I know the LP300L mic can be configured as HIz or LOWz.
However it would appear that in the HIz and LOWz modes, that the LP300L is only capable of being wired as an unbalanced device.
Although the LP300L is shipped with a 3 pin XLR male connector, a check ot the factory wiring, on the mic body's, male XLR connector will reveal that pins 1 & 2 are tied together (ground or low depending upon the device receiving the connections) --- Pin 3 has the ability to receive a wire (HIz or LOWz) via internal plug connection.
Thus it looks like you have not actually provided this mic with the ability to deliver a balanced LOz output for driving long cable runs.
Before I tear the top side of this mic apart to attempt a wiring possibility of making the LP300L a truly balanced LOz device, I thought I would write and see if you could shed any light on this device and the possibility of wiring it as a truly balanced LOz device.
Yes. It can be internally rewired as a balanced mic. We have a data sheet (dated 1981) showing the internal wiring and will mail you a copy. Please provide a mailing address.