THX® AAA™ Technology

by: Benchmark Media Systems, Inc.



December 21, 2014 - AHB2 receives the EAN "Product Of The Year" award!

December 31, 2014 - AHB2 receives "The Best Gear of 2014" award from Enjoy the

Experience the Full Potential of High-Resolution Audio

The musical details and emotion captured on today's finest High-Resolution Audio (HRA) recordings can only be fully appreciated when every component in the signal chain is capable of true high-resolution performance. The AHB2's extended frequency response, ultra low noise, and vanishingly low distortion are key parameters contributing to accurate reproduction of high-resolution musical recordings. Experience the full emotion and detail captured in your finest recordings.

A New Benchmark

Experience high resolution audio as you have never heard it before. The AHB2 a ground-breaking product. Benchmark has leveraged patented technology from THX to create an amplifier that defines a whole new level of performance. No audio amplifier delivers lower noise or lower distortion. Bandwidth exceeds 200 kHz in order to accurately deliver fast transients with accurate.  At the opposite end of the audio spectrum, the frequency response extends below 0.1 Hz.

The THX Story

Founded in 1983 by legendary filmmaker George Lucas, the THX mission is a truthful delivery of the artist’s vision to audiences around the globe. Collaborating with content creators, CE manufacturers, automakers and cinema chains, THX develops technologies and certification standards that enable the art of musicians and filmmakers to be experienced as close to the original as possible — at home, in the cinema and on the go.

A recent THX project focused on improving audio power amplifiers. By examining real-world programs and their demands upon an audio amplifier, THX invented an analog amplifier that combines the qualities of the finest Class A amplifiers with greatly reduced energy consumption.

This patented technology is known as the THX® Achromatic Audio Amplifier™ (AAA™) – audio power that is clean and green.

*ach•ro•mat•ic / 'akre'matik,'ākre-/ adjective 1. neutral 2. uncolored

The Key to THX® AAA™: Patented Distortion-Reduction Technology

THX engineers focused on ways to minimize distortion in the audio electronics chain. The THX patented technology uses a unique combination of feedback and feed-forward error correction to make the distortion vanishingly small.

THX engineers then used their distortion-reduction scheme to reduce some of the common sources of distortion in amplifiers in a variety of ways — the result is an amplifier topology with unparalleled performance and benefits for the audiophile.

Every Low-Level Detail, Revealed

Crossover distortion occurs in many amplifiers when the audio signal is “handed off” from an amplifier’s positive-going output device to its negative-going device and vice versa. This transition is never perfect, resulting in crossover distortion that is spiky in nature and rich in high-frequency distortion products.

Moreover, the problem becomes more audible as the signal level decreases. The more delicate the music, the more it will be masked and obscured by crossover distortion.

The THX patented distortion-reduction circuits reduce distortion to vanishingly low levels (less than 0.0001% @ 1 kHz), resulting in a more accurate reproduction of the original content.

Less Noise, More Music

The distortion reduction in the THX® AAA™ technology has an additional benefit: it dramatically reduces power supply-induced distortion and noise — a high PSRR (power supply rejection ratio).

In any amplifier, when the power supply works hard under heavy load conditions, it can introduce unwanted distortion and noise in the output signal. The THX patented solution is particularly effective in reducing these components to unprecedentedly low levels.

That means more of what you hear is music, and less of what you hear is the character of the power supply associated with the amplifier.

Combining this with meticulous layout and design, the THX® AAA™ technology delivers a signal-to-noise ratio (SNR) in excess of 130 dB — this is 30 dB greater than most amplifiers. That’s 30 times less noise than typical amplifiers — the perfect amplifier for a high-resolution audio playback system.

THX® AAA™ - Today’s Most Advanced Amplification Technology

The THX® AAA™ technology truly delivers everything that demanding audiophiles could want, including the ability to drive heavy and difficult loudspeaker loads to full output while maintaining impeccable performance.

It produces the purest performance of any amplification technology now available, ensuring that the art of musicians and filmmakers can be experienced as close to the original as possible.

The AHB2 Eliminates the Weak Link

Other than loudspeakers, power amplifiers are usually the weakest link in the audio chain. Until now, high-resolution recording formats and converter technology have rapidly outpaced the development of audio 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.

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 HRA formats.

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.

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.

High Output Current

The AHB2 can deliver up to 29 A peak into each channel simultaneously. This easily handles some of the most demanding loudspeakers. Best of all, the AHB2 stay clean while delivering high current.

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 these low impedance regions with ease. Most power amplifiers produce higher levels of distortion when the load impedance decreases. In contrast, the feed-forward error correction system in the AHB2 prevents any increase in distortion. The AHB2 produces almost no measurable distortion at any rated load condition.

Distortion is Below Audibility

In most playback systems, the distortion produced by the AHB2 will never reach the threshold of hearing. The AHB2 allows you to escape the distortion limitations of classic amplifier topologies and enter the world of high-resolution audio playback.

