Dispelling ground myths

Speedskater

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They also will likely tell you nothing about AC voltage as multimeters are very limited in the frequency range for which they can give an accurate ac measurement

So who said anything about using a cheap multi-meter?

With good modern test equipment, making measurements at -120 to -130 dB's is common.

You measure the signal to noise ratio at the loudspeaker terminals.

Measurements done by skilled engineers/scientists using the correct test equipment for the task at hand.
 

jkeny

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So who said anything about using a cheap multi-meter?
Folsom mentioned using a multimeter - maybe you or he can you give some examples of multimeters with a relevant accurate measurement across the frequency range we may be interested in?

With good modern test equipment, making measurements at -120 to -130 dB's is common.

You measure the signal to noise ratio at the loudspeaker terminals.

Measurements done by skilled engineers/scientists using the correct test equipment for the task at hand.
That would be great - can you give us an example of SNR measurement differences at speaker terminals which show a difference in noise that RogerD is perceiving as audibly improved sound as a result his PEC techniques?
 

RogerD

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I had a similar conversation with Don Herman about chassis grounding...aka PEC

"Same principles apply to controlling noise currents/voltages on the ground/shield paths.

Chassis grounding in audio is no different than for any other circuit sensitive to noise. Keeping a good chassis ground relatively independent of signal ground can do anything from nothing to profound improvements in the noise floor depending on the circuit design and implementation. You generally want the "noise" path to ground to be different than the signal return path, and often that means a heavy chassis ground to provide the lowest impedance path for noise while the signal return goes through the signal cables.

strap everything so all ground noise is common-mode
, then shielded cables for low-level signals and only low-impedance (e.g. speaker) or isolated (e.g. power) connections should control noise for the vast majority of folk.

Like many things, conceptually simple, straight-forward good engineering practice, but not well known or recognized and can be unexpectedly difficult to implement well. There are numerous texts and courses teaching noise control."

Don Herman
 

jkeny

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I'd expect broadband AC noise from 60 Hz on up. Possible sources are induced ground loops, leakage currents, local emf...

It seems obvious that certain substances can actually serve as a "sink" for noise. Silicon carbide, quartz, tourmaline and carbon, probably many more. Hearing what a Furutech GTX receptacle sounds like in regular vs NCF versions is astounding...
It's not obvious to me how "Silicon carbide, quartz, tourmaline and carbon" act a a sink for electrical noise?
 

Speedskater

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Folsom mentioned using a multimeter - maybe you or he can you give some examples of multimeters with a relevant accurate measurement across the frequency range we may be interested in?
Are you a skilled scientist/engineer? It's not about the tools, it's about how the craftsman uses the tools.

That would be great - can you give us an example of SNR measurement differences at speaker terminals which show a difference in noise that RogerD is perceiving as audibly improved sound as a result his PEC techniques?
How would I know what RogerD heard?
The measurements and the listening test need to be done on the same setup at the same time. But if the noise measurement differences are great enough, you might not need to do the listening test.
 

jkeny

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Are you a skilled scientist/engineer? It's not about the tools, it's about how the craftsman uses the tools.
Part of being skilled is knowing what tools are not suitable due to their limitations & a multimeter is just not suitable for doing what was suggested


How would I know what RogerD heard?
I expect by his reports of the audible improvements.

The measurements and the listening test need to be done on the same setup at the same time. But if the noise measurement differences are great enough, you might not need to do the listening test.
I agree but the opposite also applies - if listening reveals audible changes which measurement doesn't you may discount the measurements as using inappropriate equipment or techniques to reveal what is audible
 

Speedskater

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Part of being skilled is knowing what tools are not suitable due to their limitations & a multimeter is just not suitable for doing what was suggested
A person with skill would not need to ask that question.

I expect by his reports of the audible improvements.
How can we test his situation, without testing his situation?

I agree but the opposite also applies - if listening reveals audible changes which measurement doesn't you may discount the measurements as using inappropriate equipment or techniques to reveal what is audible
Then we need to find a person with greater skill or get the correct test equipment. Because there will be measurable differences.
 

jkeny

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A person with skill would not need to ask that question.
I was pointing out that a multimeter is not suitable measurement device for this application as Folsom seemed to suggest - I asked for an example of such a multimeter measurement if this was under dispute.
You specifically stated that a multimeter could be usefully used
Yep it is. Common Impedance Coupling noise is when two chassis are at different leakage current potentials and use the interconnect shields to equalize. So short Safety Ground wires or chassis-to-chassis PEC wires wire reduce the leakage potentials.

More likely measurements will reveal problems the are not easily audible.
So when you talk about "More likely measurements will reveal problems the are not easily audible." you include this in the same post as suggesting using a multimeter.
How can we test his situation, without testing his situation?
You mean test his reports of audibility?


Then we need to find a person with greater skill or get the correct test equipment. Because there will be measurable differences.
Right & as I asked before to back up your claim but I'll change my request slightly as you focused on a particular aspect that avoids answering "That would be great - can you give us an example of SNR measurement differences at speaker terminals which show a difference in noise" which shows a change due to PEC being applied? Not something which is a ground loop hum or buzz - these are gross intrusion of electrical noise into signal ground.

I mentioned RogerD's reports specifically as he did not hear any ground loop hum or buzz prior to his beginning this PEC technique.

