[Randy] had a cheap megaphone, and like most models in this price range, it didn’t have an audio input jack on board. He wanted the ability to pipe both music and audio from an external mic through the megaphone, and in a brief tutorial, he shows how he modified his bullhorn to do just that.
Most megaphones carry their electronics near the built-in mic, just outside the battery compartment. Removing the screws from the cap in [Randy’s] model revealed a circuit board and a couple of wires connecting it to the on board mic. His megaphone happened to play some canned music from a secondary circuit board, and he spliced in an audio jack with a built in cutoff switch between that and the main PCB. He also added a resistor in between his jack and the microphone circuitry to attenuate the line level signal properly. Once he reassembled everything, and then tested his input using a portable audio player, slowly ramping up the volume to the desired level.
It’s not every day that you require the ability to blast music through a bullhorn, but [Randy’s] modification is a great addition when you do need it.