Benchmark AHB2 Amplifier

Essentially Perfect

Equipment report
Solid-state power amplifiers
Benchmark Media Systems AHB2
Benchmark AHB2 Amplifier

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.


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

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