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Old 2nd October 2003, 09:24 PM   #1
JoeBob is offline JoeBob  Canada
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Default Buffered IGC and global feedback?

I am currently using a opamp buffer for got an inverted LM3875 and was wondering what people thought of taking the feedback from the output of the LM3875 to feed to the opamp buffer? I know I would need a voltage devider for the feedback coming in, and wouldn't the feedback go to the + terminal since it would already be inverted? Hmm... was just thinking about it and was wondering if anyone had done it and what people thought the pros/cons were. Of course I would keep the opamp very close to keep the feeback path short.
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Old 3rd October 2003, 12:23 PM   #2
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Default Re: Buffered IGC and global feedback?

Quote:
Originally posted by JoeBob
I am currently using a opamp buffer for got an inverted LM3875 and was wondering what people thought of taking the feedback from the output of the LM3875 to feed to the opamp buffer? I know I would need a voltage devider for the feedback coming in, and wouldn't the feedback go to the + terminal since it would already be inverted? Hmm... was just thinking about it and was wondering if anyone had done it and what people thought the pros/cons were. Of course I would keep the opamp very close to keep the feeback path short.
I wouldn't advise it... the total open loop gain would be humongous! Besides, what's wrong with nested feedback? In almost all cases (there may be some instances I can't think of right now) this should be considered advantageous. Far better (and easier) to use a UGS (Unity Gain Stable) IC as buffer, then experiment with an LPF (which won't do within a loop). Even better, use a tube:
members.ozemail.com.au/~lisaras. There is no easier or safer tube project than this.

Joe R.
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