Benchmark AHB2 Power Amplifier

Benchmark AHB2 Power Amplifier

The Benchmark AHB2 solid-state stereo power amplifier immediately grabbed the audio world’s attention about 7 years ago when it was introduced. Combining state of the art specifications, cutting-edge technology, and amazingly small size and light weight, the $2999 amplifier quickly became a must-audition. There are already a number of reviews, so the purpose of this one is to add another data point, another reaction to add to the knowledge base of this remarkable amplifier. 

Just looking at the amplifier’s diminutive size of about 11 inches wide, 3.9 inches high, and 9.3 inches deep, and 12.5-pound weight will not prepare one for the quality of performance delivered by the nicely finished package. Rated at 100 Watts per channel into 8 Ohms, 190 Watts into 4 Ohms, or, when switched to a single channel, mono amplifier for 380 Watts into 8 Ohms. Benchmark publishes a very complete set of specifications. Especially noteworthy are the following:

132 dB A-weighted Signal-to-Noise ratio
Frequency response better than 0.1 Hz to 200 kHz, -3 dB
Adjustable input sensitivity assures compatibility with any stereo system
Trigger connections
Full protection against shorts, distortion, over current, and over temperature
Worldwide voltage compatibility
XLR inputs. Unbalanced (RCA) inputs require RCA to XLRM adapters

One might well assume that due to these specs the amplifier is some kind of Class D “digital” tech. Not so! The amplifier has a low-bias bipolar class AB output stage which produces far less heat than most other amplifier bias schemes, especially those with high bias Class A output stages. The key to the small size and weight is the “tightly regulated resonant switching power supply”, which is claimed to be over 90% efficient. A switching power supply does not require “big iron” power transformers and large capacitors.

Other significant technologies include patented THX-AAA feed forward error correction. This is critical to the excellent sound of the amplifier as it eliminates crossover distortion, the common bane of push-pull amplifiers. The result is the sonic purity of a single ended amplifier with much greater power output and dynamic capability.

Other components on hand during the audition include a VPI Aries 3 turntable with a Kuzma 4-Point or Tri-Planar VII SE tonearm, Holbo Turntable System, Clearaudio Ovation turntable with Universal tonearm; ZYX UNIverse Optimum and Miyajima Madake moving coil cartridges; B.M.C. MCCI ULN and Aurorasound VIDA Prima phono preamplifiers; custom Windows 10 music computer running JRiver Media Center; Wyred 4 Sound DAC 2v2SE 10th Anniversary DA converter; RME ADI-2 Pro AD/DA converter with external power supply; Pass Labs XP-22, BAT VK-43SE, and Wyred 4 Sound STP-SE Stage 2 preamplifiers; Valvet E2 SE, Wyred 4 Sound ST-750LE, Cary SA-200.2 ES, and Mivera 1200AS2 power amplifiers; Magico S1 mk.2 loudspeakers with the lowest few Hertz engaged by a pair of JL Audio e110 subwoofers, Focal Chorus 714 and Dynaudio Evoke 30 loudspeakers borrowed from the HT system. The audio cabling is Audioquest WEL Signature, MIT MA-X SHD, Cardas Clear Beyond and Mogami interconnects and speaker cables. USB cables are Straight Wire USB-F. Power protection and purification are provided by an Audioquest Niagara 5000 or PS Audio Dectet for the preamplifiers and source components, and a PS Audio Quintet for the power amplifiers. The Quintet includes a standard 1/8" trigger for remote turn-on and -off of power amplifiers that lack a 12V remote trigger. Power cords include my DIY power cord, Straight Wire Pro Thunder, and Audioquest Blizzard 20A (for the Niagara 5000). 

The AHB2 requires significant break in to sound its very best. Although it sounds good when brand new, notes can occasionally sound somewhat broken and discontinuous. At 75 hours of use, the sound is improved. After 200 hours, break in is mostly complete, and evidenced by the perception that musical notes are floating in air. There did not seem to be any further changes after 500 hours. Note: These intervals are a guide only, and it is suspected that changing the break in parameters of speaker load and system loudness could cause significant changes in these times.

