Specification:
Power Supply: DC 3.7-30 V
Size: 93mm * 55mm * 25mm
Resistance: 47K
Judging by googling, the NE5532P microcircuit is quite popular in the amateur radio environment ...
Given the large range of supply voltage, the subject can be used not only for as an amplifier for headphones. You can for example apply in car when connected to an AUX MP3 player, for example, I have a weak sound without an amplifier. An important positive quality of this constructor is the price. Anyone can buy who needs an amplifier of this kind. And it will be determined whether he needs it and whether it should continue on an increasing basis.
Cost: ~ 498