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In Reply to: Hope you mean Zero Global Feedback posted by pmkap on December 07, 2001 at 13:14:31:
To refine the query further, would you say a circuit with a DC servo
had global NFB or not? The A18, for example has an op-amp based
servo loop from the output to the input stage, which to me at least
constitutes global negative feedback.Alex
Follow Ups:
global negative feedback; just not within the audio band. The lc audio amplifiers also have dc servos. The ESP source follower, with a single rail, avoids this with an output cap. (due to a youth spent in unhealthy pursuits, I've seriously compromised my ability to percieve infrasonics) Then again, I do hope that I base my evaluations of different components on their ability to recreate the musical experience, not their topologies.
Since the feedback is at DC, and up to a few Hz, and higher frequencies are filtered out of the (active) feedback loop, it is zero loop NFB as far as the music is concerned. A passive feedback loop can be made a bit easier, with feedback only at DC, and zero LNFB at signal frequencies.
Just like so many zero NFB tube amps out there have cathode resistors that are bipassed with a cap, they all have NFB at DC and very low frequencies.
Regards, Nick.
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