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Current noise between DC coupled op amps?
Current noise between DC coupled op amps?
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Old 24th October 2012, 05:59 PM   #1
miallen is offline miallen  United States
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Default Current noise between DC coupled op amps?

Does DC coupling op amp stages add current noise?

I have a line-level input consisting of a very simple non-inverted unity gain op amp stage followed by an inverting op amp stage with it's inverting input connected to the wiper of a pot to control the input level. The op amps are NE5532 which of course have a little bit more offset than most so I'm wondering if I need to be concerned about current flowing between the two stages.

So my question is - what would yield better noise performance:

a) leave out a coupling cap so that I can use small resistors with the inverting op amp stage or

b) use a coupling cap to eliminate any current flowing between stages and use larger resistors sufficient to get low frequencies

?

Note: The input op amp is located 8 inches away from the level control.

Any advice would be appreciated.

Mike
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Old 24th October 2012, 09:41 PM   #2
DF96 is offline DF96  England
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Keep DC currents away from volume pots, if you want low noise.
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Old 25th October 2012, 04:45 AM   #3
miallen is offline miallen  United States
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I think I'm going to use the baxandall active gain stage circuit on page 237 of Small Signal Audio Design by Douglas Self. That section makes it pretty clear that coupling caps are important when using bipolar op amps.
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