I'm using the following input stage for an audio application:
The audio signal is analog and single ended. The connector side is exposed, so a person could touch it. The TVS should protect the circuit from ESD. The C10 is a DC coupling capacitor and the other components are used to filter out GSM noise. The amplifier is a 2W class D audio amplifier.
The problem is that in certain situations, when a person touches the connector, a DC voltage is induced on the connector side of the C10 capacitor, which causes a whistling sound, although the only thing I can measure on the audio line is a DC voltage (no sinus-like wave).
The blue line in the following image shows the induced voltage on the connector side of C10. The sound fades out after about 60 seconds.
My question is: is there a way to prevent this or to discharge the capacitor quickly? Alternatively, why is the whistling sound there and can I prevent it?
For the sake of completion: I use the following parts now and touching the connector pins doesn't generate noise anymore.