Why an AC Power Cord cannot make a difference

[pma]

Time after time we can hear or read that a change of amplifier power cord made a difference in perceived music signal spectrum, like more bass, cleaner middle frequencies etc. Please let me show that it is technically impossible. I made measurements of class AB amplifier input mains spectrum, transformer secondary voltage spectrum, DC power supply rails spectrum, amplifier output noise spectrum and finally the measuring system error noise spectrum. Everything measured in the same safe configuration with full scale range of 615Vac.

Please note that spectrum at secondary winding of the mains transformer (no. 5 trace) has noticeably higher amplitudes above 4kHz than the 230V input mains spectrum! This is due to mess produced by diode bridge rectifiers in the traditional DC power supply, diodes + capacitor bank.
If there is any small change of mains spectrum as a result of line filter or power cord change, it happens at high frequencies and is totally overlapped by amplifier self-induced EMI voltages. The power amplifier is a generator of its own interferences unaffected by power cord exchange.
Note: please note how amplifier output power (here 100Hz signal 100W, dashed line no.2) affects DC rails spectrum.

 

[Blumlein 88]

This grounding box with magic dirt inside proves you are WRONG!

Your own signature line:
oversimplification always leads to false conclusions

 

[Keith_W]

Whenever I meet a person who says that power cords make a difference, I just smile at them and walk away. These people are the same as religious fundamentalists, conspiracy theorists, UFO believers, etc. If they have given up rational thinking and evidence, they will not be persuaded by rational thought and evidence.

 

[DonH56]

Power cords make a difference in the sound when they are (far) too small to support the load, are broken (e.g. bad ground), or the component is poorly designed (usually sensitive to the safety ground). A shielded power cable can reduce coupling into adjacent cables, and if capacitive enough might filter some RFI from getting inside the component (which also means a poor component design if it is that sensitive to RFI). In the vast majority of cases it is nothing but a marketeer's dream.

One point that gets lost again and again is the last point Pavel @pma made: "linear" power supplies have rectifiers that switch nonlinearly and generate large noise spikes. These spikes occur at the power line frequency (or twice depending upon rectifier configuration) and have broadband harmonics often well past the audio band. Linear supplies also have transformers that couple noise and can saturate, spewing more noise. A SMPS (switch-mode power supply), while often having higher-amplitude spikes, creates those spikes starting at frequencies a decade or more above the audio band where they do no (or much less) harm.

As @pma shows, any competent power supply filters power line noise by 60~100 dB or more, and circuits themselves have similar power-supply rejection ratio (PSRR), meaning power-line noise is typically suppressed to well (100~140+ dB) below the signal.

 

[pma]

Power cords make a difference in the sound when they are (far) too small to support the load, are broken (e.g. bad ground), or the component is poorly designed (usually sensitive to the safety ground).

Yes, but I am not speaking about broken cables or heavily undersized cables. I am speaking about cables with proper cross section area and clean plugs. Comparing "standard" power cords priced at several $ compared to power cords like Oyiade, Mogami etc. priced at several hundreds $ and I am saying there is no difference in amp parameters after exchanging a standard cord for an expensive one.

 

[rank]

Whenever I meet a person who says that power cords make a difference, I just smile at them and walk away. These people are the same as religious fundamentalists, conspiracy theorists, UFO believers, etc. If they have given up rational thinking and evidence, they will not be persuaded by rational thought and evidence.

Examples needed.

 

[Keith_W]

Examples needed.

Examples of what?

 

[DonH56]

Yes, but I am not speaking about broken cables or heavily undersized cables. I am speaking about cables with proper cross section area and clean plugs. Comparing "standard" power cords priced at several $ compared to power cords like Oyiade, Mogami etc. priced at several hundreds $ and I am saying there is no difference in amp parameters after exchanging a standard cord for an expensive one.

Understood, just stating when I have seen a power cable problem, nothing to do with your post. Anticipating the rash of subjective responses.

 

[DonH56]

Examples needed.

If you want examples of people saying power, interconnect (analog or digital), speaker, etc. cables can have night and day differences with what appear to be insignificant material changes check out some other audio forums. There are reasons some cables might sound different, but when it gets to things like audible differences between 0.9999 and 0.999999 silver cables I'm out. Or things like silk is better than cotton is better than Teflon dielectric and so forth.

 

[Timcognito]

Amazon.com

These are nice; tested for EMI, RFI, Certified for use in surgical suites and catheterization labs under IEC 60601. $9

 

[Salt]

Another MMF aspect: using a Stromtank makes all power cords sound the same
Thanks @pma for the elaboration, highly appreciated.

 

[AaronJ]

Amazon.com

These are nice; tested for EMI, RFI, Certified for use in surgical suites and catheterization labs under IEC 60601. $9

These idiots even charge more for the shorter cable!

