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Ground loops - measurements and solutions

Wombat

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@Wombat , at least here in Germany any industrial quality cable drums are additionally rated for coiled-up duty (with de-rated power specs, ususally 1/3rd of the un-coiled max power) and also don't have metal core. Plus they always have the resettable thermal fuse. Anything else would be a complete nightmare, for example for construction workers.

Don't use your grandfather's stuff you found in some dusty corner of your basement/garage!

Or in deregulation-mad countries. The average bod is ignorant re industrial law or electrical theory, all the same.
 

Wombat

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NSL32SR3 are not just any L pad, try it to find out - and report back your findings.

There is a lethal dose of arsenic. Try it and find out.

@KSTR posted a reasonable response to your statement. If you can't explain it just say so. It is not reasonable to expect everyone to try out other people's druthers. :)
 
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DonH56

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The only thing I find is an Advanced Photonix NSL-32SR3 opto-isolator, not an L-pad... Fortunately for my time I don't care enough to dig further.
 

Speedskater

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This problem was first pointed out by Neil Muncy (RIP) some 25 years ago, in an Audio Engineering Society paper:
"Noise Susceptibility in Analog and Digital Signal Processing Systems"

This became known in XLR interconnect systems as the "Pin 1 Problem" but it applies to all shielded interconnect systems.

It later was published in the excellent June 1995 AES Journal Volume 43 Number 6.
"Shields & Grounds"

This 85 page journal has 7 papers and engineering reports including the one by John Windt for how to test for this problem, with his "Hummer Tester".

This journal can still be purchased from the AES for $15US (by anyone). (and it's well worth the price)
https://customer258769455.portal.me...ontextID=dfb59c4a-0066-cfc7-defb-0b3b8d837468
 
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pma

pma

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Or search for Bill Whitlock's papers, they are for free and he covers everything. I haven't seen better analysis yet. And he shows the hum injection tester as well. However, proper complex measurements are more accurate and allow to quantify precisely.
 

stereo coffee

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The only thing I find is an Advanced Photonix NSL-32SR3 opto-isolator, not an L-pad... Fortunately for my time I don't care enough to dig further.
OK well that's your choice, to keep on needlessly searching,
 

Speedskater

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Or search for Bill Whitlock's papers, they are for free and he covers everything. I haven't seen better analysis yet.
Yes, there is a Bill Whitlock paper on the next page of that AES June 1995 Journal.
"Balanced Lines in Audio Systems: Fact, Fiction, and Transformers"
They often reference each other and John Windt in their papers.
And he shows the hum injection tester as well. However, proper complex measurements are more accurate and allow to quantify precisely.
While Bill Whitlock has some short construction notes on the John Windt "Hummer Tester", the AES Engineering Paper has a measurement protocol that allows one audio component to be tested at a time, rather than a system test.
 
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pkane

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A L pad comprised of 4x NSL32SR3 suitably powered

Looks like you are producing a passive pre-amp board that's using these. Do you have any measurements to show how these perform? From the data sheet these appear to have a fairly slow rise/fall time (5-10ms)?
 
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KSTR

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Whatever it does, isolated transmission of analog audio it sure doesn't.... at least not with any bandwidth, even the fastest Vactrols are way too slow to allow the LDR being modulated with an audio signal.
Don't know what's his point after all...
 

graz_lag

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@pma

Hi Pavel:

Were you referring to the same type of symmetrically balanced isolation transformers in the recommendation you have been giving in your earlier posts?
https://www.audiosciencereview.com/...ains-line-noise-emi-filtering.976/post-124856

Briefly, in my setup:
CD player, Blu-ray, PC and USB DAC are all feed via the transformer #1, whilst the HiFi amplifier via the transformer #2.
The connections are:
PC - DAC = USB
DAC - HiFi Amplifier = RCA's
CD Player - HiFi Amplifier = XLR's
Blu-ray - HiFi Amplifier = SPDIF 75ohms
(All my electronics are Class II)

Can I count to be in a ground loop-free configuration? Thank you so much.
 
