Why an AC Power Cord cannot make a difference

[D2013]

When was the last time you dragged your amp around the living room while it was plugged in? Ive had to replace power cords that have been used constantly outdoors for 5 years, so what?

Imo, the point is some people here espouse an overly simplistic point of view. Some even like to be passive aggressive and antagonistic about it.

Ever worked as a dj or been involved in a live event production? If you have you know cables of all kinds can take a real betting.

 

[egellings]

Vacuum cleaners' cords are subject to a lot of mechanical stress; amplifier cords, not so much (I hope!).

 

[Holmz]

Vacuum cleaners' cords are subject to a lot of mechanical stress; amplifier cords, not so much (I hope!).

But some amplifiers also suck.

 

[egellings]

But some amplifiers also suck.

..but not air, though.

 

[antcollinet]

..but not air, though.

chunky goats vomit though a straw.

 

[Devnull]

..but not air, though.

Last time I checked my pro sound amps suck cold air (and a lot of dust) in the back and blow hot air out the front.

 

[Paffi]

If you have a class-I ground loop scenario, then a higher resistance of the cable can help because then the second GND connection via the interconnects has better chances to be lower (dominating) impedance. A weapon of choice in many recording studios is a large 50m cable drum which creates a significant resistance and common-mode inductance.

A second aspect is EMI (electromagnetic interference). There is a reason why ferrite-loaded mains cables do exist (industrial stuff from Eupen cable company). Such a cable, or at least lots of clamp-on ferrites on a regular cable, can improve the EMI situation big time. In an audio system this can reduce background noise. Clamp-on ferrites should generously be used on each and every cable in a system.

Do you have a specific product recommendation?

 

[NTK]

Do you have a specific product recommendation?

IF 13 | Schaffner Holding AG

High frequency attenuationShielding and ferrite cableEasy to integrate in any designRetrofit for any IEC C14 inletRated current up to 10AVarious powerline…

www.schaffner.com

[Edit] Note: The usual purpose of these cables is to prevent electromagnetic interferences that originate from the devices to leak back to the AC source or radiate to the outside (such as from a SMPS, to pass emissions tests), not the other way around (stopping the noise from getting in).

 

[solderdude]

Do you have a specific product recommendation?

And this is where it becomes difficult.

Clamp-on ferrites should be used close to the 'garbage emitting' end of the cable and or on the 'overly sensitive input' side of that device.

Furthermore there are a few different types of ferrites suited for specific frequency ranges. Just slapping one on a cable may not be enough.

Also the hole thickness of the ferrite must be tight around the cable.... that is if you are not looping the cable through the ferrite.

Looping the cable through a ferrite drastically improves its efficiency in lowering RF. About 4 loops is optimal.

So ... difficult to recommend something based on the science that is involved.

 

[JohnnyAudio]

In the case of VFD's and servos, the correct cables are essential to proper operation.
Shielded cables, shielded conductors, conductor twisting and proper connectors all play a carefully engineered role in making automation work correctly and to peak performance. I have worked with Rockwell Automation, Siemens and ABB as a power and motion engineer, cables are as important as drives (amplifiers) and motors (speakers).
Audio may not be as stringent and revealing as automation but since the components are similar, power and signal cabling may have positive and negative effects on the total system.

 

[RickS]

Earlier this week, this thread started to drift off-topic. If you are not posting about power cabling, move on or post on a appropriate thread.

Thanks for your consideration!

 

[antcollinet]

In the case of VFD's and servos, the correct cables are essential to proper operation.
Shielded cables, shielded conductors, conductor twisting and proper connectors all play a carefully engineered role in making automation work correctly and to peak performance. I have worked with Rockwell Automation, Siemens and ABB as a power and motion engineer, cables are as important as drives (amplifiers) and motors (speakers).
Audio may not be as stringent and revealing as automation but since the components are similar, power and signal cabling may have positive and negative effects on the total system.

Completely different beasts from audio amps.

Industrial VFD's are putting out high DV/DT Switched pulses going typically 650V or more p-p (on 460V supplies), with absolutely no output filtering. This creates a horrendous EMC environment **. Screened cables on the output are mandatory, and careful routing of all IO is needed as well as screening on such cables. Under EU regs, due to the EMC class, it is illegal to sell them for consumer installation. It is mandated that they are installed by "qualified" engineers.

Audio gear is nothing like this. Even class D amplifiers which (superficially) work in a similar way are
1 - switching much lower voltages (<10%)
2 - Have output filters that reduce that square wave at the output to (typically) a sine wave at <1V.

(Where did you work for Siemens?)


