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Recommended Component 2024 Class A – Stereophile
"An Amplifier That Must Be Heard"
Benchmark's AHB2 is the ideal power amplifier for coaxing the maximum performance limits out of High-Resolution-Audio (HRA) formats. The AHB2 delivers musical details without introducing the masking effects of amplifier noise and distortion. The dynamic range of the AHB2 is 132 dB, making it 10 to 30 dB quieter than some of the very best reference-quality power amplifiers.
The frequency response of the AHB2 extends beyond 200 kHz. With the AHB2, you will discover previously overlooked nuances, dynamics, and detail in your favorite recordings and experience the full potential of the latest high-resolution 24-bit PCM and 1-bit DSD audio formats.
"Recommended Component" Honors
Stereophile honored the AHB2 by awarding it the magazine's coveted Recommend Component Class A status for 2024.
"Combine the AHB2's superb sound quality with its low weight, low noise, low heat, and low cost, and it's clearly an amplifier that must be heard – even by those who can afford amps costing as much as 10 times more," reports Kalman Rubinson. "That makes the AHB2 more than a Benchmark. That makes it a bargain."
Experience the Emotion
The musical details and emotion captured on today's finest High-Resolution-Audio recordings can only be fully appreciated when every component in the signal chain is capable of true high-resolution performance. Power amplifiers are a weak link in most audio systems. Most power amplifiers are well matched to the limitations of the CD format, but they fall well short of the capabilities of high-resolution formats. In contrast, the revolutionary AHB2 was specifically designed to deliver true high-resolution performance.
The Need for Better Amplification
D/A conversion technology has outpaced the development of new power amplifiers. This means that the power amplifier has become a limiting factor in many audio systems. For example, the noise and distortion produced by the Benchmark DAC2 D/A converter is 20 to 30 dB lower than that produced by most high-quality power amplifiers. Until now, this meant that the DAC2 could not be fully appreciated. Benchmark set out to solve this problem by creating an amplifier that matches the performance of the DAC2.
A New and Different Power Amplifier
Benchmark had to look beyond existing amplifier technologies and explore some new and radical solutions. In its search, Benchmark engineers learned of two new patents on a new amplifier technology from THX. This was exactly the technology needed to build the new amplifier.
The AHB2 uses the new and revolutionary THX-patented AAA™ technology to virtually eliminate all forms of distortion. This technology uses feed-forward error correction to eliminate the distortion that is normally produced by the output stage. No other audio amplifier comes close to delivering the clean, quiet, and robust power of the AHB2.
In its quest, Benchmark also focused on frequency response, output noise, drive current, damping factor, and reliability. The result is an amplifier that stands head and shoulders above the competition.
The Quietest, Cleanest Audio Amplifier on the Planet
From the first watt to the last watt, no audio power amplifier offers lower noise or lower distortion than the Benchmark AHB2. Benchmark has raised the bar by introducing a new and revolutionary amplifier!
"If ever there were a giant-killer of an amp, this is it," raves Hans Wetzel at SoundStage! "It is one of the – if not the – quietest, most resolving amps I've heard. Time and again, without ever having intended to, I wound up hours deep in listening to the fringes of my music collection, thanks to the AHB2's reference-level transparency and obscene athleticism."
Sonic Purity that Surpasses Class A
The AHB2 is a linear amplifier that surpasses the sonic purity of all Class A amplifiers. No amplifier delivers lower noise or lower distortion. The small, passively cooled chassis, cleanly delivers 480 Watts bridged mono into 6 Ohms, with additional reserves for driving difficult speaker loads. Unlike power-hungry Class A amplifiers, the AHB2 achieves a power efficiency that rivals that of a Class D (switching) power amplifier.
The AHB2 will never produce audible distortion. In most playback systems, the distortion produced by the AHB2 will never even reach the 0 dB SPL threshold of hearing. This means that the distortion could not be heard, even if it could be played while the music was muted.
"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," reports Frank Alles at Stereo Times.
