I bought this set for my son: Echo Valley Express DCC Sound Value Ready To Run Electric Train Set - HO Scale.   It comes with a DCC controller that has a red cable that connects to the EZ Track.  The red cable has a round connector on the controller end that looks like an audio (headphone) connector.  That cable has become damaged and I need to either buy a new one (can't find it anywhere), or buy a replacement for that round connector.  Where can I get one of those connectors?  What size is it supposed to be?