This circuit works as both an injector and a signal follower. We found it in the May 1994 issue of Electronics Now. The Z1 headphone must be high impedance.
This is the project found in a 1981 publication, but it is still viable. It is a simple AM...
This commercial earphone receiver was manufactured in the 1960s in Japan. It was powered by a 9 V...
This circuit was found in a European publication from the 1980s. The transistors can be the BC548...