Audio Power Amplifier Design Handbook, 4th Edition

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History, architecture and negative feedback

A brief history of amplifiers

A full and detailed account of semiconductor amplifier design since its beginnings would be a book in itself – and a most fascinating volume it would be. This is not that book, but I still feel obliged to give a very brief account of how amplifier design has evolved in the last three or four decades.

Valve amplifiers, working in push-pull Class-A or AB1, and perforce transformer-coupled to the load, were dominant until the early 1960s, when truly dependable transistors could be made at a reasonable price. Designs using germanium devices appeared first, but suffered severely from the vulnerability of germanium to even moderately high temperatures; the term thermal runaway ...