Electric Guitar
The electric guitar is similar to the acoustic guitar in that it has six strings and a fretted neck, but the way the electric guitar produces sound is unique. The electric guitar does not use a sound box to amplify the sound made by the string vibration. In fact, many electric guitars have solid bodies that only serve to support the strings and the pick-ups. Pick-ups, or electromagnets, are positioned on the body of the guitar to sense the frequency produced by string vibration. The pick-up changes the frequency into a current which is sent to an amplifier. The amplifier acts as a speaker. The tone and volume of the sound produced is altered through the amplifer, which changes the current into a sound.
Synthesizer >> 
Synthesizers are machines that produce preprogrammed sounds, usually meant to mimic another instrument. To produce sounds, some synthesizers use electric currents to produce vibrations which are transformed into sound in the speaker. These electric currents can be regulated at the push of a button, however, the sound produced isn't always consistant. The invention of MIDI -- an interface designed to control synthesis digitally -- as well as all digital synthesizers, made synthesized sound produced much more consistant. It also created standard file format (.mid) for exchanging music between computers.
The first synthesizers were invented in the late 1950s and early 1960s. These machines used paper tape punched with holes to control the sound produced. For each new piece of music, the system had to be completely reset. In the early 60s, Robert Moog invented a playable, configurable music synthesizer. It took hours to set up each new sound, and was considered little more than a novelty at first. However, by 1970, a model that was much more portable, playable, and easier to configure was invented. Since then, many musicians have started to incorporate synthesizers into their music.
Denis D'or (the Golden Dionysus)
Invented in the mid 1700s, the Denis d'or was possibly the first electrified musical instrument in history. Unfortunately, the place of the instrument's location was lost hundreds of years ago, and there are only a frew remaining documents about it. We do know that the Denis d'or was a novelty instrument invented and created by Czech theologian Vaclav Prokop Divis. The instrument was about 5 ft by 3 ft by 4 ft and was played using a keyboard. The Denis d'or supposedly had 790 strings that were struck to be played. The Denis d'or was a novelty because it could imitate other instruments such as the harpsichord, harp, the lute, and some wind instruments. It was able to do this because of the combination of it's stops.
The Denis d'or could also be electrified. Divis would temporarily charge the metal strings to enhance sound quality. Divis also installed a mechanism that allowed the player to be shocked anytime Divis wished.
The Mellotron/Sampler
The Mellotron was a keyboard instrument used from the early 1960s to the early 1980s that was designed to recreate sounds of other musical instruments. The Mellotron keys were pressed down to create sounds. Pressing each key triggered a strip of magnetic tape underneath the key to play the sound. Mellotrons were an earlier form of samplers. Modern samplers generally use more digital processing to produce recorded sounds instead of a strip of magnetic tape. Since the first sampler in 1979, sound quality has gotten better and the recorded sounds sound more realistic.
Learn More...