 

[BrooklynNick]

Whenever I meet a person who says that power cords make a difference, I just smile at them and walk away. These people are the same as religious fundamentalists, conspiracy theorists, UFO believers, etc. If they have given up rational thinking and evidence, they will not be persuaded by rational thought and evidence.

Dozens of companies sell audiophile power cords and make claims for how they improve sound. Often these claims use fake science that is carefully written to sound plausible to a layperson. Review sites, Youtube videos, as well as print magazines like Stereophile, which many people trust, also claim power cords make a significant difference. Audiophile forums are bursting at the seams with all sorts of claims for how essential expensive cables are. The manufactures, the dealers, the reviewers, the "experts," and countless posters in forums all say that high end power cables make a difference in sound.

When everyone you trust is spreading misinformation or outright lies, it is only human to believe it. I think blaming the average person for getting suckered by the highend cable conspiracy is really arrogant. What is more remarkable is how many people have come to understand that it is all BS.

 

[Timcognito]

When everyone you trust is spreading misinformation or outright lies, it is only human to believe it. I think blaming the average person for getting suckered by the highend cable conspiracy is really arrogant. What is more remarkable is how many people have come to understand that it is all BS.

Without naming names, or taking sides, the same could be said of politics. Since the dawn of the internet propaganda has flourished and spread like wirefire.

 

[BrooklynNick]

These idiots even charge more for the shorter cable!

I have no idea why they want $4 more for the shorter cable, but hospital grade power cables are a real thing. They need to be rugged, properly grounded, and not cause RF interference in medical equipment. Look up UL 60601. Certification costs money. The real thing to learn from them is how inexpensive they are compared to so-called "audiophile grade" power cords which have no certification at all!

 

[Timcognito]

I have no idea why they want $4 more for the shorter cable

Because they are more desirable and rarer in the shorter lengths. So many of these things exist and a new one comes with every piece of medical hardware. They are long so they can be used in variety of settings. They are universal so they are rarely scrapped. Home use is shorter.
Edit: the ends are molded on for strength so its difficult to neatly shorten.

 

[rank]

These people are the same as religious fundamentalists, conspiracy theorists, UFO believers, etc.

Political, so forbidden here and rather unclear

 

[Salt]

Amazon.com

These are nice; tested for EMI, RFI, Certified for use in surgical suites and catheterization labs under IEC 60601. $9

Of course they deliver transparency to sound seeing these connectors...

 

[Timcognito]

Of course they deliver transparency to sound seeing these connectors...

Well they are poor antennas so no bad stuff gets in or good stuff out

 

[PHP]

Dozens of companies sell audiophile power cords and make claims for how they improve sound. Often these claims use fake science that is carefully written to sound plausible to a layperson. Review sites, Youtube videos, as well as print magazines like Stereophile, which many people trust, also claim power cords make a significant difference. Audiophile forums are bursting at the seams with all sorts of claims for how essential expensive cables are. The manufactures, the dealers, the reviewers, the "experts," and countless posters in forums all say that high end power cables make a difference in sound.

When everyone you trust is spreading misinformation or outright lies, it is only human to believe it. I think blaming the average person for getting suckered by the highend cable conspiracy is really arrogant. What is more remarkable is how many people have come to understand that it is all BS.

I agree that a lot of power cords are not efficient because they do not work to cure the pb of EMI and RFI activated by the power cord itself. I work with many manufacturers of audio gears (very famous) that do not believe in power cords. I made some demonstrations with on of them, may be the most reluctant about PC action. After a long explication why PC could not work (He is Engineer in electronic and designer of probably the best amplifiers), I (engineer too but mainly in acoustic and mechanical vibrations, formerly professor in a University) made a test : blind listening with standard power cord of his famous amplifier and then with a highly regarded power cord that ASR say he could not work. All the people in the room said the second listening was vastly better! collective hallucination? electric compensation of ...? In fact I know why it's better and yes I agree 90% of PC change the sound but not improve it, but some do. I also made tests (blind) with audiophiles and same result. I conducted finally the same test with skilled musicians, same result. Some PC improve music playback and not only change it for a different taste.
The conclusion: as a scientist I always try to find why and how a phenomenon occurs.
This is the same subject that power conditioners. 95% do not work well because they wrongly "depurate" 230V. 230V should be perfect sine wave with no deviation with no harmonics... even if some electronic power supply make a very good job to filter AC at the input and they store energy. Only hearing transformers "singing" without music because there is some DC or too much pollution in AC that the power supply could not treat enough. This time too, proof is in the listening.
Scientist approach is mandatory but it should be well done and not conclude to wrong judgments due to inappropriate measurements (I spent 10 years making measurements).