You can turn an old tape deck into an echo machine.
Secondhand, open-reel tape recorders have served generations of audio tinkerers. If you are handy with electronics, you can rewire the deck's tape heads and turn the recorder into a homemade echo machine.
Heads
The tape deck uses a set of tape heads--sugar-cube-sized metal blocks that put magnetic signals on the tape. Good-quality decks have three heads: one each for erase, record and playback functions.
Feedback
During recording, the erase head removes any old signals from the tape; the record head then records new signals on the tape. The playback head works in play mode, but it is also active during recording. If you send the signal from the playback head back to the record head, it will form a feedback loop, echoing the recorded sounds endlessly.
Mixer
To make an echo machine from a tape deck, record from the output of a two-input mixer. The mixer's first input will be the normal music source. The second input comes from the playback head. By varying the volume on the second input, you will change the amount of echo from none to extreme.
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