History of the AHB2 Power Amplifier

The DA101 - Benchmark's First Power Amplifier

Benchmark DA101About 33 years ago, Benchmark's founder, Allen H. Burdick,  began building analog audio distribution amplifiers for television networks. This application demanded an audio amplifier with a very wide frequency response, very low noise, and very low distortion. The Benchmark DA101 distribution amplifier had a 160 kHz bandwidth, THD+N of 0.00044%, and a SNR of 130 dB, but the power output was only about 40 watts in bridged mono. These amplifiers were designed to simultaneously drive 10 balanced audio lines, and were not originally intended for driving speakers. Nevertheless, they were capable of driving 8-Ohm speakers and, for many years, we used our distribution amplifiers to drive the speakers in our listening room. We couldn't buy an amplifier that came close to the performance of our distribution amplifiers, and Allen had often talked about building a bigger amplifier that could match the performance of the DA101.

The "PA1" Project

Allen retired in 2006 due to health issues, and in 2011 we began to talk about making Allen's dream for a power amp a reality. The goal was to meet or exceed the performance of Allen's DA101, while scaling up the power by a factor of 10. One obstacle was that push-pull crossover distortion can be hard to manage in a large amplifier. We began to look at unconventional solutions to this problem, and had a design code-named "PA1" in progress by June of 2011. It was to have a switched-mode power supply and a unique servo-biased push-pull output stage. We were going to have to think out of the box if we were going to reach our performance goals.

The THX Connection

In  November of 2011, I was attending the AES conference and I ran into Laurie Fincham and Jayant Datta, some good friends from THX. We met for lunch and they began to tell me about a new amplifier topology that they were working on. They had applied for patents and were looking to turn their ideas into a product. This was the classic lunch with schematics and numbers scribbled on napkins. We realized that our two companies had complementary skills that could make a joint project a success. Their patents offered an elegant solution to the crossover-distortion problem and we were already planning to build an unconventional power amplifier with ground-breaking performance. By the time we finished lunch, we had outlined the performance requirements for the new amplifier. These specifications, written on a napkin in 2011, are almost identical to those of the production AHB2.

Much of 2012 was spent testing and improving low-power THX prototypes. The THX team was split between California, New York, Canada, and England, while our team was located at our headquarters in Syracuse, NY. It was an international effort tied together with email, Skype, air travel, and a common love for music and great audio.

The "PA2" Project

In November of 2012 we set the final specifications and code-named the project the "PA2".  We completed the designs for the casework and custom transformers. We then began the final circuit designs for the full-power prototype.

The AHB2 Name

On September 27, 2013, everything was ready, but we still didn't have a name for the new amplifier. The faceplates were machined and finished but needed to be printed with the product name. I began thinking about the technology in the amplifier and how this could be incorporated into the name. The amplifier delivered class-A performance, had class-H tracking rails, and a class-AB output stage. It then struck me that the letters A, H, and B were Allen H. Burdick's initials. Instantly it was clear to me that the new amplifier should be named after the man who inspired it! At this moment, the PA2 became the AHB2. I announced the name to my staff, and we placed the order for the printing. Less than an hour later we got a phone call with the sad and shocking news that Allen had passed away.

First Working Unit

In October 2013 we demonstrated the first working AHB2 prototype at the AES show. We then completed a 20-unit pilot run in early 2014, and spent several months completing compliance and safety testing. By October of 2014 the first production run was nearly ready, and we hoped to take the very first unit to the 2014 AES show.

The First AHB2 Meets The First AP555

Through heroic efforts, the first production AHB2 was ready just in time for the 2014 AES show, where an amazing coincidence occurred. Through similarly heroic efforts, Audio Precision completed their first production APx555 audio test station just in time for the same show. This last-minute success was important for AP because they were planning to celebrate their 30th anniversary on the show floor. They invited us and our new AHB2 to their booth for their 30th anniversary celebration. Top engineers from Audio Precision, THX and Benchmark all gathered around the test station to see APx555 run tests on the AHB2. The group included Laurie Fincham, and Jayant Datta (THX), Bruce Hofer and Tom Kite (AP), and John Siau (Benchmark). Everyone was so impressed by what they saw, that the festivities faded into the background. The APx555 was the best audio test station we had ever seen, and the performance of the AHB2 was pushing the limits of the test station. It was hard to say who was the most excited.

 




John Siau
John Siau

Author

John Siau is VP and Director of Engineering at Benchmark Media Systems, Inc.