Headphone jack issue

My new to me system includes Rotel electronics, circa 1995. Preamp has a headphone jack but plugging in a headphone does not shut down the speakers, so the jack obviously does me little good.
Is this a preamp flaw or are there options such as a headphone amp, which I had never heard of until my wife started saying, "Sheesh, that's loud. Couldn't you use headphones or something???".
This stuff IS greek and/or rocket science to me, so I would appreciate suggestions made with the electronically challenged in mind. Thanks