I have a circuit in my car which emulates the protocol the radio uses to communicate with a CD changer. The goal of the emulator is basically to make the radio open up it's audio channels.
The circuit works, but the audio lines pick up noise from the data lines (evidence of this is that for instance when a button on the radio is pressed, a different sound burst will occur).
When the audio cable is connected to my phone, the noise will be attenuated a bit, but nowhere near eliminated. Using a ground loop isolator does not do anything at all (I put it between the audio connector and my phone).
In the circuit, the left right and common audio signal wires are effectively directly connected to my phone, with only the connectors in between.
I would like to eliminate the noise by effectively making the audio signal go only 1 direction.
What would be the best way to achieve this? I was thinking along the lines of using a 1x gain amplifier, but I wouldn't know where to start with that.
Schematic:
PCB layout:
