Jneutron, stock power cords and ground problems?

[Tony_Montana]

Hi John

John, any time issue of power cords comes up and if we get any benefits by changing stock cords on audio components, you always bring up the reference ground and loop issue problem.

You said that Most, if not all, of the power cords made do not worry about that [loop issue]...just current delivery to the equipment. Could you explain that issue in more detail as regard to PCs?
You also gave an example such as when we hear a thump in powered subwoofer when something electrical turns on or off. I also have this problem:when turning off my fluorescent light, I always get a loud thump from the Sub.

So my question is how do we address ground problem associated with AUDIO (not industrial equipment), by changing of power cord-such as Sub thumping when something is turned off (what causes this anyway)?
I still don't see the relation between stock power cords and ground problem, and how changing power cord can address that issue.

And please don't draw any more diagrams. The last one you drew, didn't make any sense

Also bringing up this link as you discussed this problem in detail:
http://www.audioasylum.com/audio/cab...ges/94314.html

[Beckman]

Hi John

John, any time issue of power cords comes up and if we get any benefits by changing stock cords on audio components, you always bring up the reference ground and loop issue problem.

You said that Most, if not all, of the power cords made do not worry about that [loop issue]...just current delivery to the equipment. Could you explain that issue in more detail as regard to PCs?
You also gave an example such as when we hear a thump in powered subwoofer when something electrical turns on or off. I also have this problem:when turning off my fluorescent light, I always get a loud thump from the Sub.

So my question is how do we address ground problem associated with AUDIO (not industrial equipment), by changing of power cord-such as Sub thumping when something is turned off (what causes this anyway)?
I still don't see the relation between stock power cords and ground problem, and how changing power cord can address that issue.

And please don't draw any more diagrams. The last one you drew, didn't make any sense

Also bringing up this link as you discussed this problem in detail:
http://www.audioasylum.com/audio/cab...ges/94314.html

Here is a link that explains ground loop problems:
http://www.epanorama.net/documents/g...oop/index.html

Here is a link that gives causes of ground loop problems:
http://www.epanorama.net/documents/g...e_systems.html

You should be able to solve your ground loop problems with this info.

[Tony_Montana]

Thanks Beckman for the links. There are alot of good information in there.

I did read the main article and couple of links, but still did not find any information specific to power cords, and how upgrading from stock power cord (on existing audio components on the market) to a better power cord can reduce ground loop problems.

John always claims that stock power cord on audio equipments can cause ground problems, and should be upgraded to a better PC. I was wondering what type of improvements can be done [specifically] to stock power cords-so it will be less of a problem with ground loops.

Back to the reading

[jneutron]

I did read the main article and couple of links, but still did not find any information specific to power cords, and how upgrading from stock power cord (on existing audio components on the market) to a better power cord can reduce ground loop problems.

I also find little regarding the issue..That is because most people do not understand the underlying physics.

John always claims that stock power cord on audio equipments can cause ground problems, and should be upgraded to a better PC. I was wondering what type of improvements can be done [specifically] to stock power cords-so it will be less of a problem with ground loops.

No, you are incorrect...I have never claimed that stock power cords cause grounding problems, or that upgrading to a better PC will address the ground loop issue..because, from what I've seen, there are no power cord manufacturers who understand the problem enough to attempt to address it in an engineering fashion..

What I have stated, is that the geometry of the power cord conductors can change the amount of coupling the ground loop will have to external influences..as well as that loop's susceptibility to the haversine currents within the cord itself.

Your light example..it is, what, 40 watts? That disconnects what, half an ampere plus any stored energy. A 100 watt incandescent turns on at about 8 times draw, figure 8 amps spike...a motor turns on with locked rotor current of from say 4 to 8 times nominal, figure 15 to maybe 30 amps spike...My AC motor really got my sub.. Now, if you have low eff speakers and some monster amps, it's current peaks will be in that range or higher..Why in the world would anyone assume that the large spikes in a power amp line cord do not couple to the ground loop formed by that power cord??? Worse yet, the spikes only occur when the amp is drawing power, so the output of the amp will tend to hide the problem.

To try to use PC's in a random gesture to solve ground problems is, just, random, and isn't really a good method..

The problem is...it's a loop..get rid of it, or minimize it..

See...no pictures..but, it would have been clearer if I had drawn some....trust me...:-)

Cheers, John

[skeptic]

Before you experiment with eliminating ground loops, here are a few things you should know.

The National Electrical Code and Underwriter's Laboratory exist to protect everyone's life and property. Your home, whether you own or rent was designed to meet the provisions of the National Electrical Code by someone recognized by your state as an expert who stamped the design drawings and specifications with a seal, it was built by a licensed electrical contrator, and it was inspected and approved by your town's electrical inspector. The National Electrical Code is part of the National Fire Code which is supported by and written for the insurance industry. It is periodically updated usually every three years although older homes are usually grandfathered so that they don't have to be brought up to the latest provisions of the code. Most jurisdictions in the United States adopt the code as law but in places like New York City which don't, they have their own electrical code which is even stricter. The codes change as the result of the tragedies which occurred to people who complied with the provisions of the previous code and were hurt or killed anyway. While the code is open to interpretation of its nuances by experts, for the layman it is the law. It is unconcerned with whether or not electrical power systems are efficient, somewhat indifferent as to whether they function at all, and totally preoccupied with safety. The single largest chapter in NEC is article 250 dealing with grounding. BTW, the first thing the code tells you is that it is not a manual or specification for untrained people.

Underwriter's Laboratory is concerned with the equipment you plug into the electrical outlet. Their seal tells you that if you follow the manufacturer's instructions, you can operate his equipment with a good degree of confidence that it will perform its function safely.

Both NEC and UL do not absolve anyone from operating damaged or defective equipment. Obviously, a frayed power cord or a loose electrical connection in a wall outlet or circuit breaker panel needs to be repaired.

If you have a ground loop problem, before you do anything, consider this. Any modifications to your equipment or to the electrical wiring of you home whether performed by you or directed by you, you take at your own risk. If your modifications result in damage, injury or death, your insurance company will not cover you if they find out and you may be liable for civil and even criminal penalties as a result. This can include installing unapproved power cord assemblies or making you own. I strongly urge you not to try in any way to change or defeat the safety provisions incorporated in your home or equipment, especially the grounding provisions.

If you have a ground loop problem, look to solve it by changing the signal wiring, antenna or cable feed, or if it is connected to a computer, the internet line feed to the computer. The NEC calls these power limited circuits under 50 volts and treats them as inherently much less dangerous than the power circuits you plug your equipment into.

BTW, most of the electrical problems I have encountered were not related to grounding problems and sometimes the illegal and bizzare schemes proposed and even demanaded by so called experts created far more problems than they solved.

[jneutron]

I personally do not recommend disconnecting grounds..

I only recommend understanding and identifying the loops and sources, then working to either eliminate them, or compensate for them.

A good example I had was a phono input thingy..I put two turntables into a really small coffin, added a pair of RS preamps to the box, and some analog stuff to make it useful for DJ'ing. Inside the middle of the coffin, was the preamp ac cords, my mixer ac cord, and a small extension cord..(didn't say it was safe, but I made it in '78, before I learned much)

Hummed like an SOB...because the phono runs were in close proximity to ac runs and xfmrs. (close proximity is defined as a wadded up mass of wires stuffed into too small a box). But I used the ground wire, so what was going on???

I learned that I had to wrap the ground wire tightly around the phono cable pair of each turntable independently. By doing that, I eliminated the loop that was between the phono in-shields and the ground wire. Once I did that, nothing I did to the wire arrangement caused hum...not xfmrs, not wires...nuttin.. It also eliminated the huge sensitivity the thing had to light switches in the room.

Cheers, John

[skeptic]

Wrapping the ground wire around the power cord provides some shielding from capacitive and inductive coupling between the power cord conductors and the signal cable. However, there is a minor problem here. If the ground wire is too tighly wound, it compromises the ampacity rating of the power cord by restricting the flow of air. The rating of the power cord is in free air. I saw this problem on a massive scale about 10 years ago at a pharmaceutical company I visited. They had a magnetic field problem in an office area directly above a transformer vault which was actually a couple of substations with a 4000 amp bus duct connecting them. They tried to solve the problem by installing a magnetic shield completely around the bus duct. It wasn't entirely effective but the ampacity rating of the bus duct was completely compromised. For the engineer who was so proud of it, it was an OH $**+ day. On the other hand, you can shield the signal cable to your heart's content. I shield mine by using a single strand of bare copper wire along the entire length and wrapping the whole thing in aluminium foil. It seems to work pretty well for me.

An incandescent light is a purely resistive load. There should be no noise in your house electrical system or rf noise when you operate it or switch it unless you have a light dimmer in the circuit. Light dimmers are electrical trouble for audio systems big time. The noise they impose on the electrical system in your house is terrible and often shows up in audio systems as a buzzing. If switching an incandescent light in your house causes a popping noise in your sound system, you should consider the possibility that the switch contacts are carbonized and the switch should be replaced. Mercury switches should never have this problem. Compressors in refrigerators and air conditions do pull locked rotor current on startup and can generate an arc on shutoff. The arc comes because the current cannot change instantaneously in an inductor and the voltage across the switch will increase to whatever is necessary to maintain it and is often sufficient to arc. Switches for compressors are designed for this with platinum contacts so they have a long but not indefinite life. This can pull the voltage down thoughout your entire house and cause a thump in your sound system. The solution is an effective power conditioner or even a UPS.

