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Benchmark AHB2 Amplifier

I don’t have much to say about the sonic qualities of Benchmark’s new AHB2 power amplifier because there isn’t that much to say. Used within its limitations and for its intended purposes it is in any practical sense perfect. I know this is not the sort of thing we’re supposed to say about products, but it has been evident for a very long time now that solid-state electronics, particularly linestage preamplifiers and power amplifiers, have reached a point where they are effectively a solved problem such that it is exceeding difficult to tell one from another even in the most exacting A/B comparisons. Ferretting out differences typically involves zeroing in on a very specific and limited characteristic or set of characteristics with such concentration as to leave one tired, uncertain, or both: in other words, an activity that is the very antithesis of what is involved in listening seriously, even critically—to say nothing of pleasurably—to music. [I must point out that this view is not shared by the TAS editorial staff. —RH]

That said, even by contemporary standards of the most sophisticated, exotic, and expensive electronics, this new amplifier is something of a technological tour de force. The AHB2 boasts a signal-to-noise ratio that exceeds 132dB and total harmonic distortion figures of –131dB (3rd harmonic) and –122dB (2nd harmonic) under no-load conditions; it also exhibits, so Benchmark claims, “no trace” of crossover-notch distortion, though it is Class AB, not Class A. (I should immediately add that these figures have not been achieved by heaping on huge amounts of negative feedback, à la those wretched solid-state designs of the Seventies: assisted by a feed-forward error-correction circuit, the AHB2’s noise and distortion hold up under dynamic, not just static, conditions.) The power output is 100Wpc, with a claimed 18 amperes of current in stereo mode, bridgeable to 380W mono. The amp, which is THX certified, is outfitted with a number of protection circuits, the operation of which is monitored by front-panel LEDs, is unconditionally stable, and, like all Benchmark products, is backed by an impressive five-year warranty.

I front-load my remarks with these numbers to get your attention. While Benchmark products have made serious incursions into the audiophile community, they are made for the professional market (where they are ubiquitous) and designed to the most exacting standards of performance and reliability. They are also for the most part minimalist as regards function and size: You won’t herniate yourself toting this amplifier around because it measures 11″ x 4″ x 9″ and weighs a mere 13 pounds. I auditioned the AHB2 on my Quad 2805 electrostatics, Harbeth Super HL5pluses, and the new Falcon LS3/5as. (Digital sources are a Marantz 8000 SACD player and a Benchmark DAC; vinyl, a Basis 2200 and Vector IV ’arm with an Ortofon Windfeld pickup.) Allowing for differences in the speakers, the amp sounded identical on all, its 100 watts more than sufficient to drive them to levels far higher than I could comfortably sustain for more than a few minutes. The sensitivity of all these speakers is around 85–87dB and they present reasonable impedance loads.

An adjective that came to mind when I first fired up the Benchmark was “crisp.” “Ah, see,” I hear several of you saying, “solid-state.” Well, yes and then again no. For the past year and longer, the amplifiers I’ve been mostly listening to have been the Zesto Audio Bia, an all-tube unit, and the Quad 909 solid-state, but solid-state with limited bandwidth both top and bottom (the AHB2’s bandwidth is extremely wide). Now both of these amps are, generally speaking, neutral within what I call acceptable boundaries of neutrality, but neither of them is dead neutral. As I pointed out in my review, the Bia is perhaps best described as classic tube sound brought up to date: very dynamic, excellent transient response, well-defined and articulate bass, gorgeous midrange. But it is decidedly a tube sound with all the lusciousness and romanticism thereby suggested. The 909 is bandwidth-limited at the very bottom (below 13Hz), which inevitably translates into some phase shift that confers a little extra warmth on the presentation, and also at the very top, which lacks the almost crystalline clarity you get from frequency response that extends out to 100kHz and farther. But its supreme musical authority and naturalness are second to none and never fail to satisfy me when it’s in the circuit (which is often).

