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Electronics => Beginners => Topic started by: dfox416 on November 12, 2013, 05:18:24 pm

Title: Opamp gain control
Post by: dfox416 on November 12, 2013, 05:18:24 pm

What are the advantages/disadvantages/differences between using a pot as the feedback resistor for an opamp to change the gain and using a pot after the output to attenuate the signal?

Title: Re: Opamp gain control
Post by: tszaboo on November 12, 2013, 06:27:58 pm

http://www.maximintegrated.com/app-notes/index.mvp/id/1828 (http://www.maximintegrated.com/app-notes/index.mvp/id/1828)
anything particular?

Title: Re: Opamp gain control
Post by: Jon86 on November 12, 2013, 09:22:59 pm

Well you've got to remember that a potential divider's output voltage is dependent on load current. If you use a pot on the output of your opamp you'll end up with an output that isn't stable if you've got anything loading it. Put the pot into the feedback loop, and the opamp will obviously correct any error on the output. Whichever way you do it, you'll have noise generated, but the feedback resistor is more common.
Also, if you have the pot in the feedback, you can change the gain ranges from 1 to huge, while keeping the low ranges clean. If you're always using a high gain and just attenuating it afterwards, you're going to create a load of unnecessary noise.