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In Reply to: RE: I lifted my grounds, reached new heights of "Audio Nirvana" and then......... posted by Awe-d-o-file on August 23, 2008 at 00:28:17
Do a search in the archives under my name and posts with the word "ground". There is a very minimal safety risk involved, so be sure to read my posts completely to understand what the risk is. Then you can make up your own mind about lifting all the grounds from your system.
Me -- I will never listen to a grounded system again.
Bummer about your amp -- sounds like an under-specified part or something. Three times in a row is too much. That's not what CJ normally does. If you read the forums, there are virtually no complaints about their gear. Good luck getting a permanent fix.
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appliances, hand power tools, etc. to use a two-prong power cord, there may well be a cost issue involved, but there may also be other considerations. From what little I know of the subject (mainly observation) these devices often use a non-metallic (nylon, plastic, etc.) case as part of the 'double insulation' process, so perhaps increased RFI would be a potential drawback for audio playback electronics. Though I suppose a work-around could be found...
Anyway, good question.
"Dammit..."
> > If you're referring to the 'double insulated' designation that allows manufacturers of small appliances, hand power tools, etc. to use a two-prong power cord, there may well be a cost issue involved, but there may also be other considerations. From what little I know of the subject (mainly observation) these devices often use a non-metallic (nylon, plastic, etc.) case as part of the 'double insulation' process, so perhaps increased RFI would be a potential drawback for audio playback electronics. Though I suppose a work-around could be found... < <
> > > > > > > > > > > > > > > > > > > > > >Actually most Cd and DVD players do not use the safety equipment ground. The AC power wiring is double insulated. The case is floating.... And the case is made of a conductive metal material to reject RFI.
A Faraday cage does not need to be grounded to reject RFI.
Also more and more manufactures of A/V equipment are going to the two wire power cord. Less ground loop hum problems and complaints.
Marantz is a good example of one.
< < The AC power wiring is double insulated. The case is floating.... > >
Actually the case is connected to the signal ground of the internal circuitry.
I think the main reason that most manufacturers use 3 wire power cords with a safety ground is ignorance. It's the easiest way to ensure safety, and it's also the method most commonly espoused in textbooks.
Kind of like FETs versus bipolar transistors. All the textbooks focus on bipolars. Not much is generally known about FETs. So designers follow the path of least resistance. It's too much work to dig up all the stuff to learn about some other technology like FETs or double insulation.
I have had a custom amp and preamp made for me in which the designer does not connect the ground to the either components IEC. Just the hot and neutral. He says it's a source of noise. In essence is this similar or the same as a "floating" ground?
< < the designer does not connect the ground to the either components IEC > >
I assume you mean he does not connect the chassis (normally tied to signal ground if the designer knows anything at all about grounding) to the ground pin of the IEC inlet, which would in turn be connected to the AC safety ground of your house.
In this case, the AC safety ground only connects to the IEC connector and not the circuitry nor the case. This achieves the same effect as "floating" the component with a "cheater" plug, but without the extra contact resistance of the "cheater" plug.
This does avoid the introduction of RFI noise that is present on the AC safety ground. But it also requires that the unit be "double insulated" to provide safety to the end user. If he doesn't use "double insulation" the risks are minimal (as long as he uses good construction techniques). But if he starts selling them this way, he should use double insulation so that he doesn't get sued on the off chance that somebody *does* get hurt.
Thanks for the response.
Your first paragraph is correct.
However, I'm a little confused about your second paragraph. If I look inside the chassis at the IEC inlet, nothing is connected to the ground pin. Does this affect your response?
Using a three-blade IEC connector and not connecting the safety-earth pin inside is the low frequency equivalent of lifting the ground at the AC plug with a cheater.
However, it does connect the safety-earth wire inside the power cord to the house AC safety-earth wiring. This allows the power cord safety-earth wire to resonate and receive noise, and convey the noise to the house AC safety-earth wiring network. It also allows this wire to convey noise already on the house AC safety-earth wiring network to the hot and neutral wires in the power cord.
This is a compromise. A better approach would be to use a two-wire power cord.
If you disconnect a guitar string at one end it will not resonate. If you strike the string vibrations will travel down it and dissipate quickly but it will not resonate.
