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opamp voltage bias question.? Answered

Hello. i have a question about voltage bias.In some schematic of opamp use single power source , they use R1=R2 to make voltage bias (please see the example bellow) . But the value of R1 and R2 in other schematic i found are diffirent (R1=R2=100k or R1=R2=47k ,.... etc) How did they effect the circuit ?

Thanks for advance !

sorry for my bad English .


It depends on the op-amp type - FET inputs take very little bias current, so you can get away with large value biasing resistors.

There are better biasing circuits than this: One good trick is to set up another op-amp as a voltage follower after the biasing resistors, and use THAT to feed your virtual ground point.

Thanks you, can you please tell me what value should i use for NE5532 ?
and how to modifiy this circuit to make it work with single power source ?
Thanks you very much!


For an audio application, you will always get better performance with bipolar supplies, but try exactly what I said - add a voltage follower after a couple of 10 K resistors set up as a voltage divider, and use the output of the follower to drive all the "grounds" shown in your diagram.