I have an audio signal running through a device that switches it over using a mechanical relay, as a result of the DC offsets and the parasitic capacitance on the output (which also connects to a high Z input) I can hear a 'pop'.
My original plan was to use a device called TLP222G which I had around to shunt the signal to ground quickly (before the relay action starts) and release it after a few ms, after the relay was set.
I had to use the same signal that feeds the relay's coil when that triggers I'm creating a pulse which should open the MOSFET, short the path to ground and keep it that was for about 0.2ms which is enough time for the relay to switch over.
The problem is that I can hear noise when the MOSFET opens or closes. Is there something else I should add to the circuit in order to keep the switching action completely silent?
Below you can see the simple circuit. The 360 Ohm resistor is fed from the 5V pulse that also activates the mechanical relay.
The LED inside the photocoupler has a max forward voltage of 1.3V so with the resistor it gets about 10mA.
This is a typical output stage of a device that is connected to the input of a high Z amplifier. The relay in the system shorts the input to the output so the entire device is bypassed. This creates a noise.