Can I only use a crystal earpiece for my crystal radio?

I am building a crystal radio for my science fair project, and I am having some issues. For my earpiece, I am using a telephone receiver which may be the issue. For my ground, I am using a water spigot in my backyard which is completely metal. My diode is a germanium diode, which works. My coil is a bottle wrapped in enamel coated magnet wire that is between 18 and 22 gauge. Instead of sanding a section of the wire and using a wiper blade, I have taps with the enamel sanded off. I have tested all of my parts with a voltmeter, so the circuit isn't the issue. Any advice? What might I be doing wrong?