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.

See John Siau's application note: "A Radical Approach to Power Amplification" for more details.

Introducing THX Achromatic Audio Amplifier Technology™

The patented THX-AAA Technology™ uses feed-forward error correction to reduce distortion to vanishingly low levels while enabling several power-saving techniques.

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.

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 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.

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, we have faced this 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.

Passive Cooling

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 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.


The letters A, H, and B allude to the unique topology of the amplifier's output stage. The AHB2 combines class-AB, and class-H topologies using a feed-forward error correction system.

But there is much more to the story -

The initials A.H.B. can be found on many of the circuit diagrams of Benchmark's early products dating back to the late 1980's. These are the initials of Benchmark's founder, Allen H. Burdick.

Allen had a life-long passion for audio, and became one of the leading innovators in the pro-audio industry. The AHB2 is named in his honor.


Output Power

1 kHz, < 0.0003 % THD+N

  • 100 W/channel into 8 Ohms, both channels driven
  • 130 W/channel into 6 Ohms, both channels driven
  • 190 W/channel into 4 Ohms, both channels driven
  • 240 W/channel into 3 Ohms, both channels driven
  • 200 W Bridged Mono into 16 Ohms
  • 380 W Bridged Mono into 8 Ohms
  • 480 W Bridged Mono into 6 Ohms

 SNR & Dynamic Range

Relative to rated output, inputs shorted

  • 132 dB A-weighted, Stereo Mode
  • 135 dB A-weighted, Bridged Mono
  • 130 dB Unweighted, 20 Hz to 20 kHz, Stereo Mode
  • 133 dB Unweighted, 20 Hz to 20 kHz, Bridged Mono


1 kHz, 80 kHz LPF, at full rated output into any rated load

  • < -118 dB (< 0.00013%) - Stereo Mode
  • < -118 dB (< 0.00013%) - Mono Mode


1 kHz, 20 kHz LPF, at full rated output into any rated load

  • -119 dB (< 0.00011%) - Stereo Mode
    • < -120 dB (< 0.00010%) - Mono Mode


    • Better than -115 dB at 1 kHz
    • Better than -92 dB at 20 kHz

    Frequency Response

    • Better than 0.1 Hz to 200 kHz, +0/-3 dB
    • -0.01 dB at 20 Hz, -0.17 dB at 20 kHz, 8-Ohm Load
    • -0.23 dB at 20 Hz, -0.32 dB at 20 kHz, 4-Ohm Load

    Maximum Audio Output Current

    • 29 A peak per channel, both channels driven

    Input Sensitivity

    • Low-Gain = 22 dBu (9.8 Vrms)
    • Mid-Gain = 14.2 dBu (4 Vrms)
    • High-Gain = 8.2 dBu (2 Vrms)
    • Use Mid-Gain or High-Gain settings for unbalanced inputs
    • Unbalanced inputs require RCA to XLRM adapter cables 

    Input Impedance

    • 50 k Ohms, normal mode
    • 1 M Ohm, common mode

    Input CMRR

    • 80 dB at 20 Hz, typical
    • 80 dB at 1 kHz, typical
    • 65 dB at 20 kHz, typical

    Trigger I/O

    • 12 VDC 200 mA current-limited output to trigger turn-on of remote devices
    • DC input for slaving to remote devices
    • Input responds to 3.3 V logic and higher, VIL = 1.26 V, VIH = 2.7 V
    • Absolute maximum input voltage = 30 VDC
    • Absolute minimum input voltage = -0.3 VDC
    • Input Impedance = 20 k Ohms


    Non-rack-mount version:

    • 11.04" W x 3.88" H x 9.34 " D - Including feet and binding posts
    • 11.04" W x 3.47" H x 8.33 " D - Excluding feet and connectors
    • Faceplate height is 2RU

    Rack-mount version:

    • 19.00" W x 3.88" H x 10.62 " D - Including binding posts, handles and removable feet
    • 19.00" W x 3.47" H x 8.33 " D - Excluding feet and connectors
    • 9.09" rack depth, including binding posts, excluding cables
    • 11" rack depth, including cables
    • Faceplate height is 2RU


    • 12.5 lbs., 15 lbs. shipping - Non-rack-mount version
    • 13.5 lbs., 16 lbs. shipping - Rack-mount version

    AC Input

    • Auto-ranging AC Input
    • 100 to 120 VAC +/- 10%, 8 Amps, 50 - 60 Hz
    • 220 to 240 VAC +/- 10%, 8 Amps, 50 - 60 Hz


    Detailed specifications and performance plots are available in the downloadable manual.

    AHB2 Manual


    AHB2 Reviews


    This Benchmark product was designed, assembled, and tested in the USA using USA and imported components. Most major components are made in USA.