When using a SM58 it reads on the channel display, however, I must talk very loudly to get the mic to "turn-on" or kick in to the speakers. Can you help?
Please provide complete technical details of the PA mixer into which you have plugged the SM58. This information is critical for us to have in order to solve your problem
Our guess is that your PA mixer has high impedance inputs using 1/4" female phone jack inputs. If that is the case, you need to add a Shure A85F low-to-high impedance transformer to the end of your SM58 cable. Or you might have a problem in the mic cable.