If conditions permit, it is generally recommended to use differential input, which can avoid interference and background noise problems in many situations.
The background noise is directly proportional to the amplification factor. Under the condition that the volume meets the requirements, try to reduce the amplification factor as much as possible.
Background noise is generally introduced by the power amplifier itself or the preamplifier circuit. When the two input terminals of the power amplifier are short-circuited and connected to GND, listen to see if the background noise has improved significantly. If it has improved a lot, it is judged to be introduced from the outside. At this time, it is recommended to reduce the gain of the preamplifier to lower the background noise. If the noise floor of the preamplifier is fine, it is necessary to check the peripheral circuit of the power amplifier, such as the following points
(1) For the noise of the power amplifier itself, one can reduce the amplification factor and check the traces of PVDD and GND. If the background noise is at a high frequency, you can try parallel filtering capacitors for PVDD. Or the power amplifier can be powered externally separately. Determine whether it is caused by the power supply or the ground.
(2) Noise caused by the outside: In some cases, the power amplifier and the main chip are far apart, and the large current traces of the intermediate power devices radiate in. At this time, it is best to have a clean GND trace "escort" from both sides of the audio source trace to the power amplifier to avoid interference. Another situation is that when single-ended input is used, noise is often introduced. This is mainly because some projects choose the nearby GND for the convenience of wiring, rather than pulling a wire from the GND at the audio source end. It is recommended that this GND be routed separately (as a signal line), for example, a 0 to 10-ohm resistor can be placed on this ground wire. Thus, the network is disconnected from other GND.
(3) For the background noise caused by PCB routing, the signal lines should be as short as possible, and the two signal lines should be routed as parallel as possible. Even if it is a single-ended input, the ground end is best to be routed parallel to the signal line from the audio source end. Moreover, it should not be routed parallel to the power line, even if they are on different layers.
(4) Background noise caused by suspension, especially when AUX is input alone and no AUX line is inserted, the signal is suspended (commonly seen in demo boards). Suspension will naturally introduce noise. To avoid suspension, a 10K resistor can be connected in parallel at the suspension end to GND.
(5) When inserting devices such as PCS, there is noise. The GND output of the AUX of devices like PCS is often accompanied by other interferences, such as 50HZ AC, which can be conducted to the power amplifier.