Many Siedle call stations can be rewired internally so that the loudspeaker is led out at terminals 12 and 13 (without the built-in transistor amplifier). Connect terminal 12 of the Siedle module to one of the door intercom contacts (make contacts 1/2 on the TSA-a/b), connect the other door intercom contact to terminal LSP of the TSA-a/b. Connect terminal 13 of the Siedle module to the 0V contact on the TSA-a/b. This results in a greater maximum volume.