I am trying to installing an external amplifier onto a existing intercom system. When switching from the talk mode to the listen mode the unit uses the speakers as a microphone which is causing the system to feedback. I wanted to know if I installed a diode between the intercom and amp will that isolate the signal and eliminate the feedback by only letting the signal go to the speakers and not from them? If this will work does anyone have an idea of what type and size of a diode? Also should it be installed on the positive or negative side or both? Any help would be greatly appreciated.