Reason 1: The front stage does not open, but it is connected to the rear stage, and then the rear stage is also closed, which is caused by the front stage closing, causing the rear stage to impact the horn.

    Generally, the rear stage is equipped with a horn protection circuit. When the power is turned on, the horn is turned on after a delay and the horn is turned off immediately. The horn is disconnected - after 2-5 seconds of power on, a "click" sound is heard, which is a relay action. The contact controls the output of the power amplifier and the connection or disconnection of the speaker to avoid the impact of power on the speaker. When the power amplifier is turned off, this relay will immediately disconnect, thereby protecting the speaker.

    Reason 2: The output of the previous stage does not match the input of the power amplifier.

    This can be one of the reasons for the impact sound of "connecting the front stage, but not turning on and off the power amplifier". This is related to the output of the front stage and the input circuit of the rear stage, and it is also possible that the "input" circuit of the rear stage affects the "relay control" circuit of the rear stage. This is why if you do not connect the front stage and then turn off the rear stage, it will not be possible. It may be that there is a shared power supply between the two circuits in the design, and the specific situation depends on the circuit.