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Old 2nd July 2004, 07:49 PM   #1
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Default GC offset

I, ehh, ahum, err, have these two LM3886's gathering dust, maybe I should built something usefull with them?
There's one aspect bothering me, the offset. If I leave out the series cap in the feedback network, also leave out a servo, what range of offset can I expect? The data sheet difference between 'typical' and 'max' is rather great. I would use a gain of 20.
Anybody has any experience in this respect?

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Old 3rd July 2004, 06:40 AM   #2
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The datasheet doesn't promise you anything really and reports tell us that you can get +- 200 mV and all values in between. So if you don't want surprises prepare for offset adjustment or DC-servo if you really want to be sure. If you are lucky you may not need any trimming.
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Old 3rd July 2004, 06:56 AM   #3
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With a gain of 30, I never got more than 80mV and usually it's much lower: 30-40mV being an average. It will also depend on input impedance.
That is for LM3875.
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Old 3rd July 2004, 07:57 AM   #4
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Peter,

The LM3886 datasheet specs 10mV worst case. That's 200mV @ 20 x gain. I could live (or rather, my speakers could) with the 30-40mV you quote. I think I'll put a placeholder for a cap on the PCB and see how it works out.

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Old 3rd July 2004, 08:10 AM   #5
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Don't forget the input bias currents. They contribute also.
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