The Grounding Thread to end all Grounding threads

[trancedental]

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?

From the long SSL thread.................. :

"My ground scheme is a star ground scheme and works as follows.

IEC Earth is mounted to the Star Ground
Seperate wires from Input XLR's Pin 1's to Star Ground.
OV from the Main PCB to Star Ground
OV from PSU to Star Ground
NO Ground wires on the OUTPUT XLR's to Star Ground
And the unit is SILENT, no hums from grounding or EM problems"

I followed this Star ground wiring on my SSL build exactly & it works fine, I would think in certain other builds / projects it's possible that other grounding schemes might be required?

There are other ground schemes in use for guitar amps (buss ground) but star ground seems the most popular http://www.geofex.com/Article_Folders/stargnd/stargnd.htm

 

[Whoops]

+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

So its not possible to answer in a simple and practical way to this questions:

Should Pin1 on all XRL 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?

 

[JohnRoberts]

+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

So its not possible to answer in a simple and practical way to this questions:

Should Pin1 on all XRL 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?

The pin one problem is so popular it has it's own website  http://pin1problem.com/ and over 800 google hits. http://www.google.com/search?hl=en&client=safari&rls=en&q=%22pin+one+problem%22&btnG=Search .

This one has been pretty well beat to death but short answer is hard bond pin one to chassis. Read the Brown article, and/or Bill Whitlock's.

http://www.rane.com/pdf/whitlock.pdf

http://www.audiosystemsgroup.com/Pin_1_Revisited.pdf

"Star" ground,  AKA single point ground has it's it's own pros and cons, but deserves more than a drive by treatment to do it justice.

I'm not going to even try but one useful fact to realize about grounds is they are not a voltage reference or potential, but a conductor for current. All voltage is relative to some other voltage potential.

Text books are your friend... 

JR

 

[Whoops]

Nice one, thanks a lot for your explanaitions.

I will read much more about the subject. In the meanwhile I have a project to finish so I will just do it as Trancedental described.

If it works without hum in the end I achieved my goal, and will just leave it like that.
I was really just looking for a way that works.

thanks

 

[e.oelberg]

btw, I once repaired a bunch of V72 with lots of deadly voltage inside and didn't hurt myself being very carefull. So I went into my bedroom and electricuted myself at the lamp beside my bed. I'm very lucky I survived stll have scars in my left hand, I was sticking to it.

took me half a year to fully recover, nicholas

 

[guavatone]

This book has been indespensable:

http://www.amazon.com/gp/product/0750663707

-This is great for PCB design and there is much on grounding



I have learned from grounding a tube pre, that when you use a CT Power Transformer and the CT goes to ground, bring the CT close as possible to your filer cap neg. terminal.  Originally i had the CT to Chassis star which sent to the filer Cap but there was much noise.

 

[Whoops]

btw, I once repaired a bunch of V72 with lots of deadly voltage inside and didn't hurt myself being very carefull. So I went into my bedroom and electricuted myself at the lamp beside my bed. I'm very lucky I survived stll have scars in my left hand, I was sticking to it.

took me half a year to fully recover, nicholas

Oh man,
I'm happy you are alright now.

Hod did you electrocuted yourself? problem with the lamp?

 

[JohnRoberts]

btw, I once repaired a bunch of V72 with lots of deadly voltage inside and didn't hurt myself being very carefull. So I went into my bedroom and electricuted myself at the lamp beside my bed. I'm very lucky I survived stll have scars in my left hand, I was sticking to it.

took me half a year to fully recover, nicholas

Glad you're ok.. 230v has more of a sting than 120v here.

JR

PS: in english the word is "shocked". Electrocuted, means you died from the shock.

 

[Whoops]

EDIT: I'm not showing this as a bad or good example. Pictures are commented in the follow up posts.


Star Ground pictures, I'm really sorry but I don't remember the thread I've seen this.

 

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[JohnRoberts]

As pretty as those pictures are, that doesn't look like best grounding practice from a casual observation. All of those long wires to the star ground point will have IxR losses.

It's hard to second guess a design without schematic, but just looking at the PS current flow. the common from the PS reservoir capacitors connects to the single ground point through one wire, and presumably power ground from the circuit boards connects back to the star ground though another long wire. Some 9 or 10 wires connect back to this common point, as if it could be trusted as a ground voltage reference.

