K6LL writes:
> Sound card microphone inputs require a stereo plug, even
> though computer microphones are all mono. Mic audio goes on
> the tip, shield goes on the shell. The ring is used to
> provide DC power to electret mikes, which includes virtually
> all mikes designed for computer use. When you use a regular
> Heil dynamic element, there should be no connection to the
> ring. If you stick a mono plug into a sound card mic input,
> strange things happen. Sometimes the DC gets superimposed
> onto the audio, which screws up the audio. Sometimes the DC
> gets grounded to the shell, which should be ok in a
> well-designed sound card, but should be avoided. Some sound
> cards have an extra preamp that can be switched in for
> low-output mics like the Heil. Some sound cards are ok for
> Heil without the preamp, and some cards don't have the
> preamp and the Heil can't drive them hard enough.
Unfortunately, not all sound cards keep the bias an mic audio
separate ... many use mono jacks with bias on the audio line
just like Icom radios!
Anyone using a dynamic microphone should consider installing
a .47 uF to 1 uF capacitor in series with the element to
prevent problems from the DC. Those problems can include
damage to the element (burning out the element from the DC),
magnetization of the element (long term DC) or low/tinny
as the "magnetic bias" makes the element less sensitive.
73,
... Joe, W4TV
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