Let’s say you have a CD player and a power amplifier, between these two do you have a dual pot to both positive and negative signal wire, no grounding at all. Or you could say a variable resistor in the middle of the cable.
Would the variable input resistance do anything negative?
Or should the impedance be constant even under change in the attenuators resistance?
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Most likely, the resistor would do little to nothing, depending on values. To change the level you would need to create a voltage divider, which you can do with the variable resistor if one end of the elements is tied to ground (for it to act like a normal level control, it would be the left terminal looking at the pot from the front), the other (right terminal) is connected to the CD player and the wiper (middle terminal) connected to the power amp in. All grounds connected together.
Without the ground, most likely nothing much would happen. The output impedance of your CD player is pretty low and the input impedance of the power amp is pretty high, so not much current flows between the two, therefore very little voltage drop across the resistor in between.
Since you have a volume control on the CD player, why do you want to add a resistor in-between?
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