middle and lower posts are for connecting speakers rated as a 4-ohm load and the upper and lower posts are for connecting 8-ohm (and higher) speakers. Ive heard others complain about these posts, but for the life of me I cant understand why. They were very easy to use, with my spade lugs slotting right in, with a snug fit once the post was tightened. The post can be tightened manually with no need for a post wrench and theres no risk of over-tightening. Too bad all amps dont come equipped with them.
Although the left lower corner of the A-100's rear panel has a rhodium-plated socket for an aftermarket power cord, Esoteric recommends using the supplied power cord, stating that use of other power cords may result in fire or electric shock. The last item on the rear panel is a bias switch at the top for setting the bias current for the KT88 output tubes. There are two modes -- A and B, with B being the standard setting. According to Esoteric, the A mode has a slightly reduced bias voltage, which may result in a slightly finer sound with enhanced detail suitable for classical music, but in non-blind and blind testing, I could not appreciate any difference between the two settings and left the amp in B mode for the duration of the review.
The top panel fastens to the sides of the chassis with recessed hex bolts and is vented on the top surface and the sides. The complement of tubes can be seen glowing faintly within, but even though the top panel is removable, the tubes are not to be replaced by the user (no tube rolling!), as special measurements are necessary to adjust the tubes. Standing over the amp, I could feel the heat radiating out of the top, but despite prolonged use of the A-100, even at high output levels, its top plate never became too hot to touch, nor did my listening room become too warm.
Warm and fuzzy -- not
After unpacking the A-100, I immediately connected my source and speakers. I was eager to hear how it all sounded, and as soon as the power button light began to glow blue, I started my listening. I was a bit too eager, I guess, as the sound at first was thin and pinched and the soundstage was compressed. After a half an hour had elapsed and the amp had a chance to really warm up, I began to listen again with much better results and no further change in the quality of sound, despite the A-100's not having been broken in prior to my receiving it.
This was one dead-quiet integrated amp! Whenever I connect a new amp into my system, I like to turn up the volume with no source playing in order to see at what level the hiss will be audible from my listening position. I turned the A-100 waaaaay up and was unable to detect any hiss at all until I nearly hit the maximum volume. Wow!
Right away, I noticed that all recordings, regardless of genre, had increased warmth to them. Not surprising, you say. What was surprising, though, was on how many different levels this warmth had an effect on the music. Regardless of whether the recording came from the studio or was live, the ebb and flow of the music was so natural that it was as if I had been transported to the musical event and the musicians were performing in front of me. The soundstage was so wide and deep that it overcame the limitations of my current (and much compromised) listening room. More than anything, this warmth added a dimension to the music that allowed an accurate, physical re-creation of the venue that Ive never experienced before.
Im a sucker for a great jazz piano trio, but the upper registers of some of these recordings can sometimes sound hard. The added warmth that the A-100 brought to piano went a long way to ameliorating that effect. On Keith Jarretts My Foolish Heart [ECM 2021/22], this quality was superbly demonstrated, as Jarrett displayed a delicate touch on the title track, with his right hand conveying the quiet elegance of the tune.
If youre thinking that this warmth burnished the tone so much that fine detail was obscured and the treble and midrange were colored, think again. Sonic images were holographic and finely rendered with the blackest of backgrounds, and even familiar recordings had previously subtle elements that were more fully revealed. The soft brush strokes that James Cobb employed on "Blue in Green" from Miles Daviss seminal Kind of Blue [Columbia/Legacy CK64935] sounded crisp and snappy, with no masking of detail. No doubt the low noise floor of the A-100 contributed to this sonic realism.
Acoustic music, particularly jazz and classical, is usually well engineered and recorded, but amplified music, especially pop and rock'n'roll can be hit or miss -- mostly miss. One exceptionally fine recording, Govt Mules eponymous debut record [Relativity 88561-1515-2], was recorded mostly in the studio with minimal overdubbing, and the A-100 allowed the band's brand of spooky, gothic, blues-inflected rock to flow through my speakers with all its intensity intact. Soundstage width was superb, with sonic images so stable that I felt as if I was in the studio with the band.
Despite being a modestly powered integrated, the A-100 was not at all shy about rocking out. On the Govt Mule disc and Peter Framptons Frampton Comes Alive [A&M 069 490 563-2], I was able to drive my speakers to almost concert level with commensurate visceral impact and no sense of strain. The A-100 had a seemingly endless reserve of power and never felt as if it was going to run out of juice, even though its rated power output was under 50 watts.
While treble and midrange reproduction were excellent, bass reproduction was simply outstanding. One weakness of tube-powered amps has been soft or flabby bass. The A-100 disproved that notion convincingly with solid control of my speakers woofers. On the King Crimson Songbook Volume One by the Crimson Jazz Trio [Voiceprint VP373CD], both bass guitar and bass drum were forceful and didnt get lost in the mix. On "21st Century Schizoid Man," Tim Landers fretless bass lines were tight, tuneful and resonant with such deep extension that they recalibrated my expectations of the bass reproduction that my Wilson Audio Sophia loudspeakers were capable of. Bass drums can often be subtle, with the exception of those heard in solos, but on "Schizoid," Ian Wallaces bass drum had the kind of taut, punchy, propulsive surge that so rarely is achieved.
And so it went with my listening , the A-100 not only contradicting its tube-based circuitry but also readjusting my understanding of my system and reproduction as a whole. This was a special performance by a special piece of audio equipment.
Tubes vs. tube-like solid state
In some ways the A-100 and my Jeff Rowland Concentra ($5600 when available) are evenly matched. Both deliver their power -- 100Wpc in the Concentra's case -- with ease and no sense of strain. With both integrated amps, the treble is grain-free and the midrange is free from colorations. Where its absolutely no contest, however, is the A-100s dead-quiet noise floor, superior bass control and -- damn -- that magical vacuum-tube warmth that makes the music seem more alive. Ive always felt the Concentra was a fairly neutral-sounding integrated with a slight bias to warmth and, compared to others that Ive heard, this is an accurate assessment. But in comparison to the A-100, it sounds more tonally cool. Some may argue that the A-100s warmth is an artifact that adds coloration to the sound, but in listening to it, Ive come to the conclusion that this warmth returns a vital aspect of the music -- its soul.
While I am still somewhat ambivalent about tubes -- adding them to my life, that is -- I have to admit that the A-100 simply sounds better than my Jeff Rowland Concentra, and in ways that a solid-state integrated amp should beat one that uses tubes. Of course, there is an immense difference in price, but I admit that it's easy to hear why the A-100 costs so much more than the Concentra.
Im gonna miss her
For me, the Esoteric A-100 was a perception-altering, paradigm-shifting component. When I first began putting together my system, I spent as much money as I could possibly afford, confident that I would have to spend considerably more money for only incremental improvement in resolution and overall sound quality. Was I ever wrong -- except for the money part. No, I havent had a crisis of confidence, and Im not about to start tossing out components and starting from scratch, but, believe me, the A-100 is so good that if I had the scratch, Id certainly consider buying it.
But at almost $20,000, the A-100 is like that smart, funny, vivacious and beautiful woman across the room -- out of reach for most. As for Esoterics stated goal of capturing the beauty on the master tape, Id say its "mission accomplished" with the A-100.
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