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In Reply to: Chassis ground vs. source signal ground? posted by A.A. on April 25, 2007 at 18:54:27:
There is absolutely NO operational requirement for an audio circut to be connected to an Earth Ground. The term *ground* with regards to electronic circuts actually refers to circut Common return. With correct terminolgy, there then is no such thing as a floating ground. During the early days of crystal Radio, an actual Earth connection was required to boost weak Antenna currents. The old timers, out of habit, continued to refer to the circut Common return as a *ground* when active detection & amplification devices (vacuum tubes) became available. This continued use of a now erroneous terminology (circut Ground instead of Common return) is responsible for much confusion per circut operation today. Only a SAFETY Ground needs to be connected to the chassis, and at one point only, and separate from the signal or circut Common connection to chassis. Signal or circut Common should NEVER have a direct connection to AC Mains; only via the chassis lest SAFETY be compromised.
Follow Ups:
> There is absolutely NO operational requirement for an audio circut to be connected to an Earth Ground.An earth ground is an absolute necessity for minimizing RFI/EMI issues in audio gear. I have a kilowatt transmitter to prove it. :)
Hi.Earth grounding is important for:
(1) it ensures personal safety (DC grounding)
(2) it protect equipment involved (DC & AC grounding)
(3) it is necessary to pass the electrical authority approval if appliable; (DC grounding)
(4) it prevents EMI/RFI. (AC grounding)
(5) it provides a known reference to the control signals for control
equipment. (AC/DC grounding)DC grounding to the chassis is imperial in case of HV insulation breakdown in HV carrying devices, e.g. power & O/P transformers, HV chokes etc in audio amps. The split-second shorting DC currents can be drained away via the chassis & the earth ground (green) wire of the 3-wire AC mains supply cord. The earth grounding wires must be thick enough ie. of the min gauge sizes) to conduct away the shorted DC currents.
The contact of the green earth ground wire must be bolted or properly soldered to the chassis to allow zero contact DC resistance.
AC ground is more complicated issue as we are dealing with RF energies which require adequate SURFACE AREA (of the chassis, etc) to drain away of RF currents. The conductors/contacts must have very little inductive & capacitive reactance to ensure lowest impedance to drain away of harmful RF energies.
There is why for digital/RF systems, effective AC grounding a hell of big issue to address.
My point is that the application of the term ground is ubiquitus for circut Common. The circut will function (as a circut) without an actual Earth Ground connection, irregardless of the SAFETY or EMI/RFI benefits of likewise sharing a chassis connection to Earth for AC-operated devices. By refering to such circut Common returns as the ground, confusion per wiring schemes can arrise & often does with novices.
and I am seeing some serious misinformation in some other posts.As I see it your main point is that the signal circuit could be entirely floating. Given that the (hot) signal is from the plate of a tube (usually) and that plate voltage is rectified AC with the filter cap's negative side going to normal electrical ground it seems to me signal is already (AC) referenced to ground. Given that the return path for the signal is the tube's cathode and said cathode is referenced to the same ground the filter caps are, which is normal electrical ground, you are still involving electrical ground. Even if you don't have a 3-wire cord the neutral wire is referenced to normal electrical ground and at the least there is a cap between neutral and chassis if the neutral isn't simply bonded to the chassis.
About the only way you are truly getting away from normal electrical ground is if you transformer couple. Even balanced IO's involve electrical ground.
BTW, irregardless isn't a word. American electrical code requires the chassis to ground bonding be done with a minimum of a #8 screw and never soldered. And a separately derived ground via running to a water pipe is highly illegal and potentially very dangerous. Okay, I have had my rant for the day and nothing personal gents :)
"irregardless isn't a word"Oh, how I wish that were true. Unfortunately, it is in my Websters Unabridged as a synonym of regardless...
Well, you are saying that the DC power supply establishes *electrical ground* as a current return pathway for the circut. I am saying that your *electrical ground* is actually the circut Common return path, and that no actual connection to an Earth Ground is required for said circut to function as a circut, therefore why refer to such as a ground vs Common? By refering to such as ground, confusion can arrise & in fact did with the OP. Thanks for the English language lesson, but what does that have to do with the topic under discussion? Unless you were making the same point that correct terms DO matter after all.