Difficult Speaker Loads Are Handled with Ease
Many loudspeakers have frequencies at which their impedance drops to levels that are much lower than the "nominal" impedance. The AHB2 drives difficult phase angles and low impedances with ease. Stereo loads as low as 1.4 Ohms can be cleanly driven to full output levels. Most power amplifiers produce higher levels of distortion when the load impedance decreases. In contrast, the feed-forward error correction system in the AHB2 keeps the output clean when driving difficult loads. The AHB2 produces almost no measurable distortion at any rated load condition.
High Damping Factor, High Output Current
The AHB2 has a high damping factor that augments its extended low-end to deliver solid, well-controlled bass. This high damping factor also keeps the frequency response absolutely flat while driving speakers with large frequency-dependent impedance variations.
The AHB2 can deliver up to 29 A peak to each channel simultaneously. This robust drive current easily handles some of the most demanding loudspeakers. The AHB2 has tightly regulated power supplies that keep the output clean while delivering high current.
Extreme Performance Often Requires a Radical Approach
The AHB2 amplifier is radically different than traditional audio amplifiers. Two new THX-patented feed-forward error-correction technologies eliminate most sources of distortion. An unconventional power supply maintains tight regulation and low ripple while minimizing magnetic fields. A low-gain topology optimizes the gain staging between the D/A converter and the power amplifier while minimizing noise. Sophisticated shielding and star-quad signal distribution provide outstanding immunity to interference. A unique output stage incorporates Class H tracking power supply rails to improve efficiency. The result is that the cool-running AHB2 has a signal to noise ratio of 132 dB while distortion is at or below the measurement limits of the finest test equipment.
The AHB2 is the only amplifier that leverages the patented THX-AAA Technology™. This patented system reduces distortion to vanishingly low levels while enabling several power-saving techniques. A bipolar Class AB output stage delivers high output current and low noise. The THX-AAA Technology provides accurate cancellation of zero-crossing errors, exceeding the performance of the best Class A amplifier.
"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," notes Frank Alles at Stereo Times.
Feed-Forward Error Correction
Traditional Class AB amplifiers generate crossover distortion every time the push-pull output stage crosses 0 volts. This crossover distortion can be especially problematic at low playback levels.
In contrast, Class A amplifiers eliminate crossover distortion by keeping all output devices turned on at all times. This brute-force Class A approach solves the crossover distortion problem but it consumes lots of power while delivering very little to the speakers. The wasted power produces heat which must be dissipated into the listening space.
Class A amplifiers eliminate crossover distortion but they suffer from high power consumption, poor damping, and limited output power. The AHB2 is the first amplifier to virtually eliminate crossover distortion without incurring the undesirable side effects of Class A amplification.
The Importance of the First Watt
Dick Olsher once said that "the first Watt is the most important Watt". From the first Watt to the last Watt, the AHB2 shows no evidence of crossover distortion.
In contrast, all conventional Class AB amplifiers have crossover-distortion artifacts. Traditional Class AB designs attempt to control distortion through the use of feedback. Unfortunately, these feedback systems have a limited ability to reduce the abrupt transients that are caused by output device crossover transitions. Feedback networks attempt to correct errors after they occur. In contrast, feed-forward networks can prevent errors before they occur.
THX-AAA Technology includes an ultra-clean low-power error-correction amplifier that runs in parallel with the high-power main amplifier. The correction amplifier actively drives the output while the main output devices transition between push and pull states. Like a Class A amplifier, the AHB2 shows no signs of crossover distortion. The feed-forward system virtually eliminates the errors that would have been produced by the output devices in the main amplifier.
High Efficiency – Green Never Sounded So Good!
The THX-patented feed-forward error correction used in the AHB2 is so effective that biasing of the Class AB bipolar output devices can be reduced to unusually low levels. Benchmark has chosen to maintain a small bias current in the output stage, but this bias current is not critical to the distortion performance of the unit. The benefit of low bias current is that very little power is wasted as heat when the amplifier is idle. The AHB2 only draws 12 watts when idle, and less than 1/2 watt in standby.
The feed-forward error correction also allows the use of Class H tracking power supply rails without the usual distortion-performance penalty. These tracking rails significantly improve the overall efficiency of the amplifier while the error correction keeps distortion nearly nonexistent. The AHB2 rivals the efficiency of Class D amplifiers while exceeding the sonic performance of power-hungry Class A designs. Green never sounded so good!
