very old Yamaha, new wireless headphones

by Lesley

I have an old but well-loved Yamaha piano I had purchased for my daughter when she was a little girl Clavinova PF p100. She brought it to college and just graduated. Anyway, we have a pair of Sennheiser chordless headphones and the pin is much too small to plug in, and the adapter has been lost. Anyone know how to replace this? There is already an adapter on it, from 2-pin to one, but the 1 pin is too short and too thin compared to the pedal pins. Sennheiser offers nothing.
thanks
Lesley