Adding an audio input jack to a megaphone allows you to play music, sound effects, or use an external mic with your megaphone. This is a great mod for most cheaper model megaphones that do not come with an audio input jack. This was a quick and easy hack to perform and did not require permanently disabling any of the megaphone's functionality, such as the microphone. Follows are directions to help you perform this mod yourself.
Step 2: Open it up
Open the battery compartment. The electronics should be accessible inside of the battery compartment's lid.
Simply remove the screws holding the electronics in place and free the circuit board.
Step 3: Drill a hole
Before drilling a hole in the battery compartment cover, make certain the hole will be in a location that will not interfere with any of the electronics when megaphone is reassembled.
Once you have decided on a spot, drill a 1/4" hole.
Step 5: Trim
This is the tricky part. It is now time to determine where they audio is entering the board and at what audio level.
This particular megphone has a separate board which played the "Ole Song" for European soccer (a.k.a. football) matches. This board then connected to the main board at three junctions. Presuming two of the connections were power and ground, it was fair to say the third was an audio connection operating at or around line-level.
I figured out which connection was which, and cut the audio pin to separate it from the main board.
Should you not have this functionality in your megaphone, you will want to splice into the signal wire from the mic.
However, when sending line-level audio into the microphone circuitry, you will want to add a lot of resistance. Try 100K to start. If that is too much, reduce it gradually (68K, 47K, etc.)
Step 6: Insert
Insert the audio jack into the hole that you drilled in the megaphone cover and fasten it in place.
Step 7: Rewire
First, connect the signal wire to the junction on the main board where the "Ole Song" board used to connect.
Next, connect the switch terminal to the Audio terminal on the "Ole Song" board.
Last, connect the ground barrel connection to ground on the main board.
Basically, what will now happen is that it will play the "Ole Song" whenever there is no plug inserted. When the audio plug gets inserted into the jack, it will break this connection and feed the audio into the main board in place of the "Ole Song."
If you are doing this for the microphone, you would want the signal going to the main board (with appropriate resistance in series), the switch going to the microphone and ground going to ground on the main board.
Step 10: Plug it in
Plug in your audio source.
You will want to start off with the volume down on the megaphone and with the audio player set to a low volume.
Turn the megaphone on and set it to whatever input you spliced the jack into (i.e. the "Ole Song" or mic).
Slowly start to increase the volume.
It should now be playing your audio.