So, yes, coming after both of these units, the Benchmark would by comparison sound a bit crisp. Within a remarkably short period of time, however, this adjective dropped from mind as my mental processes shifted from comparison mode to enjoying music, all the attention drawn to the source material and the rare sensation of feeling as if I were listening back to the source. The Tokyo Quartet’s valedictory recording of the late Beethoven quartets is close up and slightly dry but the instruments are nevertheless warm and beautifully rendered. By comparison, the Belcea’s traversal is recorded more distantly, the acoustical space—a lovely one—far more enveloping, and it sounds that way. In neither case does the Benchmark appear to overlay any sound of its own—nor would I expect it to. What is there to overlay? Used within its specifications, distortion is nonexistent, while the noise floor is claimed to be lower than the lowest digital by as much as 10dB.

You will notice, by the way, that I’ve said almost nothing about detail and resolution. There are two reasons for this. First, the Benchmark resolves and thus reproduces all the detail there is on every recording I played that I know well, so there’s no real need to accrete half a dozen examples to buttress the point. But let me cite the toughest resolution test I know: for the a cappella introduction of “Moon River” on her Johnny Mercer album, the soprano Jacintha was placed in an isolation booth while occasional chords from a piano were played through her headphones so that she could stay in tune. Despite heroic measures to ensure isolation, the chords nevertheless bled through her headphones and can be heard during the silences. Now these are extremely far down in level; in a couple of instances they are all but inaudible. If a component can reproduce them, that’s about as much resolution as you are ever likely to need. Suffice it to say the Benchmark did.

But second, and more important, is that I’m getting tired of hearing detail and resolution used as be-alls and end-alls in audio reviewing. Too much detail is unnatural and it’s certainly not realistic, and because you hear it with some components and not with others does not necessarily indicate the former are accurate, the latter not. The reality is that it’s easy to phony up detail with rising top ends. This is the case with speakers, phono pickups, and even some kinds of electronics. Try it sometime: Borrow an equalizer or simply a control unit with a treble control and boost the highs even slightly—voila!—more detail. I’ve gone out and auditioned many components that are raved about for their so-called resolution and in virtually every instance I’ve found they do not sound truly neutral or natural when it comes to reproducing musical instruments and voices. [See my editorial “Too Much of a Good Thing?” in the February 2016 issue for my substantially different perspective on this subject. —RH]

 

As a remarkable number of audiophiles still tend to listen with their eyes rather than their ears, there continues to be a prejudice in favor of size, weight, and bulk, especially as regards speaker systems and amplifiers. I have no wish to engage the double-blind test debate here, but I do think there’s a lot to be said for not knowing what you’re listening to when evaluating components, particularly when it comes to electronics. The truth is that if electronics, particularly solid-state electronics, are correctly designed, they just work: When they don’t sound neutral the reason is typically some limitation or flaw in the design, being pushed beyond their rated power, an interaction with untoward speaker loads and/or cabling, or a flavor the designer consciously built into it (e.g., the exceptionally pretty Gundry dip Bob Carver designed into his Sunfire amplifiers). The Benchmark will reproduce a bright, forward sound if it’s in the source, as it is with a vengeance in Bernstein’s New York recording of Copland’s Appalachian Spring, and it will produce a warm and intimate sound if that is in the source, as in Ofra Harnoy’s Arpeggione sonata by Schubert.

What about the big stuff? Well, I don’t know much bigger stuff than the lowest organ notes on Kei Kioto’s Bach recital, and they’re not transients, either, but deep, long, sustained notes. No problem on the Quads or the Super HL5plus. But the response of those speakers does not descend into the deep, deep depths (the Falcon LS3/5a obviously doesn’t go anywhere near as deep as even the 2805 or the Harbeth), so I will defer to REG for further comment on that. But Benjamin Zander’s recording of the Mahler Sixth with its hammerblows was awesome enough in slam and weight to satisfy. If you need more power, you can always add a second AHB2 and bridge both for mono operation.

As part of the evaluation, I auditioned a single AHB2 driving the Harbeths in a room considerably larger than my own: 18 feet wide by 32 feet long with a pitched ceiling that rises to 13 feet at its apex. This combination filled the room as loud as I and the owner could stand and at no point did the clipping indicators illuminate, even during loud organ music with sustained very low notes. That said, there is one aspect of the design that must be emphasized: The power supply is very strictly regulated, the 100 watts of continuous power generating only about 110 watts on instantaneous peaks. This is salutary because it keeps the amp within its noise and distortion specifications vis-à-vis its power output. But there are other amplifiers with less tightly regulated power supplies that allow for much greater power output on instantaneous peaks (this is a design feature on the NAD amps). The price there is increased distortion, but the argument goes that because the music is so loud, and the duration so brief, the extra distortion goes essentially unnoticed. Both approaches are valid, so you pays your money and takes your pick according to your needs, desires, and wallet. 


