# Why not vary the opamp feedback resistor to change output levels?

I'm thinking of circuits that feature an operational amplifier like the venerable 741. Extremely often, you see a variable resistor in the final output acting as a potential divider to adjust the level of the output signal. The feedback resistor would be fixed in this case to provide the appropriate gain.

Why do you never instead see a variable resistor as the feedback resistor for the op amp? It seems that it would achieve the same objective. You would be adjusting output level by changing gain instead. Is there some reason to always have a fixed feedback resistor and adjust output level through other means?

• In audio, variable resistors are used in feedback networks for tone controls. One issue for volume is that if you want to go down to zero volume, it's only possible in inverting mode. Under non-inverting feedback, the gain is at least one ($1 + R1/R2$). – Kaz Aug 10 '16 at 1:07
• You do see it. See Douglas Self, Small Signal Audio Design, p231&ff, also the Quad 34 and 44 preamplifiers and no doubt many others. – user207421 Aug 10 '16 at 1:07