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Negative feedback - right or wrong to use?
Negative feedback - right or wrong to use?
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Old 26th November 2017, 03:28 PM   #11
Mikelandjelo is offline Mikelandjelo  Serbia
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Things are simple.Having feedback makes amp to be power source which doesnt care about load but about it self only.If i measure 7498 WITHOUT any load on 80% of max output voltage at certain range i will have huge distorsions....if i have load it will be same thing but about 1-10% in comparison with previous situation.It has feedback as many amps do.On other side i made my first design without feedback and i noticed same thing .... from 3khz to 7khz and latter from 17khz to 25khz i had effect on output like resonance and voltage boost and huge distorted sine wave.So i worked last few years on that and i made feedback less design which doesnt suffer any more from this issues.....it acts like AB class amplifier ....with or without load i have same output amplitude on any output voltage level including max one.And i have linear response on output without feedback on pure resistive load (zero inductance - hand made load)....and i DONT have linear response on different speaker boxes.BUT i have on some which was very interesting for me.Thats why i decided to discuss about feedback.Feedback less sound is uncomparable with feedbacked sound....Feedback should be discussed as term here.What feedback should be and what it should represent and do to make amp sound better ??? or to make constant power output on any frequency ???? or both ??? or something else.With simple graphic equalizer i am able to tune amp to have linear output on any speaker box (not idealy flat but 98%) ....so do we need feedback to kill all good and have "great" amplifier or we need feedback but at first ....something else that we will call feedback and not whats present in books?I expected to hear some new idea for feedback that we all can benefit from.I dont have new idea about it but i decided that its time to start working on it which i will do no matter how long it will take me to reach the goal.
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Old 26th November 2017, 04:16 PM   #12
MarcelvdG is offline MarcelvdG  Netherlands
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Voltage drive, current drive, negative resistance drive and anything in between all have their advantages and disadvantages when you drive loudspeakers - and all can be made with the right combinations of series and shunt feedback.
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Old 26th November 2017, 06:33 PM   #13
jan.didden is offline jan.didden  Europe
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The issue you are experiencing is due to variations in the amplifier output impedance and is a well-kown and described phenomenon. The output impedance largely determines the interaction of the amplifier with the speaker.

As Marcel mentioned, feedback can be used to manipulate that output impedance and thus the interaction of the amp with the speaker.
But it is not the feedback directly that determines the interaction.

You can change the amplifier output impedance directly with external resistors and a low-output impedance amp (except negative Zout) , and that will allow you to investigate, without having to worry about feedback.

Jan
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Old 26th November 2017, 09:00 PM   #14
Mikelandjelo is offline Mikelandjelo  Serbia
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I made D class amplifier which has very small output impedance already.I can manipulate it through voltage,curent or mixed type feedback ...i know that.Overal response is almost linear even amp is feedback less....i am talking about response on speakers.I have small differencies on different speakers.All of them i can correct with graphic equalizer.So main question is do we need feedback at all in this case....and also question is what concept of feedback is ideal for this "issues" ?
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Old 2nd December 2017, 04:34 PM   #15
Mikelandjelo is offline Mikelandjelo  Serbia
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When vinyl is recorded is there any feedback used?
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Old 2nd December 2017, 04:41 PM   #16
Davey is offline Davey  United States
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I'm not an expert, but I would suspect yes. No doubt there is some servo-control of various aspects of the cutting process. And there is certainly feedback used somewhere along the way before the music arrives at the vinyl recording stage.

I suggest to secure all devices in your everyday life that use feedback and see how that goes for you.

Dave.
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Old 2nd December 2017, 05:14 PM   #17
ICG is offline ICG  Germany
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Quote:
Originally Posted by Max Headroom View Post
Assumptions are fine in theory but not in practice in the audio realm IME.
20:1 impedance variation is too much for most amplifiers, and the result is a smattering of distortion products.
Er, no. Most amplifiers with clean, working design work fine even without any load without clipping, wave form changes/deformations or distortion. That means high impedance peaks are not a problem (well, except for impedance peaks of the tweeter which leads to frequency response peaks too at class D amps). Low impedances on the other hand are because the high current lets the voltage drop (limitations of the power supply i.e.) which also might cause clipping etc.
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Old 2nd December 2017, 05:23 PM   #18
KSTR is offline KSTR  Germany
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Vinyl cutting heads explicitly have feedback coils:
http://www.aardvarkmastering.com/westrex.htm
http://www.vintagewindings.com/gen%2...mann-SX-74.pdf
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Old 2nd December 2017, 05:28 PM   #19
scottjoplin is offline scottjoplin  Wales
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Feedback is great. I'm going to stand up now and engaged my feedback circuits........I hope.....
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Old 2nd December 2017, 05:57 PM   #20
ICG is offline ICG  Germany
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Quote:
Originally Posted by scottjoplin View Post
Feedback is great.
Ofcourse. The forum gives a lot of it.
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