So this is a very simple circuit. Basically a microphone amplifier directly connected to some earphones with a volume knob. No frequency control of any kind. I'm wondering why this sort of device is not already available like loupe type glasses that we can easily find. I'm thinking this has something to do with legislation and maximum allowed earphone sound levels? Or maybe it is too crude to be actually useful?
It is available, even as in-ear style "hearing aid", for <$10 from the usual factories. I gather it's a little problematic selling them in the US due to medical device regulations...
