This unit has a balanced bridging input with 100 kilohm input impedance and 50 dB loss. Use the A15LA to connect high-level line or Aux Outputs to low-impedance microphone inputs. It will attenuate the output from such devices as mixers, tape recorders, tuners, or phono preamps to make them compatible with balanced low-impedance units. The A15LA can be directly connected to either balanced or unbalanced sources. If the source is unbalanced, connect it to pin 3 ("hot") and pin 1 on the A15LA input; no connection is required to pin 2.