- Because unit use microphone/s for android and Bt calls, which are connected together. That make the mic very weak and sound bad, just like you connect two speaker on one speaker output. So if we separate fro each input other mic then everything is fix
How to do Mic separation?
1 - First you need external Mic (any good mic is ok), and an external mic jack.
2 - Cut pin 4 instead of remove c32 (much easier and easiest to fix if something goes wrong.)
3 - Use shielded cable/s (I use fat speakers cables and shielded enough) and solder pin4 + to the back of the module and pin5 - to the front of the module (I was lazy enough and don't want to remove board that why). You can solder both of them to the back and everything will be ok.
4 - No needed any other mod as internal mic is used only by android and its sound is good enough now.
Now BT calls are perfect. I use my old pioneer microphone.
My other work
1. Radio fix http://forum.xda-developers.com/andr...-kgl4-t3279439
2. Red apps. http://forum.xda-developers.com/andr...radio-t3278054