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Old 9th February 2013, 06:49 PM   #34591
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Now that everyone is listening, HOW do you create DC in the power line? OK, just take a power diode, 5-10A should do with 400V min rating, then put it in series with an old fashioned light bulb and plug the combination into the wall socket. Try it! It is a test that we use at Parasound to find or verify noisy power transformers.

Last edited by john curl; 9th February 2013 at 06:53 PM.
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Old 9th February 2013, 06:59 PM   #34592
bcarso is offline bcarso  United States
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Originally Posted by john curl View Post
Now that everyone is listening, HOW do you create DC in the power line? OK, just take a power diode, 5-10A should do with 400V min rating, then put it in series with an old fashioned light bulb and plug the combination into the wall socket. Try it! It is a test that we use at Parasound for noisy power transformers.
I have a variac I use to adjust the power of a heated footrest. Nearby is a torchiere floor lamp with a three-position switch, off-low-high. The second position inserted a diode in series with the incandescent lamp (the switch contact in that position, or the diode, has failed now).

It was easy, until it failed (open-circuit) to notice the effect of position two, due to the quite audible buzz out of the variac. I did not attempt to measure the d.c. offset, but the noise was very irritating.
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Old 9th February 2013, 07:09 PM   #34593
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Good for you.
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Old 9th February 2013, 08:09 PM   #34594
DF96 is offline DF96  England
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Originally Posted by john curl
NO, when second harmonic is generated from a primary sine wave, it CREATES A DC OFFSET as well as adding second harmonic.
Nobody is denying that; indeed I said precisely that.

It is a completely different statement to say that an asymmetric waveform must contain DC. I am surprised that you can't tell the difference between these two different statements. One is true. The other is false.
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Old 9th February 2013, 08:43 PM   #34595
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when they show the Cramer-Rao boundary for the stimulus on the same plot we get excited
That does bring a smile to my face.
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Old 9th February 2013, 09:10 PM   #34596
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Nobody is denying that; indeed I said precisely that.

It is a completely different statement to say that an asymmetric waveform must contain DC. I am surprised that you can't tell the difference between these two different statements. One is true. The other is false.
If I try to piece it togehter, both sides on this argument are equaly wrong because both sides are equaly right.

In a practical application, like John showed, with a fixed ground or neutral, by clipping or distorting a waveform assymetrically, you create harmonics and a DC offset,compared to this fixed ground (the area under the wave form above and below the zero will not be identical).

In a mathematical representation as mentioned by Scott and DF96, you can stack sines in order to achieve the same wave form. But the zero then floats (by method it is there where the area under the wave form above and below the zero are the same). So there is no DC offset.

Different perspectives.
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Old 9th February 2013, 09:29 PM   #34597
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Originally Posted by vacuphile View Post
In a mathematical representation as mentioned by Scott and DF96, you can stack sines in order to achieve the same wave form. But the zero then floats (by method it is there where the area under the wave form above and below the zero are the same). So there is no DC offset.

Different perspectives.
Not the same waveform, I would consider a diode a pretty gross non-linearity causing modulation products that are not possible by simple linear addition. You square a sine wave and you a second harmonic plus DC no simple addition of sine waves of any frequencies will give the DC component.

EDIT - Here's a previously published example, this waveform has no DC and is highly asymmetric.
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Last edited by scott wurcer; 9th February 2013 at 09:39 PM.
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Old 9th February 2013, 09:55 PM   #34598
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Kgrlee, you have it all wrong! The title 'JC-2 mk1' was a working title for the JC-3, that when ultimately finished got 'preamp of the year' in several publications. Please get your facts straight before confronting me with your comments.
JC, please tell us what you want to call the circuit you posted as phono.pdf? The one that you told us was caned by the reviewers.

I'm glad you've finally remembered what 'JC-2 mk1' means to you.
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Read more at: Human hearing beats the Fourier uncertainty principle

Understand that these where discrimination tests performed on people, and their hearing.

That a few musicians turned out to be 'good', ie, 10x better than theory.

Now, imagine the golden eared audiophile. Some that are at the peak of the trade and group?
I can well believe that musicians did well in these tests.

Contrary to some other researchers, my nearly 20 years of Double Blind Listening Tests show that musicians are usually above average in their sensitivity to faults though none of my tests explored Fourier uncertainty. This probably cos I was more interested in testing with music.

Sadly, "Golden Eared audiophiles" are well below average compared to the man or woman in the street. In fact, in nearly 2 decades, I failed to find a single Golden Pinnae, whose discriminatory ability didn't vanish miraculously, the moment the lights were turned off and he couldn't see what he was listening to.

But I've been often surprised at the aural acuity of true golden pinnae. There have been times when some of my Listening Panel could reliably pick up differences which my poor test equipment in those days could hardly pick up.

And of course there are the true 'Elite' like JC who don't even have to listen to a product to tell you what it sounds like. They can do it by simply looking at the price tag and the labels on the evil OPAs.

So lets not confuse the hearing acuity of some true golden pinnae from the ravings of deaf Golden Pinnae audiophiles.

I'm disappointed that my request for suggestions of true golden pinnae has not produced any recommendations even among this august company.

Surely there must be people who can (or think they can) distinguish Blowtorch from evil 4558 devices in a Blind Listening Test bla bla and are prepared to interested in testing this proposition ?
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JC, while you have provided some useful practical pearls of wisdom on testing power transformers, you might like to re-read Electronic 101 or even the notes that Quan so kindly restored to you.

There is much there about even harmonics & DC that would help you understand what actually happens to transformers. I also recommend Wireless World back to the original Williamson articles and particularly anything by Great Guru Baxandall.

If DF96 starts his "basic physics/maths/EE ... " thread, you would be well advised to take advantage of this.

There is much about ".. elementary circuit theory, Fourier, algebra, calculus, feedback, stability etc" that you could profit from if you refresh your basics.

In the meantime, close study of datasheets by true gurus would help you make less mistakes with evil OPAs.
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Old 9th February 2013, 10:08 PM   #34599
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Not the same waveform, I would consider a diode a pretty gross non-linearity causing modulation products that are not possible by simple linear addition. You square a sine wave and you a second harmonic plus DC no simple addition of sine waves of any frequencies will give the DC component.

EDIT - Here's a previously published example, this waveform has no DC and is highly asymmetric.
Scott, this example only proves what I already thought. Ofcourse there is no DC here. How could it be after galvanic uncoupling? The zero floats.

I thought all waveforms could be produced by simple additions of sinoids, including those caused by diodes clipping a sinewave. You can mathematically arrive at the same waveform that John created with his test setup. But then ofcourse DC does not show up. Isn't this what you originally meant?
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Old 9th February 2013, 10:17 PM   #34600
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Originally Posted by vacuphile View Post
Isn't this what you originally meant?
It need an infinite time to can assert if there is DC or not in a signal .
Neither Scott or John can win this contest.
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Last edited by Esperado; 9th February 2013 at 10:22 PM.
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