I am trying to hook up an Electro Voice 457A Dynamic mike to the 718, it's a 3 conductor cable. I have connected: mike out to pin 1 ground to pin 7 and the 3rd wire is the problem. I have tried every pin except pin 2 which has 8 vdc. no audio in VOX mode. also attempted with PTT and no audio, checked mike with my Marantz PMD660 digital recorder and it works perfect with XLR connector. Any ideas..