History of the AHB2 Power Amplifier
The AHB2 Power Amplifier was Introduced in 2016 on Benchmark's 33rd Anniversary. Here is the full story behind this award-winning amplifier:
The DA101 - Benchmark's First Power Amplifier
Over 33 years ago (in 1983), Benchmark's founder, Allen H. Burdick, began building analog audio distribution amplifiers for television networks. This specialized application demanded an audio power amplifier with very low noise, very low distortion, and a very wide frequency response. The Benchmark DA101 distribution amplifier had a 160 kHz bandwidth, THD+N of 0.00044%, and a SNR of 130 dB. The power output was about 40 watts in bridged mono. These amplifiers were designed to simultaneously drive 10 balanced audio lines while withstanding short circuits on as many as 1/3 of the 30-Ohm outputs. This requirement meant that the amplifiers needed to be capable of driving an 8-Ohm load. The DA101 distribution amplifiers were not intended for driving speakers. Nevertheless, they were capable of providing spectacular performance when driving 8-Ohm speakers. For many years, we used our DA101 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, so we used them in all of our critical listening tests. Allen had often talked about building a bigger general-purpose power 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
Much of 2012 was spent testing and improving low-power THX prototypes. The THX team was split between California, New York, Canada, and England. Benchmark's 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" (Benchmark's second power amplifier - Power Amp #2, or PA2). The photo above is an early concept drawing. We soon completed the designs for the casework and custom transformers. We then began the final circuit designs for a 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 that 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. I am still stunned when I think about the coincidence of these two events.
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 APx555
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, March 17, 2016
Also in Audio Application Notes
Interpolator Overload Distortion
Most digital playback devices include digital interpolators. These interpolators increase the sample rate of the incoming audio to improve the performance of the playback system. Interpolators are essential in oversampled sigma-delta D/A converters, and in sample rate converters. In general, interpolators have vastly improved the performance of audio D/A converters by eliminating the need for analog brick wall filters. Nevertheless, digital interpolators have brick wall digital filters that can produce unique distortion signatures when they are overloaded.
10% Distortion
An interpolator that performs wonderfully when tested with standard test tones, may overload severely when playing the inter-sample musical peaks that are captured on a typical CD. In our tests, we observed THD+N levels exceeding 10% while interpolator overloads were occurring. The highest levels were produced by devices that included ASRC sample rate converters.
Audiophile Snake Oil
The Audiophile Wild West
Audiophiles live in the wild west. $495 will buy an "audiophile fuse" to replace the $1 generic fuse that came in your audio amplifier. $10,000 will buy a set of "audiophile speaker cables" to replace the $20 wires you purchased at the local hardware store. We are told that these $10,000 cables can be improved if we add a set of $300 "cable elevators" to dampen vibrations. You didn't even know that you needed elevators! And let's not forget to budget at least $200 for each of the "isolation platforms" we will need under our electronic components. Furthermore, it seems that any so-called "audiophile power cord" that costs less than $100, does not belong in a high-end system. And, if cost is no object, there are premium versions of each that can be purchased by the most discerning customers. A top-of-the line power cord could run $5000. One magazine claims that "the majority of listeners were able to hear the difference between a $5 power cable and a $5,000 power cord". Can you hear the difference? If not, are you really an audiophile?
Making Sound with Plasma - Hill Plasmatronics Tweeter
At the 2023 AXPONA show in Chicago, I had the opportunity to see and hear the Hill Plasmatronics tweeter. I also had the great pleasure of meeting Dr. Alan Hill, the physicist who invented this unique device.
The plasma driver has no moving parts and no diaphragm. Sound is emitted directly from the thermal expansion and contraction of an electrically sustained plasma. The plasma is generated within a stream of helium gas. In the demonstration, there was a large helium tank on the floor with a sufficient supply for several hours of listening.
While a tank of helium, tubing, high voltage power supplies, and the smell of smoke may not be appropriate for every living room, this was absolutely the best thing I experienced at the show!
- John Siau