Why do AC cords make so much difference?

Because the AC cords and the AC power in general, is part of your power supply, and the power supply becomes part of the signal as it is modulated by the audio equipment to create the sound. It is the foundation electricity that the signal is created from, and if it is infected with crap, then that will become part of the signal.

I agree with Twl 100%. As such, power cords would NOT make a difference if the gear was built to a proper level to begin with. As i've mentioned before, the more susceptible to AC power cord changes your gear is, the more under-designed that it is. Sean
>

The better ones do a good job of filtering out common mode noise from electrical and magnetic fields and also filter noise from equipment (digital) to the outside. But not surprising, some of the cheaper ones can do as good of a job, if not better, than some of the more obscenely expensive ones.

...and I absolutely agree that the power supply design is everything, where a well shielded power cord compliments it rather than trying to wrestle it into submission.

Although I have not experimented with AC cords (for lack of time .. young daughter, and daipers being a key reason) my theory is that cords can make a difference for two reasons :

1) they can act as low pass filters. I believe that for digital components this can be important to prevent the digital component from polluting the power supply of your analogue components (preamp, amp etc). It also helps that the digital component doesn't receive noise.
2) They must allow free flow of potentially large amounts of current to the power amp.

I can quite understand why power cords might be good in different applications : a CD transport might benefit from a cord with tons of ferrite to prevent it from modulating noise back onto the power supply. This cord might strangle the dynamics of a power amp that requires large bursts of power.

Ultimately I agree with Sean that if a power supply is built correctly the device should have enough reserve current and should not be either susceptible to incoming noise, nor radiating its own noise back onto the power supply.

Interesting theories ... I hope that potty training will soon give me some more time to experiment.

I've come to believe that the quality of dielectric used can have a bearing on performance, in addition to shielding and current capacity. Hence I'm a fan of well-shielded all-Teflon designs. Write me for details if you wish. Cheers.

Cables are mysterious ~! But I think I am getting close to figuring it out. There is a great deal more to why power cords effect the sound of a component than simply "cleaning" the power or filtering out all the bad stuff.

Applying power to a conductor causes the conductor to resonate. The resonant frequency of the conductor establishes a base line for the cables sonic signature. But this is only the beginning.

As I understand it (I am not an EE) with 60Hz power there are 120 pulses per second. A pulse is the time when power can flow through the power supply transformer - when the rectified secondary voltage is higher than the stored voltage in the filter capacitor.

During the pulse, a heavy magnetic field is created and collapsed quickly within the power cord. Conductive material within reach of the magnetic field will dissipate energy through circulating currents, however some materials will attempt to store some of the magnetic field energy until the next pulse (or dissipate it as heat).

By adding material to a power cord one can change the resonant frequency of the wire, dielectric properties, and the pulse itself.

For example Taking a 10' long twisted pair of copper wire and applying more force - to twist it down to 6' in length will change the resonant frequency of the wire. Shielding that wire with tight braided copper, sticking that wire inside a tube & then filling with iron powder, fiberglass, sand, crushed aluminum, sawdust, crystals, or whatever, will again change the resonant frequency, dielectric properties and the pulse.

Each combination of materials will react differently to the magnetic field created by the pulse and presto... you have a new sonic signature in your system.

hmmm, thanks bwhite, that sort of makes sense to me.

so far though, swapping PCs in my system hasn't made much difference. other cables, both interconnects and speaker cables, i hear marked differences. but not PCs.

The filtering aspects would suggest a shielded cable. I can easily hear differences with unshielded cords, so there must be other factors. If you are comparing to a cheesy 18 gauge OEM cord there is a real difference. Perhaps it is the lower inductance, dielectrics, and wire size factors in high-end cords that make them sound better.

