Benchmark Media AHB2 Achromatic Audio Amplifier
The Benchmark AHB2 amplifier is named for Benchmark’s Founder Allen H. Burdick, who founded the “Benchmark Sound Company” in Dallas, Texas in 1983 and changed the company name to “Benchmark Media Systems, Inc” in 1985 when he moved the enterprise to Syracuse, New York. Burdick was one of the leading innovators in the Pro-Audio Industry and had a life-long passion for advancing the quality of audio reproduction. Unfortunately Burdick passed away in September of 2013 and the AHB2 amplifier is dedicated to the honor of his memory. Burdick will be missed but not forgotten.
The AHB2 amplifier is essentially a Class AB amplifier that moves into Class H operation engaging extra voltage rails when high power is demanded. It uses bi-polar output devices to insure low noise performance and has ultra-wide bandwidth extending from 0.1Hz to beyond 200kHz.
THX has patented this Achromatic Audio Amplifier technology (AAA™) and applied it in Benchmark’s AHB2 amplifier in a collaborative effort. This new AAA™ technology takes a novel approach to virtually eliminating noise and distortion from the amplifier especially in the critical areas where the input signal passes through the zero-voltage point as it swings from positive to negative voltage (crossover distortion) and again at the juncture where the amplifier transitions from Class AB operation to Class H.
The AHB2 employs some global and some local negative feedback to keep the distortion extremely low but perhaps more importantly the amplifier uses THX’s Feed-Forward Technology that applies a different signal to the amplifiers output in the crucial crossover regions I mentioned above. Because of this technology operating bias current can be kept low while still providing excellent sound quality, greater efficiency and ultimately results in far less heat that needs to be dissipated out of the amp and into the room. THX claims that this technology (unlike standard negative feedback topologies) keeps the amplifier very stable even at very high ultra-sonic frequencies so the highs do not sound hard or edgy as they can and do in many other amplifier designs. It also keeps the inherent noise level of the amplifier extremely low — down to -132dB A-weighted in Stereo Mode. This is phenomenal performance by any yardstick.
I can verify that the amplifier does not get hot even after extended listening at healthy volume levels. When I’ve grasped the heat sinks under such conditions they feel luke-warm but far from hot. Bear in mind that this amplifier is physically quite small and yet provides 100 watts per channel into 8-Ohms, 190 Wpc into 4-Ohms, and a whopping 480 watts into 6-Ohms in its Bridged Monophonic Mode.
Being a basic power amplifier the AHB2 does not have many operational features. The front panel contains the Power On/Off button and a row of LED’s to indicate amplifier clipping, high temperature, and muting for each channel. When the amp is first turned on or off the Muting lights will come on for a brief time and then shut off indicating the amplifier is fully operational. There are no turn-on or turn-off thumps or noises with the AHB2.
The rear panel houses the AC IEC input connector and a decent quality locking AC cord is supplied. For many, the stock cord will work fine and those who would like to use the aftermarket power cord of their choice can do so. It also has standard high-quality speaker binding posts for each channel as well as the very low-distortion Pro-Audio SpeakON output sockets for those who want the lowest distortion level possible, although, in practice, I doubt that you could hear the difference between the standard speaker posts and the SpeakON connectors.
Only Balanced XLR input connectors are provided so to use RCA-type inputs you will need to buy adapters. This will of course raise the noise level a bit, which is just basic physics and would work the same for any Balanced input amplifier converting to RCA inputs. In any case the resulting noise level will still be much lower than the best-case noise level of most amplifiers. There are also 12-volt trigger In/Out connections, and a switch that selects either mono or stereo operation. Benchmark has thoughtfully provided a 3-position gain selector switch which allows the user to select between low, medium, and high input sensitivities. In my particular installation I found that the medium position worked best to allow the Master volume control on my preamplifier to be set in the range that I prefer for listening.
