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Benchmark AHB2 power amplifier

Benchmark AHB2 power amplifier

Benchmark made its mark on the audio fraternity in the late 2000s with the unusually compact, yet full featured, converter and preamplifier… the DAC1, the latest DAC2 incarnation of which I reviewed in these pages a couple of issues back. But, the brand’s origins start in founder Allen H. Burdick’s garage back in 1983, when he started making electronics for the broadcast industry. The company was incorporated two years later and moved to its current home in Syracuse, New York. It still has a pro-heavy product range, but until last year that range didn’t include a power amplifier, even if there has been a reference amp that Benchmark engineers have used for product development for some time. This former in-house only model was designed by Burdick himself (hence his initials gracing the facia of the AHB2), but it went through some major changes when Benchmark started working with THX and its achromatic audio amplifier technology, or AAA for short.

You get some indication of this technological back-story when unboxing this power amplifier, but what hits you first is its unusually compact size for the power output rating. The AHB2 is less than half the size of most power amps; you can tell by the back panel if you look at the relative size of the speaker outputs just how small. This challenges the usual assumption that size equals power quite seriously and this must make marketing a bit of a challenge in some regions. But Benchmark must be encouraged by the success of the even more compact DAC1 and 2, and perhaps it sees the end of the era of room-filling electronics more clearly than most.

As ever with Benchmark, it seems size does not limit feature count; not only does the AHB2 have conventional four-way binding posts, but there’s a pair of Neutrik’s Speakon connectors as well. This is an indication of its studio inclinations in one respect, but also a reflection of the fact that Benchmark makes a monitor (the SMS1) with matching inputs and a bi-amp or bi-wire option when using them. The AHB2 only has balanced inputs however, it being a fully balanced design. This is fine for pro applications and Benchmark DAC/pre owners, but less convenient for many domestic users who remain firmly single-ended.

Getting back to the THX connection, apparently the core design of this amplifier and its Class H power supply were designed by that organisation. At its heart the AHB2 has a switching power supply, which explains its diminutive size: it’s a Class H design rather than Class D because it features a Class AB output stage, and it uses multiple supply rails to improve efficiency. The Class AB output stage is a bit different from most: the AAA element consists of a feed-forward error correction amp that seeks to minimise distortion by “measuring, inverting, and buffering errors in the main amplifier”. It is claimed to be superior to conventional feedback designs when it comes to measured distortion.

 

This amp threw me a bit when I first tried to use it; my routine way of working with power amps is to leave them to warm up for an hour before listening, but I returned to find the amp was no longer powered up. A spot of manual diving later, I discovered that the ABH2 goes into standby if there’s no signal for 45 minutes. It claims to reach its operational peak within minutes, so there’s no need for permanent power up – something polar bears and studio bosses alike will undoubtedly appreciate (many in the recording industry might fail to spot the difference between polar bears and studio bosses, polar bears being moderately less ferocious when cornered). However, this feature along with the tiny display on the matching DAC2, and a volume control that turns itself down at power up, means there are a host of potential no-sound-although-the-source-is-playing scenarios. But this is a learning curve rather than an idiosyncratic issue, and I approve of Benchmark’s eco credentials.

As well as in- and output connections, the rear panel features bridging and gain switches, where the latter has three positions: low, mid, and high. These vary gain from 23dB to 9.2dB, making the amp more flexible in application presumably for pro-audio situations.

The majority of the auditioning with the AHB2 was done with the partnering DAC2 preamp/converter, its XLR outputs being better suited to the task than the RCAs on my resident Townshend Allegri. Listening started with PMC fact.8 speakers and the Melco N1-A as a digital source straight into the USB input on the DAC2. This combination was very revealing and rhythmically secure: Herbie Hancock’s ‘Maiden Voyage’ [Maiden Voyage, Blue Note] revealed the broad dynamic range available by building up slowly with a very quiet background. Orchestral dynamics were also well served, as the amp has considerable speed and an ability to deliver serious power with alacrity, and there’s no sense of overhang in the bass. This, conversely, also means that the quieter moments have considerable delicacy.