Has anyone here measured the capacitance between primary and secondary of a toroid transformer as opposed to an EI core? You will find about ten times as much capacitance with the toroid compared to a twin bobbin EI core which allows a sneak path for all sorts of RF nasties....Some IBM folks presented a study a few years ago to the IEEE of noise on power lines in major metropolitan areas and found huge spikes at 5mhz and 50mhz rather than the 27Mhz citizen's band they were expecting....With the profusion of toroid transformers, most of them center tapped to save on diodes, the noise is put right back into the neutral through the ground.......The vehicle I use to deal with RF noise is high capacitance and low self-inductance.....

Bob: Would your post above be one reason, or perhaps the main one, why many cords sound their best with the ground disabled?

Hdm, I wouldn't know as have not had a ground in over twenty years....The ground in my house only extends as far as kitchen, baths and laundry....

The info that Mr Crump presented about iron core transformers vs toroidals is pretty well known to anyone that has ever measured various aspects of transformer performance. Bob and i are basically on the same page in this regard and on several other AC related "beliefs". As such, you now know several of the reasons why i have preached the superiority of "old school" Iron Core ( E-I ) transformers in the past. They are quieter ( blacker background ) due to increased AC filtration and they ( typically ) offer better dynamics / bass performance due to reduced core saturation. I don't know anyone that doesn't want equipment with a lower noise floor and increased dynamic range.

I mentioned something similar to what Bob brought up earlier today prior to seeing these comments. You can follow along on the thread entitled Best Cable Tweak Ever. I'm trying to find a source on the web to support some of the info that i posted and as soon as i can, i'll forward a link to it in that thread or cut and past the info that i find. Sean

Here is my explanation - and the theory behind my cable designs:

Amplifiers demand current from the power-line when the capacitors in their power-supplies become momentarily discharged due to high-current transients in the music signal. This discharge condition must be quickly recharged from the power-line, through the power-supply transformer, or a voltage sag will occur. Such voltage sags can cause audible distortion at the loudspeakers. If the power-line has significant series inductance in the path from the power panel to the amplifier, this can prevent the capacitor bank from recharging in time to prevent a voltage sag from occurring at the amplifier output transistors. With a low-inductance cable, the voltage drop across the cable will be insignificant during high-current transients, minimizing the voltage sag. This allows all of the current needed by the output transistors to be supplied when they need it, resulting in fast, dynamic response to transient signals.

A typical 6-foot 14 AWG rubber cord and 25 feet of ROMEX has inductance of 7.2 uH and resistance of 235 mohms, ignoring the plug resistance effect. Therefore, the voltage drop at 20kHz will be I*(wL+R)= I*(.905+.235) = I*(1.14). With a 6-foot Magnum2 (my older cord) and 25 feet of ROMEX, the inductance is 5.9 uH and the total resistance is 147 mohms. This is an 18% reduction in inductance and a 37% reduction in resistance. The voltage drop for this combination will be I(wL+R) = I(.741+.147) = I(.888). So at a fixed dynamic current I, the voltage drop in the entire power feed at 20kHz is 22% smaller with a Magnum2 power cord. I would consider 22% to be significant. The reality is even more compelling. When you add in lower plug and receptacle resistance and the fact that the di/dt on the power cord will have spectra well above 20kHz with some amplifiers, the low-inductance cord makes an even bigger difference.

Thanks, Audioengr. Can anyone add to BWhite's initial comments on a parallel thread re resonance-damping?... i.e.,
use of fillers to isolate/absorb/quench electro-mechanical stuff (60 or 120Hz?...higher?) thought to be functional here.
Furutech yells about non-magnetic materials, and even grounds the steel clamp-screws in their IEC, while a cable manufacturer or two fills their stuff with steel grit or even magnets (!), and obviously totally opposite approach!
I'm experimenting with high-density NON-ferrous dampers as a moderate-cost methodology to address these purported nasties. Could I be just creating a low-pass filter rather than further cleaning up the noise-floor?? Thanks for the input. Ern

Depends on the dampers and their position with respect to the conductors. In general, adding parallel (shunt) capacitance is not a problem, but adding series inductance is. If you had an LCR meter this would tell you whether you are degrading it or not. As long as the fillers are non-ferrous you can be relatively sure they will not increase inductance.

