Hey,
yes thats possible:
You can set the talk power of your default channel to a high value that your user groups don’t have = people are unable to speak. Example your user groups have talk power values of 10; 20 and 50 so you set the talk power value of the channel to at least 51.
For the chat you need to go to server permissions and then to channel permission, find your channel in the list and untick the “Send Text Message to Channel”.
