Myths, tricks and hey, that's neat!

[b_force]

The question then is for whom is the article. Those who know know and would not learn anything. Those who do not know are lost in orientation in symbols. I think that more usual and less general symbols like transistors and opamps, resistors and capacitors would help. It would not be that universal, however still working, clear and IMO more understandable. Explaining technical points to general public is not easy, it is a special discipline.

I was just literally thinking about that!

Maybe that's actually what I was trying to say to @jan.didden
Because it now kinda falls in between.

Plus I think there are also plenty of people who do know, but who think, what on earth am I looking at?
If you read in depth articles from guys like Bruno Putzeys, they also all use standard/general symbol notation.

For students and interns I coach, I always start with the general symbols, and after draw in the more "familiair" symbols and circuits.
In my experience that really helps recognizing any circuit, no matter if it's a opamp, Class-D amp, or tube-amp.

From a feedback point of view, they are all the same thing, just with different parameters and some additions.

 

[Mark Tillotson]

I am speaking about a bit different phenomenon. Look at this, please, when tight FB is closed around pure H2 nonlinearity. The rise of high order harmonics is inevitable, you will find it in many publications, Douglas Self on amps to name one.

Real sources already have all the harmonics present (typically falling into the noise ultimately), there is no such thing as an H2 only device (*), so in practice (a reasonable amount of) feedback reduces all the harmonics and doesn't introduce new ones. Certainly very much the case for any BJT circuit as the exponential dependence on Vbe, and definitely the case for cross-over in class-B, and you'll find even FETs aren't really accurate quadratic law in reality (perhaps the closest though).

Naive measurement of a device might only show H2, but point a lock-in amplifier and notch-filter at it and you'll be able to find those other harmonics and even measure them well below the noise floor.

BTW for another article perhaps the use of feed-forward? Its often neglected but shouldn't be! The best control solutions usually use both feed-forward and feed-back in combination.

(*) That would imply a perfect multiplier circuit is possible, and they don't exist.

 

[b_force]

In order to understand this

https://www.diyaudio.com/community/attachments/1702219797842-png.1244781/

you have to understand transfer functions and to get over the fact that it is neither a system diagram nor a schematic, but something in between. In particular, the subtraction point makes no sense: what's the point of subtracting zero from something? I understand what you mean because I know the op-amp circuit it is based on, if I didn't I would have a hard time understanding it.

I should have put a bheta block in there instead.

But this is the general more simple notation for a feedback loop;

or more specific something like this;

In my case it's a bit of a hybrid, that's true.
Although in electronics circuitry there aren't many variations, so I often just skip right to that hybrid.

Anyway, my point was that I think it's easier to read for most people instead of voltage controlled sources
They are technically correct, but talking about hybrid circuits....

 

[b_force]

Btw, the picture on the post description it's a bit more clear;

 

[MarcelvdG]

I should have put a bheta block in there instead.

But this is the general more simple notation for a feedback loop;
View attachment 1244864

or more specific something like this;
View attachment 1244868

In my case it's a bit of a hybrid, that's true.
Although in electronics circuitry there aren't many variations, so I often just skip right to that hybrid.

Anyway, my point was that I think it's easier to read for most people instead of voltage controlled sources
They are technically correct, but talking about hybrid circuits....

For Jan's story, you need to include the low-pass behaviour of the forward path. Putting a transfer function in there means half the readers won't understand it anymore. Abstract it to a pure integration to time? Or explain in some separate figure that it is a first-order low-pass with high gain?

 

[b_force]

Putting a transfer function in there means half the readers won't understand it anymore. Abstract it to a pure integration to time? Or explain in some separate figure that it is a first-order low-pass with high gain?

I literally just said it was a general example? Jus to show Jan what's possible within LTSpice.
So I think that the answer to your question was already no to begin with.

As for visuals, you can just put a low-pass filter block in there. (which I literally mentioned in a post before)
Obviously you don't want to show some fancy transfer function that nobody cares about.

Which is exactly what I am trying to explain, keep to simple fundamental blocks, instead of showing the practical circuit that's being used for simulations, or use that just as a sort of additional insight for those who want to play along at home

Don't get the confusion here...

 

[PMA]

Maybe the goal is an intellectual interchange between the AudioExpress authors and editors 😉.

 

[thermionic]

Tomorrow will mark 40 years to the date that Harold Black left us. Good work, Jan.

To some, his invention is considered the most important breakthrough of the twentieth century in the field of electronics,

It'd be a freaky world if it hadn't been invented. Although you could argue that, like Newton, he didn't 'invent' it, but documented how to apply it.

 

[tomchr]

Putting on my Pedantic Hat here: Respiration regulated by the amount of carbondioxide in the blood? You wrote carbon monoxide in the intro. There are other chemical sensors too, but CO2 is the main one. More here: https://pubmed.ncbi.nlm.nih.gov/8566733

I'll invite those who think Jan's article is too academic to read an actual academic research paper. Sure. Jan's article won't present well as a TicToc video but I would in the academic world he'd get dinged for colloquialisms. 🙂

Tom

 

[jan.didden]

For Jan's story, you need to include the low-pass behaviour of the forward path. Putting a transfer function in there means half the readers won't understand it anymore. Abstract it to a pure integration to time? Or explain in some separate figure that it is a first-order low-pass with high gain?

Or people could just read the short text that goes with it? Or are we all reduced to reading comics only now?

BTW Good suggestion to do one on feedforward. And error correction.

Jan

 

[jan.didden]

Tomorrow will mark 40 years to the date that Harold Black left us. Good work, Jan.



