Stereo to mono

Problem: MP3 player, stereo only output, 3.5mm female; stereo headphones, non-switchable to mono, 3.5mm input. I am partially deaf in my right ear and thus not hearing properly right channel. Very annoying. Is there a simple way to convert headphones, I.e. without rewiring them (beyond my capabilities), to produce mono sound both L&R? Thanks

 

I am in a very similar situation and would suggest joining the 2 cables inside the jack plug or even better by knocking up a short extension lead with the 2 cables joined inside one of the two end plugs, either male or female. That way you can choose between listening in stereo or mono at your whim without butchering anything.

 

A pair of resistors should be used to combine the L and R channels otherwise the output of one channel will be trying to drive the other channel when there is a substantial difference between the L and R channels. Resistors of around 10 Ohms should be suitable. This will reduce max volume somewhat but if it went more than loud enough in the first place then it should be OK.