Innovative Low-Noise Power Supply
Most high-quality power amplifiers have linear power supplies, large toroidal transformers, and large banks of energy-storage capacitors. These linear supplies are usually unregulated and the capacitors help to remove ripple produced by the audio and by the AC line. In contrast, the AHB2 uses a tightly regulated resonant switching power supply that includes a very fast control loop. This control loop responds to audio-frequency load changes and keeps the supply voltage constant without the use of a large bank of capacitors. This active regulation is much more effective than capacitive energy-storage. Consequently, the peak power output of the AHB2 does not vary with line voltage or audio loading. The power supply rails maintain a constant voltage during audio peaks.
The power supply in the AHB2 switches at frequencies that are well above audible frequencies. This eliminates mechanical hum while significantly reducing the strength of stray magnetic fields. For a given amount of power, magnetic field strength decreases as switching frequency increases. The lower field strengths also provide a significant reduction in size. High-frequency transformers and coils are also much smaller than line-frequency components. This size reduction contributes to the small physical size of the AHB2.
The switching power supply used in the AHB2 is a zero-voltage switching, resonant power converter. This means that the power devices in the supply switch near zero voltage and zero current, eliminating the large switching transients produced by conventional switching power supplies. The power supply in the AHB2 is actually much cleaner and quieter than a conventional linear supply.
The power supply In the AHB2 is well over 90% efficient, much more efficient than linear supplies. This means that little power is lost to heat. The power-efficient AHB2 uses passive heat sinks to maintain cool operation. The AHB2 delivers high power without the need for fans. The unit runs cool, even when playing audio at full output levels. The absence of fan noise is absolutely essential in a high-resolution listening environment.
Low-Noise Input Amplifiers
The precision balanced inputs on the AHB2 are equipped with low-noise input amplifiers. Benchmark considers balanced inputs essential in a true high-resolution system. If balanced sources are not available, Benchmark sells unbalanced to balanced adapter cables that extend a 3-wire balanced connection back to the unbalanced source connectors. These adapter cables provide many of the advantages of fully balanced interconnects while providing full compatibility with all unbalanced sources.
Low Gain for Low System Noise
The AHB2 is a low-gain design. Maximum output is not reached until the balanced inputs reach +22 dBu. This is a much higher signal level than is used at the input of most power amplifiers. High interface signal levels are required to achieve the best possible system signal to noise ratio (SNR). Most power amplifiers have far too much gain and consequently they suffer from poor noise performance. The AHB2 is 10 dB to 30 dB quieter than some of the very best power amplifiers on the market. A rear-panel gain switch can be used to set the AHB2 at higher gain settings if necessary. The low-gain setting is designed to interface directly with Benchmark DAC2 converters and other professional audio products.
Bulletproof Protection System with No Relays
The AHB2 has a unique protection system that prevents damage from overloads and short circuits. The protection system monitors output voltage, output current, output distortion, output device SOA (safe operating area), power supply current, power supply voltage, AC line voltage, case temperatures, and power device temperatures. Fault conditions silently mute both output channels in order to protect the speakers and amplifier from damage. The amplifier outputs are also muted while the amplifier is turning on or off.
The mute circuits are fully electronic. There are no mechanical relays in the mute circuits. Our tests showed that relays are too slow to protect against certain fault events. Our tests also showed that relay contacts can add significant distortion as they deteriorate with use. The AHB2 is one of very few amplifiers that avoids the use of relays in the output stage. This means that the AHB2 will maintain its rated distortion performance after an unlimited number of power on/off cycles.
Benchmark's unique distortion monitoring system mutes the amplifier if it is excessively driven into clipping. This system protects tweeters from an overdriven amplifier.
Benchmark's short circuit detection system is fast enough to fully protect the amplifier from events occurring at any output voltage or current. This system detects abnormal loads and instantly mutes the outputs. A status display shows the exact cause of the fault so that the problem can be corrected.
SpeakON Output Connectors
The AHB2 is equipped with high-quality binding posts, and SpeakON output connectors. The high-current SpeakON connectors are designed for heavy-duty commercial sound systems and provide much better electrical connections than binding posts. Benchmark highly recommends the use of the twist-lock SpeakON output connectors. We also highly recommend the use of our top-quality professional-grade speaker cables.