It'd be a freaky world if it hadn't been invented. Although you could argue that, like Newton, he didn't 'invent' it, but documented how to apply it.

He didn't invent it, technically, because it was working already since after the Big Bang. He discovered it, and documented it. Still a monumental achievement.

@tomchr - yes, carbondioxide. I stand corrected.

Jan

 

[Markw4]

All other things are just shortcomings of the practical system.

True. However, it may be some shortcomings of practical systems that has given negative feedback a bad name among some audiophiles. What they hear may not always be imaginary nor always be real. I think EEs should consider and admit that possibility too. I mean admit it to audiophiles: sometimes problems can be imaginary and sometimes they can be real; its not all one thing or the other.

 

[PMA]

I'll invite those who think Jan's article is too academic to read an actual academic research paper

But it is not a research or scientific peer reviewed paper. That is a big difference. The article aims at general audience, not at researchers, not at scientists.

 

[b_force]

He didn't invent it, technically, because it was working already since after the Big Bang. He discovered it, and documented it. Still a monumental achievement.

@tomchr - yes, carbondioxide. I stand corrected.

Jan

Offtopic,

That era is absolutely fascinating.
Because at that time feedback loops have been around already for quite a while.
One very good example are governors on engines, which was already being invented by Christiaan Huygens a century before.

Impedance analogies were also known for quite a while from Maxwell, but I guess it's this that created the AHA! moment for Harold:

Henri Poincaré in 1907 was the first to describe a transducer as a pair of linear algebraic equations relating electrical variables (voltage and current) to mechanical variables (force and velocity).[29] Wegel, in 1921, was the first to express these equations in terms of mechanical impedance as well as electrical impedance.[30]

source wikipedia.

 

[MarcelvdG]

Christiaan Huygens lived in the 17th Century. In fact from 1629 to 1695 according to the Dutch Wikipedia.

 

[b_force]

Christiaan Huygens lived in the 17th Century.

Sigh

Centrifugal governors, also known as "centrifugal regulators" and "fly-ball governors", were invented by Christiaan Huygens and used to regulate the distance and pressure between millstones in windmills in the 17th century.[1][2]
In 1788, James Watt adapted one to control his steam engine where it regulates the admission of steam into the cylinder(s),[3] a development that proved so important he is sometimes called the inventor. Centrifugal governors' widest use was on steam engines during the Steam Age in the 19th century. They are also found on stationary internal combustion engines and variously fueled turbines, and in some modern striking clocks.

The impedance analogy is sometimes called the Maxwell analogy[5] after James Clerk Maxwell (1831–1879) who used mechanical analogies to explain his ideas of electromagnetic fields.[26] However, the term impedance was not coined until 1886 (by Oliver Heaviside),[27] the idea of complex impedance was introduced by Arthur E. Kennelly in 1893, and the concept of impedance was not extended into the mechanical domain until 1920 by Kennelly and Arthur Gordon Webster.[28]

So, yes, that is basically a century before all these other guys came with impedance analogies, is what I meant.
Yes, a little more than that, but that is not the point here.
Let's get nitpicky here instead.....

If you wanna know the history, just open your history books or wikipedia.
Point is, LONG before all of the other stuff.

 

[jan.didden]

The big step forward came at the start of WWII when the US Navy realised their AA guns couldn't slew fast enough to catch those Japanese Zero fighters.
So they increased the power and gain of the control loop that did the slewing and found that the guns overshot their commanded position and then after some oscillations got to the right position. They comissioned people from Bell Labs like Henry Bode (Bode diagram?) and Harry Nyquist to find a solution and they came up with compensation techniques and required Q for the control loop for max slew rate without overshoot.

Read Vannevar Bush's Pieces of the Action.

I personally found an application in search radars for anti aircraft missile systems I ran in Germany, when I found that the antenna drive was an ordinary audio amplifier with two EL34 output tubes driving the antenna positioning motor.
What goes around comes around.

Jan

 

[Bonsai]

The article is being praised by those who already understand. Perfectly fine if that's the target audience but don't kid yourself that you have reached any musicians , trades people, doctors, history teachers and other diyers without a career investment in math who will continue to ignore your forum conversations in favour of those threads rehashing the supremacy of zero feedback, non-oversampling and fatter speaker cables.

Understanding feedback and electrical engineering is hard and it does require a good grasp of math. That’s why people go to university and study it for 4 yrs.

The problem is, those ignorant of these matters seem to believe they are qualified to trash the science and engineering involved and propose absolute nonsense in its place. Unfortunately that is where we find ourselves on many issues today, to the extent that in another field, immunology, someone suggested bleach injections to combat a viral infection which is the equivalent of claiming zero feedback amplifiers sound better than those employing feedback without any proof.

YMMV

🙂

 

[MarcelvdG]

Sigh





So, yes, that is basically a century before all these other guys came with impedance analogies, is what I meant.
Yes, a little more than that, but that is not the point here.
Let's get nitpicky here instead.....

If you wanna know the history, just open your history books or wikipedia.
Point is, LONG before all of the other stuff.

I thought you meant that Huygens lived approximately one century earlier than Black, which is just plain wrong. Anyway, I'll just substitute "centuries" for "century" in my mind.

 

[b_force]

claiming zero feedback amplifiers sound better than those employing feedback without any proof.

You know what is interesting about history?
That it teaches you some fascinating details.

I was browsing just some old magazines the other day.
In the 50s-60s, every self respected high quality (tube) amplifier had feedback.

For some reason that all of a sudden became out of fashion when it comes down to tube amplifiers.
It seems to be back to feedback again, the last 5 years or so.

lol.