An initial concern with any new design, attributable to the vastly different tonal perspectives of different amplifier technologies, regards the accurate delivery of high frequency content. Class D amplifiers, including the latest IcePower IceEdge, seem to edit linear treble response, sounding limited in their extension and ultimate resolution: dark. Immediately upon cuing up the first musical selection, it was perfectly obvious that the AHB2 has outstanding extension in the upper treble, seemingly unlimited. In this regard, the Benchmark amplifier should be compared to excellent Class A or AB amplifier technology. 

However, the AHB2 lacks the characteristic, almost subliminal harshness in the upper frequencies that is observed in some push-pull amplifiers, but absent in single-ended amplifiers. This is possibly a cause of dissatisfaction with many of these amps and why we see a constant turnover of amps in the $2,000-15,000 range. You already know the brands because we see new listings almost every day for them on Audiogon and Audio Mart.  

The bass has outstanding definition, with just slightly less dynamic power in the lowest bass, below about 30 Hz, as a big solid state amp might perform. Of course, this is very much related to the loudspeaker and the listening room. The AHB2 is not at all deficient in the bass. This observation is just comparative, not qualitative. This observation is also nitpicky, relevant to a review.

The overall sound is very true to the recording with regular 'virtual reality'-like experiences. These last for long periods of a listening session, not just as a momentary feeling of great sound. This is due to the exceptional linearity across the musical spectrum. The coherence and resolution of all sounds - which have stunning low level resolution - is special, encouraging the listener to maximally enjoy a musical performance. This used to be called "digging it".

The imaging and sound stage is 3D, large and stable. It is a simple exercise to point a finger directly at a performer, even when several are present in the recording. The sonic image is remarkably focused and apparent.

The Benchmark amplifier’s dynamic performance is exemplary. I value my hearing and rarely listen at average sound pressure levels (SPLs) exceeding 85 dB, which gives peaks around 100-105 dB. At these levels with the 86 dB sensitivity of the Magico speakers, the front panel clipping/fault indicator lights never lit up. Both small, micro dynamic nuance and huge, explosive changes in volume are always delivered with a clearly defined leading edge and plenty of energy.

The one noticed character is entirely relative in nature to other power amplifiers. The AHB2 is more open and forward than the latest Class D, but in a good way. The Benchmark amp is slightly more upper-midrange-centric than the single-ended Class A Valvet E2 SE. The latter could be considered more lower-midrange-centric, relatively speaking. For the first 2-3 weeks after installing the AHB2, I missed the more relaxed, less urgent sound of the Valvet amp, going back to it often. But after a month or so, I realized that the Valvet amp had not been substituted in quite a while. Clearly, as both me and the Benchmark amplifier broke in, my mental benchmarks for great sound had adjusted a bit to accommodate the different perspective that the Benchmark amplifier offers. It is important to repeat that the differences were “a little more of this, a little less of that”, but never related to quality. Both are fine amps and beautiful sounding. This difference in perspective could be compared to changing your seat at an acoustic concert from row 20 to row 2. 

In order of this “forwardness” or treble apparent character, the Benchmark is first, closely followed by the Valvet E2 SE, with a Mivera IcePower IceEdge amp offering the “darkest” presentation.

The Valvet is a very fine amplifier, but not the best match for the Magico speakers. While the amp can manage SPLs in the upper 70 dB range, the sound becomes compressed as the volume nears its 20-Watt power rating. Below that volume level, the single-ended amp is still slightly purer and more nuanced. Above that level, the AHB2 takes over with great competance and pulls ahead in power and dynamics at more normal listening levels. The Benchmark amplifier sounds better louder.

The Benchmark AHB2 is a very fine sounding, easy to live with, zero-maintenance power amplifier that has enough power for most systems. If more power is needed, two amplifiers configured for mono can provide it. The decision to purchase the review sample and make the Benchmark AHB2 a new, long term reference took over a month of listening and comparisons. This long audition is actually a good thing, since components that offer immediate “improvements” are usually the ones that become tiresome in short order. The outstanding musicality of the Benchmark AHB2 takes some time to convince the listener of its wholly musical presentation. This subtle excellence assures long term satisfaction.

Overall Rating: 10 LPs

10 Audio 'Perfect 10 Award'

 

Link to manufacturer: Benchmark Media Systems

This review would not have been possible without the very kind support of Rory Rall at Benchmark Media Systems. Thank you, Rory!