Here is a "complete transistorized Mixer circuit". This is not just a simple Mixer module, this is a "complete mixer".

This circuit incorporates a microphone input, and four line inputs. The inputs are buffered and the microphone input incorporates a "Pan" circuit to alter the electronic position of the announcer between the left and right channels. The mic input is for a dynamic microphone that uses a standard 1/4" phone plug. So you are not limited to High End or Expensive Ballanced 600-Ohm Impedance Microphones.

....

....