A good number of the early EP-4 Echoplexes in the seventies had a compression circuit board installed. It was rushed into production and was an abject failure. A lot of people complained about how it negatively affected the tone of the Plex, and they stopped manufacturing them with the compressor installed. They even added a page in the manual stating how to remove it.
Fortunately it is an easy modification to remove the compressor board. For all you EP-4 owners I reproduce it here. Just in case the text is not legible, here are the instructions:
Cut the +22V wire and ground wire (Both brown).
Unsolder output wire (Red) noting where it terminates.
Unsolder input wire (Bare)and remove board.
Connect input wire (Bare) where output wire (Red) was removed.
