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Multichannel Power Amplifiers: The Evolution Of “Heavy Metal”

Tracing the origins of audio power amplifiers to the state the technology today...

By Frederick Ampel January 19, 2015

Using our Stephen Hawking approved design for a real time machine, we journey to the dawn of the last century.

It’s the summer of 1905 and in under a year the mechanical age will give way to the dawning of the electrical age. At this time the world is dominated by giant machines that can truly be called “heavy iron.” Machines like this:

These 200-plus-ton behemoths are the quintessential embodiment of the leading edge of engineering and technology, and have already dramatically changed the world by making it possible to go to far away destinations in a few days, not a few weeks or months by sea.

But like all great machines, they were also doomed to extinction by the need for more speed, more pulling power, more efficiency, and… just plain more!

What there was of an audio industry or sound business was based around the mechanical phonograph and other mechanical apparatuses for recording and reproducing sound – none of which would have worked at all if it weren’t for horn-gain in recording and playback. (Horn gain would surface in early PA systems as well, as we’ll discuss later.)

Somewhere in the quiet suburbs near Chicago, Lee DeForest was experimenting with the then brand-new technology of radio, seeking to invent a solution to improving the power and distance over which “wireless telegraphy” – as radio was usually called in those days – could be sent.

The calendar’s pages turn and it’s now 1906. DeForest has succeeded (at least partially) in creating the key invention that would lead to the “electrical age” and many of the technologies we consider commonplace today. He’s created the first amplifier (a triode vacuum tube) called the Audion. As a historical note, his vacuum tube would not have been feasible if Edison had not invented the light bulb a few years earlier, because the Audion’s glass vacuum tube was largely a derivation of Edison’s bulb designs.

The Audion.

The invention of the Audion triode is crucial to this story because it created and introduced a new idea to the world: the concept of amplification, or the ability to make electrical signals more powerful. Until the Audion, this wasn’t part of the knowledge base of the whole electrical, wireless telegraphy and sound industries.

The fuse had been lit! DeForest’s creation would explode into the early 20th Century.

But just as massive steam-powered engines would be replaced in less than a quarter century by faster, quicker, super-streamlined diesel electric engines from the U.K., and less than four decades later by the astonishing 200 mph Japanese Shinkansen (bullet train), DeForest’s original triode would, within just a few decades, evolve beyond recognition.

Amplifier Genesis
In the beginning, or for about the first decade (1905-1915) of the newly birthed age of electrical amplification, even the era’s best engineers were profoundly puzzled by the new, complex, and truly non-intuitive mathematics of vacuum tube amplifiers and oscillators.

Remember that what we call electronic engineering today was, at that point in actuality, electrical engineering. Any development or improvement had to be focused on the only two things that had commercial backing – keeping AC power transmission systems in phase, and the monopolistic Bell Telephone System’s desperate need to improve the quality and reliability of long-distance telephone service to prevent the (U.S.) government from allowing potential competitors to enter the fray.

There were huge profits at stake and the Bell System threw everything it had into the fray, and by about 1910, the company’s engineers had improved the unreliable and short-lived Audion by increasing the vacuum, removing manufacturing impurities, establishing the requirement for negative bias, and creating the first viable mathematical models of diode rectification and triode amplification.

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About Frederick

Frederick Ampel
Frederick Ampel

Dr. Frederick J. Ampel has been involved in the professional A/V industry for more than 40 years, working as a systems designer, consultant, sales and marketing professional and market researcher. Presently he runs Technology Visions Analytics, a consultancy and market research firm.


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