Global Feedback - A huge benefit for audio

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#1,601
sottomano said:
Attached in smplified schematic in that very post.
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You can't argue with simplified schematic with no data or any simulation.
I have a threads with NGNFB amps here, but thy are not simple.
I would like to see your real project not just simplified schematic, I like to learn, if you don't want to share you are in wrong forum. This is about DIY.
 
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#1,602
dadod said:
You can't argue with simplified schematic with no data or any simulation.
I have a threads with NGNFB amps here, but thy are not simple.
I would like to see your real project not just simplified schematic, I like to learn, if you don't want to share you are in wrong forum. This is about DIY.
Click to expand...
Thank you for letting me know.
I alway thought DIY is also putting some own effort, and not all on silver tablet.

And this thread is abot general discussion, not a project.
 
#1,603
sottomano said:
I can say that I do not need feedback, and therefore to me it is not "a huge benefit for audio", just unnecessary.
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But feedback has nothing to do with someone needing it or not and there s indeed some GNFB on your amps, it s just that it s the worse kind of GNFB..

As for a 20 DF being enough as you pretend, well that means that 1W of reactive power will yield an error signal of 0.63V amplitude..
 
#1,604
Audiophile Myths About Amplifier Negative Feedback Debunked, by Bruno Putzeys, July 18 2020
Audiophile Myths About Amplifier Negative Feedback Debunked | Audioholics

[ Summary of Key Talking Points about Amplifier Feedback

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  • Feedback is a natural process that happens all around us. Engineers have learned to use it to solve many difficult problems. Building precise amplifiers and filters are some audio related examples.
  • The central myth about feedback is that it's easy to pile on more at will. This is only true at subsonic frequencies. Higher up the audio band every dB of feedback is hard fought for.
  • The proverbial 70's amp that had lots of feedback only did so at low frequencies, but had very little left at high frequencies. Unfortunately they used a type of input stage that only works properly if you really do have a lot of feedback. That caused TIM.
  • Increasing global feedback quickly produces a massive reduction in TIM. This is the exact opposite of a widely circulated myth.
  • Nesting local and global loops is the most common way of increasing feedback. Almost all modern class AB amplifiers work like that. They are not low-feedback amplifiers, even if they're often marketed as such.
  • Full global feedback is not easy but is technically superior to nested or partial feedback.
  • Feedback theory is highly advanced in the field of Sigma-Delta AD/DA converters. Methods developed there are also often used in class D amplifiers.
  • Feedback flips the shape of the distortion over. This can turn a distortion with few higher harmonics into one with more higher harmonics or vice versa. In practice the effect is only significant in lab curios specifically built to demonstrate the effect.
  • Feedback is one of the most effective tools to improve sound quality. Although the R&D outlay can be substantial, using feedback barely affects the cost of the circuit. ]
 
#1,605
sottomano said:
Oh this tone...I'm tempted to say, search yourself for open loop designs, there are plenty.

But since I'm a nice guy, some hints and even a simple schematic.

http://www.diyaudio.com/forums/atta...ill-little-amp-might-100w-amp-board-match.pdf
Only the right side, i.e. the power buffer, starting from Q7+10.
Courtesy Steve Dunlap.


Or the F4 from Nelson Pass.
As easy as it gets, but a bit more power "waste".
For power, drive it balanced.

Both do not need a biasing circuit (VBE multiplier), i.e. have a single point input

For the voltage amplifier, take a AD844 simplified circuit and maybe change the four input bias transistors and current sources for a complementary JFet pair. And obviously without output stage.

There are schematics around which mîght be similar to Blowtorch:
Uskok preamplifier

Make it balanced if you want more power. Gives also more freedom for the voltage regulation of input power supply, as current draw is rather constant.

Think current, not voltage btw.
Biasing and offset trimming needs some more thinking (and resistor netwoorks), I do not share everything.

This has to suffice.
For my audio listening, such designs suffice. I can say that I do not need feedback, and therefore to me it is not "a huge benefit for audio", just unnecessary.
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There is a local negative feedback in almost every stage.
These are emitter (source) followers 100% and resistors in emitters (drains).
An integrator is a global negative DC feedback.
 
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#1,607
Electromechanical negative feedback is possible in the area of the loudspeaker piston action (up to 300 Hz).
Various aperture velocity or acceleration sensors can be used.
In the region of higher frequencies, current speaker control is used.
Multiband amplification offered.
 
