The Phonograph
On December 4, 1877 Thomas Edison became the first person to ever record and play back the human voice.
The technology that led to the phonograph came from developments that Edison made in the telegraph and telephone. Edison at the time was experimenting with how a moving diaphragm linked to a coil, could produce a voice modulated signal. Meanwhile, he was also experimenting with a telegraph repeater which was simply a device that used a needle to indent paper with the dots and dashes of the Morse code.
Out of these two ideas, came the concept of attaching the stylus from a telegraph repeater to the diaphragm in the mouthpiece of a telephone. The first test in July of 1877, involved a sheet of paper pulled under the needle mechanically coupled to a diaphragm, as he shouted into the mouthpiece..... Sadly, It didn't work..... though it did produce an unrecognizable sound which was luckily, just enough to prove the concept and spark intense interest in developing a solution to the problem of recording the human voice. (Had he only imagined at the time what it would all lead to !)
For the next year Edison and his staff worked on the solution. Tin foil replaced paper, and thus tin foil became the first viable recording media. A band of tin foil was mounted on a cylinder, and the cylinder was turned via a hand crank during the recording and the playback. Edison turned the crank and spoke the first recorded words. "Mary had a little lamb, its fleece was white as snow, and everywhere that Mary went, the lamb was sure to go." Of course, the rest is history !
On December 4, 1877 Thomas Edison became the first person to ever record and play back the human voice.
The technology that led to the phonograph came from developments that Edison made in the telegraph and telephone. Edison at the time was experimenting with how a moving diaphragm linked to a coil, could produce a voice modulated signal. Meanwhile, he was also experimenting with a telegraph repeater which was simply a device that used a needle to indent paper with the dots and dashes of the Morse code.
Out of these two ideas, came the concept of attaching the stylus from a telegraph repeater to the diaphragm in the mouthpiece of a telephone. The first test in July of 1877, involved a sheet of paper pulled under the needle mechanically coupled to a diaphragm, as he shouted into the mouthpiece..... Sadly, It didn't work..... though it did produce an unrecognizable sound which was luckily, just enough to prove the concept and spark intense interest in developing a solution to the problem of recording the human voice. (Had he only imagined at the time what it would all lead to !)
For the next year Edison and his staff worked on the solution. Tin foil replaced paper, and thus tin foil became the first viable recording media. A band of tin foil was mounted on a cylinder, and the cylinder was turned via a hand crank during the recording and the playback. Edison turned the crank and spoke the first recorded words. "Mary had a little lamb, its fleece was white as snow, and everywhere that Mary went, the lamb was sure to go." Of course, the rest is history !
How Modern Phonographs Works
Phonographs play records made by analog disc recordings. An analog (which means likeness) of the original sound waves were stored as jagged waves in a spiral groove on the surface of a plastic disc. As the disc went around on the phonograph, a needle called a stylus moved along the groove. The waves in the groove caused the stylus to vibrate. These vibrations then were turned into electric signals that were changed back into sound by speakers.
Cartridge Types
In early high-fidelity systems, crystal and ceramic pickups were used. They have been replaced by the magnetic cartridge, using either a moving magnet or a moving coil. Magnetic cartridges provide much lower tracking forces (and thus damage the record much less). They also have a much lower output voltage than a crystal or ceramic pickup, in the range of only a few millivolts, thus requiring greater amplification. At this point in the hi-fi stereo system it is considered pre-amplification.
a) Moving Magnet (MM) cartridges
In a moving magnet cartridge, the stylus cantilever carries a tiny permanent magnet, which is positioned between two sets of fixed coils (in a stereophonic cartridge), forming a tiny electromagnetic generator. As the magnet vibrates in response to the stylus following the record groove, it induces a tiny current in the coils. Because the magnet is small and has little mass, and is not coupled mechanically to the generator (as in a ceramic cartridge), a properly adjusted stylus follows the groove far more gently and faithfully, requiring less tracking force.
b) Moving Coil (MC) cartridges
Moving coil systems are extremely small precision instruments and are generally expensive. The MC design is again a tiny electromagnetic generator, but (unlike a MM design) with the magnet and coils reversed: the coils are attached to the stylus, and move within the field of a permanent magnet. The coils are tiny and made from very fine wire, so are even lighter than the small magnet used in an MM cartridge, thus improving the tracking ability of the cartridge. This can give extended frequency response as well as greater fidelity. A disadvantage however is that moving-coil cartridges generate an even smaller signal than an MM cartridge, because the moving coil cannot be large enough (too heavy) to generate equivalent voltage levels. The resulting signal is only a few hundred microvolts, and thus more easily influenced by noise, induced hum, etc. It is challenging to design a preamplifier with the extremely low noise inputs needed for MC working, so a "step up transformer" is often used instead.
c) Crystal and Ceramic cartridges
Crystal and Ceramic cartridges work on the piezoelectric effect principle. Huh? It is what is known as a transducer, basically turning mechanical motion into voltage. The piezoelectric effect was discovered by Pierre Curie in 1883. When mechanical pressure is applied to certain types of crystals, the properties of the crystals causes them to produce voltage.Certain crystals, ceramic materials, Rochelle salt, and quartz exhibit this effect.The stylus is attached to a cantilever which is attached to these crystals, ceramic materials,or salts inside the cartridge body. When it vibrates it applies the mechanical pressure or motion which in turn produces the voltage. With that said, at the other end of your stereo is the cartridge in reverse. The loudspeaker is a transducer in that it converts voltage into mechanical motion. So we have the cartridge converting mechanical motion (the stylus being drug around in the groove of the record) into voltage, the pre-amplifier and amplifier processing the voltage so the loudspeaker can understand it and reproduce this whole mess into those high fidelity sounds that we all love to hear.
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