It connects to the telephone hybrid channel of a broadcast mixer (though can be used with any mixer that has balanced audio in/out)

The VOIP traffic is a softphone on my PABX but it could equally come via SKYPE or any other such voice chat application

inside the box is a very crudely hacked £5 CPC USB soundcard and a cheeseweasel special, wired as balanced to unbalanced audio (otherwise you will get annoying noise from the computer soundcard via the earth ground of the USB))

I’ve currently set it up so if its in PFL mode audio is only sent when I press the talkback key and speak on the gooseneck mic (this also puts a red light condition to the signal lamps and mutes the monitor speakers) although it is actually possible to do phone ins etc by fading up the presenter mic. There is a clean feed output from the desk or mono PGM output but I need to build a passive mixer to select between that and talkback (as if its online streaming the cleanfeed will be 4-14 seconds ahead of what the person on the phone may be hearing which will be really confusing!)