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Audio Transformers History

Audio transformers owe their history to the basic theories of AC power. When the ideas of AC power generation and transmission were perfected and implemented in the late 1800's, the theories and practices were founded. The same formulas, materials and manufacturing processes that make large AC power transformers are the same as audio transformers, but scaled down in size. Audio transformers must pass the broadest frequency spectrum to be useful.

In the very late 1800's and early 1900's another application came about. It was called the telephone. Telephones were built with transformers that enabled transmission of a two-way conversation on a two-wire circuit. This kind of coil is commonly called a hybrid. There is also an inductor in a telephone instrument. Therefore, for a long time, the industry drove the innovation of materials, processes and theories. The need was there as was the incentive to make things better and cheaper. Organizations such as AT&T, Western Electric and Bell Labs were the early driving forces.

From about 1910 and later, the invention of the thermoelectric valve (tube) created a need of matching high impedances to low impedances (real world devices). This new industry of communications was founded. It would drive innovation, technology, manufacturing, costs and quality. During the late 1910's, World War I and all its implications made manufacturers design new kinds of devices which would require audio transformers. After World War I, prosperity and invention of the radio networks in America drove this new broadcasting industry. A lot of the new modern day phonographs and records were being developed. These devices were in the new consumer marketplace. The volume of these new devices was steadily increasing in production volume.

In the late 1920's 'talking pictures' were developed with the help of RCA and Western Electric. All these factors made the audio transformer industry grow in size. Materials, processes and manufacturing techniques were developed. The need for broader frequency response and lower distortion became necessary. Most of this innovation stopped at the outbreak of World War II. All attention was given to the military and its applications. There was development of devices for the military that would later be used for audio applications. After World War II, all attention was given to the new consumer marketplace. People had money to spend on things for leisure. This was given a lot of attention by manufacturers, large and small. In the early 1950's new things were being developed: the television industry developed both transmitting and receiving systems, high fidelity recording, 45 rpm and 33 rpm records and stereo in the mid '50s for the consumer. Live shows became amplified. Radio was developed into a large business. FM radio was to become a reality, thus increasing the fidelity of transmission. Better and better audio was being sought after for the listener. This meant that the equipment had to be improved. Thus, this drove invention, innovation and quality. New materials, processes, etc. were put in place.

In the early 1950's, a new invention would soon make the audio transformer less important - the discovery of the transistor and all its ramifications. This was a solid state device that could do all the functions of tubes, but with small power sources, less heat and smaller size. The transistor invention did not immediately replace the tube; this would take about 15-20 years. This period of time was the 'heyday' of the audio transformer. Believe it or not, the number one user of the audio transformer was the telephone industry. With an audio transformer in every telephone instrument, Western Electric was the number one customer for the materials that are used to make audio transformers. They were the leaders in developing all the materials, processes, machinery, etc., that we use today.

In the late 1960's the modern day integrated circuit was invented. The evolutionary process began to develop modern day op-amps that would someday replace the audio transformer. This would be driven by several factors, the first being the quality of sound. Broader frequency response, lower distortion and more faithful reproduction of the original source material were stated as objectives. I believe that costs were the biggest factor in this development. There have been great strides in the development of these kinds of circuits to replace the common audio transformer. The telephone industry has replaced the audio transformer and inductor in standard telephones that sit on your desk today with a complete IC chip set. In industries such as recording, broadcast and live sound, most audio transformers have been replaced by modern day integrated circuits.

In the 1980's, audio transformers were being designed out, left and right. Equipment manufacturers found that they were able to build equipment without these expensive devices and the circuits they used worked very well in controlled conditions. The problem is that devices are put in real world applications where the conditions are not always controlled - all the factors are not known or they may change for unexplained reasons. Therefore, these beautiful circuits that seem to work, don't always! The experienced audio person understands this problem and will use audio transformers in the design of critical circuits to safeguard them.

What will be the future of the audio transformer as we head into the 21st century? It is very hard to predict the future, but there always seems to be a real need for these devices. The numbers of manufacturers of audio transformers is steadily decreasing worldwide. In this limited state, we have lost some suppliers. The existing ones have taken up the slack. Materials seem to be getting better and more uniform as suppliers try to comply with ISO 9000 and pay attention to quality issues. As I see it, we are in for a better product in the future.