In order to do lessons on Skype or other video-chats, I need to pipe the sound of my grand piano, sequencer and other computer audio signals to the computer. For this, I use my MOTU interface and various preamps. I also need a headset mic/headphone so I can hear the other person, without putting their voice through the speakers (internet feedback/echo.) While there are high-quality head-worn microphones, I don’t think it is necessary for me to spend that much just for my voice in lessons.
Cheap computer headsets are everywhere, but with my setup, I need the signal to go through an XLR mic preamp, so I can include it along with the other audio going to the client. These headsets have an 1/8-inch plug designed for computer sound-cards. Upon doing some research, I found that these microphones require about 5v of bias power, delivered to the “ring” or middle conductor of the plug, with signal on the tip, ground on the sleeve.
The above picture shows an adaptor I made with some soldering. I “sacrificed” a USB cord, which when plugged in to a phone-charging adaptor can deliver the 5v power. I then wired the signal to pin 2 of an XLR plug, while grounding pin 3. (“floating” pin 3 can invite RF interference, as the wire can act as an ungrounded antenna) A 22k current-limiting resistor was added between the power and the plug. (this may or may not have been necessary.)
Now, I can use the cheap, crappy headset mic with my otherwise decent audio rig!