I need to know how to construct an audio isolation transformer that couples a mixer out 120 ohm to a transmitter mic input with approx. 600ohm input, but am going to use a 1K pot instead of a set resistance as to adjust for PAD. What's confusing me is the transformer I have TMO 13-R has three leads which I think it needs, but, all the schematics I seem to find show only two on each side of the transformer. I goes from top left of primary side 1,2,3, then up the other side 4,5,6. I'm not sure what lead is what. Please help

Already Tried:
Well I ordered a transformer and they sent me a different one than I ordered because I told them what I was doing and they said this one would be better. The one I was going to order just has two leads on each side. This one has three so havent tried exept trying to find info on transformer and did find out that it goes from primary side down 1,2,3 then up the other side 4,5,6. I don't know what is what and can't find ANY info