Are there different mechanisms in play with RF and wire?
The electrical wave comprises electric and magnetic fields. An unterminated conductor supports a series of standing waves, where the boundary condition is that the current be zero at the unconnected end. The electric field components of the standing waves will be maximum at the unterminated end, and the magnetic field components will be null (because the current is zero).
The fundamental frequency is the mode where the unterminated wire is half the wavelength of the electrical wave. The harmonics are related by integer multiples of the fundamental. Thus, the first harmonic (the second mode) has the full sine wave contained on the unterminated conductor, the second harmonic (the third mode) has 3/2 of the sine wave contained on the unterminated conductor, etc.
This oversimplifies what happens in a power cord, because there are also modes to do with waves between pairs of the conductors, and the velocity of propagation may not be constant for all important modes.
I would also need to float the grounds on my power cords. If I recall correctly Charles also mentioned something about lifting the ground on the outlet the system is plugged into as well (I'm assuming this would also be true for a power strip I'm using).
Of course this is all at my discretion and risk.
Many systems are plugged into a power strip, which is plugged into an outlet. If you plug some three-wire audio components into a power strip, then float the power strip by using a cheater plug at the wall outlet, you will still have ground loops in your system. The individual power cords will have their safety-earth conductors connected together in the power strip. You may experience a reduction in noise (see my essay "Noise and distortion" in a thread above), from disconnecting the system from the house wiring AC safety-earth, but this arrangement will still pick up local noise.
To fully experiment with "floating the grounds," you need to make sure the individual component safety-earth wires are all disconnected, from each other as well as the house AC wiring. This is at your own risk.
Please explain why the signal ground is connected to the case.
With the case connected to the signal ground it puts the case at signal ground potential, correct?
Would the case otherwise act as an antenna or something?
Thanks.
The only way that the case can provide any shielding for the audio circuitry is if it is connected to the signal ground. In addition, if it is left unconnected from the signal ground, then it will create unwanted capacitive feedback loops (both positive and negative) between various parts of the circuitry. Refer to Morrison's books for additional details.
In my last house the internal house ground was not even grounded to earth thanks to the contractor. But I assume the cases were grounded to the non ground throughout my system to what effect, I know not.
Greetings from the sunny Brønshøj riveria on the banks of the lovely Utterslev Mose
> > In my last house the internal house ground was not even grounded to earth thanks to the contractor. < <
> > > > > > > > > > > > > > > > > > > > > > > > > > >In my area the power company will not do a hook-up if the main entrance neutral is not connected to earth ground properly.
But before the Power company will even come out for an inspection a release must first be given by the city inspection department.
==================> > But I assume the cases were grounded to the non ground throughout my system to what effect, I know not. < <
> > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > >That means the equipment grounding conductor was connected to the neutral conductor at the main electrical service panel.
In the event of a leakage or short from the hot conductor to the case of a piece of equipment, with an equipment grounding conductor connected to a branch circuit with an equipment grounding conductor, then the equipment ground would have carried any ground fault current back to the source. If only a small ground fault leakage the current returning to the source would just become part of the circuit and be dissipated in the form of heat at the utility transformer.
If the ground fault from the Hot conductor to the case of the piece of equipment, resistance low, then the ground fault current will be high and cause an overload on the branch circuit breaker causing the breaker to trip open, thus doing its designed job.....
============Now back to why the main service entrance neutral is connected to earth.
The main purpose is for lightning protection. Another reason is for a common ground plane through out your home as well as the surrounding area outside your home where you might use power. There in main incoming metallic water, gas piping, or what ever else might be at earth ground potential......Though they will not admit it, connecting the entrance neutral to earth at every electrical service gives the utility company a somewhat added protection if for some reason their neutral conductor from their transformer becomes broken, for what ever reason, from the transformer to the house.
Also for lightning protection the neutral is connected to ground at every utility transformer...... Connecting to earth of the neutral up the ying yang for lightning protection.
Thanks for your post Charles. I know CJ will take care of things for me, it's just kind of drag to be w/o my system for a week or two especially now that it sounds so good! The ground lifting provided an amazing improvement, I thought it would just quiet the annoying hum audible only when the system was idle. Wrong! It's one of those "time to listen to everything again" upgrades.
