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Why an AC Power Cord cannot make a difference

Are all these discussions about ferrites and filters intended to cast light on the question of this thread? Because if they are, they are (IMO) promoting (or at best as I have pointed out above muddying the waters with FUD) the snake oil cables this thread was created to debunk, and which have absolutely no influence on the audio quality out of a device whether due to RFI or anything else.

If not, they are off topic, and should probably be taken elsewhere.
 
Well designed amplifier must have no issues and no audible effects from speakers even if you put the cell phone on the top and let it operate receive the calls or make the calls. Same if it is near signal cables. At least I want it to be fulfilled.
How about an old school trunk radio system? Simply keying them could often make various electronics go nuts. The old 741 op-amp could be made to go into an unrecoverable oscillation, and TTL logic gates would suffer latch up.
 
this is because real components have package parasitics which start to dominate above the self-resonance frequency

by adding different values in parallel you can target different ripple/noise bands
View attachment 421662View attachment 421663
(plot from http://electronics.stackexchange.com/questions/129888/parallel-capacitor-conundrum)

Very large C values will help provide the additional current peaks for deep bass beats, but will do almost nothing at higher frequency, such as the TDMA mentioned
I think you read it backwards.
yep - remember that from cell phones in cars causing the radio to go nuts. Other edge cases are people who live with KW or higher radio transmitters on the other side of the garden fence.

I'm still unconvinced that a ferrite bead on a power lead would prevent that from happening.
A radio/cellphone is an example of radiated susceptibility issues, not conducted which is what ferrites may be used for.
 
A radio/cellphone is an example of radiated susceptibility issues, not conducted which is what ferrites may be used for.
All radiated interference becomes conducted when it couples onto whatever conductor they are interfering via. I think @KSTR was suggesting ferrites might help when the high power radiation couples in via the power cable.

I personally (as you can see) am somewhat skeptical.

We still seem to be off topic for this thread.
 
How about an old school trunk radio system?
How about a GSM mobile phone signal? How about irrelevant?

*Groan*
 
You may want to book a guided tour or seminar in am EMC test lab and witness the effectiveness of cable ferrites first hand
I spent quite some time in my previous life in such test labs. We had one in the R&D facility I worked in, in the UK, and others in the facilities in Germany and China where some of the products for which I was responsible were developed. Though these were not certification compliant so we had to go to external labs for final verification tests.

My skepticism comes specifically from seeing ferrites used in an attempt to reduce emissions from the EUT.

Typically (in the tests I witnessed) used as a sticking plaster/kludge (or sometimes just a diagnostic tool) for failing designs where some emission peaks were over the limit line. They would normally make a difference - but often not at the frequencies needed. But even where they did make a difference/improvement I don't think I ever saw more than a 10dB improvement. And that at the RF frequencies that they are designed to filter.

Lets translate that to a typical audio situation.

You have to have RF interference getting into the audio device,
It has to be getting into the device via the power cable.
The RF band interference has to interact with the device to create an audio band audible effect.

Outside of the case mentioned above with old cell phones interfering with a car radio, I've never seen a situation where an RF field caused an audible effect. And even in that case the influenced device was a radio receiver designed to be responsive to RF fields, so with a specific route (the antenna) for the stuff to get in.

But even then - if we find a situation with RF coupling via the mains lead creating an audible effect. And we assume that the audible effect is proportional to the magnitude of the RFI, and that the ferrite can specifically reduce the frequencies causing the problem - then with only a 10dB reduction, we will only get a perceived halving of the volume of the noise.

I will retain my scepticism until someone can point to an actual audio device/system in a real world use case where a power cable ferrite has been shown to eliminate audible effects from RFI.
 
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this is because real components have package parasitics which start to dominate above the self-resonance frequency

by adding different values in parallel you can target different ripple/noise bands
View attachment 421662View attachment 421663
(plot from http://electronics.stackexchange.com/questions/129888/parallel-capacitor-conundrum)

Very large C values will help provide the additional current peaks for deep bass beats, but will do almost nothing at higher frequency, such as the TDMA mentioned
I said that TI has reversed there stance on multiple bypass caps. They now recommend using just one. They say that the complexity of multiple caps and there inductance/resistance makes it hard to predict the outcome and often its worse than the one cap. For the details read the paper I linked to.
 
After 100s of kilometers of high voltage transmission lines, transfer stations, regional transmission lines, substations, local transmission lines, neighborhood transformer, neighborhood lines, domestic power meter, domestic circuit breaker box, home wiring, and finally your outlet. And somebody actually thinks the final 1m of wire will make a difference? I understand the psychology. It's because it's the only 1m of wire the normal person pays attention, although there's a circuit breaker box somewhere in the house, a power meter on the side of the house, a neighborhood transformer at the end of the row, utility lines out at the street, a substation surrounded by a fence on the property behind the community library, and big transmission towers leading out of the city ...
 
