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All amplifier measurements are performed independently by BHK Labs. All measurement data and graphical information displayed below are the property of the SoundStage! Network and Schneider Publishing Inc. Reproduction in any format is not permitted.

Notes: Measurements of the Benchmark AHB2 were taken at the balanced inputs of both channels at 120V AC line voltage, both channels driven. Unless otherwise noted, the data reported below are for the left channel.

Power output (stereo mode)

  • Power output at 1% THD+N: 110.0W @ 8 ohms, 201.0W @ 4 ohms
  • Power output at 10% THD+N: 130.0W @ 8 ohms, 255.9W @ 4 ohms

Power output (mono mode)

  • Power output at 1% THD+N: 403.6W @ 8 ohms
  • Power output at 10% THD+N: 450.0W @ 8 ohms

Additional data

  • Input/output polarity: noninverting
  • AC line-current draw at idle: 20.0W, 0.37A, 0.46PF
  • Gain (stereo): output voltage divided by input voltage, 8-ohm load
    •      2V sensitivity: 14.2X, 23.1dB
    •      4V sensitivity: 7.5X, 17.5dB
    •      9.8V sensitivity: 2.92X, 9.4dB
  • Gain (mono), output voltage divided by input voltage, 8-ohm load
    •      2V sensitivity: 25.2X, 28.0dB
    •      4V sensitivity: 14.2X, 23.1dB
    •      9.8V sensitivity: 5.8X, 15.3dB
  • Input sensitivity for 1W output into 8 ohms (stereo)
    •      2V sensitivity: 199.1mV
    •      4V sensitivity: 377.0mV
    •      9.8V sensitivity: 968.5mV
  • Input sensitivity for 1W output into 8 ohms (mono)
    •      2V sensitivity: 112.2mV
    •      4V sensitivity: 199.4mV
    •      9.8V sensitivity: 487.6mV
  • Output impedance @ 50Hz
    •      Stereo mode: 0.027 ohm
    •      Mono mode: 0.054 ohm
  • Input impedance @ 1kHz, stereo and mono: 47.0k ohms
  • Output noise 2V sensitivity (stereo mode), 8-ohm load, balanced inputs terminated with 600 ohms, Lch/Rch
    •      Wideband: 0.120mV/0.099mV, -87.5dBW/-89.1dBW
    •      A weighted: 0.0114mV/0.0112mV, -107.9dBW/-108.0dBW
  • Output noise 4V sensitivity (stereo mode), 8-ohm load, balanced inputs terminated with 600 ohms, Lch/Rch
    •      Wideband: 0.104mV/0.0905mV, -88.7dBW/-89.9dBW
    •      A weighted: 0.0084mV/0.0085mV, -110.5dBW/-110.4dBW
  • Output noise 9.8V sensitivity (stereo mode), 8-ohm load, balanced inputs terminated with 600 ohms, Lch/Rch
    •      Wideband: 0.098mV/0.088mV, -89.2dBW/-90.1dBW
    •      A weighted: 0.0072mV/0.0076mV, -111.9dBW/-111.4dBW

Measurements summary

The AHB2 is Benchmark’s attempt to produce a very-low-distortion, low-noise power amplifier using THX’s AAA Technology, which linearizes the amp’s class-AB output stage without using large amounts of overall negative feedback. I must say that they’ve succeeded; I measured less distortion and noise in the AHB2 than in any other of the many power amps I’ve measured over the years.

Because the AHB2 can be switched between stereo and bridged-mono modes, some measurements were taken with the amp in both modes; the charts labeled “B” indicate measurements in bridged mode. The AHB2 has input sensitivities of 2V, 4V, and 9.8V. Most of the testing was done at the 2V sensitivity; the distortion results were pretty much the same at the 9.8V sensitivity.

Chart 1 shows the AHB2’s frequency response into different loads. The slightly greater high-frequency rolloff in bridged-mono mode (not shown) is due to the series-connected nature of that mode, which caused the HF deviation with load to show up more than in stereo mode. Because the AHB2’s output regulation is so good, its measured performance into the IHF dummy load showed no significant variation within the audioband.

Chart 2A illustrates how the AHB2’s total harmonic distortion plus noise (THD+N) vs. power varied with 1kHz and SMPTE intermodulation test signals and amplifier output load into loads of 8 and 4 ohms. Chart 2B shows the mono results into 8 ohms; in bridged mono, the AHB2 is not rated for use into a load of 4 ohms.

The AHB2’s THD+N as a function of frequency at different power levels is plotted in Chart 3. High-frequency THD+N is admirably low, and in stereo and mono modes, the AHB2’s level of distortion throughout most of the power range is amazingly low.

The plot of the AHB2’s damping factor vs. frequency (Chart 4) is of a value and nature typical of many solid-state amplifiers: high up to 1-2kHz, then rolling off with increasing frequency.

Spectra of the THD+N residue of a 10W, 1kHz test signal are plotted in Charts 5A and 5B. The magnitudes of AC line harmonics are relatively low, and the signal harmonics -- consisting of the third and fifth harmonics in stereo mode -- are extremely low in amplitude. Chart 5B shows this to be similar in mono mode, but with the fifth harmonic being higher, and the seventh and higher harmonics visible but at extremely low levels.

Chart 1 - Frequency response of output voltage as a function of output loading

Chart 1

Stereo mode
Red line = open circuit
Magenta line = 8-ohm load
Blue line = 4-ohm load

Chart 2 - Distortion as a function of power output and output loading

Chart 2A

Chart 2A

Stereo mode
(Line up at 50W to determine lines)
Top line = 4-ohm SMPTE IM distortion
Second line = 8-ohm SMPTE IM distortion
Third line = 4-ohm THD+N
Bottom line = 8-ohm THD+N

Chart 2B

Chart 2B

Mono mode
(Line up at 100W to determine lines)
Top line = 8-ohm SMPTE IM distortion
Second line = 8-ohm THD+N

Chart 3 - Distortion as a function of power output and frequency

Chart 3

Stereo mode
(4-ohm loading)
Red line = 2W
Magenta line = 20W
Blue line = 60W
Cyan line = 120W
Green line = 180W

Chart 4 - Damping factor as a function of frequency

Chart 4

Stereo mode
Damping factor = output impedance divided into 8

Chart 5 - Distortion and noise spectrum

Chart 5A

Chart 5A

Stereo mode
1kHz signal at 10W into an 8-ohm load

Chart 5B

Chart 5B

Mono mode
1kHz signal at 10W into an 8-ohm load

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