A Question of Mic Connections

by Charles S. Fitch

Some readers of our recent article “Make Cheap Talk Even Cheaper” have noticed that our schematic really doesn’t show that the mic input is a mini tip-ring-sleeve and doesn’t differentiate the mic connections.
Most computer sound cards follow a convention for wiring but there really is no standard per se that I’ve been able to identify.
The top end units in their mono wiring have the DC source separated on the ring and the audio input on the tip. This allows all the options of either using a pure audio input or an electret mic.
Our observation is that the typical cheaper sound cards and definitely cards with stereo mic inputs have the mic input on the tip with the DC voltage needed for the mic already available through a load resistor.
Thus far, all the inexpensive mic/headsets that we’ve tried have worked well in this wiring configuration. So the initial connection should be that the tip is what is wired as audio in to the interface, and ground is connected to the sleeve.
Since we just grabbed some 1/8-inch jacks from the junk box for this project, we neglected to list a typical/suitable jack for the mic input on the parts list. Consider the jacks available from Radio Shack as possibilities, try here or here. The headset jack could be something like this.

Once complete, if your adapter doesn’t work properly, let me know the details of the problem and we’ll see if we can help.


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