Electrical – Any solution to avoid humming sound / speaker noise for MP3 bluetooth module

modulemp3speakers

So I have here sub woofer Simbadda CST 5100N and I want to convert it to bluetooth, so bought an MP3 bluetooth module to convert it. The module needed 5 to 12 volt DC to operate. Inside the speaker, there is step down transformer 220 to 9 volt (that is what is written on the transformer), but I connected the power supply for MP3 module from a capacitor after full bridge rectifier. Before I connected it though, I measured the voltage running through the capacitor (2200 uf), and it says 12 volt. So I can directly connect the module and it would operate. On the module though, there is LM 7805, so I know it runs with 5 volts. The problem is the humming sound is louder. Is there anyway I can reduce the humming sound ? Or it would be best to eliminate it.?

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Best Answer

The problem is a ground loop, or possibvly a short-circuit caused by the common connection of the audio signal

To fix it use an audio isolating transformer to carry the music signal between the MP3 player and the amplifier board