Audio Engineering Society

Chicago Section

Meeting Review, April 10th 2002


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4/10/02 Meeting Highlights
by Bob Zurek

Audio Power Amplifiers: a Brief History

On April 10th the AES Chicago Section was honored to have Gerald Stanley of Crown International present ďAudio Power Amplifiers: a Brief HistoryĒ. Geraldís presentation was a historical overview of the evolution of audio power amplifiers beginning with thermionic emission in the 1870ís through the development of Class I amplifiers in the late 1990ís. Mr. Stanley primarily showed the development of audio amplifiers through patent documents highlighting inventions such as the first class-A push-pull amplifier in 1916 and the patenting of negative feedback in the late 1920ís and 1930ís. Mr. Stanley stated several observations he has made concerning amplifier design over the years. Observations such as, Technology is not static, and amplifier designs are limited by the electron devices they use. Gerald discussed how the belief in obsolescence is a self-fulfilling prophecy, and the value of a product in the customerís eyes is the ultimate driver in design. He also showed that most audio amplifiers are based on old technology, citing the invention of the first class-D amplifier in 1958 and the first class-H in 1967. Mr. Stanley also observed that many designers have not learned from the lessons of the past and are recreating the problems that amplifier designers experienced and solved years ago. Mr. Stanley then transitioned into a discussion of the state of amplifier design today, which is switching from highly dissipative designs to high efficiency designs, and from manual design to computer aided design tools. Mr. Stanley continued his presentation with a discussion of the Class-I or Balanced Current Amplifiers that Crown is now producing. He discussed the advantages of the interleaved class I amplifiers such as that they require no deadtime, since the shoot-through is eliminated. The presentation ended with a question and answer session followed by a display of Crown amplifier products including their JBL branded 6000 watt Class-I car amplifier. The Chicago Section would like to thank Gerald for his presentation, Crown Intl. for providing the display of Crown amplifier products for the meeting, and RC Communications for providing the audio-visual equipment for the meeting.