However, all was not entirely happy balance-wise, as the system sounded too lean when the level was cranked. However, this is not solely attributed to the amplifier: not all amp/speaker pairings work perfectly. So I moved onto a rather different option in the form of Bowers & Wilkins CM10 S2 floorstanders. This ported design has a warmer balance than the PMC and as I’ve discovered tends to prefer different amplifiers. This speaker allowed the Benchmark to reveal just how much power it can muster; the first movement of Symphony No.7 in A, Op.92 [Barenboim, Beethoven For All 24/96, Decca] sounds vigorous and full scaled as a result. Another Hancock album [Gershwin’s World, Verve] features Stevie Wonder singing ‘St Louis Blues’, in a performance that reminds you of just how great an artist he is. Here the voice is calm and effortless, the keyboard is played with a perfect groove, and the sound becomes a physical presence in the room. The bass, however, could not be tamed. I pulled the speakers out from the wall more than usual, but the bass remained overblown so that ultimately I came to the conclusion that the CM10 S2 was not the right speaker either, albeit not before Dr Feelgood’s ‘Roxette’ [Down By The Jetty, United Artists] raised the hairs on the back of my neck. The Benchmark has an immediacy that makes for uncanny realism, so a track like this is more intense and vital, more powerful in fact.

However, the bass was beginning to grate a little, but there was still one option on the speaker front to try: the Benchmark SMS1 that had been supplied with the amps with a view to doing a whole system review, a state of affairs that came to pass with gusto when I discovered just how well the combination gelled. The £2,699 SMS1 is a two-way bookshelf design with a fancy aluminium grille, hardwood cheeks, and an infinite baffle suspension, so no ports or transmission lines. It couples a 170mm copolymer mid/bass with a 25mm soft dome tweeter in a 343mm high box containing what by the sound of it are high quality components. As it would have been churlish not to, I used the matching Speakon terminated cables that the distributor supplied, and I have to admit the system was a blast.

 

The immediacy noted earlier came into another league and was joined by serious dynamics and a degree of resolution that made sense of the pricing if not the size of the components. The new Food album [This Is Not a Miracle, ECM] was palpable even at low levels, muscular and visceral in such a way that the blend of horns and electronica made a deeper impression than it had done initially. The Benchmark pairing proved analytical (in typical studio style) but not dry – just very revealing of recording style and balance. This meant that source quality was rather too obvious for the relatively crude nature of the standard WD NAS drive used in my second system. Put a nice slab of vinyl under the needle of a Rega RPM10, however, and you are in for a treat. The dynamic range, subtlety, shadings, and dynamics of Anouar Brahem’s Barzakh [ECM] were all in evidence in the context of an extremely quiet background and considerable tonal depth. It showed off the finesse of both the turntable and the low noise of the Benchmark duo in analogue mode. The Rega Saturn-R CD player’s lack of tonal finesse in the treble was however rather clearly revealed; it’s the price you pay for transparency of course.

The AHB2 is a very impressive amplifier for its size and the it’s about the best compact power amp I have encountered. It seems fussier about speaker partnering than usual, however, and I would recommend trying it with your speakers before purchase. But the fact that it’s smaller and more efficient than most of the competition, and that it can bring the ‘electricity’ of the original recording into your living room makes it seem rather good value. With the right system, this comes highly recommended!

Technical Specifications

Type: solid state stereo power amplifier

Analogue inputs: One pair balanced (via XLR jacks)

Analogue outputs: One pair of speaker taps (via 5-way binding posts), one pair of Neutrik Speakon connectors

Power output: 100Wpc @ 8 Ohms, 190Wpc @ 4 Ohms at 1kHz at < 0.0003 % THD+N

Bandwidth: Not specified

Sensitivity: 2, 4 or 9.8 Vrms

Distortion: < –119 dB (< 0.00011%) at 1 kHz, 20 kHz LPF, at full rated output into any rated load

Signal to Noise Ratio: 130 dB Unweighted, 20 Hz to 20 kHz

Dimensions (H×W×D): 98.5 × 280 × 237mm

Weight: 5.7kg

Price: £3,299

Manufacturer: Benchmark

Tel: +1 315-437-6300 

URL: benchmarkmedia.com

UK Distributor: SCV Distribution

Tel: +44(0)3301 222500

URL: www.scvdistribution.co.uk

Tags: FEATURED

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