The Grounding Thread to end all Grounding threads

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ENS Audio

Well-known member
Joined
Oct 23, 2007
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425
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Hello to all those seasoned techies and newbies (such as me) lets make this the grounding thread that will end the confusion and the annoyance of this topic by making this a very simple straight to the point with as many visual references that can be used.

Mainly I think that problem with the reason why so many dont get it at first is because many of us im sure are "visual" learners so an actual "real world" visual example would dissolve much of the confusion. To begin, I'll post some basic FAQs that really need to be clarified (will edit along the way)


Should Mains Ground be Isolated or connected at the same junction "starground" point with the other grounds???




Now please I'll even pay money for someone that can show a very basic example/photo of what "chassis ground" should be "wired as"


Is balanced AC grounds really something that should always be followed??? I mean is it really worth it if the builder is willing to do the wiring??? If so, a visual representation would be great.

Placing .01uf cap in parallel with a 100 ohm resistor should be wired at the star ground point??? or at each XLR input???




Now for the meat and potatoes....


Chassis ground

|_|_|


Earth ground/ Safety ground

**V**


Signal Ground



More to follow....
 
[quote author="ENS Audio"]
Now for the meat and potatoes....


Chassis ground

|_|_|


Earth ground/ Safety ground

**V**


Signal Ground



More to follow....[/quote]

AFAIK the whole point of stargrounding is to make sure there are no potential differences between chassi ground, signal ground and safety ground by connecting them at the same point in the chassis.

Also safety ground from the mains should always be connected to chassis, that way if by accident any mains powered leads come in contact with the chassis you will blow a fuse, instead of having the whole chassis carrying mains power. Touching that chassis could easily kill you.



BTW I started a similar thread a year or so ago, so someone correct me if I need to be schooled. :green:
 
This should clear some things up also:

From 'Basic Electronics' Vol. 1 (c)1955; pg. 1-48

"In the basic full-wave rectifier circuit two cathodes are used but since they are connected together a single common cathode can be used instead in a typical circuit. Also in the basic circuit one end of the load resistor connects directly to the transformer secondary winding centertap and no ground connection is used. This connection can be made by grounding the centertap and one end of the load resistor to different points on the chassis."
 
AFAIK star ground can be implemented both internally within the circuit layout and externally with the chassis grounds of the many devices. . the point being this dedicated path is the only path ground currents can take and therefore do take. one branch touching another arm would pollute both circuits. Ive seen analog circuits and digital circuits using seperate stars. combining as close to the chassis ground as possible then both sperately connected to chassis ground.
 
I got this one from Keith, he stated in one of his posts to not hard-wire signal ground (technical ground) to chassis ground, but rather to connect these up through an SPST switch. The point was that if you have two devices which both have mains ground (safety ground, chassis ground) wired to technical ground and you connect them with your audio cable, you have a loop. If you can lift the technical ground from the safety ground, you can pull the technical ground to mains ground at your patchbay and thereby have one huge star ground point for your entire studio. My console has two ground connectors in the back, one standard mains and one big fat one for technical ground.

I recently hooked up my GSSL to a 5.1 unbalanced setup (from DVD player to CD IN on the reciever) and it hummed away. One flip of the groundlift switch-silence. Keith talked about taking commercial devices and opening them to install a groundlift switch, I can easily understand why now.

This is also the reason all these XLR sockets and plugs have two ground connections, one being pin 1=technical ground, and one separate little tab for the socket or plug chassis. I used to just wire these together, thinking that ground=ground, now I have work for my pliers.

One thing I feel is important to add on lifting: In the beginning, I ran around with a mains cable that was two-pronged and fit a 3-prong IEC connector, proudly calling it a "groundlift cable", thinking this was a smart way to defeat hum. In effect a very stupid idea:

1. If your device is standing there on its own and you have a fault, it'll just sit there with a live front panel waiting for someone to fiddle with it (if not an entire live rack)

2. If it's connected to another device with audio cable, it'll find the star ground point there and blow the fuse. If there are any circuit boards in its way...well...

These are worst case examples, as there is almost always a short to ground somewhere and you're most likely to just blow a fuse, but if the conditions are right, lifting mains ground to defeat hum can be a very effective way of destroying equipment and people.

Try that one on the next guitar amp you build...It gives the name "electric guitar" a whole new meaning...maybe this is where all these shock rockers get their name ;) They certainly look the part...
 