When I first hooked up the Benchmark AHB2 amplifier to my VMPS RM40 speakers and began listening the sound was quite clean and musical but a bit light in the bass compared to my reference amplifier, the Rogue Medusa. But after 25 or 30 hours of play time, the deep bass began filling in and became more articulate yet robust.
Indeed, after more break in the AHB2 was rocking my house with cuts like Madonna’s “Beautiful Stranger.” Then, from the Chicago CD soundtrack (Epic/Sony EK 87018) “He Had it Comin’” showed off the amp’s ability to handle powerful low bass transients without any bloating or overhang—but with no shortage of impact and startle factor. And on Cat Steven’s rendition of “Don’t Let Me Be Misunderstood” from his An Other Cup CD (Atlantic 94550-2) the very low notes in the song’s opening showed the AHB2 is capable of producing sustained power and depth in the deep bass without running out of steam. In fact, the bass became even more solid and taut than that of my Rogue Medusa, which up until this juncture had delivered the best bass performance of any amplifier I had tried in my system.
In addition to the AHB2’s impressive bass performance, the midrange sounds extremely pure and clear, not only on vocals, but on many other midrange instruments such as brass horns, woodwinds, piano, and strings of all kinds. But it isn’t merely the stunning clarity of the Benchmark amp that lets one know it’s very special, it is the musicality and authenticity one hears from his or her favorite recordings.
Not only is the AHB2 tonally convincing, but it is quite dynamic as well. Depending on the recording, vocalists and instruments sometimes virtually leap out of the speakers and into the room. And, because of its extremely low noise floor it is very good at excavating previously undetected low-level details and nuances. I believe it is the purest sounding and lowest noise amplifier in my experience. Is the AHB2 the “perfect amplifier?” The truth is that it could be when paired synergistically with certain components and speakers.
Playing through tracks on Eagle Eye Cherry’s Desireless CD (Sony DK 69434) again showed wonderfully deep and satisfying bass on “Worried Eyes,” and a nice natural female vocal as well. And on “Rainbow Wings” the reproduction of the percussion was excellent and the male vocal was very well rendered with natural tone and impressive lyric comprehension.
What is perhaps most impressive about the AHB2 is its very natural presentation of brass horns, piano and percussion in general. On many of recordings hand claps had more body as did wood blocks or drum sticks being beat together. And with cymbals the amp grabbed more of the fundamental note of each shimmering strike providing a little more weight and a sense of body.
When I began my evaluation, I was using my reference VMPS RM40 ribbon hybrid speakers. The AHB2 matched very well with them and I believe part of the reason for that is because the VMPS are a little laid-back sounding while the AHB2 is somewhat more forward in its presentation. Later in my testing I switched to the Legacy Audio Focus SE speakers (also in for review) and found that while the sound was still very clean and musical, it was a bit more forward sounding than I would like in the long term. I attribute that to both the AHB2 and the Legacy Focus SE to be slightly forward sounding components. And this lower treble prominence seemed to actually mask or dominate the upper high frequency harmonics.
I believe this forwardness has implications in the imaging department as well. Although the AHB2 threw a very wide image with the Focus it did not extend very deep. But on the VMPS speakers the image depth was both wide and deeper and was more neutral in its localization of instruments and vocalists. This is why I began to prefer the sound of the AHB2 on the VMPS and liked the slightly more laid-back character of the Rogue Medusa amp on the Legacy Focus SE. So if you own speakers that are already forward sounding, especially in the lower treble area the AHB2 will sound very good, but it may not be the ideal match. Of course your other associated components will also come into play to determine the final presentation.
Other than a slight lack of air in the very high treble I can’t find much to criticize about the sonic character of the AHB2 amplifier. And using silver-based audio cables (instead of copper) could help that situation.
Because Benchmark wanted to keep the amp’s noise level way down they elected to only provide XLR Balanced inputs but I think some audiophiles will miss not having single ended RCA inputs… especially those that bought expensive single-ended RCA-type interconnects. But inexpensive RCA to XLR adapters can be used if necessary.