After 100s of kilometers of high voltage transmission lines, transfer stations, regional transmission lines, substations, local transmission lines, neighborhood transformer, neighborhood lines, domestic power meter, domestic circuit breaker box, home wiring, and finally your outlet. And somebody actually thinks the final 1m of wire will make a difference? I understand the psychology. It's because it's the only 1m of wire the normal person pays attention, although there's a circuit breaker box somewhere in the house, a power meter on the side of the house, a neighborhood transformer at the end of the row, utility lines out at the street, a substation surrounded by a fence on the property behind the community library, and big transmission towers leading out of the city ...
That argument gets countered by the claim that only the last six or so feet (power cord) counts for noise removal. Get a fancy cord, and it's a supposedly done deal.
 
That argument gets countered by the claim that only the last six or so feet (power cord) counts for noise removal. Get a fancy cord, and it's a supposedly done deal.
So what is the required length of that magic power cord? Why do they sell difference length power cords then? Why don't they tell their customers to use the minimum length one, and make up the rest of the distance to the outlet with a cheap extension cord? Do they not have their customers' best interest in mind?
 
So what is the required length of that magic power cord? Why do they sell difference length power cords then? Why don't they tell their customers to use the minimum length one, and make up the rest of the distance to the outlet with a cheap extension cord? Do they not have their customers' best interest in mind?
It's not the length so much as the distance from the electrical outlet and the equipment. What ever that may be, it takes a magical cord to cover it.
 
I said that TI has reversed there stance on multiple bypass caps. They now recommend using just one. They say that the complexity of multiple caps and there inductance/resistance makes it hard to predict the outcome and often its worse than the one cap. For the details read the paper I linked to.
They still strongly encourage multiple bypass caps, just that they all should be lowest possible inductance and hence physically small. This leads to small values as well, and for reduced BOM complexity you'll tend to choose one single value.

Multiply caps of different values were commonplace back in the day when there were no large-valued ceramic caps. So you had to use the typical 10uF or whatever tantalum or alumimum e-cap and localized 100nFs. That worked because frequencies of interest were lower and the larger caps had enough ESR so that the CLC resonance tank was well-damped.

Today, if you have a 10uF ceramic paralleled to 100nF ceramics but with trace inductance in between you may easily get high Q resonances where supply impedance peaks at several ohms worst-case, a true disaster for signal integrity (and often source of EMC issues). Network analyzer is your friend.

Showing one relatively benign example of the above (my own measurement on some digital board), supply impedance as seen by a certain chip. Unpowered board, but the regulator is a slughish 1117 3.3V.
1737146656789.png

Actual frequency scale is x1000, so end stop is 200MHz, not 200kHz

Multilayer PCBs (4, 6, or even more) are now standard and invite to use full plane capacitors, further augmented with lots of physically small (0402 or smaller) distributed caps (and most of them really close to the chips' supplies). By this, low and flat impedance up to several 100MHz can be achieved.
 
"Curtain burners" :eek:


View attachment 421938

Just when you thought that the series string, AC-DC, transformerless (my father called them "killer") chassis was bad enough -- that "120 ohm" resistor was one side of the power cord! zut alors!


View attachment 421937
View attachment 421939
I can only reply by quoting a line from Apocalypse Now.
"The Horror"
 
After 100s of kilometers of high voltage transmission lines, transfer stations, regional transmission lines, substations, local transmission lines, neighborhood transformer, neighborhood lines, domestic power meter, domestic circuit breaker box, home wiring, and finally your outlet. And somebody actually thinks the final 1m of wire will make a difference? I understand the psychology. It's because it's the only 1m of wire the normal person pays attention, although there's a circuit breaker box somewhere in the house, a power meter on the side of the house, a neighborhood transformer at the end of the row, utility lines out at the street, a substation surrounded by a fence on the property behind the community library, and big transmission towers leading out of the city ...
See my reply here:

https://audiosciencereview.com/foru...udibly-the-same-discussion.60134/post-2202213
 
shielded ac cord could be helpful for eliminating AC hum .. isn't necessary if it isn't a problem.. lot cheaper than audioquest wants you to think.
 
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One should measure the EMC that is present on the safety ground in your average home situation. :D
Let me be very clear about it ... safety ground is not 'clean' in any way.
It is there for safety reasons in case a device fails in such a way that touching it becomes lethal.

There is nothing 'clean' about safety ground and even screened cable connected via an IEC or other not fully shielded connector on both ends is not working as a shield but as a nice RF antenna.
 
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