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PostPosted: November 25th, 2017, 3:16 pm 
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Location: Parkville, Maryland
Many of you know me and some of you have auditioned my music system. That said you may also know that I am particularly careful about isolating my system from RFI/EMI infiltration through an isolation transformer, input power filtering, and ferrite filters on cables. I have had a difficult time explaining how these things are important other than it definitely has an impact on sound quality -- all for the better when implemented.

Paul Miller, the editor of Hi-Fi News & Record Review, a British publication, published the results of his study with his findings that was originally published in June 1989 and reprinted in the recent June 2017 issue of the magazine.

The article is comprehensive and loaded with what I call "word salad" but it is quality word salad to say the very least. Paul's findings confirm my experiences with keeping the interference out of the signal path with the end result of better sound.

I knew the multiple isolation methods that I have used works -- but the reasons and how RFI/EMI infiltration actually impacted the electronics was beyond my knowledge base.

Paul "'splained it to Lucy." After reading his piece my first reaction was "OMG!" RFI and EMI is like electronic "roaches." They get everywhere in the electronics and and effectively mess with the delicate audio signal.

Attached are pages 1, 2, & 3 (The full size <*.pdf> file would not be accepted) Page 4 to follow.



Attachments:
00 0A RFI_EMI_Paper_Page_3.jpg
00 0A RFI_EMI_Paper_Page_3.jpg [ 538.55 KiB | Viewed 1822 times ]
00 0A RFI_EMI_Paper_Page_2.jpg
00 0A RFI_EMI_Paper_Page_2.jpg [ 464.16 KiB | Viewed 1822 times ]
00 0A RFI_EMI_Paper_Page_1.jpg
00 0A RFI_EMI_Paper_Page_1.jpg [ 465.63 KiB | Viewed 1822 times ]

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PostPosted: November 25th, 2017, 3:18 pm 
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Joined: July 24th, 2015, 4:17 pm
Posts: 603
Location: Parkville, Maryland
Many of you know me and some of you have auditioned my music system. That said you may also know that I am particularly careful about isolating my system from RFI/EMI infiltration through an isolation transformer, input power filtering, and ferrite filters on cables. I have had a difficult time explaining how these things are important other than it definitely has an impact on sound quality -- all for the better when implemented.

Paul Miller, the editor of Hi-Fi News & Record Review, a British publication, published the results of his study with his findings that was originally published in June 1989 and reprinted in the recent June 2017 issue of the magazine.

The article is comprehensive and loaded with what I call "word salad" but it is quality word salad to say the very least. Paul's findings confirm my experiences with keeping the interference out of the signal path with the end result of better sound.

I knew the multiple isolation methods that I have used works -- but the reasons and how RFI/EMI infiltration actually impacted the electronics was beyond my knowledge base.

Paul "'splained it to Lucy." After reading his piece my first reaction was "OMG!" RFI and EMI is like electronic "roaches." They get everywhere in the electronics and and effectively mess with the delicate audio signal.

Attached is page 4 (The full size <*.pdf> file would not be accepted)



Attachments:
00 0A RFI_EMI_Paper_Page_4.jpg
00 0A RFI_EMI_Paper_Page_4.jpg [ 576.21 KiB | Viewed 1821 times ]

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PostPosted: November 25th, 2017, 10:36 pm 
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I have an Alphalab EMI meter and it is shocking g to see what is coming on the power lines. My system has two dedicated lines, a 15A for sources and a 20A for amps. Both of these dedicated lines are noisy as hell.


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PostPosted: November 25th, 2017, 11:44 pm 
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Joined: April 22nd, 2013, 12:58 pm
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I've done EMI/RFI testing for CE certification and it's amazing how much noise there is out there.


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PostPosted: November 26th, 2017, 8:31 am 
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Joined: January 15th, 2015, 7:19 am
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Location: Baltimore MD
Can this noise be seen on a Oscilloscope?


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PostPosted: November 26th, 2017, 12:26 pm 
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Pelliott321 wrote:
Can this noise be seen on a Oscilloscope?



Look at the images in the article. That's how Paul Miller developed his findings.

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PostPosted: November 27th, 2017, 12:09 pm 
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Location: Potomac, MD
Good article, Walt.

And yes, Paul, lots of RF stuff can be observed on a scope with 100 or so MHz bandwidth.

Incidentally, wide-bandwidth filters are tricky to do. You can't just have one large inductor and one cap to ground to make a good filter. You have to generally have several inductors optimized for different areas of the spectrum. Caps themselves all have resonances too. You need to dissipate the energy in resonances, otherwise a simple ideal cap-inductor combination will simply resonate stronger. This is why ceramic caps are more desirable for wideband filters as they are somewhat lossy. Then the ground itself is problematic as it has its own inductances.

Amplifiers that use high feedback can be very susceptible to RF problems since the feedback breaks down at high frequencies as the open-loop gain goes to pot. To successfully use high feedback in a high-frequency environment, very careful attention to input filtering must be done. With careful filtering, the feedback is not asked to force the amp to linearly reproduce the an input signal with RF components.

I have to pay attention to a lot of this stuff as I use switching power supplies and the output-transformerless ZOTL I use generates RF switching noise as well. But it is possible to deal with it successfully.

David


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PostPosted: November 27th, 2017, 12:24 pm 
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dberning wrote:
Good article, Walt.

And yes, Paul, lots of RF stuff can be observed on a scope with 100 or so MHz bandwidth.

Incidentally, wide-bandwidth filters are tricky to do. You can't just have one large inductor and one cap to ground to make a good filter. You have to generally have several inductors optimized for different areas of the spectrum. Caps themselves all have resonances too. You need to dissipate the energy in resonances, otherwise a simple ideal cap-inductor combination will simply resonate stronger. This is why ceramic caps are more desirable for wideband filters as they are somewhat lossy. Then the ground itself is problematic as it has its own inductances.

Amplifiers that use high feedback can be very susceptible to RF problems since the feedback breaks down at high frequencies as the open-loop gain goes to pot. To successfully use high feedback in a high-frequency environment, very careful attention to input filtering must be done. With careful filtering, the feedback is not asked to force the amp to linearly reproduce the an input signal with RF components.

I have to pay attention to a lot of this stuff as I use switching power supplies and the output-transformerless ZOTL I use generates RF switching noise as well. But it is possible to deal with it successfully.

David



David's response is exactly what I expected and was not surprised when he pointed out that his amplifier design could actually exacerbate the problem. Of course like everything electronic there are ways to address issues.

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