HSE - Hidden Sound Explorer
Hidden Sound Explorer is a circuit that allows to amplify small voltages coming from piezo-electric transducers or from inductors (coils).
The output is a 1/8" stereo jack in which you can plug your headphones to discover a new world of hidden sounds.
Use a 100mH inductor to scope out power supplies, electric motors, smartphones. Any electromagnetic source will produce a distinct sound. Also a piezo disk attached to a vibrating surface can reveal some unheard sounds. Use it on guitar, violin, toothpicks or a broom...whatever.
In this repository you can find the schematic and the PCB production files to build your own device.