The sound source switching of audio amplification part, whether DVD or CD, has the same effect. Only some use mechanical switch mode, and some use electronic switch mode.

For example, on the power amplifier, when the audio source is inserted into the CD interface from the back, the changeover switch on the front panel must be switched to the CD position. There is abnormal noise. First, the mechanical change-over switch has poor contact; The second is the failure of electronic conversion circuit.