User nali posted this mod in the the amc forum. He wanted to play MP3 on a vintage car radio, because he did not want to spent $$$. So, he got a normal jack socket with mechanical connection break. This socket is like a normal stereo jack socket, but it has an additional NC contact. When a jack is inserted in this socket, the contact breaks. Then he connected the output of an MP3 player to the potentiometer of the volume control of his vintage radio. The signal that originally was going directly to the volume pot, was now redirected through the NC contact of the jack socket. Normally, the radio receiver operates as... a radio receiver, with the original signal going through the NC contact. But when he inserts a jack in the socket, the contact breaks and the radio signal is cut, the MP3 signal is then sent to the volume pot, the radio's amplifier is then used to amplify the MP3 signal and there it is! An inexpensive MP3 player!