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Old 18th February 2004, 07:27 PM   #31
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There is always some bias current flowing into (or out of, depending on the type) the inputs of an opamp. If that current has no path to ground, the input node starts to float up (or down). Use a resistor to gnd (not too large, as small as possible wrt the source resistance) and you're home free.

And yes, you can share the input cap among parallel amps.

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Old 15th August 2008, 10:22 PM   #32
lineup is offline lineup  Sweden
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Default Re: Amp Feedback

Originally posted by wrenchone

The circuit in the attached file labeled "A" is the one discussed in this thread so far.
The disadvantage of this approach is that C1 must be relatively large,
and it does see some reverse bias when the output swings negative.
I would try using an Oscon for C1 in circuit A,
as they are supposed to tolerate substantial reversal without ill effects.

I first learned about the Circuit labeled "B" over 20 years ago in Audio magazine.
I use this circuit ("B") in my projects almost always instead of the conventional one ("A").

one new way, for me, to deal with DC offset feedback
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