# How are potentiometers connected in an amplifier gain circuit?

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.

• The diagram clearly shows "B" connected to "C". Jun 1, 2021 at 21:36
• @DaveTweed If that is the case then the gain setting will not be linear, Meaning turning the gain knob will not linearly increase the voltage? It will be more like an exponential increase as the 100k of resistance always present in the circuit regardless of wherever the wiper pin is meaning relative resistance will not vary linearly. Is this statement seems right to you? Jun 1, 2021 at 21:55
• NO - only the part of the 100K pot to the left of the wiper is active in the circuit - the part to the right of the wiper is shorted by the B-C connection, so will have no effect on the circuit. As drawn, the effective resistance of the pot will vary from 0 to 100K as the wiper moves left to right. Jun 1, 2021 at 23:23

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).

• This answer is explained everything just exactly as I wanted from the perspective of my problem statement. Mr. Dave is also correct but this answer feels more fulfilling. Jun 1, 2021 at 22:23

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.