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Subject: Re: Need help designing an Intercom system

Date: 03/09/01 at 8:34 AM
Posted by: John Dunn - Consultant
E-mail: ambertec@ieee.org
Message Posted:

In Reply to: Re: Need help designing an Intercom system posted by Ray on 03/01/01 at 6:18 AM:

Hi, Scott.

Ray is right on target! A suggestion: Let each channel be an audio bus with a finite termination resistance such as 600 ohms and let user's sendinging amplifier be configured as a current source feeding that 600 ohms. Let the compliance voltage capability of each current source be equal to the maximum signal voltage developed by one user's output multiplied by the number of intended users to make sure that each stays a current source at all times. Then you can connect one, two or as many users as you see fit to talk over each bus without encountering the analog equivalent of a bus contention problem. The current source outputs will simply add togehter. Be sure to use a ground wire between the audio buses in the ribbon cable to minimize crosstalk.

Good luck.

John Dunn - President
Ambertec, Inc.

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