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RE: How does "negative" feedback work in an electronic circuit

Think of it as a comparator - a sample of the output is 'compared' to the original input instantaneously and if it differs, a correcting difference signal is generated to make the output come back into line."

Tre'- "That assumes that there is no phase shift in the loop. There always is and that introduces it's own distortion."

There is no phase shift over the band pass region of a closed loop amplifier except near the corner frequencies. The solution is to design a higher band pass than necessary.

Open loop SET designs cannot correct for any nonlinearities

Tre" - "True but where is the mechanism for creating these nonlinearities?"

You stated that nicely in another post on this thread - "I have never seen a tube with perfectly even grid lines, thus harmonic distortion occurs" (or something close to that)

Tre'- "If you take beam power tubes (which are not linear at all) in PP and then try to "fix" it with loop feedback you will end up with very low even ordered and low 3rd but you will have HD orders out to the 81st."

Not with an appropriate band width design!

Tre'- High 2rd HD doesn't sound like distortion to the human ear. Even a little 3rd is quite tolerable but the slightest amount of upper order HD will sound bad.

Tre'- "I believe that the reason well designed DHT amps sound "pleasant" is because they are very low in the kinds of distortion that matter. They are (in terms of what matters) "reproducing the input signal as accurately as possible".

All distortion matters. Any present distortion means that the output deviates from the input signal. Closed loop amplifier designs have lower overall THD than open loop designs.




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