Hi @Timo Kerminen,
Great question. Yes! There is voltage spike protection for the 3.5mm output should phantom power inadvertently be sent through that connection. This protection is in place for all of our microphones.
We really discourage the use of unbalanced to balanced connector cables. These cables can cause issues with the signal and may introduce some ground noise. Whenever possible, plug the 3.5mm output of the 3Dio into a line input rather than an XLR. This will keep the signal unbalanced, protect against accidental voltage surges and reduce the possibility of grounding issues.
I hope this info helps. Let us know if you have any other questions.
3Dio Customer Care