On the bottom of the charging base!
Mic volume, speaking volume, and configuration controls are all on the bottom of the base station for CS510/ CS520 / CS540 systems.
If you look at the base station head one and tilt it backwards, you’ll see two dials one on top of another and a sliding switch to the right,
-The top dial is Listening Volume (1-4)
-The bottom dial is Speaking Volume (1-6)
-The sliding pointer to the right is your configuration switch (A-G)
These are all pretty similar to the ABCD (Mic volume), 1234 (Speaker volume), and 1/2/3/4 Compats on older CS series headset systems.
Recommended settings are
-Listening Volume: 3
-Speaking Volume: 3
-Configuration: A (Cisco headset jack: E)
MY HEADSET ECHOES...
Make sure your telephone's volume control is set to a mid position or lower.
If necessary, adjust your microphone volume on the headset to a lower setting.