Echo machine

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An echo machine is the early name for a sound processing device used with electronic instruments to repeat the sound and produce a simulated echo. The device was popular with guitarists and was used by Brian May, Jimmy Page and Syd Barrett among others. Nowadays it would normally be called a Delay or Echo.

Early versions (1970) called "plate echoes". They were analog and consisted of one or more transducers on one end, a coil spring of 1-2 feet in length, and transducers on the other end, each connected to a separate spring. The transducer turns the audio signal into mechanical vibrations which travel down the spring experiencing a delay before they arrive at the transducer at the other end. At that point, the sound is reproduced and fed back into the amplifier as an echo. The size and tension of the springs creates different delays, and could be applied to any audio source. These devices were inexpensive, hobbyist grade, and sometimes sold in kit form so every garage band could have one.

A second type of echo machine is the "tape echo". Originally they were made with tape recorders where the tape speed and distance between record and playback head determined the delay for the echo and were quite expensive. The more common type of tape echo is a small portable unit. One example is the Echoplex which used a tape loop. The length of delay was adjusted by changing the distance between the tape record and playback heads. An example is the Roland Space Echo with a record and multiple playback tape heads and a variable tape speed. The time between echo repeats was adjusted by varying the tape speed. The length or intensity of the echo effect was adjusted by changing the amount of echo signal was fed back into the pre-echo signal. Different effects could be created by combining the different playback heads. Some models also had a Spring Reverb.