Which is only to say that the AHB2, like any amplifier, is not for all speakers or all users. When the Muraudio electrostatics arrived here, REG and I hooked them up and the sound was not good: undynamic, muffled, poor imaging, little control. But at 82dB the Murs are ridiculously low in sensitivity, requiring at least a couple hundred watts of clean power per side, and preferably a whole lot more. We didn’t have a second Benchmark at the time, so I can’t say how a bridged pair would have done (though there’s no reason to suspect it would have been less than excellent). Benchmark also specifies that the amp should not be used with impedance loads that go way south: 2.2-ohms is the specified bottom limit, so how it would fare with speakers that drop substantially below this figure (e.g., certain Wilsons), I am not in a position to say. (Rory Rall, Benchmark’s sale manager, tells me that in fact a single Benchmark in stereo mode does very well with several Wilson models they’ve tried it on, which makes sense since Wilsons are pretty efficient, although some models’ impedances dip well below 2 ohms.) If you’re uncertain, the company allows generous home trials, so you’ve nothing to lose (except perhaps some prejudices about how physically large and heavy power amps have to be). But to repeat, used within its specifications, the AHB2 is unconditionally stable, sonically neutral, and operationally flawless. (Toward the end of the review period, Benchmark supplied a second amp, alas too late for the Muraudios. REG, who has less efficient speakers than I, will comment on AHB2 in bridged mode.)

A few technical matters before I close. First, the amp has balanced inputs only, so you will need to use an adapter for a single-ended preamp. Benchmark markets balanced to single-ended cables that are reasonably priced and excellent. (If you have your own adapters, check with Benchmark before using them, as the company recommends a particular form of wiring the three conductors.) Benchmark also markets excellent balanced interconnects and recommends full balanced operation if possible (see sidebar and REG’s comments for more on this). The speaker outputs accept banana plugs or, alternatively, Neutrik speakON connectors, which is how Benchmark’s speaker cables are terminated. Benchmark supplied me with both its interconnects and its speaker cables and they performed superbly, consistent with the quality of the electronics themselves.

Because accuracy allied to absolutely reliable performance is the goal of all the Benchmarks, they are not products that tend to attract cults or other sorts of starry-eyed enthusiasts, wholly lacking any of the quirks, foibles, idiosyncrasies, sonic flavorings, euphonic distortions, and so on that characterize the objects of most audio cults. Professionals buy Benchmark because they know the products work and are reliable and accurate—indeed, reference caliber. Music lovers buy them because they are neutral and accurate and thus reproduce the tonal character of voices and instruments correctly (and also, I presume, because they are reasonably priced, most musicians, like most other people, being typically not wealthy). But audiophiles? Well, the longer I’m in this racket, the less I sometimes think I understand what audiophiles really want except that a lot of dallying about with components, equipment swapping, and coloration matching seems to be what amuses them. I’m not sure I can in good conscience recommend this amplifier to them as I am not sure they are in search of what it offers: a precision instrument designed to perform the precisely defined task of reproducing music and sound accurately, which it does essentially to perfection. But to anyone else, the AHB2 gets as high, enthusiastic, and confident a thumbs up as my arm is capable of reaching.

SPECS & PRICING

Output: 100Wpc into 8 ohms, both channels driven; 190Wpc into 4 ohms, both channels driven; 380W bridged mono into 8 ohms; 480W bridged mono into 6 ohms
THD+N: 1kHz, < 0.0003%
SNR & dynamic range: 132dB A-weighted, stereo mode; 135dB A-weighted, mono mode; 130dB unweighted, 20Hz to 20kHz, stereo mode; 133dB unweighted, 20Hz to 20kHz, mono mode
Frequency response: 0.1Hz to 200kHz, +0/-3 dB
Input impedance: 50k ohms, normal mode; 1M ohms, common mode
Dimensions: 11.04″ x 3.88″ x 9.34″
Weight: 12.5 lbs.
Price: $2995

BENCHMARK MEDIA
(800) 262-4675
benchmarkmedia.com

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