i'm not exactly sure what you're getting at but i think you are asking whether to use grounded shields on microphone cables and long wiring in high gain circuits. yes it's always a good idea. generally if you have long wires in the feedback loop of an op amp going to a pot on the front panel, it's always a good idea to have them shielded, but with the shields terminated only at the circuit board end. just be careful what kind of shielding you use, as with high gain circuits, the capacitance of shielded cable can have an effect on frequency response. with the mic cable, if the FET preamp is in the mic capsule, then the impedance is low enough to use standard microphone cable. if the FET preamp is not in the capsule, but on the board, use low capacitance cable. even small amounts of capacitance with high microphone impedances cause high frequency rolloff.