It is permissible to install a redundant grounding system such as a single point reference or quiet ground in addition to the safety ground in your house. The two MUST be tied together at one point. This is sometimes done in industrial installations for data and telecommunications networks, data centers, and telephone switches. It would be extreme in a home audio system but it is legal. It isn't particularly pretty.

[jneutron]

Wrapping the ground wire around the power cord provides some shielding from capacitive and inductive coupling between the power cord conductors and the signal cable. However, there is a minor problem here. If the ground wire is too tighly wound, it compromises the ampacity rating of the power cord by restricting the flow of air. The rating of the power cord is in free air.

Wrapping a non dissipating wire around the PC won't decrease it's ampacity in any measureable way..you're example is extreme.. It does point out that if anyone chooses to use one of those cord snake thingy's to dress up the wires, that is a factor to consider. I had that problem back in '81, where I had one of those zippertube covers melt in a diode burnin rack.

An incandescent light is a purely resistive load. There should be no noise in your house electrical system or rf noise when you operate it or switch it unless you have a light dimmer in the circuit.

I've seen it..well, heard it....don't forget, incancescents still have inrush current about 8 times the hot current.

Compressors in refrigerators and air conditions do pull locked rotor current on startup and can generate an arc on shutoff. The arc comes because the current cannot change instantaneously in an inductor and the voltage across the switch will increase to whatever is necessary to maintain it and is often sufficient to arc. Switches for compressors are designed for this with platinum contacts so they have a long but not indefinite life. This can pull the voltage down thoughout your entire house and cause a thump in your sound system. The solution is an effective power conditioner or even a UPS.

The thump I encountered was during turn on..but, never one at turnoff..go figure..
The power conditioner or ups has to be near the load, otherwise it will still be able to broadcast to a ground loop. It will also work well if the pop is going to the distri panel.

Cheers, John

[skeptic]

"The thump I encountered was during turn on..but, never one at turnoff.."

This is common. The inrush current pulls the entire local distribution system voltage way way down. The thump probably occurs on recovery as the return of normal voltage to the transformer causes it to have inrush current and overshoot on the secondary. This is usually surpressed on turn-on especially in audio power amplifiers which delay their output for a second or two until the amplifier power supply statalizes or have a soft start but not on transients. If you have a dual trace storage scope, you can check by having the comressor turn on pulse trigger the scope and then see when the audio thump occurs.

On turnoff, the arc generates rf but it is usually too far away and too well shielded to be a problem for audio equipment.

[Tony_Montana]

Thanks guys for info.

What I have stated, is that the geometry of the power cord conductors can change the amount of coupling the ground loop will have to external influences..as well as that loop's susceptibility to the haversine currents within the cord itself.

Could you please explain that in more detail? What type of geometry would be ideal to combat problems you mentioned.

Why in the world would anyone assume that the large spikes in a power amp line cord do not couple to the ground loop formed by that power cord??? Jn

And how do we reduced that problem with power cord design?

And the final question is beside the [ground] problems you mentioned with stock power cord, would we get any benefits by upgrading to better PC. Jon mentioned that shielded PC cord might be better [than non shielded pc] due to the fact that it will lessen contamination of nearby audio cables. I agree with that statement since IC, and speaker cables (to lesser degree) can be effected by nearby PC cords.

See...no pictures..but, it would have been clearer if I had drawn some....trust me...:-) Jn

May be if you use some type of software such as Pspice to draw the picture-rather than by hand-would probably make more sense

Compressors in refrigerators and air conditions do pull locked rotor current on startup and can generate an arc on shutoff. The arc comes because the current cannot change instantaneously in an inductor and the voltage across the switch will increase to whatever is necessary to maintain it and is often sufficient to arc.

So would you say that the Arc is causing my sub to pop when I turn off the fluorescent light? They are on the same plug.

[jneutron]

May be if you use some type of software such as Pspice to draw the picture-rather than by hand-would probably make more sense

It is five here..I'm off..

I will go to the bar with my girlfriend..I will get a bar napkin...I will draw on it, and scan it at work tomorrow..

Hey, if it's good enough for Compac...it's good enough for you..

I told the chief engineer at a rather large company that I would hold off a few days, allowing him to either confirm or deny that he wishes to collaborate on this issue. If he does not respond in a few more days, I'll post what I have hypo'd about regarding methods of compensating for this via pc's and amp topologies.

Cheers, John