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I am trying to understand the circuit below. Please look at the highlighted circle, Imagine that the potentiometer has 3 pins namely, A, B, and C.
If A is connected to -ve inverting input of the op-amp and if C is connected to the output of the op-amp, where would B pin of the potentiometer connect to? To ground?
If my assumption is wrong please correct me with simplified diagram/pin assignments.
Assuming that pin B is the wiper, then it could be connected to either pin A or C depending on whether you want the gain to increase or decrease with clockwise rotation. In either case, though, assuming the potentiometer has a linear resistance vs rotation characteristic, the gain will change linearly with rotation since the gain of the circuit is linearly proportional to the value of the potentiometer. At one end of the rotation the potentiometer resistance will be 0 (thus the gain will be o) and at the other end it will be 100k(and the gain will be maximum).
If that is the case then the gain setting will not be linear, Meaning turning the gain knob will not linearly increase the voltage?
Here's a simplified version of what's going on in the potentiometer when B and C are connected.
Imagine the situation when B is set turned to different spots within the pot.
In the first case the resistance between A and C is 25K, in the second case 50K and in the third case 75K. The short between B and C cancels any resistance in the pot between B and C. Only the resistance between A and B remains.
simulate this circuit – Schematic created using CircuitLab
Remember that Ohm's law works here. All the current in the input resistor goes through the pot. Thus the gain in the diagram as draw will be proportional to the setting of the pot.
