I am having a lot of difficulty using an external microphone with my iMac. I am on my third microphone, a Plantronics 355 headset with mic. As with the first two (Radioshack brand - not sure of the make or model) the headphones are working fine, but the mic is not working yet.

I have gone to System Preferences > Sound > Input and selected "Line In / Built-in Input." Not hearing anything and there is no visual activity on the input level meter. (btw when I select "Internal microphone," I can record audio just fine and the meter shows the level changing.)

Running 10.5.8 on an iMac 2.4 ghz Intel core 2 duo

Mic is Plantronics brand, #355

Any advice? Many thanks!

**EDIT** Boyfriend figured it out. The mac built-in input is a line in, meaning there is no amp for the mic signal. You need to plug in a pre-amp, or purchase a mic that has one built in. Hope that is helpful to someone else.