Balanced input impedances are usually (although not always) defined based on the sum of the impedances of the two signal "legs," while of course unbalanced inputs have only one signal leg (per channel).
In many and probably most power amp designs providing both XLR and RCA inputs the same receiver circuit is used for both inputs. When the unbalanced input is used the amp’s circuit ground is connected in place of one of the two signals that would be present in a balanced pair of signals. That connection is sometimes implemented via an external jumper applied between a signal pin and the ground pin of the XLR connector, and sometimes via a rear panel switch instead.
Therefore it is typical in those cases for the balanced input impedance to be twice the unbalanced input impedance.
There are other cases, though, in which completely different receiver circuitry is used for the two kinds of inputs, with a switch to select which input is used. In those cases the balanced input impedance may be much higher, much lower, or similar to the unbalanced input impedance, depending on the specific design.
Also, be aware that there are a few amp designs, such as many fully balanced Audio Research amps which ONLY provide XLR inputs, that will not work properly unless they are provided with a balanced pair of input signals.
Regards,
-- Al
In many and probably most power amp designs providing both XLR and RCA inputs the same receiver circuit is used for both inputs. When the unbalanced input is used the amp’s circuit ground is connected in place of one of the two signals that would be present in a balanced pair of signals. That connection is sometimes implemented via an external jumper applied between a signal pin and the ground pin of the XLR connector, and sometimes via a rear panel switch instead.
Therefore it is typical in those cases for the balanced input impedance to be twice the unbalanced input impedance.
There are other cases, though, in which completely different receiver circuitry is used for the two kinds of inputs, with a switch to select which input is used. In those cases the balanced input impedance may be much higher, much lower, or similar to the unbalanced input impedance, depending on the specific design.
... does this impedance apply to any incoming signal through XLR balanced and unbalanced?I believe you are asking what the input impedance would be if an unbalanced signal is provided to the XLR connector via an adapter or adapter cable. If so, the input impedance applied to the unbalanced signal would usually (although not always) be 1/2 of the specified balanced input impedance.
Also, be aware that there are a few amp designs, such as many fully balanced Audio Research amps which ONLY provide XLR inputs, that will not work properly unless they are provided with a balanced pair of input signals.
Regards,
-- Al