[quote author="livingnote"]Try that one on the next guitar amp you build...It gives the name "electric guitar" a whole new meaning...maybe this is where all these shock rockers get their name ;) They certainly look the part...[/quote]


..I thought that electric shocks were supposed to *treat* manic depression :wink:
 
[quote author="beatpoet"]..I thought that electric shocks were supposed to *treat* manic depression :wink:[/quote]
They have a way of making sure you'll never be depressed afterwards.

...Or do anything else in fact... -Such as "breathe", or any other activities which you might take for granted...

:wink:

Keith
 
[quote author="livingnote"]If you can lift the technical ground from the safety ground, you can pull the technical ground to mains ground at your patchbay and thereby have one huge star ground point for your entire studio.[/quote]

Excellent idea! Never thought of that! :thumb:

My set-up is always so simple I could easily try that out.
 
It's not too hard to pull a #12 wire out to a ground rod for signal ground..

[quote author="Viitalahde"][quote author="livingnote"]If you can lift the technical ground from the safety ground, you can pull the technical ground to mains ground at your patchbay and thereby have one huge star ground point for your entire studio.[/quote]

Excellent idea! Never thought of that! :thumb:

My set-up is always so simple I could easily try that out.[/quote]
 
It's a good and useful subject. (Prune the OT posts?)

So, here are some links for background reading:

http://www.gbaudio.co.uk/data/ground.htm
Ground loops

http://www.tcaas.btinternet.co.uk/jlhearthing.htm
Grounding

http://sound.westhost.com/earthing.htm
Grounding

http://www.dself.dsl.pipex.com/ampi.../balanced.htm#7
Balancing and grounding

http://rane.com/note151.html
Grounding and shielding from Rane

http://rane.com/note110.html
Interconnection from Rane

http://www.elecdesign.com/Articles/...cleID=5944&pg=1
Grounding in ADCs

http://peufeu.free.fr/audio/extremi...mplement_2.html
Supply and ground in digital systems

http://www.geofex.com/Article_Folders/stargnd/stargnd.htm
Star grounding in tube amps

http://openbookproject.net//electricCircuits/DC/DC_3.html
Mains shock hazard / electrical safety

(The above links are live as of 23.08.08)

Remember that ground is just a name. In reality ground is...

a) a point of safety with respect to your fusing / circuit breaker system
b) a point of reference with respect to your power supply
c) a signal return line


There is an interesting free presentation download (zip file) here:
http://home.comcast.net/~zenkai-audio/
'Grounding and Transportable Sound Systems'


: )
 
I found an interesting AES audio lecture in mp3 format with Bill Whitlock from Jensen transformers that covers balanced audio, grounding and a bit of interesting info on the THAT line recievers. Length 2 hours.

http://www.aes.org/sections/uk/meetings/a0705.html
 
It all boils down to Ohm's Law. Simply put, your ground wires and traces have impedance. If there's a noise current flowing through a ground wire or trace, then it will have a voltage across it. The secret to avoid ground-couple noise is to not use a ground point that has a noise voltage on it as a reference for a sensitive piece of your circuit. That's the point of the star ground.
In most good pro audio gear, the chassis is conductive and serves as a shield. The power line safety ground is attached to it in one spot, and the circuit ground is attached in one spot. I used to get hung up on this because of the need to connect XLRs to chassis, which on multi-channel units gives multiple ground points. But then I learned that Pin 1 of an XLR should be considered a chassis ground, NOT a circuit ground. Remember, a balanced audio connection does not require a ground connection at all to function. The shield is just that - a shield - and can be thought of as the chassis of the cable. Pin 1 and the shell of the XLR should be connected directly to chassis ground, and not to audio ground.
In most cases I consider three grounds: Audio, power, and chassis. The power line safety ground is practically synonymous with chassis ground in that it bonds directly and permanently to the chassis, before any other circuitry comes into play. Audio and Power ground are sometimes difficult to keep apart, but it's usually pretty simple to make sure they only join the chassis in one spot. The basic premise of star grounding is that the audio circuitry shouldn't use as a ground reference any point that is at the far end of a ground trace for a noise source, such as power supply filter and bypass caps. So at the very least, I connect all my main filter caps together and home-run them to the star ground point separately from any audio grounds.
 
One exception to pin 1 on XLR's. If an XLR is used for a mic input
requiring phantom power, It should go to the star ground point.
This is the return path for the phantom circuit and carries current.
The chassis should not be used as a return path for any circuit.
Shields in XLR cables should be connected to the provided "tabs" in the
XLR cable connectors. Good high quality mic cables are wired this way.


