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Old 11th May 2012, 09:12 PM   #1
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Default DC offset question...

Apologies if this has been asked before but I've searched dozens of posts but can't find anything regarding measuring my DC Offset question that I understand so....

To find out the DC offset of a chip-amp itself (a LM4780) is it possible just to put a 10 ohm(?) resistor across signal/earth of the input rca plugs and measure the DC offset from the amp output?
Or is there more to it than that? - I thought the only thing that may change the amps DC offset (with the input connected) was if there was any DC on the signal going into the amp.

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Old 11th May 2012, 09:49 PM   #2
Did it Himself
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Your method is fine. Even if there was DC on the source, the input capacitor on the chip amp will block it. Unless you didn't fit the capacitor...
www.readresearch.co.uk my website for UK diy audio people - designs, PCBs, modules and more.
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Old 11th May 2012, 09:56 PM   #3
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I've always just shorted the input and measured from the speaker output terminals (no speakers connected). That won't give the chip's offset per se, but the offset for the amplifier's entire circuit.
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Old 12th May 2012, 10:37 AM   #4
AndrewT is offline AndrewT  Scotland
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The dummy Rs fitted to the input can be chosen from 0r0 to 1M0.
The output offset and output noise results will be different over than enormous range of RS. Useful information about the amplifier performance can be gleaned by looking at a range of Rs, rather than just shorting the input with Rs=0r0.
regards Andrew T.
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