Rule #1 about grounding, "wires have impedance". So redraw that wiring diagram with resistor symbols (or inductors at RF) in place of all those wires, and that star ground point is no longer some solid reference voltage, while indeed a single voltage by definition. However the voltage at the other end of each green wire is that star point voltage +/- the current flow in that green wire times the wire's impedance at the frequency of that current. The ground current flowing from the PS into ground at the circuit board, must pass through the star point on its way back to the PS board so there can be current flow in both wires, and the star point will be divided by the ratio of the wire impedance somewhere between those two different local ground potentials. (The significance of this depends on balance of PS current demand in circuit, local decoupling capacitance, etc.) I would also be very careful about where the PS ground point is chosen. It needs to be well after the the transformer and reservoir cap common, preferably at some common point between and after the two regulators, if that's what's on those heat sinks.

Liberal use of transformers in the audio path may make this design work in spite of that grounding approach. Again not to second guess this design from "photographs", but I'd be tempted to bond the mains cord ground to chassis, and perhaps the XLR grounds to chassis. Rather than long separate wires to a star point on the bottom cover. I'd use shorter wires to the chassis right at the different connectors. This has the benefit of lower impedance at RF. I'd also connect to the U-channel rather than bottom cover in case the bottom cover is painted and doesn't make a robust electrical connection to the U-channel. I would carry the PS ground though a heavier gauge wire in the same wire bundle as the +/- voltage wire bundle to keep the area of that loop small (perhaps twisted).

A common star ground point could be located on the main audio circuit board near where the PS wire bundle connects. A single wire from there can connect to the chassis. As long as audio paths are properly differential between inputs and outputs grounds shouldn't be problematic, but pay attention to any internal single ended circuit blocks.

JR

PS: very nice looking package. just a little too literal on the star ground concept for my taste.

 

[owel]

Am I just being "lucky?"

I haven't use any "star" grounding in any of my projects... especially those that look like spider webs.

I just short the Neutrik XLR metal tab to pin1 for both input and output XLRs. I don't even use a wire!  Even an inch long wire is too long for me. I just put solder glob on it, smooth molten solder connects both terminals (XLR metal tab and pin1) together.  The metal Neutrk XLR jacks are then screwed to the metal case, so each XLR jack makes ground contact with the case too. No wires needed even!

The pin1 from the XLR is also brought back to the PCB ground plane via twisted wires (along with the hot/cold wires, all twisted).  I need the ground connection there for 48V phantom to work. PCBs have ground planes on top and bottom. Each chip has it's own bypass caps, millimeters away from the chip's power pins.  There's also a bigger 47uf and another bypass cap at the power entry.

The IEC mains safety ground has a crimp terminal and secured to the metal case with screw and bolt.  110V AC goes to power transformer, then secondary AC goes to PSU PCB. I connect all DC wires from PSU PCB to preamp board, V+,V-,GND and +48V.

That's it.

No noise.

And once everything is finished, loosen the nut on the toroid transformer, turn it around slowly listening for the point of lowest noise, sometimes even a 1-degree turn is the difference between some little noise and very little noise. Tighten nut.

Done!

 

[abbey road d enfer]

There's no way the tricky science of grounding can be taught in a few lines. It takes a number of experiments and mistakes, in addition to a solid mastering of electicity (Kirschoff's model in particular).
More confusion is added by the safety aspect, which is very often adding difficulties in implementing the right scheme.
Just a few points:
Audio gnd should never be left fully floating from earth (chassis ground), but semi-floating, with 100R and 0.1uF is good and efficient practice.
Think of ground connections as resistors; as a result, ground connections should follow the signal flow, i.e. first-stage gnd goes as short as possible to second-stage gnd, and so on, up to the last-stage gnd goes to raw ground (that's the PSU gnd, where the smoothing caps are referenced)
IMO, star-ground is not a good idea (in terms of audio performance) on a stand-alone unit, although it makes sense on units where the inputs and outputs grounds may be connected, as is the case with mixers.

 

[Whoops]

Thank you all for your information and advises.

I can see how deep and complex the subject is.

now it's time to read books, articles, more books - and Learn!

 

[Mbira]

RE those pictures, I have had bad luck with screw-down connectors for many wires  like that staying tight for a long period of time.  I generally solder all the ground wires together into one thing and then screw down that one fat wire with a locknut. 

 

[sodderboy]

Luck might be right, because the Neutrik tab, especially on the black anodized, does not make a good chassis connection, either to the chassis or to the shell.
With inter or intra-chassis grounding, the rule book is small, but the appendix of exceptions is large.
Anyone ever look at the SECK intra grounding?  Uh, anyone even have one of those anymore?
Mike

 

[owel]

I'm using the Nickel plated XLR jack, not the anodized black version. Also, the aluminum case is CNC milled after anodizing/painting, so bare aluminum is on the edges of the milled holes that make contact with the XLR body. 

But that's a good point. Make sure there is actual good contact between the cases and jacks. Anodized and painted surface are good insulators.