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Puritan Audio PSM156 Review (AC Filter)

sarumbear

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While I get your general point about not wanting to argue on this, it's also not like there are factually incorrect things on those specific pages, I think, and the references are there, so please let's not go down the slippery slope of dismissing arguments when they use wikipedia because it's not 'real' science.
The word "NO!!!" is not making an argument hence no reference would helped me to understand why there is a disagreement. I am not prepared to argue with someone simply throwing references to me. References only mean something if you have the basic knowledge of how certain things work. They cannot teach you. They may only help you to accentuate your argument. In this case there was no argument just a declaration of a disagreement.

About your phrase about Wikipedia not real science: most often it is not (whatever real science means). Wikis are written collectively hence they do not have the educational quality of a book on a subject. They are excellent reference sources and the footnotes are there if you want to delve deeper but that is all, a reference. You cannot learn from Wikipedia. You need to read books to educate yourself or take a course on the subject(s).
 
D

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I wrote: There are a few things at play here and in audio all devices have rectifiers and no PFC.
I don't know if all devices have no PFC - I have not opened all of them. PFC are becoming a thing in quality computer power supplies so they become available at amplifier powers.
However, PFC is just an advanced version of input filtering. If you don't use one, you need input filtering to reduce the current peak. Even your example uses filtering, otherwise a diode bridge rectifier current looks different.

All the power needed by the devices comes from short current peaks.
Few people realize that so that's what I pointed out in more detail amongst some other aspects.
There was nothing inaccurate nor misleading about that.
That is the point - the current pulses are usually _not_ the problem. They are only a problem if they affect (distort) the grid voltage.
At low, e.g. DAC or preamp, power levels, this is almost impossible.
An example why this matters: interfaces like RMI, MOTU (and I think also Topping DACs) use switched power supplies and achieve something like 110-120db SNR. Onboard, they use capacitors (and likely a linear regulator) to decouple AC from DC. They can achieve this while being quite dirty on the grid and moving to a linear power supply would not change performance at all.

Anyhow, I did _not_ say that your post was misleading. It came to the right conclusion but using an argument that _is_ easy to misuse.
It even fooled researchers and is still partially in the grid codes.
For clarity sake
- your/old argument: current harmonics = bad -> let us restrict these,
- new argument: voltage harmonics = really bad -> let us restrict these (this also restricts current harmonics but not for lowest power devices)
Example why this matters: in the 90s and 00s, power conversion devices (including consumer devices like kitchen appliances with power electronics) were able to blow out other devices, e.g. computer power supplies. This is actually more EMI related than low frequency harmonics but similar concepts apply. It is largely mitigated since EMI restrictions are in place.
 

aslan7

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People seem obsessed with these power conditioners now. One major discount internet dealer advertises a whole product line of them. I suspected this is all hooey, especially when he gives you a free cable if you buy the pricey one. Amazing.
 

beefkabob

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@amirm Can you test a UPS with a "pure sign wave"? I'm sure it won't improve audio, but maybe it will clean up the power, at least when on battery?
 
D

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Please don't be offended if I don't do that. I have two masters degrees from a global top 10 university. I can't make myself argue with someone who is using material sourced from a crowd sourced publication. I was simply trying to pass on my knowledge to a forum of like minded people.
I was expecting that sooner or later you would run out of arguments and start throwing around titles. It is always sobering to see science-minded folks bs-ing and then need to resort to titles/CV to try to save themselves.
Respects and congratulations on your MS degrees (really!). However based on your answers, I doubt they are in electrical engineering or if they are, I'd be quite curious of having a look at that universities curriculum.

Regarding wikipedia: no it is not a scientific source but, yes, it is quite accurate especially for concepts this basic. Researchers use it behind the scenes quite a lot. You should try it some time as well ;)
 
D

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References only mean something if you have the basic knowledge of how certain things work. They cannot teach you. They may only help you to accentuate your argument.
Are we at the point where we need to explain the concept of "textbook" or "encyclopedia" to you?
 

solderdude

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Even your example uses filtering, otherwise a diode bridge rectifier current looks different.

Nope. It is simply the current I measured in the secondary winding. There was no filtering involved.

- your/old argument: current harmonics = bad -> let us restrict these,

Nope, that's not what I claimed. I claimed that filtering from 500Hz (what the filter in question does) makes a lot of sense and that one should not filter any lower.
Current harmonics are not 'bad' they are a fact of life because of the way the rectifier works. All electronics have rectifiers, some directly on the mains (SMPS) others via a transformer.
 

sarumbear

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However based on your answers, I doubt they are in electrical engineering or if they are, I'd be quite curious of having a look at that universities curriculum.
My credentials summary is in the footer of every post I make with full details in my about page.

By all means look at the Imperial College London's curriculum. :facepalm:

Ignorance runs deep...
 
D

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Nope. It is simply the current I measured in the secondary winding. There was no filtering involved.
What does the transformer inductance then?