I am simply trying to understand you. Good chance we are saying the same thing in different words. The neutral is considered an "earth grounded" current carrying conductor. So we can't get away from the fact that out power transformer primary has a ground connection.I think I must be missing an important point you are making. The only way I see is with balanced inputs and differential amp stages. Even then any unbalanced stuff can have the potential to go to ground.
Of course it goes without saying that the signal from a preamp goes only to the input tube's grid (and not through said tube) and straight to chassis/signal ground by way of grid leak resistor. If one has a 3-wire cord, or a cap from neutral to chassis, then you have signal connected to electrical ground.
If we wish to avoid electrical ground then best we avoid single ended stuff in general. But home audio, as well as 120VAC in the states, are both single ended in nature. Personally I run 60-0-60 balanced power and avoid a neutral. But I still reference signal ground and chassis to electrical/earth ground for safety reasons.
For instance, if your circut (any circut) were battery powered, then there is no actual Earth Ground connection. Yet the circut still operates, because there does exist a Common pathway for current return. With AC Mains powered equipment, the separate power supply circut derives the DC voltage to operate the audio circut, and again except for Safety with such AC Mains powered devices, there is no audio circut requirement for an Earth connection. But refering to the current Common return as an electrical ground DOES sometimes cause confusion as to how & where to make a Safety Earth Ground connection to the circut. Another example is *ground loops*, which are actually current loops that may exist even when no Earth connection is present. I must wonder if anyone bothered to read my original text, or just the subject header. Anyway, guess old habits are hard to discard, especially after a century of use.
Hi.I know where you come from. This is very common sorta misunderstanding btween signal return reference "ground", & actual electrical "earth" ground, or whatever yu can put it.
You're correct for audio amps DC powered, as long as the signal in & return circuit is completed, the amp functions.
But if the amp is working in an EMI/RFI noisy environment, like in many modern homes today, where tons of computers, notebooks, flat panel TVs are all over the place, the poor amp is subject to HF rash.
So metal chassis of the amp still needs to be earth grounded so that the harmful RF energies can be drained away via the earth path as per my post above despite the in/out signal circuit is completed.
As I posted earlier this week, my SS phonostage, a dual-monaural stereo design, full battery powered, still got its plastic housing full laminated with aluminum foil, which is AC grounded to the turntable chassis ground wire as well as the ground rod of the tube phonostage/line amp where the SS phonostage unit hooked up to its "
AUX" input.EACH of the I/P jacks of the SS phonstage unit is AC grounded to the plastic housing aluminum foil shield via a 0.1uF3KV ceramic disc cap,
an excellent potential RF rash short-cut from the amp return reference ground.c-J
bot
Russ> > Even if you don't have a 3-wire cord the neutral wire
> > is referenced to normal electrical groundI have found many houses where the polarity
of some of the outlets were switched so
if you are thinking that the polarity plugs
mean anything you are mistaken.> > a separately derived ground via
> > running to a water pipe is highly illegal
> > and potentially very dangerous.Do you realize that most houses are earth grounded
through the water pipe which goes into the ground.
How is this illegal let alone dangerous?
The pipe which is filled with water is a
better conductor than the house wiring and
it is buried in the ground outside the house.
But I can't abide telling someone to break them in an open public forum.Yes, you are correct that the neutral, ground rods, and utility service pipes (even building steel in some cases) should all be bonded together. But the important point is that they are to be bonded together at one place and with one unbroken wire. Just like in your amp you don't establish one main star ground point and take half your grounds there and just solder the other half to the chassis any old place. That leads to ground hum due to a differnt impedance (or potential) to ground even though the chassis is a large conductor compared to the currents involved.
Now if unknown to you, said water pipe had a high impedance for any number of reasons....like a poor screw/solder joint....or a bit of plastic pipe...or whatever....it could indeed have a high enough impedance to prevent the breaker from tripping. 120volts/20amps=6ohms so if you have anywhere near 6 ohms difference between water pipe and neutral the circuit breaker would not work....plus if someone was in the tub bad news. Also keep in mind that during a true short circuit said breaker will actually develop fault currents near 10,000 amps....and that is no small current. Best to follow code and have all grounds originate and terminate in one location.
RussI could refute each and every one of your statements
but the imformation is out there let people decide.
