General Information
Benchmark AHB2 Power Amp
Product page: https://benchmarkmedia.com/products/benchmark-ahb2-power-amplifier
by John Siau,chief engineer at Benchmark at DIY audio forum
"The THX patents are:
8,004,355
8,421,531
The patented topology uses feed-forward error correction to virtually eliminate crossover distortion. The technique is so effective that the output stage can be run in class-B operation while achieving very low distortion. This also allows class-H or class-G tracking rails without the usual distortion problems associated with these designs. THX has demonstrated a design that rivals the efficiency of class D amplifiers.
The THX topology was interesting to Benchmark for an entirely different reason:
The same feed forward error correction can be used to remove crossover distortion from a class-B amplifier can be used with class AB biasing to create an amplifier with extraordinarily low distortion.
Our goal was to achieve very low distortion, with a focus on low crossover distortion. We were willing to increase the power dissipation as much as necessary to optimize the distortion performance. The optimum solution uses some bias current, but much less than a traditional class AB. Distortion of the AHB2 is at the measurement limits of our AP 2722 and 2522 test stations.
The THX topology also allowed us to utilize two power supply rails in a class-H (or G) configuration without any measureable distortion penalty.
The AHB2 is significantly more efficient than a traditional class AB, and has much lower distortion. Power consumption is only 20W idle. A traditional class-AB of equivalent power would consume 100 to 120 W idle. For example, the similarly sized Bryston 3B consumes 120W idle.
Benchmark chose to build the amplifier with very low gain. Gain is only 9 dB instead of the more typical 20 to 30 dB gain found in most power amplifiers. This means that the AHB2 clips with a 22 dBu input instead of an 8.2 dBu (2 V RMS) input. The AHB2 is designed to accept studio-level input levels and this can significantly improve noise performance between connected devices. In my opinion, most power amplifiers have far too much gain.
Our design goals included a 130 dB SNR relative to maximum output. To achieve this performance we used very low impedances, and some very unique PCB layout techniques. We also chose to use a switching power supply so that we could eliminate 60 Hz magnetic components. The magnetic fields produced by a high frequency switching supply are much lower and are out-of-band.
We also chose a tightly regulated power supply. Most power amps use unregulated supplies because this is the most efficient use of resources if switching supplies are not used. Given switching supplies, tight regulation comes almost for free. Better yet, the power supply control loop can be made fast enough to react to all audio frequencies. The AHB2 does not rely on secondary capacitive storage."
Product page: https://benchmarkmedia.com/products/benchmark-ahb2-power-amplifier
by John Siau,chief engineer at Benchmark at DIY audio forum
"The THX patents are:
8,004,355
8,421,531
The patented topology uses feed-forward error correction to virtually eliminate crossover distortion. The technique is so effective that the output stage can be run in class-B operation while achieving very low distortion. This also allows class-H or class-G tracking rails without the usual distortion problems associated with these designs. THX has demonstrated a design that rivals the efficiency of class D amplifiers.
The THX topology was interesting to Benchmark for an entirely different reason:
The same feed forward error correction can be used to remove crossover distortion from a class-B amplifier can be used with class AB biasing to create an amplifier with extraordinarily low distortion.
Our goal was to achieve very low distortion, with a focus on low crossover distortion. We were willing to increase the power dissipation as much as necessary to optimize the distortion performance. The optimum solution uses some bias current, but much less than a traditional class AB. Distortion of the AHB2 is at the measurement limits of our AP 2722 and 2522 test stations.
The THX topology also allowed us to utilize two power supply rails in a class-H (or G) configuration without any measureable distortion penalty.
The AHB2 is significantly more efficient than a traditional class AB, and has much lower distortion. Power consumption is only 20W idle. A traditional class-AB of equivalent power would consume 100 to 120 W idle. For example, the similarly sized Bryston 3B consumes 120W idle.
Benchmark chose to build the amplifier with very low gain. Gain is only 9 dB instead of the more typical 20 to 30 dB gain found in most power amplifiers. This means that the AHB2 clips with a 22 dBu input instead of an 8.2 dBu (2 V RMS) input. The AHB2 is designed to accept studio-level input levels and this can significantly improve noise performance between connected devices. In my opinion, most power amplifiers have far too much gain.
Our design goals included a 130 dB SNR relative to maximum output. To achieve this performance we used very low impedances, and some very unique PCB layout techniques. We also chose to use a switching power supply so that we could eliminate 60 Hz magnetic components. The magnetic fields produced by a high frequency switching supply are much lower and are out-of-band.
We also chose a tightly regulated power supply. Most power amps use unregulated supplies because this is the most efficient use of resources if switching supplies are not used. Given switching supplies, tight regulation comes almost for free. Better yet, the power supply control loop can be made fast enough to react to all audio frequencies. The AHB2 does not rely on secondary capacitive storage."
