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The following measurements and scope photos demonstrate the effectiveness of the feedforward system in the AHB2. 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.
Dick Olsher once said that "the first Watt is the most important Watt". We agree!
In most listening situations, an amplifier spends most of its time near the 1-Watt output level. At these low levels, push-pull crossover distortion can be the dominant type of distortion. This non-musical distortion must be minimized or eliminated. Until the AHB2 was introduced, the only solution was class-A operation.
Now everything has changed. The patented feedforward error correction system in the AHB2 offers a better alternative to class-A amplifiers. The AHB2 exceeds the performance of all class-A power amplifiers, and it does so without generating the massive amount of heat produced by class-A amplifiers. The AHB2 is nearly as efficient as a class-D amplifier, but it outperforms all class-A amplifiers. This is why we say that the AHB2 is "the cleanest, quietest amplifier on the planet".
The 1-Watt THD+N measurements demonstrate that the AHB2 is free from any crossover distortion. Note that the AHB2 also stays clean at 1/3 power and at its full rated output power. Also note that there is almost no measurable difference between 8-Ohm and 4-Ohm loading. The same holds true for bridged-mono operation.
-108dB (0.0004%) at 1 W (1 W is -20 dB relative to rated power)
-114 dB (0.0002%) at 33 W (1/3 rated power)
-113 dB (0.0002%) at 100 W (full rated power)
-106 dB (0.0005%) at 1 W
-107 dB (0.0004%) at 1.9 W (1.9 W is -20 dB relative to rated power)
-113 dB (0.0002%) at 63 W (1/3 rated power)
-112 dB (0.0003%) at 190 W (full rated power)
-105 dB (0.0005%) at 1 W
-109 dB (0.0003%) at 3.8 W (3.8 W is -20 dB relative to rated power)
-114 dB (0.0002%) at 33 W (1/3 rated power)
-113 dB (0.0002%) at 380 W (full rated power)
Pictures can help to demonstrate what these numbers mean, so we captured some scope photos from our Audio Precision 2722 test station.
The following oscilloscope screenshots demonstrate the differences between the Benchmark AHB2 and a typical competing class-AB amplifier (with a similar power rating).
All scale factors are identical between the two amplifiers, and they can be compared directly. In all screenshots, the distortion waveforms are boosted by 60 dB relative to the output waveforms.
Note the difference in noise, and note the differences in the distortion waveforms. The competing amplifier clearly demonstrates the crossover distortion artifact that is common to all conventional class-AB amplifiers.
Notice that the performance of the AHB2 does not change as the power level increases. Also notice that there is no hint of crossover distortion.
In contrast, the typical class-AB amplifier shows a pronounced crossover distortion artifact. The relative sizes of the crossover distortion artifacts show that this distortion is a higher percentage of the signal when the competing amplifier is operating at low power (and especially the first Watt).
All scale factors are identical.
Note that there is no indication of crossover distortion.
Note that crossover distortion is clearly visible as sharp transients in the distortion waveform. The transient shows a fast attack time followed by the recovery time of the feedback loop. This distortion waveform is typical of virtually all class-AB amplifiers.
If an audio system is composed of multiple components, we may have detailed specifications for each component, but we will not know the performance of the combined system without doing some calculations. You may have questions such as these:
Use Benchmark's online audio calculators to find answers!
For example, if we know the output power of an amplifier, as well as the sensitivity and impedance of our loudspeakers, we can calculate the maximum sound pressure level that our system can produce.
This application note provides interactive examples that help to answer the questions listed above.
We have added an "Audio Calculators" section to our webpage. Click "Calculators" on the top menu to see more like these:
Secrets contributor Sumit Chawla recently caught up with Benchmark’s VP and Chief Designer, John Siau to get a little more in-depth on several subjects.
Q: "Benchmark is one of the few companies that publishes an extensive set of measurements, but you also balance that with subjective testing. Can you talk about the equipment, the listening room, and the process for subjective testing?"
Q: "Was there ever a time where you learned something from a subjective test that was not captured by measurements?"
Q: "You conducted some listening tests to determine whether distortion in the “First Watt” was audible. What test material did you use for this, and what did you find?"
Q: "The AHB2 amplifier incorporates THX Audio Achromatic Amplifier technology. When and how did the partnership with THX come about?"
Q: "Linear power supplies have been and remain quite popular in high-end devices. You favor switch-mode power supplies. When and why did you make this switch?"
... and more!