I'm going to start marketing some power cords very soon and decided to share the design here with you folks.

First of all, you start off with heavy ( 8, 10 or 12 gauge ) bare copper wire. You then take all three conductors and twist them together as tightly as possible. Select one wire as the hot, one as the neutral and one as the ground and wire them into the AC plug and IEC jack accordingly. I will GUARANTEE that this design will allow a greater amount of current flow in less amount of time than any commercially available UL approved design on the market. The initial amount of energy that is drawn upon first use of this cord will amaze you. I guarantee that the results will be so drastic that you would swear it was like the first "bang" for those of you that believe in the "BIG bang" theory. On top of that, you will not believe just how quiet your system is and how much the noise floor has been lowered. You would swear that your equipment was not even turned on it is so quiet. Your "black background" will be SO black that it resembles charcoal. I GUARANTEE IT !!! Sean
>

PS... The above is all a hoax. Do not follow these directions unless you want to burn down your house : )

Audioengr,
I love your calculations and I think your intentions are good, but unfortunately -

1) Capacitor banks in power supplies are designed to handle transients at peak power levels. At normal listening levels only a fraction of that capacity is used. I agree that peak transients at full volume might distort due to voltage sag on the power rails, but I would be more worried about hearing loss than distortion in this case.

2) The AC power in the U.S is 60HZ, not 20KHz. (Duh...) If you are worried about a 20KHz component getting into the signal path through the power cord, then you would want a power cord with higher capacitance to filter it out. Any amplifier that doesn't have adequate bypass and isolation in the power supply shouldn't be in your system in the first place... so any power cord that results in an audible improvement would be a band-aid rather than a fix to the root cause of the problem.

To be fair, I should say that there are probably homes out there with enormous amounts of noise on the AC power. While replacing the power cords to all of your equipment could conceivably make a difference, the proper remedy would be to install a power filter/conditioner.

I'm another guy thinking the cords act as a band pass filter. A couple of years ago i read an article about using home electric wiring as the house computer network as well. The network signal was designed to operate at a higher frequency outside of the "noise band" on the power cable. high end power cords are likely to act the same way. THe question i have, however, is once you get rid of the crap on the power signal and you are setting with a pure 110 ac current why should there be a tonal effect. Bwhite has some interesting thoughts but i would think that the magnetic field of a large power transformer would overwhelm the effect of a magnetic field in the power chord. the lower inductance arguement stands up well for amps but for a low draw component like a cd player?? On the positive side the mystery gives the ole brain something to feed on

Piezo: Your comments about low inductance to Audioengr are something that i've tried to stress to him in other posts. It is not so much the low inductance than can be helpful in low current demands as it can be the added capacitance that many such designs bring with them. If someone doubts the effectiveness of added capacitance, try sticking an AC rated cap into an outlet and measure / view the differences in the power provided at that outlet.

Redbeard brings up added capacitance in his post ( rightly so ) and also touches on the lack of filtering in components making the differences in power cords being noticeable. I agree with him whole-heartedly in this respect and am glad to see that someone else shares this view. Most products are NOT properly filtered, regardless of price paid or brand name "prestige", and that is why one can hear the differences with various AC delivery systems. The only problem with Redbeard's suggestion to install a power line filter / conditioner to remedy such problems is that they too are mostly under-engineered and end up being a "band-aid" rather than a "cure-all". As such, poorly designed filter based products can bring with them almost as many side effects / problems that they try to solve. Sean
>

Redbeard - I suggest you measure the current in your power cords. I suspect that you will find spectral components higher than 20 kHz. Current, not Voltage ...Duh. Unless you have an expensive power supply that is designed properly in your component, this will always be the case.

Also, I recommend strongly against filtering, except on the ground lead to eliminate ground-loop currents.

I do not buy the capacitance argument. My cords add only a few hundred pF of capacitance, yet they are 10X lower inductance than the ROMEX in the wall. Until you have heard a really low inductance cord for yourself, you cannot know what the improvements are.