I found a minor problem with the amp freezing up on turn on if my finger had any static discharge when I touched the amp. The solution was to turn the amp off, wait 30 seconds and turn it back on again. I alerted Benchmark to this problem and they have fixed it with a factory-only firmware update and by the time you read this review the updated version will be the only one available.
The Benchmark AHB2 is a powerful and efficient amplifier with prodigious low levels of noise and distortion. The fact that it is also very musical and non-fatiguing, courtesy of THX’s patented AAA™ technology, is the icing on the cake. Benchmark Media and THX have a lot to be proud of for the development and implementation of the new technology the AHB2 represents.
The AHB2 provides deep, impactful, and articulate bass, a very musical and transparent midrange, and ultra-clean high frequency reproduction. It did not deliver the last bit of air or soundstage depth in my particular system, but perhaps with different associated components or cables it would improve in that area. Ultimately, the choice of an amplifier all boils down to system synergy and what combination of components will sound best to the particular buyer.
I very much enjoyed my time evaluating the Benchmark AHB2 amplifier and can heartily recommend it to those seeking one of the lowest distortion and lowest noise amplifiers on the planet—one that is very musically transparent and easy on the ears to boot.
I sent this review to Benchmark Media for a technical fact check prior to publication, which is my usual policy. Benchmark’s Vice President, John Siau took the time to confirm my technical statements and offered some further thoughts that provide additional insight regarding the development and performance of this exceptional audio amplifier. Read Mr. Siau’s manufacturer comment below:
Thank you for reviewing our AHB2 power amplifier. Your observations generally coincide with what we have experienced. The AHB2 will sound different than other amplifiers.
We believe power amplifiers are a weak link in many audio systems. Converters, line-level audio components and digital formats have all outpaced the development of power amplifiers. We wanted to build a power amplifier that would deliver the full performance of the Benchmark DAC2 all the way to the speaker terminals.
The AHB2 is the result of a multi-year collaborative R&D project that was focused on eliminating the disparity between power amplifiers and the rest of the audio chain. The THX patents gave us a tool to virtually eliminate distortion from high-power push-pull output stages. In developing the product, we focused on distortion, frequency response, phase accuracy, damping factor, noise, and efficiency ... in that order.
The AHB2 is not intended to enhance or sweeten the music. Its job is to render a near perfect high-power replica of the incoming line-level signal. It does this very well. Consequently it may sound significantly different than other amplifiers. Familiar amplifier-induced distortion components are gone, and this will often be perceived as a change in frequency response. Low-frequency distortion can give the impression of increased bass, but this distortion is absent in the AHB2. Likewise, the AHB2 does not have the familiar high-frequency push-pull crossover distortion, or the high-frequency sizzle produced by class D amplifiers. This absence of distortion may give the impression of a reduced high-frequency response. But, after adapting to this difference, the result is a natural and non-fatiguing listening experience. At the end of a long day transparency wins.
The performance of the AHB2 is dramatically different than that of other power amplifiers. It is at least 15 dB quieter than all other amplifiers, and is 30 dB quieter than most. When driven directly from a Benchmark DAC2, no noise should be audible from any of the speaker drivers unless it is contained in the recording. The reduction in distortion is just as dramatic, but is much more important to the musical accuracy. The extended 0.1Hz to 200 kHz frequency response is well matched to High Resolution audio formats. This extended frequency response plays a critical role in eliminating the phase shifts and L to R phase differences that often alter the stereo image produced by other amplifiers.
Benchmark Media Systems, Inc.
Benchmark Media AHB2 Power Amplifier
Dimensions: 11.04" W x 3.88" H x 9.34 " D – Non-rack mount including feet and binding posts
Net Weight: 12.5 pounds
Please visit www.benchmarkmedia.com for detailed specifications.
Benchmark Media Systems, Inc.
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Syracuse, NY 13206 USA
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