The model 515SBG microphone is supplied with the mic circuit Normally Closed when the mic switch button is up. This means I cannot connect two (or more) 515SBG mic in parellel. Can the mic circuit be modified to Normally Open?
Yes, the mic circuit can be modified.
However, note that the disassembly of the mic and the re-assembly is quite difficult.
The steps below are a general outline of the process:
1) Remove the grill assembly. It is held on by a set screw.
2) Remove the mic element.
3) Remove the "E" clip that attaches to the shaft of the switch button.
4) Remove switch button for the mic handle.
5) Remove the hex nut and washer that holds the switch to the mic handle.
6) Slowly remove the switch from the interior of the mic handle.
7) Locate the switch terminal that has a red wire and green wire soldered together.
8) Remove the red wire and green wire from the switch terminal.
9) Re-solder the red wire to the green wire and insulate with electrical tape.
10) Start at step 6 above and work backward to re-assemble the mic.
Once again, this is not a simple procedure. Think carefully before proceeding.