It's too bad that so many things in life have to be "protected" as intellectual properties. Otherwise, some real progress in technology / science / medicine / etc... might really be made by those with common goals yet different ideas and experiences. Sean
>

Sean,

If you are right about the power filter/conditioners that are currently available then this would be a great opportunity for an enterprising entrepreneur to come up with an audiophile grade filter and make a killing in the market.

I think the reason this hasn't happened yet is that it is easier to come up with a fancy, whiz-bang AC cable than it is to do some basic engineering on a power filter.

Redbeard: The parts to make a "real" AC filter are all commonly available. One need not even buy parts as you can buy commercial grade units that will work phenomenally well. Just make sure that you have a freight truck to transport them, a dolly to wheel them in on, the physical room to mount them and an electrician to wire them into the system. Obviously, what i'm getting at is something that will "work right" is NOT a "lightweight toy".

The reason that most audio based manufacturers make cables and "audio grade" PLC's is that the profit margin is WAY, WAY high. This is not to mention that one can build, package and ship a "Super Duper AC Snake" for peanuts as compared to what it would cost for the chassis alone of the type of device that i'm talking about. If you were in business strictly for the money, what route would you take ???

As such, P.T. Barnum was right. Most of the people that he's refering to are audiophiles and they are investing in wires / cables rather than forcing the companies that build their active equipment to do it right. On top of that, when the "snake oil" wires, cables or PLC's don't live up to the hype, they disregard everything else in the same category. After such an experience, many folks will even "black-ball" products with real research and technology invested in them and remove the mass majority from their systems. Either that or they keep throwing good money after bad trying to find something that truly is "magical".

It's too bad that many folks that are truly seeking to upgrade their system end up resorting to buying such products based on industry hype rather than educating themselves and finding the "real deal". Sean
>

I believe Sean is fundamentally correct in significant parts of what he is saying. Good recording studios routinely use large transformers, shielded low inductance in-wall wiring, dedicated circuits, and extremely low noise grounding systems for house current. It's not cheap to do, but it makes more sense than buying equally expensive audiophile line conditioners that are basically inadequate to do the a/c cleanup.

On cables, the jury might still be out. Perhaps it's just tone controls interacting with poor component design, but it would be nice to have a consistent understanding of why sound changes so much with cable design.

Back to the "floating ground" issue. I was told by a supposed cable guru that one shouldn't "float" the ground on digital gear, because digital gear uses the ground to shunt the digital garbage, "grunge", "error bits", or whatever you want to call it, away from your system. Therefore, I was told, using the "cheater" plug to defeat the ground eliminates the route of escape for this unwanted byproduct of the digital gear allowing it to enter the other components in the system.

Any thoughts out there from the experts?

Baloney - there is no requirement for an earth ground. There is no "shunting" of noise necessary unless the power supply is letting power line HF noise through - this is unlikely. My transport has no earth ground and it is superb.

Digital is NOT an audio signal at it's point of origin or when being transferred in digital form. It is an RF based signal that operates above 3 MHz. As such, a design that makes use of some type of bandpass, high pass or low pass filtering or has bypass caps in the design may require a low resistance Earth ground for optimum operation. The reason that a designer would shunt such signals to ground would be to try to keep stray signals from "leaking out" or interfering with other sections of the player. While the device would still "work" without having a low resistance path to ground, it might not be performing up to snuff or meet spectral purity as documented by the FCC in terms of spurious emmissions / interference. As such, not all designs are the same when it comes to grounding, nor should they be treated as such. Sean
>

Great post, Sean. Thanks.

I am sure that others will offer reasons that I will not have covered, but these are very good starters.

1. The original cable you were using prior to the switch was very poorly constructed and/or of a very high gauge wire for power supply use.

2. You have some form of electrical interference and the better shielding is helping with the problem.

3. There may be a problem with the way the power supply was designed in the equipment you are switching power cables with.

4. You are convinced that a difference will take place and therefore it does.

Let me know if these heip.