In the words of MXR:

When the Echoplex EP-3 came out, guitar players were hooked by the way its preamp sweetened up their sound. Soon, the EP-3 made its way onto the records of top guitar playersfrom Jimmy Page to Eddie Van Halen and Eric Johnsonas much for its tone conditioning ability as its tape echo effect. Now, you can put the EP-3s legendary secret sauce right on your pedalboard.