The Zin resistance does not affect the frequency response of the cable connection.
You normally have a Source connected. That Source has a Source Impedance.
The amplifier (or receiver) sees the Zin resistor and the Source impedance as parallel loads. The source impedance being ~ 10 to 100times lower dominates what the Receiver sees. You can choose either 10k, or 22k, or 47k, or 100k, or 220k.
When you disconnect the Source with the Receiver still turned on, the receiver now sees the Zin resistor as it's sole load. This now works as an interference aerial. You will hear and/or measure a higher output noise level. If this is a concern during switching of inputs using a selector switch that opens and leaves the "hot" signal line disconnected, then a lower Zin can help reduce this momentary increase in interference.
Try it with your switching and listen to hear if it is a concern.
You normally have a Source connected. That Source has a Source Impedance.
The amplifier (or receiver) sees the Zin resistor and the Source impedance as parallel loads. The source impedance being ~ 10 to 100times lower dominates what the Receiver sees. You can choose either 10k, or 22k, or 47k, or 100k, or 220k.
When you disconnect the Source with the Receiver still turned on, the receiver now sees the Zin resistor as it's sole load. This now works as an interference aerial. You will hear and/or measure a higher output noise level. If this is a concern during switching of inputs using a selector switch that opens and leaves the "hot" signal line disconnected, then a lower Zin can help reduce this momentary increase in interference.
Try it with your switching and listen to hear if it is a concern.
Most input stages have an input offset current.
This current can be into the input stage, or out of the input stage.
It is normal to use a resistor connected to Signal ground to allow this offset current to flow.
Rin/Zin provides this route.
The input stage MUST have some way to source/sink input offset current.
And it provides a Maximum Source impedance, if the real Source is disconnected even momentarily.
This current can be into the input stage, or out of the input stage.
It is normal to use a resistor connected to Signal ground to allow this offset current to flow.
Rin/Zin provides this route.
The input stage MUST have some way to source/sink input offset current.
And it provides a Maximum Source impedance, if the real Source is disconnected even momentarily.
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