I have two USB-connected Logitech headsets. One works fully with Linux, the other appears only as an output device (i.e., the microphone cannot be used). Both work properly with Windows 7, and both exhibit the same sympton on two installations of Mint with the Cinnamon desktop (a notebook and a desktop).
The one that works is identified by lsusb as a "Clear Chat Comfort USB Headset", while the troublesome one is a "Logitech B530 USB Headset" The latter is somewhat newer, but neither is exactly cutting-edge.
If I plug either (or both) into my desktop, it appears in the output tab of the (Cinnamon) Sound settings dialog, and if I select it there, sound is routed to the correct earphones. However, only the Clear Chat model appears in the Input tab; if I select it, its mic is used for input as I would expect. The microphone built into a Logitech webcam also appears in the Input tab, and works normally when selected.
These behaviors are the same whether the headsets are connected directly or through a USB hub.
I've checked with alsamixer, but nothing seems to be muted.
I installed pavucontrol, which gives one clue: its Input Devices tab shows all three mics, but only the web cam and working headset have a Port associated with them; this is missing from the entry for the nonworking headset. The B530 mic does have a level indicator, though, and it responds to noise near that mic. Ports are shown for both headsets in the Output Devices tab.
Any suggestions of how to get this mic working, or an explanation of why it will never work, would be most welcome. And thanks for reading through all this.