[Matthew Ross]

Further tests and help from AKG showed the problem to be just a good ol’ fashioned ground loop. The AC adapter for the Marantz has no ground plug, so attaching ground to its chassis made the problem go away. I figure the Sennheiser mic did not have the issue simply because it’s shielded differently. Indeed when you hold the AKG lav in your hand for testing rather than on a lapel, the buzz issue was at its worst. And when holding the lav in your hand with the buzz in full effect, if you touch the Marantz chassis, the buzz goes away. That fact was the final troubleshooting step that showed the problem was with ground. And I figure the AKG did not buzz on the other AC-powered system I had initially plugged it into because that system is grounded.

[Matthew Ross]

Thanks for the response, Bill.

Since the initial tests, I connected the lav and its phantom power adapter to a Sony EX1, and ran that off battery power, then AC. Sure enough, the AC recording had a slight buzz in it (though not nearly as pronounced as from the Marantz). I believe you are correct that I’m not getting properly balanced audio coming from the mic through this phantom power adapter.

Now I just have to figure out if there is anything I can do about that, or if I’m stuck running the recorder on batteries for now.