This high impedance headphone amplifier was found in American documentation from the 1990s. Any general-purpose FET can be used.
In the figure we have a wireless wiretapping circuit for the frequency range determined by L1. For FM...
This voltage follower or amplifier with unit gain uses an unusual operational amplifier nowadays. The...
Found in a 90’s Electronics Now, this circuit has its output connected to an audio amplifier. The...