I recently upgraded the VHF/UHF part of my station with an ICOM IC-9700. The IC-9700 is the VHF/UHF brother to the much-heralded IC-7300 and the two rigs share many design aspects. I presume the mic circuitry is identical and so my question could as well apply to the 7300. Which is... I own three headsets... a Heil Pro 7 w/dynamic mic element (used on my Kenwood TS-590SG), a Heil Pro Set w/IC electret mic element (sold by Elecraft and used on my KX3), and a Yamaha CM-500 (vintage, one-year-old) w/electret mic element (also used on my Elecraft KX3). Wanting to be able to use these three headsets with my new ICOM rig, I purchased the Heil AD-1I and Heil AD-1IC adapters. https://www.hamradio.com/detail.cfm?pid=H0-003261 https://www.hamradio.com/detail.cfm?pid=H0-016653 The AD-1I includes the DC blocking capacitor and (I thought) was for interfacing dynamic mics with ICOM rigs. The AD-1IC does NOT include the DC blocking capacitor and (I thought) was for interfacing condensor/electret mics with ICOM rigs. Alas. My Heil Pro Set headset, using the AD-1IC adapter cable works fine. Phone works, mic works. All good. But curiously, neither my Yamaha CM-500 headset, using the same AD-1IC adapter cable nor my Heil Pro 7 headset, using the AD-1I adapter cable, work. In both cases, I get phone (audio in my ears), but no mic output. Changing mic gain has no effect. Any ideas?