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#1,609
sser2 said:
Putzey's article is fine, but completely misses one point: feedback is disaster if amplifier' s output is a real life speaker. He notes though as #1 caveat: "Beware of error sources outside feedback loop". A speaker is exactly such error source.
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I am 75% sure I do not understand your point, if it's at all being made technically vs philosophically.

The other 25% says you have to manage your reactances in order to maintain phase margin, which case, yes, that is an important aspect. (Also, yet *another* advantage of going to active crossovers)
 
#1,610
Might be a bit useful to consider the history of this issue, and why unfortunately it is so divisive

Feedback: A Short History

Feedback is an extremely well researched branch of science ('Control Theory') and the earlier poster was quite right to point out that it is a completely natural phenomena. Nature worked it out first and applied it all over the place - metabolic pathways, a star's fusion process, birds in flight - you name it.

It so happens that amplifiers are a very simple application of the theory. A few basic rules and you can build a 100% stable amplifier that deals with any kind of load within its power rating.

As for stories about feedback 'affecting the sound' they are complete nonsense. Don't fall for that baloney.

Feedback is good. Nature would not work without it and amplifiers are better with it.
 
#1,612
sser2 said:
Putzey's article is fine, but completely misses one point: feedback is disaster if amplifier' s output is a real life speaker. He notes though as #1 caveat: "Beware of error sources outside feedback loop". A speaker is exactly such error source.
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Seems you missed the point. Feedback makes the amp better as intended. Whats the disaster? You make it sound like no feedback amps somehow fix the speaker errors, which is riduculous.
 
#1,613
Bonsai said:
Might be a bit useful to consider the history of this issue, and why unfortunately it is so divisive

Feedback: A Short History

Feedback is an extremely well researched branch of science ('Control Theory') and the earlier poster was quite right to point out that it is a completely natural phenomena. Nature worked it out first and applied it all over the place - metabolic pathways, a star's fusion process, birds in flight - you name it.

It so happens that amplifiers are a very simple application of the theory. A few basic rules and you can build a 100% stable amplifier that deals with any kind of load within its power rating.

As for stories about feedback 'affecting the sound' they are complete nonsense. Don't fall for that baloney.

Feedback is good. Nature would not work without it and amplifiers are better with it.
Click to expand...

Could not agree more with you Bonsai.

One thing someone mentioned in a previous post is the effect of the speaker. So feedback makes the output voltage of the amplifier very low distortion. Then we hope the voltage to sound conversion from the speaker is linear too. Feedback does not help with this last step. For that, buy good speakers.
 
#1,614
Global negative feedback or non global negative feedback is not important. The important is achieving low distortion. Dr. Arto Kolinummi in his book demonstrated design with global negative feedback and non global negative feedback with very low distortion.

If you can not design amplifier with very low distortion, it is your fault, not the technique that being used.
 
#1,615
#1,618
sser2 said:
Putzey's article is fine, but completely misses one point: feedback is disaster if amplifier' s output is a real life speaker. He notes though as #1 caveat: "Beware of error sources outside feedback loop". A speaker is exactly such error source.
Click to expand...

It's a bit more subtle. Without feedback you have the junk of the amp AND the errors of the speaker.
With feedback, only the speakers' errors.

But, feedback can even cure that - motional feedback. If you know how to implement it.

Jan
 
#1,619
analog_sa said:
High feedback amps are engineering marvels. Perhaps not very conducive to music appreciation, but isn't that nitpicking? 😎
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Feedback is really not an engineering marvel. Feedback is nature's answer to almost everything. Feedback is a natural thing in the extreme.

The fact that you are breathing - nfb from the CO level in your blood.
And try riding a bike without nfb - you wouldn't last 3 feet!
Not to mention all those planes that would fall out of the sky.
Also, no baseball player would ever be able to catch a ball.
Etc, etc.

Jan
 
#1,620
bimo said:
Global negative feedback or non global negative feedback is not important. The important is achieving low distortion. Dr. Arto Kolinummi in his book demonstrated design with global negative feedback and non global negative feedback with very low distortion.

If you can not design amplifier with very low distortion, it is your fault, not the technique that being used.
Click to expand...

Design is a reasonable compromise of complexity, cost, speed, precision, stability, repeatability.
The essence of engineering work.
That does not exclude champions in certain types.
 
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