Just a question - do you believe that there are other audible effects from such electrical noise intrusion into signal grounds, besides the typical hum & buzz?
 
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microstrip

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It's not obvious to me how "Silicon carbide, quartz, tourmaline and carbon" act a a sink for electrical noise?

These materials are known for its high microwave absorption - it is why I always unsuccessfully ask for a rigorous specification of bandwidth when debating noise ...
 

jkeny

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These materials are known for its high microwave absorption - it is why I always unsuccessfully ask for a rigorous specification of bandwidth when debating noise ...

Ok, yes I agree electrical noise needs to be characterised as regards spectrum, amplitude & temporal aspects & not treated as one amorphous blob
 

microstrip

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Part of being skilled is knowing what tools are not suitable due to their limitations & a multimeter is just not suitable for doing what was suggested (...)

+1!

IMHO you need an audio frequency and an wide band spectrometer (-200 MHz) with differential input to properly carry these measurements.

I regularly use a RTA to optimize cable layout in my system , particularly when using single ended electronics and moving coil cartridges.
 

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DaveC

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It's not obvious to me how "Silicon carbide, quartz, tourmaline and carbon" act a a sink for electrical noise?

Something to look into then. I don't have any info for you as I haven't done any testing or measuring yet besides hearing other companies products, but it's very obvious in a simple subjective listening test of something like the Furutech NCF parts vs the non-NCF parts where the main difference is the addition of tourmaline powder. There are many other companies putting out products that use piezoelectric materials to attenuate noise as well.

And just because I don't specify frequencies doesn't mean it's "one amorphous blob", I simply haven't done any testing to know the specifics. One member here did use a handheld AC power quality meter that showed the Furutech NCF receptacle reduced noise significantly. Some of us have observed through listening that it reduces noise and distortion. It's not subtle either.

We've had 7 pages of leading questions now... enough I think? ;)
 

jkeny

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Yea but the ~5dB rise in noise floor (& some spikes) shown in your plots are down at -130dB & typically dismissed as inaudible.
Are you just showing these plots as an exercise in engineering or as something that is audible?
 

jkeny

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Something to look into then. I don't have any info for you as I haven't done any testing or measuring yet besides hearing other companies products, but it's very obvious in a simple subjective listening test of something like the Furutech NCF parts vs the non-NCF parts where the main difference is the addition of tourmaline powder. There are many other companies putting out products that use piezoelectric materials to attenuate noise as well.
I will read about the NCF parts, thanks

And just because I don't specify frequencies doesn't mean it's "one amorphous blob", I simply haven't done any testing to know the specifics. One member here did use a handheld AC power quality meter that showed the Furutech NCF receptacle reduced noise significantly. Some of us have observed through listening that it reduces noise and distortion. It's not subtle either.

We've had 7 pages of leading questions now... enough I think? ;)
Didn't mean to accuse you of anything - sorry if it came across like that - just a general point that noise is often just a term used as a general category without recognising that it has specific characteristics
What do you mean by the part I bolded?
 

microstrip

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(...) One member here did use a handheld AC power quality meter that showed the Furutech NCF receptacle reduced noise significantly (...)

Do you remember what was this meter?
 

microstrip

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Yea but the ~5dB rise in noise floor (& some spikes) shown in your plots are down at -130dB & typically dismissed as inaudible.
Are you just showing these plots as an exercise in engineering or as something that is audible?

Yes, probably inaudible but I felt proud to have achieved such low noise hum.

It was surely as an exercise in very amateur audio engineering, but my point is that people probably could easily complement their points with measurements not just with hyperbolic subjective statements.
 

DaveC

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I will read about the NCF parts, thanks


Didn't mean to accuse you of anything - sorry if it came across like that - just a general point that noise is often just a term used as a general category without recognising that it has specific characteristics
What do you mean by the part I bolded?

Well, you started out by showing the path of least impedance for return currents on a pcb's ground plane and asking specific questions about the characteristics of noise so I figured there gotta be some main point you're getting to?
 

DaveC

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Yes, probably inaudible but I felt proud to have achieved such low noise hum.

It was surely as an exercise in very amateur audio engineering, but my point is that people probably could easily complement their points with measurements not just with hyperbolic subjective statements.

Alas, I still have limited equipment to make such measurements... right now Omnimic, DATS and a nice Kiethley multimeter... but do plan on buying an o-scope and signal gen in the near future. Maybe we need a new thread on recommended equipment for analyzing audio systems?


I do not remember which meter was used for the NCF test.
 

jkeny

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Well, you started out by showing the path of least impedance for return currents on a pcb's ground plane and asking specific questions about the characteristics of noise so I figured there gotta be some main point you're getting to?

I showed the different preferred paths for different frequency return currents on a pcb to illustrate the principles that apply. When we consider cables where is the path of least that impedance - is it the shield, the ground wire or one of the signal wires? What about cable construction - how does it affect the return current path? What about skin effects?

The main point is that ground currents & ground returns are not simple matters & I was hoping this thread could focus on matters.
 

jkeny

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Alas, I still have limited equipment to make such measurements... right now Omnimic, DATS and a nice Kiethley multimeter... but do plan on buying an o-scope and signal gen in the near future. Maybe we need a new thread on recommended equipment for analyzing audio systems?


I do not remember which meter was used for the NCF test.

Ok I wasn't aware of these high quality DMMs - thanks for correcting me
 

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