Bob Cordell Interview: Error Correction

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#1,545
Bob Cordell wrote:
No doubt the zero feedback crew will get excited about the possibilities of output stages with EC distortion down at the 0.003% level, though I don't count myself in that number. For example, there are those for whom local feedback in tight loops is OK as long as there is no global feedback. But there are also the more strict sects where even local feedback loops are forbidden. The "feedback-in-disguise" view of EC might not go over too well in this case. And if any of them got wind of the view that EC included POSITIVE feedback, God knows how much fire and brimstone would reign down on them and their ancestors if they used it 🙂.
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True. On the other hand, I've noticed that most people are very pleased to hear positive feedback even when accompanied by significant distortion of the truth. 😛
 
#1,546
mikeks said:
Nixie, dear fellow, you cannot use purely passive components because you need to invert the extracted error before re-introducing it to output stage.
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Quit misinterpreting what I said. Either you enjoy making arguments, or have poor reading comprehension. I never said using purely passive components! Obviously block a in Hawksford's paper remains active. What I was asking, and I'm writing this for the third time!, is why introduce a second active stage R, as he does, on the input sample, rather than attenuate the inverted-by-the-output-stage output sample.
 
#1,547
The first image is the one from Hawksford's paper, with feedforward loop removed. The second one is what I mean. He has R = A_t as an active amplifier, and a = 1 / A_t, where A_t is the target gain. In my case, there's no R, a passive 1/R (1/A_t) instead, and a = 1. I never said there's no active part, just removing the extra active part A.
 

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#1,551
Yes. I'm talking about single-active device output stages with gain: common source/emitter/cathode -- all three inverting. Examples: Aleph-X and other Pass-related amplifiers, single-ended triode amps, the electrostatic headphone amp I mentioned elsewhere.
 
#1,557
Will you answer my original question? Actually, I'm hoping someone else would comment; I'm tired of mikeks, as he only seems interested in arguing.

Assuming an inverting gain stage, is there any downside to what I proposed instead of the configuration in the paper with a reference amplifier?
 
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