Audio Amplification (part i)

Exploring the ancient technologies, origins and Heritage

If we dig down into the history, we will reach the revolutionary Tesla/Edition era when lot of technological breakthroughs and inventions were happening and we come across the very first audio amplifier cum recording device which was purely mechanical invented by Edison. He called it phonograph. Before we get technical and explore the bits & pieces of this device it will be of a matter of curiosity and of interest to hear what it sounded like.

I Am The Edison Phonograph

This 1906 recording enticed store customers with the wonders of the invention.
[Courtesy: Wikipedia]

Not bad indeed, for the world’s first amplifier!

Edison’s phonograph was ingeniously simple yet accurate in doing its job. It was actually a recorder as well as player.

Thomas Alva Edison conceived the principle of recording and reproducing sound between May and July 1877. This was an offshoot his efforts to “play back” recorded telegraph messages and to automate speech sounds for transmission by telephone.

It has 3 structural elements in it as seen on the cover image of the patent below.

Edison’s Phonograph


The Horn


Rotating Cylinder


Wax coating which served as recording media… the first Record ever made!


Rotating Handle


Stylus Assembly

There was a wooden cylinder with an attached handle for rotating it and over the cylinder was a metallic foil wrapped (In his earlier version, it was actually wax). Over this foil was a stylus at some pressure and this stylus was mechanically connected to a horn.

When someone spoke near the horn, it concentrated the vibrations and on the other end, the connected stylus vibrated as per the sound and at the same time the stylus touching the foil on the rotating cylinder imprinted a groove following the vibrations. Once spirally the stylus reached from one end to the other the cylinder with the foil created a piece of record.

An exact inverse of this process reproduced sound, that is, if an already imprinted foil over the cylinder was rotated while the stylus over it, the vibrations of the stylus was mechanically transmitted and amplified due to internal reflections & reinforcements by the horn hence amplifying up to audible levels.

Edison’s Phonograph Advertisement

Edison went ahead and formed company selling Phonographs and recording cylinders after perfecting the design.

Lessons from Phonograph

Phonograph teaches us some very fundamental building blocks of Audio Amplifiers.

  1. Source: You need to have a source with recorded information which flows in time at a speed the audio was recorded, in the case of phonograph, its the wax/foil coated Cylinder.
  2. The Sound Reader: You need to have a system to read that recorded information, in the case of phonograph, its the stylus.
  3. The Amplifier: Once the reader reads the sound, this needs to be translated to mechanical energy capable to creating pressure waves in air so that we hear it, in the case of phonograph, it is the horn connected to stylus.

With the 199 successful patents Edison invented several incremental inventions sought to improve the performance of the audio recording and reproduction.

Subsequent Inventions

The dawn of the Era of Audio Technology

After about 2 decades of Edison’s Phonograph, in 1895, a German-born American immigrant Emile Berliner introduced a commercial version of a record player he had been developing for seven years. It had a flat disc instead of a cylinder, the gramophone it was called and it became famous overnight and shook the world. Unlike Edison’s cylinders, gramophone records were made from hard rubber and later from vinyl. As a result, the gramophone dominated the consumer market, with companies such as the Victor Talking Machine Company marketing “Victrolas” to the public.

A decade later around 1907, a global market for 10” double-sided 78 RPM (Revolutions Per Minute) records was developing and demand for cylinders had started a steep decline. During this era electrically powered rotating modules have started featuring in the record players and hand wound system had started disappearing. The Post World War II era gave birth to cheap radios and there was a creative tension and a conducive ecosystem for development of Audio Technology.

Technological innovations during World War II led to the development 16” 33 RPM ‘V-Discs’ rembling modern records. Peter Goldmark, head of research at CBS-Columbia in the US, worked on 33.3 RPM 12” records with microgrooves that offered much better sound quality. The 33.3 RPM 12” album on a plastic compound called vinylite (or ‘vinyl’) rather than shellac, debuted in 1948, while rival company RCA Victor jumped in with the alternative 45 RPM 7” disc the following year.

Evolutionary Changes

What changed from Edison’s Phonograph to modern Turntable

Microscopic View of Vinyl Record Grooves

  • The Cylinder
    • The cylinder was replaced by a disc with recorded information along a converging spiral inwards.
  • The Sylus
    • The stylus rather than being coupled to the horn got connected to a coil or a magnet which upon vibrations induced electricity with a frequenecy equal to that of the vibration (Refer Lecture #2)
  • The Horn
    • The horn was replaced by the radio speaker as the turntables had facilitated connecting the output from the stylus to the household radio sets.