Negative feedback question
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 20th August 2003, 02:37 AM #1 GrahamnDodder   diyAudio Member   Join Date: Jun 2003 Location: Near Baltimore, MD 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 __________________ I had the right to remain silent. I just didn't have the ability. (Comedian Ron White)
 20th August 2003, 05:33 AM #2 JoeBob   diyAudio Member     Join Date: Nov 2001 Location: Montreal, Canada It wouldn't be positive feedback because the feedback is inverted (negative when compared to the original signal) when compared to the input.
 20th August 2003, 08:40 AM #3 Bricolo   diyAudio Member     Join Date: Nov 2002 Location: Grenoble, FR 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
analog_sa
diyAudio Member

Join Date: Aug 2002
Location: Cascais
Quote:
 It's negative feedback because your gainclone is an inverting amp
?????????

Can't you guys buy an electronic textbook?

Bricolo
diyAudio Member

Join Date: Nov 2002
Location: Grenoble, FR
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?

 20th August 2003, 09:04 AM #6 analog_sa   diyAudio Member     Join Date: Aug 2002 Location: Cascais Whether the amp is inverting or not has nothing to do with the polarity of feedback
Bricolo
diyAudio Member

Join Date: Nov 2002
Location: Grenoble, FR
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

analog_sa
diyAudio Member

Join Date: Aug 2002
Location: Cascais
Quote:
 Global feedback+invertimg amp=NFB
Coming back to my question about the textbooks

Bricolo
diyAudio Member

Join Date: Nov 2002
Location: Grenoble, FR
Quote:
 Originally posted by analog_sa Coming back to my question about the textbooks

just give me an example that proves I'm wrong

 20th August 2003, 12:11 PM #10 Beggar   diyAudio Member     Join Date: Aug 2001 Location: South East, UK dudes Its called negative feedback because it is feedback from the output to the inverting input.

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