This high impedance headphone amplifier was found in American documentation from the 1990s. Any general-purpose FET can be used.
LTC7841 PolyPhase® Synchronized Boost Controllers Mouser Announces Analog Devices LTC7841...
This circuit was found in a 1987 edition of the United States' Hands On Electronics magazine. The...
This circuit can be made usng the TIP32 transistor but must use carbon microphone (not very common these...