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pma

pma

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@pma

Hi Pavel:

Were you referring to the same type of symmetrically balanced isolation transformers in the recommendation you have been giving in your earlier posts?
https://www.audiosciencereview.com/...ains-line-noise-emi-filtering.976/post-124856

Briefly, in my setup:
CD player, Blu-ray, PC and USB DAC are all feed via the transformer #1, whilst the HiFi amplifier via the transformer #2.
The connections are:
PC - DAC = USB
DAC - HiFi Amplifier = RCA's
CD Player - HiFi Amplifier = XLR's
Blu-ray - HiFi Amplifier = SPDIF 75ohms
(All my electronics are Class II)

Can I count to be in a ground loop-free configuration? Thank you so much.

Hi,

I cannot find my post in the thread that you have linked above. If your components are all in class II, then there should not be any ohmic ground loop. However, it is difficult to evaluate at long distance, without measurements. Usually, if your system is quiet with your ear very close to the speaker, then it is OK. If not, it should be investigated. Sometimes class II components may have quite high coupling capacitance to mains. You can take a DVM and measure AC voltage between the components that are "ON" but with signal cables removed. You can also try to measure AC current between RCA connector bodies of 2 different class II components (again no signal interconnects). Then you would know what is the value of current flowing through the cable screen.

The isolation transformer that I use is not symmetrically balanced.
 

graz_lag

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Hi,

I cannot find my post in the thread that you have linked above. If your components are all in class II, then there should not be any ohmic ground loop. However, it is difficult to evaluate at long distance, without measurements. Usually, if your system is quiet with your ear very close to the speaker, then it is OK. If not, it should be investigated. Sometimes class II components may have quite high coupling capacitance to mains. You can take a DVM and measure AC voltage between the components that are "ON" but with signal cables removed. You can also try to measure AC current between RCA connector bodies of 2 different class II components (again no signal interconnects). Then you would know what is the value of current flowing through the cable screen.

The isolation transformer that I use is not symmetrically balanced.

Hi Pavel :

The post I linked at was mine in another thread ...
 

JohnYang1997

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FYI the unbalanced inputs on my Audio Precision Analyzer by default are floating (not ground referenced). This helps a lot with ground loops although sometimes I get better results by connecting ground.
In my measurements the unbalanced input of apx555 has some low impedance to earth 470ohm or so. It is misleading for amplifiers. Only way to measure amplifier output is to use the balanced input.
 
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pma

pma

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Please let me show now that even class II components and only one component in class I may not be a cure. These measurements show effect of capacitive currents flowing through an AC/DC wall supply adapter of DacMagic+. The system is compose from a DAC, a preamp, an USB soundcard and a PC. PC (and thus a soundcard) is in class I, all other components in class II.

1) DAC is supplied from its factory supplied AC/DC wall adapter. There is no ohmic groundloop, just the loops through capacitances of power supplies, either SMPS or transformers.

DAC_adapter.png

Block diagram of the system with DAC supplied from its wall adapter

DAC wall adpt.png

Noise spectrum of the system with DAC supplied from its wall adapter

2) an isolation transformer 1:1 is added before the DAC wall adapter. Its primary/secondary capacitance is about 150pF

DAC_isoltrafo.png

Block diagram of the system with isolation transformer added

DAC isol tr.png

Noise spectrum of the system with isolation transformer added


We can see that the isolation transformer added before the DAC wall adapter improved suppression of mains components considerably. This clearly demonstrates issues of the single-ended signal interconnects in audio. Properly designed balanced link would be a real cure.
 

solderdude

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Looks like you are producing a passive pre-amp board that's using these. Do you have any measurements to show how these perform? From the data sheet these appear to have a fairly slow rise/fall time (5-10ms)?

He already promised a year ago (and recently again as he has a new PCB) to send it in for measurements.
If I were him I would not do that as it might be bad for his business when poor measurements are posted for everyone to see.
It may be better for him to keep it 'magical' but in reality hope he sends it in.
He could also measure it himself using the soundcard of his PC but for some reason hasn't or decided not to publish.
 
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