Crystal Earpiece

This is a model of the old Crystal earpieces, made for crystal radios and more. Only thing you need is a piezo element with diameter 20mm. Add the element inside the earpiece with the ceramic side of it facing towards the opening. Solder 2 wires on the element and drag them through the hole on the top part.
Then just Push the top so it locks the piezo on place.
I noticed that these piezo elements you can buy from many places, is not so thin as the ones in the original earpieces was, and it has not that high impedance as they got. But they work well for amplified simple radios, for example a zn414 or ta7642 with an extra transistor stage after it.