RonL
 
This is all true, RonL. I would say that on a mike preamp, pin 1 of the female XLR(s) should still be connected to the chassis, and that should be the one point where circuit ground connects to chassis ground. This is how this stuff gets so complicated and confusing. In my designs, which use circuitboards, there is a Chassis Ground plane on the part of the circuitboard where the XLR connectors go. This lets me keep Pin 1 and the shell connected to Chassis Ground instead of Circuit Ground, but also gives me a copper conductor for the phantom return.

Also, the shield on an XLR cable can be soldered to both the shell tab AND pin 1.
 
What is Technical ground?

Is it Audio Ground = Signal Ground = 0 volts reference ?

I think the ideia for this thread is really good, but I got even more confused reading it. it would be so nice just to have some diagrams where you could just see it.



So Pin1 on all XRL should be connected to the star point?

pcb (circuit board) audio ground output should be connect to the star point?

IEC ground tab should be connected to the star point?

Star point should be a bolt thouching/connecting to the chassis?


sorry for all this questions, just trying to make it simple so I can understand.

thanks



livingnote said:
I got this one from Keith, he stated in one of his posts to not hard-wire signal ground (technical ground) to chassis ground, but rather to connect these up through an SPST switch. The point was that if you have two devices which both have mains ground (safety ground, chassis ground) wired to technical ground and you connect them with your audio cable, you have a loop. If you can lift  the technical ground from the safety ground, you can pull the technical ground to mains ground at your patchbay and thereby have one huge star ground point for your entire studio. My console has two ground connectors in the back, one standard mains and one big fat one for technical ground.

I recently hooked up my GSSL to a 5.1 unbalanced setup (from DVD player to CD IN on the reciever) and it hummed away. One flip of the groundlift switch-silence. Keith talked about taking commercial devices and opening them to install a groundlift switch, I can easily understand why now.

This is also the reason all these XLR sockets and plugs have two ground connections, one being pin 1=technical ground, and one separate little tab for the socket or plug chassis. I used to just wire these together, thinking that ground=ground, now I have work for my pliers.

One thing I feel is important to add on lifting: In the beginning, I ran around with a mains cable that was two-pronged and fit a 3-prong IEC connector, proudly calling it a "groundlift cable", thinking this was a smart way to defeat hum. In effect a very stupid idea:

1. If your device is standing there on its own and you have a fault, it'll just sit there with a live front panel waiting for someone to fiddle with it (if not an entire live rack)

2. If it's connected to another device with audio cable, it'll find the star ground point there and blow the fuse. If there are any circuit boards in its way...well...

These are worst case examples, as there is almost always a short to ground somewhere and you're most likely to just blow a fuse, but if the conditions are right, lifting mains ground to defeat hum can be a very effective way of destroying equipment and people.

Try that one on the next guitar amp you build...It gives the name "electric guitar" a whole new meaning...maybe this is where all these shock rockers get their name ;) They certainly look the part...
Click to expand...
 
Thanks for bumping this thread...could someone if they fell like doing so and that would be to post visual definitions of some of the grounding terms like a "visual" representation of what audio ground is as opposed to "earth" GND or "chassis" GND (kind of knowing all of this just would be nice for me or someone to reaffirm)
especially a difference between GND and when neutral current path feeds into the GND loop (hope this makes sense...now you see the reason why there needs visual representations of each example)


Most likely I'll do it myself if there's no volunteers and that I find the spare time this week or next.

Should I use Corel Draw??  or another type program which there seems to be some nice ones out there.
 
Whoops said:
I would do it myself if I had any deep Knowledge about the subject.

The diagrams can be done even with Paint. Paint is alright for simple stuff.
Click to expand...

ah yes...geez my overanalytical thinking does it again!
 
http://www.amazon.com/Grounding-Shielding-Techniques-Ralph-Morrison/dp/0471245186

http://www.amazon.com/Grounding-Shielding-Circuits-Interference-Techniques/dp/0470097728

Maybe a library might have copies you can read.
 
+1

I have both Ott and Morrison books on my bookshelf from decades ago. A little dated in light of modern interference sources but still solid.

I have avoided posting in this thread as one could easily write a book on the subject, and any simple treatment is subject to misapplication.

Not mysterious or magical, all pretty basic physics, but almost everything matters and must be weighed in context of the application.

While a little painful, experience is a good teacher in this area. Also look at products that work well and try to figure out why they were packaged the way they were.

JR
 

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