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Old 20th August 2003, 01:37 AM   #1
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Default Negative feedback question

The more I think about, the more confused I am getting about the NFB resistor.

In my IGC, it is running from 3 to 8, or, from the speaker out to the signal in.

Why is this "negative" feedback? On the surface it seems like it would be positive feedback and start a vicious cycle.

I searched, but there are so many references to NFB that I was unable to find this question.

In the hopes that I am not the absolute last person to understand this, could someone please explain to me and the others who may be suffering in silent ignorance?

What is the concept/purpose of the NFB resistor?

Thanks,

GnD
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Old 20th August 2003, 04:33 AM   #2
JoeBob is offline JoeBob  Canada
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It wouldn't be positive feedback because the feedback is inverted (negative when compared to the original signal) when compared to the input.
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Old 20th August 2003, 07:40 AM   #3
Bricolo is offline Bricolo  France
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It's negative feedback because your gainclone is an inverting amp (the output voltage is in the opposite phase compared to the input voltage. Example: if input=1V, out=-23V (because gain=23)

So, a part of the output goes thru the feedback resistor, and comes in the -in, in the opposite phase, and this way it cancels the input a little
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Old 20th August 2003, 07:57 AM   #4
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Quote:
It's negative feedback because your gainclone is an inverting amp
?????????


Can't you guys buy an electronic textbook?
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Old 20th August 2003, 07:59 AM   #5
Bricolo is offline Bricolo  France
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Quote:
Originally posted by analog_sa


?????????


Can't you guys buy an electronic textbook?

"It's negative feedback because your gainclone is an inverting amp and the feedback resistor goes from output to input"

are you happy now?
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Old 20th August 2003, 08:04 AM   #6
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Whether the amp is inverting or not has nothing to do with the polarity of feedback
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Old 20th August 2003, 08:24 AM   #7
Bricolo is offline Bricolo  France
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Quote:
Originally posted by analog_sa
Whether the amp is inverting or not has nothing to do with the polarity of feedback
of course it has! At least if it is global feedback (from input to output).

Global feedback+invertimg amp=NFB
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Old 20th August 2003, 09:19 AM   #8
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Quote:
Global feedback+invertimg amp=NFB
Coming back to my question about the textbooks
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Old 20th August 2003, 09:28 AM   #9
Bricolo is offline Bricolo  France
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Quote:
Originally posted by analog_sa


Coming back to my question about the textbooks

just give me an example that proves I'm wrong
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Old 20th August 2003, 11:11 AM   #10
Beggar is offline Beggar  United Kingdom
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dudes

Its called negative feedback because it is feedback from the output to the inverting input.
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