ET
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Probably. I never tried it. However, I did have a system that was completely floating and grounded it to an incoming copper cold water pipe that was only about 2 feet away from my preamp. The system sounded *very* slightly better with that ultra-clean ground. The ground on a dedicated circuit cannot be as clean as the ground I tried, so I still would recommend floating the system for best sonics.
Do this at your own risk. The danger is miniscule but real. You are a grown up. Decide for yourself if it is worth the risk. (Every house in this country built prior to 1960 had ungrounded outlets. It was only two years ago that I moved into a house with grounded outlets. Somehow I lived through it.)
nt
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Beats me.
I would guess that the "ground" is actually acting as a big antenna, dumping a bunch of RFI into your system. But I don't actually know that for a fact.
Based on my experiments I can say with confidence that the AC safety-earth wiring in my house does carry enough RF noise to affect my audio system. Any non-audio appliances that contain switching power supplies will have a Y-rated capacitor connecting the output of the supply to safety-earth, by law. These appliances may well be built to double-insulated standards, but still must have the safety-earth connection because of the switching power supplies.
Even though the safety-earth wiring is connected to earth at the breaker panel, the lengths of the wires from most outlets to the panel prevents them from effectively attenuating the RF noise presented to them.
The best approach is the one you champion: eliminate the AC safety-earth connection by design.
I bought the Morrison new edition.
Good luck. It's a great source of information, but also one of the most difficult reads I have ever encountered. He pares everything down to the bare minimum. In the older editions he would highlight a handful of concepts as "rules that cannot be ignored". I had to spend hours thinking about one single sentence. Dense, dense, dense writing.
If nothing else, it's great reading for those nights when you are having trouble falling asleep!
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much misunderstood term.
AFAIAC, the following methodology will fulfill electrical safety in any country and doesn't give you any ground loops, hum etc. in your system:
* use 3-core in-wall wiring which is active + neutral + earth.
* by all means use multiple spurs to power your total system but make sure the in-wall wires are all the same length (or you will get different earth potential at each component ... which can lead to hum).
* wall sockets have an earth hole/slit which is connected to the central household earth. In Oz that's back at the Consumer Unit ... and an earth wire goes out to a copper bar sunk into the ground.
* use 3-core mains cable to each component.
* inside each component, the earth wire in a captive mains cable (or the earth pin of the IEC socket) is bolted to the bare metal case - "safety earth".
* all RCA sockets & speaker BPs are insulated from the component case.
* PSes in each component have a star ground - but this is not connected to the case (and, hence, mains earth).
* the "system" ground is passed from one component to the next via the IC ground wire but it "floats" relative to the chassis.
All I can say is ... this works in my system.
Regards,
Andy
< < PSes in each component have a star ground - but this is not connected to the case > >
Unless the signal ground is connected to the case, the case cannot provide any shielding. Furthermore, the case can create capacitive coupling between different parts of the circuit that can introduce unwanted feedback (both positive and negative).
Much of the rest of your post is equally misleading. Go read Ralph Morrison's "Grounding and Shielding in Instrumentation" for some real information.
you would have seen that I said the earth pin of the IEC socket should be bolted to bare metal of the case. This "grounds" the case - thus providing shielding to the internals.
IMO signal ground should not be connected to case (which in my scheme of things is mains earth) and preferably, signal ground should be lifted from PS ground (also not connected to the case) by a 10ohm res, so signal and PS grounds do not interfere with each other.
Thanks for the Ralph Morrison reference - I shall see if I can get hold of it.
Regards,
Andy
< < Thanks for the Ralph Morrison reference - I shall see if I can get hold of it. > >
It's a slim volume because it's very dense reading. I had to read it at least twice to follow what he was saying. The latest version of the book is relatively expensive:
http://www.amazon.com/Grounding-Shielding-Circuits-Interference-Techniques/dp/0470097728
But used recent editions can be had for a reasonable price. (See link.) If you read the book, you will change your views on configuring your system. Connecting the chassis cases to earth ground is not a good solution.
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