** I have tried holding onto the (well insulated and screened) output cable of a VFD with one hand, and by putting a finger of another hand near a button on a switch panel caused that button to activate without making any physical contact. We had to redesign that switch panel to make it less sensitive.

 

[KSTR]

Do you have a specific product recommendation?

For example, Wuerth WE-AFB LFS series model #7427727, alternating with WE-AFB series model #74270077. Those are for direct cable mounting, not clamp-on type (which are less effective and more expensive), so you have to remove the connector on one side of the cable.
These are high quality products and thus a bit costly but they are very effective... which often is not the case with any random far-east clamp-on ferrite you can buy on the usual platforms.
Together with Eupen ferrrite-loaded and shielded mains cable (e.g. Eupen GNLM 2.5, a bit hard to get, though) this as good as it ever gets, laboratory-grade EMC level.

WE-AFB LFS | Passive Components | Würth Elektronik Product Catalog

Low Frequency Specialist | Core Material MnZn | Frequency Range 300 kHz to 30 MHz | Ø Cable 4.55 to 9.7 mm | Order Samples Free of Charge & Request Quotes Online | High Quality | Fast Delivery

www.we-online.com

WE-AFB | Passive Components | Würth Elektronik Product Catalog

Multi-purpose Bead | Core Material NiZn | Frequency Range 1 MHz to 1 GHz | Ø Cable 3.3 to 17.4 mm | Order Samples Free of Charge & Request Quotes Online | High Quality | Fast Delivery

www.we-online.com

 

[JohnnyAudio]

Completely different beasts from audio amps.

Industrial VFD's are putting out high DV/DT Switched pulses going typically 650V or more p-p (on 460V supplies), with absolutely no output filtering. This creates a horrendous EMC environment **. Screened cables on the output are mandatory, and careful routing of all IO is needed as well as screening on such cables. Under EU regs, due to the EMC class, it is illegal to sell them for consumer installation. It is mandated that they are installed by "qualified" engineers.

Audio gear is nothing like this. Even class D amplifiers which (superficially) work in a similar way are
1 - switching much lower voltages (<10%)
2 - Have output filters that reduce that square wave at the output to (typically) a sine wave at <1V.

(Where did you work for Siemens?)


** I have tried holding onto the (well insulated and screened) output cable of a VFD with one hand, and by putting a finger of another hand near a button on a switch panel caused that button to activate without making any physical contact. We had to redesign that switch panel to make it less sensitive.

Agreed they are much different and perhaps motion/ drives are more fun. If you're in this industry, you've seen some pretty amazing stuff and a lot of noise surprises. I love big and tiny power systems. I worked on Siemens gear but I worked for RA, they are the big player in North America.
BTW, my favorite machines are giant rock crushers, it's like... what do you do when a big one gets stuck?

 

[Holmz]

How do those ferrites work?
Shouldn’t only a single wire goo through the ferrite?
It seems like a twisted pair going through it would not really have any effect from the ferrite.

 

[JohnnyAudio]

How do those ferrites work?
Shouldn’t only a single wire goo through the ferrite?
It seems like a twisted pair going through it would not really have any effect from the ferrite.

This what we do with motors...

https://literature.rockwellautomation.com/idc/groups/literature/documents/in/520-in012_-en-p.pdf

 

[Speedskater]

With a ferrite, both conductors need to go thru it. If there's space, more the one loop is better.
More than one ferrite is better. Placed very near the audio component.
If only one conductor goes thru the ferrite, it won't take much current to saturate the ferrite.
Ferrites are only effective on Radio Frequency interference, above say 100 kilohertz.

 

[wwenze]

If only one conductor goes thru the ferrite, then it becomes differential-mode. And we do that for DC power supply filtering.

For the clamp-on types that we put on signal cables or whatever cables, those are common-mode since it goes onto both conductors. They do nothing to differential signals since the net current in the loop is zero. And that's exactly what we want - We do not want to affect the original differential signal, but we want to impede common-mode noise.

*And the more observant might have realized that, if the return current does not go entirely through the ferrite, then it starts to act differential-mode. Food for thought when dealing with single-ended connections.

 

[Speedskater]

an AC power line common mode ferrite choke is one thing, a digital level filter is another thing.

Jim Brown, retired Audio Engineering Society, EMI/RFI committee co-chair has a paper with more ferrite choke info than most of us need.
A Ham's Guide to RFI, Ferrites, Baluns, and Audio Interfacing

http://www.audiosystemsgroup.com/RFI-Ham.pdf

 

[pablolie]

After browsing to the replies of this topic hoping maybe I could contribute... not for the first time in ASR history did I decide to just let it run its predictable course.