On the CXA81/81 Mk II, pressing the A1 input selection button will toggle between the balanced and unbalanced inputs. The balanced input is shown by A1 being lit orange, while the unbalanced input is shown by A1 being lit blue.
Please ensure that the correct input is selected on the CXA, depending on how your CXA is connected. If the wrong input is selected, then there will be no sound from the amplifier.