It’s usually a good idea to look at what’s normally connected, when breaking a circuit, and replicate that. Which I seem to remember is a 10k resistor with a parallel capacitor (being too lazy to go back and look again).
There’s a resistor, then parallel capacitor and resistor to ground, and finally a capacitor to the amp. I could try replicating the parallel pair if that could help
add a series capacitor, if you can.
Would that be a polarised capacitor for protection? And on both the original and my added lines?