What is the power pack used with headset condenser mics like the Crown CM311A or the Audio Technica ATM75? It's not a preamp, I understand, but a power supply. What's the difference?

-Have a look at http://www.live-audio.com/messages/108944.html

& click on the data sheet. The Crown CM311A has its own preamp powered by a 9 Volt Battery

I just purchased the CM311A. It was very expensive (for me), so I hope I'm getting my money's worth.

It's my understanding that the belt pack that comes with it is a power supply and not a preamp. I believe there is a difference between the two. Please correct me if I'm wrong.

Larry