Low-Distortion Benchmark AHB2 Power Amplifier Reveals Full Scope of PCM and DSD Recordings: Extended Frequency Response, Class AB Output Stage, Patented Technology, Remarkable Efficiency
Given Benchmark's sterling reputation with digital audio, it's not surprising the company has built a groundbreaking power amplifier, AHB2, capable of delivering the full performance of its flagship converters and the world's finest high-resolution recordings. Significantly quieter than typical reference amps, the Stereophile Editors' Choice Award-winning AHB2 touts extremely extended frequency response at both spectrums, patented error-correction technology, remarkable efficiency, a bi-polar Class AB output stage, and an innovative power supply. With ABH2, you'll finally hear what you've been missing in high-resolution playback. 100% Music Direct Guaranteed.
"This is an amplifier with very serious slam, and – even better for those with less sensitive speakers, big rooms or just a hankering for ‘just in front of the PA stack' listening levels – it keeps it all together however loud you decide to play things."
– Hi-Fi News, Editor's Choice review
A New Benchmark
Power amplifiers are usually a weak link in the audio chain. High-resolution recording formats and converter technology have outpaced the development of improved power amplifiers. Benchmark DAC2 D/A converters outperform most high-end power amplifiers by very significant margins. Most power amplifiers limit system noise performance to the equivalent of a 16 to 18-bit digital system. The differences between 16-bit and 24-bit recordings are inaudible when the power amplifier can only deliver 16-bit noise performance. In most audio systems, the details captured by today's high-resolution 24-bit PCM systems are lost in a veil of amplifier noise and distortion. Benchmark's goal was to build a power amplifier that could deliver the full performance of their flagship DAC2 converters, and today's finest high-resolution recordings. The AHB2 realizes this goal.
"If ever there were a giant-killer of an amp, this is it."
– SoundStage! Hi-Fi, Recommended Reference Component
True High-Resolution Performance
High-Resolution audio is only as good as the weakest link in the playback system. Benchmark's AHB2 power amplifier delivers musical details without introducing the masking effects of amplifier noise and distortion. The dynamic range of the AHB2 is 130 dB, making it 10 to 30 dB quieter than the typical reference-quality power amplifier. 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. The AHB2 delivers a noise performance and a frequency response that is well matched to the capabilities of DSD and 24-bit PCM formats. The AHB2 is a the ideal match to the performance limits of high-resolution formats.
"As desired in a studio setting, the sonics from the AHB2 are neutral, and in my home setup, there is no observable emphasis in any particular frequency range."
– Rob Johnson, TONEAudio
Extended Frequency Response
The frequency response of the AHB2 extends beyond 200 kHz, to deliver the ultrasonic detail and fast transients captured by high-resolution recordings. At the other end of the audio spectrum, the low-frequency response extends below 0.1 Hz. The extended frequency response delivers a nearly perfect impulse response, and a nearly perfect phase response.
"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."
– Frank Alles, Stereo Times
High Damping Factor
The AHB2 has a high damping factor that augments its extended low-end to deliver solid, well-controlled bass. It's a stunning experience to finally hear full bandwidth high-resolution playback. The AHB2 allows you to escape the distortion limitations of classic amplifier topologies and enter the world of high-resolution audio playback.
"The intent was to make it an ultra low distortion design. I would have to say they succeeded as it is the lowest noise and distortion power amp I have measured and I have measured a LOT of power amps in my career."
– Bascom H. King, BHK Labs
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 a hybrid of class-H and class-G tracking power supply rails to improve efficiency. The result is that the cool-running AHB2 has a signal to noise ratio of 130 dB while distortion is at or below the measurement limits of the finest test equipment. The patented THX-AAA Technology (TM) uses feed-forward error correction to reduce distortion to vanishingly low levels while enabling several power-saving techniques.
"The Benchmark brings out nuances of reverb, quick percussive guitar attack with amazing clarity, but no over the top edginess...The -130 dB noise/dynamic range just gets us that much closer to the live music signature that we yearn to hear from our beloved electronics."
- John Gatski, Everything Audio Network
Feed-Forward Error Correction
Class-AB amplifiers generate crossover distortion every time the output stage crosses 0 volts. This crossover distortion can be especially problematic at low playback levels. Class-A output stages eliminate this crossover distortion at the expense of high power consumption, poor damping, and a limited dynamic range. 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 caused by output device crossover transitions. In the AHB2, an ultra-clean low-power error-correction amplifier runs in parallel with the main high-power output amplifier. The error amplifier feeds a correction signal forward to sum with the output of the main amplifier. The correction signal is a precise mirror of the errors produced by the main class-AB amplifier. This technique produces a near-perfect cancellation of the errors produced by the main amplifier.
“The Benchmark AHB2 embodies everything that a solid-state amp should. It is a technologically advanced and remarkable amplifier that can hang with any amp in its class because it is sonically transparent, images beautifully, and produces authoritative bass. While costing only $2,995, it is hard to imagine asking for much more in a power amplifier.”
High Efficiency - An Added Bonus
The THX-patented feed-forward error correction used in the AHB2 is so effective that biasing of the class-AB bi-polar 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. The feed-forward error correction also allows the use of 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.
Bi-Polar Class-AB Output Stage
The AHB2 has bi-polar class-AB output stage that delivers high output current and low noise. The THX patented feed-forward error correction provides accurate cancellation of zero-crossing errors. Class-AB amplifiers usually generate crossover distortion every time the output stage crosses 0 volts. This crossover distortion can be especially problematic at low playback levels. In contrast, class A output stages eliminate this crossover distortion at the expense of high power consumption, poor damping, and a limited dynamic range. Until now, this has posed a trade off between class-AB and class-A designs, a trade off between efficiency and low crossover distortion. Benchmark has now combined the best characteristics of class-AB and class-A amplification to create an amplifier that outperforms both of these traditional designs. Low-level details and reverb tails are rendered with stunning resolution.
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 resonant switching power supply that has 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. Maximum 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. Mechanical hum is eliminated while magnetic field strength is significantly reduced. For a given amount of power, magnetic field strength decreases as switching frequency increases. High-frequency magnetic components are also much smaller than line-frequency magnetic components. The supply is well over 90% efficient, and very little power is lost to heat. 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-efficient Benchmark AHB2 Power Amp 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 low-noise input amplifiers on the AHB2 are equipped with precision balanced inputs. Benchmark considers balanced inputs essential in a true high-resolution system.
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.
SpeakON Output Connectors
The AHB2 is equipped with high-quality binding posts, and SpeakON output connectors. The 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.