A Safety Ground is only required when we operate our electronics via household AC electrical wiring AND metal parts of the device (such as cable connections) can be touched. An automobile typically uses the entire metallic frame strucuture as it's electical system Common return pathway (an all-plastic car would require duplicate return wiring) but absolutely NO direct Earth Ground connection is neccessary for automobile battery-operated electronics. Same for battery powered portable audio devices. So why refer to any electrical connection in such circuts as a *ground*?
Ron> > The term *ground* with regards to electronic circuts
> > actually refers to circut Common return.Not in any circuit I have seen
in over 30 years as a technician.
Ground is EARTH ground on every circuit
I have worked on.> > With correct terminolgy, there then is no
> > such thing as a floating ground.Circut Common Return is floating, whenever
circuit current is flowing it increases
and thereby is no longer Earth ground
and is therefore floating.
That is why anything with a metal case
needs an three wire plug by law.
Also you can't recommend referencing your signal ground
to AC common and you don't recommend referencing them
to Earth ground - floating ground is all that's left.> > Signal or circut Common should NEVER have a
> > direct connection to AC Mains; only via the
> > chassis lest SAFETY be compromised.Circuit Common should never have a direct connection
to AC Mains ground inside your equipment is correct.
They are connected at the box but if you do this then
you are making your connection as an alternative
grounding route for the other devices on your circuit
and corrupting the safety providing earth ground.
But since the signal ground produces no significant current
and is using it only as reference NO safety is compromised.> > So why refer to any electrical connection
> > in such circuts as a *ground*?Because earth ground is the BEST reference
whether you are talking AC or signal.
I ground ALL my equipment without problems.
I actually run a "new" ground route usually
from a convenient water pipe nearby.
Common/return and ground are the same point
at the incoming box but are different soon after
and are more different the further you get away
from the box because accumulated resistance and
more devices drawing current.> > absolutely NO direct Earth Ground connection
> > is neccessary for automobile ...On purpose because the automobile would be
susceptable to lightning strikes.
They found that out the hard way.
As well as why to have a negative ground.
Positive grounded vehicles rust very quickly.
Please notice that virtually all inmates here write ground when refering to circut Common. You do so yourself, see link below:
RonBecause I connect the circuit ground to earth ground.
So they are the same point sir.Circuit ground and AC common are definitely different.
Do not connect AC common to ground.
Do connect circuit common to ground.
Just because you do it that way does not make it SAFE for others.
RonGrow up please - you're gotcha game is so juvenile.
Just because I can take a shock does NOT mean anything.
ALOT of people run seperate grounds,
some even run dedicated power feeds.
Nothing unsafe about this.
needs an three wire plug by law."I don't understand all the electrical laws in every state and region and every country as well.
But, I have a CD player that has an all metal case and has the obligatory three wire plug, but it only uses hot and neutral inside the box. The ground connection is unconnected. The manufacturer passes the law by double insulating the mains on the wires going to the power transformer primaries even with a metal case. They just add another layer of plastic insulation over the standard mains wire. Apparently, this is good enough by today's electrical codes.
The output signals of the CD player appear to be just floating. I guess the outer box is connected to circuit common. When connected to an amp that has its circuit common connected to Earth ground, then the whole system is shielded by ground potential.
It sounds best to have only one box grounded to Earth ground to avoid ground loops. Apparently it can still be done legally. My CD player is an Ayre, made today in the USA, and I know they know what they're doing.
KurtI know people have ground loop problems.
I always cure them with better grounding
on each and every componant.
The idea that your ground reference is
provided through an interconnect seems to me
as a problem waiting to happen.
Maybe that's just me.
I like everything grounded well.
For someone who is so sure of himself... you say a lot of really silly things.Have a nice day.
HenryIf EVERY componant was PERFECTLY grounded then
there wouldn't be any ground loop problems.
Not so silly if you think about it.DanL
"There is no such thing as Ground."That is an axiom that is posted on the cubicle of one of our star analog design gurus where I work.
What does it mean? It means there is only a mere approximation of ground. Ground is an illusion and there is no perfect ground, ever.
It's also unfortunate that Henry sometimes chooses not to expound on his knowledge, because he does indeed know a lot about what he's talking about.
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