On the bottom!. 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