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Old 12th November 2010, 03:02 PM   #1
el156 is offline el156  Portugal
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Default FEEDBACK DELAY TIME

Hi everybody ! Just a thought about NFB! The signal takes some time from the input to the output of a amplifier ,and then taken from the output to the input, with te mission to correct the linearity of this signal, but because of the delay it has (maybe a few microseconds) than the efect could be worse than without NFB? I much prefer the sound without feedback. Maybe because i dont use lots of watts....
I would like to know what do think about this....
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Silvino
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Old 12th November 2010, 03:09 PM   #2
el156 is offline el156  Portugal
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Originally Posted by el156 View Post
Hi everybody ! Just a thought about NFB! The signal takes some time from the input to the output of a amplifier ,and then taken from the output to the input, with te mission to correct the linearity of this signal, but because of the delay it has (maybe a few microseconds) than the efect could be worse than without NFB? I much prefer the sound without feedback. Maybe because i dont use lots of watts....
I would like to know what do think about this....
Thanks
Silvino
Or it is a silly question ?
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Old 12th November 2010, 03:15 PM   #3
20to20 is offline 20to20  United States
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Or it is a silly question ?
Think about the speed of light when you try to imagine any ''delay." The only real concern is of phase shift if the signal is passed through stages that create phase shifting. Otherwise, there is no delay in the signal back to the input. A few inches of wire is no match for the speed of light compared to the frequency of an audio wave.
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Old 12th November 2010, 03:29 PM   #4
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You can think of delay time dealing with microwave equipment. In audio you should worry of phase shifts.
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Old 12th November 2010, 03:39 PM   #5
el156 is offline el156  Portugal
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Okay, but from the RCA socket to the OPT the signal passes through at least 2 or 3 tubes, and it takes some time to make that way, or not?
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Old 12th November 2010, 03:46 PM   #6
20to20 is offline 20to20  United States
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Okay, but from the RCA socket to the OPT the signal passes through at least 2 or 3 tubes, and it takes some time to make that way, or not?
Electricity travels at the speed of light. The audio signal is a slow wave on a river of electrons. The wave form in the first tube is at the output transformer and back to the first tube again while the wave is still in the first tube. It's all electrical pressure that is equal throughout the circuit if phase shifting is not present.
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Old 12th November 2010, 03:47 PM   #7
Yvesm is offline Yvesm  France
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The worst offender is the output transformer itself.
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Old 12th November 2010, 04:17 PM   #8
20to20 is offline 20to20  United States
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The worst offender is the output transformer itself.
I wouldn't call the OPT an ''offender'' because without the properties a transformer provides we couldn't do want we want with electricity. It provides us with an inverted phase so we can tap it for the negative feedback if we want to. Very convienient place to grab all the distortion produced and an inverted phase, too.
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Old 12th November 2010, 04:26 PM   #9
SY is offline SY  United States
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Okay, but from the RCA socket to the OPT the signal passes through at least 2 or 3 tubes, and it takes some time to make that way, or not?
Not compared to the period of an audio (or RF for that matter) signal. The "delay" thing has been debunked thoroughly. Feedback works exactly as advertised.
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Old 12th November 2010, 04:45 PM   #10
Arnulf is offline Arnulf  Europe
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I wouldn't call the OPT an ''offender'' because without the properties a transformer provides we couldn't do want we want with electricity. It provides us with an inverted phase so we can tap it for the negative feedback if we want to. Very convienient place to grab all the distortion produced and an inverted phase, too.
I believe what Yvesm was trying to say is that it is usually the OPT in the entire tube amplifier chain that brings by far the most significant portion of phase distortions to the signal, thereby delaying certain part of the audio spectrum, possibly resulting in audible delay (such as oscillations ).
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