4x Condenser Microphone: RCA UM-3 & Calrad 10-7 Electret Omni Directional Tested. Each of these requires a AA battery. Three of them worked which are pictured on the left side of the first picture. I plug this into a basic small guitar amplifier so that’s what I had to test them on and three of them I could hear myself speaking. The fourth one on the right which is one of the RCA’s I was not able to get to work so this is for extra parts or repair.