Nope, that's not what I claimed. I claimed that filtering from 500Hz (what the filter in question does) makes a lot of sense and that one should not filter any lower.
Why not? (just curious)

Current harmonics are not 'bad' they are a fact of life because of the way the rectifier works. All electronics have rectifiers, some directly on the mains (SMPS) others via a transformer.
No they are not - there are many ways to improve them and/or not generate them at all.
All rectifiers use some form of filtering!
If you are interested in the theory, I'd suggest the following textbooks: D. Hart "Power Electronics", chapter 3 and 4 (you may also be interested in chapter 2 "power computations"), or Mohan, Undeland, Robbins, "Power Electronics", chapter 5 (more advanced).
 

storing

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They are excellent reference sources and the footnotes are there if you want to delve deeper but that is all, a reference. You cannot learn from Wikipedia. You need to read books to educate yourself or take a course on the subject(s).

Hmm, that's a bit of a stretch. Really depends on the topic and how much you need to learn from it. In my experience if you have some basic education on a certain subject already then Wikipedia (or any other online reference for that matter, for which it can be verified it is correct) is definitely a good start to learn more, and sometimes even all you need, without having to resort to full books or courses. E.g. I use online sources regularly to lookup math formulas I don't know by heart or which I don't know at all. I still call that learning.
 

solderdude

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No they are not - there are many ways to improve them and/or not generate them at all.

What needs to be improved and what is not generated with these improvements you speak of ?

All rectifiers use some form of filtering!

You mean all designers use some form of filtering depending on how much is needed in order to comply to specific standards.

At what frequency would you suggest mains filtering should be done and why ?
Common mode and or differential mode ?
 

pma

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What does the transformer inductance then?

It is a transformer, not the inductor. Quite a difference.

@solderdude is right.
1630434682774.png
 

sarumbear

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E.g. I use online sources regularly to lookup math formulas I don't know by heart or which I don't know at all. I still call that learning.
Maybe it is semantics but I call that looking up a reference :) You already know what you are looking for, just not the detail. That is why the educational and reference books are separate categories.
 
OP
amirm

amirm

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D

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My credentials summary is in the footer of every post I make with full details in my about page.

By all means look at the Imperial College London's curriculum. :facepalm:

Ignorance runs deep...

It does not look good for my colleagues at the Imperial College Dept of El. Engineering if their electronics alumni don't have a good understanding of electromagnetics or how the grid works.

FYI, I'm an EE Professor at a school that ranks quite a bit higher than the Imperial college (good school btw.).
https://www.usnews.com/education/best-global-universities/rankings
I'm also an advisor to companies and expert in patent litigation on this very topic.

However, can we please stop this childish behavior? I can explain things if you do care to ask and listen.
 
D

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It is a transformer, not the inductor. Quite a difference.

@solderdude is right.
View attachment 150729
Real transformer = ideal transformer + magnetizing/leakage inductance.
Filtering is provided by the fact that the transformer has "parasitic" inductances (not because of the ideal transformer behavior, i.e. the turns ratio). Usually, you minimize these inductances in transformer design. However, you sometimes leverage them, e.g. in power supply design or flyback converter design when you don't want a discrete inductor for cost reasons. Hope this helps.
 

sarumbear

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FYI, I'm an EE Professor at a school that ranks quite a bit higher than the Imperial college (good school btw.).
https://www.usnews.com/education/best-global-universities/rankings
I'm also an advisor to companies and expert in patent litigation on this very topic.

However, can we please stop this childish behavior? I can explain things if you do care to ask and listen.
Well professor, I am not the one being childish now am I by boasting his university is better ranked then mine? You should know that there are 1500+ schools in those rankings and we are talking the top 10 where the ranking order changes every year and by the compiler. "Quite a bit higher" indeed...

Anyway, as you wished I will not reply to you anymore. I do not like your tone of superiority anyway.
 
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D

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What needs to be improved and what is not generated with these improvements you speak of ?
You mean all designers use some form of filtering depending on how much is needed in order to comply to specific standards.
Yes, of course. At the very least you need to limit inrush currents and peak-to-RMS current ratio (relates to power factor and reduces efficiency if extreme).
Inrush current can also trigger your breakers..
This is before looking at any IEC, IEEE, or GB/T standards, which you have to do as well if you want to sell in these territories.

At what frequency would you suggest mains filtering should be done and why ?
There is not one answer - it depends on a lot of things.

Common mode and or differential mode ?
Until now, every result presented/discussed related to differential mode.
Happy to discuss common mode, leakage, and ground currents...
 
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D

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Well professor, I am not the one being childish now am I by boasting his university is better ranked then mine? You should know that there are 1500+ schools in those rankings and we are talking the top 10 where the ranking order changes every year and by the compiler. "Quite a bit higher" indeed...

Anyway, as you wished I will not reply to you anymore. I do not like your tone of superiority anyway.

Look, I only wanted to help explain things as there seems to be a lot of misconceptions in audio related to power.

I apologize if I missed the tone and came of as condescending. This was not! my intention.

However, I did also not come here to through around titles or to participate in a competition of egos.

I remain at the availability to the forum if there are question related to power supplies, switched mode power conversion, etc.
 
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