What you are describing is normal for the Sound Out connector. The RCA Sound out plugs in the back of several Power Macintosh models including the Power Macintosh 7500, 7600 and 8500 give a continuous "line-out" level used in most stereo equipment. There is no way to adjust the sound level of the RCA sound out level. You can mute the sound of the RCA sound out connectors by selecting Mute in the Computer Speaker Volume level in the Monitors & Sound control panel.
The purpose of the Sound Out Level volume control in the Monitors & Sound Control Panel is to adjust the volume of the headphone connector. With the two controls (Sound Out Level and Computer Speaker Volume), you can adjust the Internal computer speaker and the headphone connector independently of each other.
Note: Monitors & Sound control panel automatically mutes and un-mutes the Computer Speaker Volume when you plug a headphone plug into the headphone connector. You can go into the Control Panel and un-mute the control panel manually, but it defaults to mute when the computer is restarted.
This article appeared in the 21 October 1996 issue of Information Alley.