John Siau tears down a Benchmark AHB2 power amplifier to show us what is inside. Discover why the AHB2 is radically different from other power amplifiers.
The Benchmark AHB2 Power Amplifier
- Radically Different Topology
- Hi-Frequency Fully-Regulated Switched-Mode Power Supply
- Linear Class-AB output Stage with Class-H Tracking Rails
- Much more Efficient than a Traditional Class-AB Amplifier
- Feed-Forward Error Correction
- Correction Amplifier is Passively Summed with the Main Amplifier
- No Magnetic Interference
- No Relays in Output Stage
- Protection Circuits are not in Series with Output Path
- Low Gain Design
- Tweeter Protection
- 0.1 Hz to 250 kHz Bandwidth
- Stable into Inductive and Capacitive Loads
- Stable into Very Low Impedances
- 135 dB SNR
- THD is Better Than -110 dB at Full Output Power
6 comments
JD, There are two sets of output rails on the AHB2. The lower set drive the output up to a level that is about 1/3 of the total power. When the audio peaks exceed this level, the output rails increase as much as is necessary to provide the output. The rails have a maximum limit of a little over +/- 40 Volts which corresponds to the voltage rails required to deliver 100W into 8 Ohms. These tracking rails greatly improve the thermal efficiency of the amplifier, bringing it close to the efficiency of some class-D amplifiers, but without any of the negative aspects of a class-D amplification.
Unlike most amplifiers, the AHB2 does not show a significant change in THD when driving lower impedances. 8-Ohm and 4-Ohm THD performance is identical. It rises a dB or two when driving 2-Ohm speakers, but in all cases the THD will remain below the 0 dB SPL threshold of hearing.
This application note goes into this in detail: https://benchmarkmedia.com/blogs/application_notes/how-loud-is-the-distortion-from-your-power-amplifier
We have a set of 2.4 Ohm line-array speakers in our listening room. We acquired them because we had the only power amplifier that could drive them cleanly. They used our AHB2 at all of their trade shows.
Thanks John,
Please advise if these AHB2 amplifiers can be used as Monoblock amplifiers driving either 8,6,4 and possibly lower ohm speakers?
Thanks.
Hi John,
Great video, one question.
Please tell me more about “Class H tracking rails?
Thanks in advance.
Thanks John! The AHB2 is truly a “benchmark” design.