My goal is to amplify signals with a frequency from 100Hz above. My circuit is looking as the picture below. With an oscilloscope, I am trying to measure the output of the amplifier. If the input of the circuit is not connected at all, I can see a small 50Hz signal. Touching the input gives me a huge 50Hz signal which comes from the AC power supply from around the room. But I expected them to be eliminated due to the capacitor added.
I know that the oscillator's probe behaves like an antenna. Maybe it induces the noise into the feedback of the amplifier? But then, I don't understand why touching the input increases this noise.