Ground Rules --- Anyone have some good basic principles to share?

I think most people like star grounding near the input jack. But other than that I don't know much.

What rules do you use in your projects?


thanks! and interested to see what others have found. This can apply to both tube and solid state stuff.

There is no ground.

There is shielding, signal common, power common, safety connections.... multiple functions.

Using the word "ground" indiscriminately WILL get you in trouble.

PRR said:

There is no ground.

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That explains all the trouble I had walking last night! 

(or maybe it was the whiskey...)  ;D

What PRR said.

The subjects can, and have, filled books.  Especially important reading if your aiming for low noise.  

Coupla things to get the ball rolling:
People assume signal common to be this solid unmoving thing but it's very easy for it to get contaminated with crap if you don't practice
good schemes.  
As far as reproduced audio is concerned, it can't tell the difference between movement on signal common and movement on a voltage rail.  A wobble or a blip is a wobble or a blip wherever it happens and becomes part of the reproduced waveform.
Don't let your signal common become contaminated.  


Look at the AC and DC current loops of each stage.  A bypass cap or supply cap should be placed very close to the device it's bypassing or supplying current/voltage to.  If the loop has to travel far, it'll be prone to contamination.  Taking each stage's return point individually back to a common point isn't a bad idea.  It helps stop the lower current stages from getting the higher current dumps.

I don't think a planar approach for audio return/common is right myself.  Might be fine for R.F. stuff or ? but I think a ground plane on audio PCB's is asking for trouble.  It's akin to the old lazy "Point To Point" approach of using the chassis as audio common or return.  Can require many revisions and futzing with to get the best results.  Taking the returns from each stage seperately is better.  

Lots more to say but, again, there's books that say it better...


Edit:  Look at old Tektronix scopes for inspiration.  New scopes are riddled with expertise too (probably more) but harder to fathom out what they're doing

I posted this today in the API 312 for a guy having some issues, which I think are ground related. It's based on what I've gathered from this site and others as well as the odd book here and there. It'd be cool if PRR or WOB could confirm or deny the steps I posted so we don't have improper/incorrect suggestions on the board, as my memory is flaky at times.

There is also a link to a page of interesting ground articles at the bottom.

http://www.groupdiy.com/index.php?topic=246.msg412239#msg412239

mitsos said:

It'd be cool if PRR or WOB could confirm or deny the steps I posted

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Which one of us?  What if we had conflicting opinions?  Myself, I'd trust PRR's opinion over mine!

I read what you wrote but I don't quite get it, I do believe I lost the plot.  My bad.

Are we providing an option for lifting audio returns and power returns from chassis?
Are we then taking our returns out of the back of the box to some master earth reference?

Aside from that, it looks OK to me although I don't know the PCB layouts.

;D

Plot? What plot? I lost it myself, so no worries. Hopefully the poor guy in the other thread can follow it.  Anyway, I just thought the OP was looking for more specific info than PRR's answer. I did get a kick out of the "There is no ground" line. Reminded me of the spoon scene in the matrix. 

Anyway it would be good to have a ground thread that spells out how to succesfully wire up anything. Everyone is always asking, and I have just now started to get my head around it myself.  Assuming the layout is known working, using a starground you should basically guarantee no ground problems, right?

About grounding the chassis, I wrote that it should be connected permanently to the ground pin of the power cable, and that the audio ground reference should be able to be lifted from it if desired, which is easy to do with the PSU board he is using.

About the master earth reference you mention, when would you take the grounds out of the box?  Wouldn't the power earth of the building be the master earth in a properly grounded building? And wouldn't every piece of equipment plugged into the power be automatically connected to this master reference? I know SSLtech once said something about bringing both grounds to two posts in the back of the box that you could connect/disconnect as desired, but I figured a switch would do the same? 

Anyway, it's good to know I didn't entirely botch that up. Now if I could only figure out my 312 problem...

mitsos said:

I know SSLtech once said something about bringing both grounds to two posts in the back of the box that you could connect/disconnect as desired, but I figured a switch would do the same? 

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Having posts on the back that you can link together is fine.  You might need to separate them for testing (checking spurious things or whatever) or you might want to run the audio returns and power returns to a technical earth in the building instead of inside the chassis.  But you would want them connected somewhere to earth or a, hopefully steady, reference.  Some folks like to use what I've seen called a "soft earth".  Maybe this is what JLM are doing?   

Sometimes, I've artificially created a negative voltage for a tube design (for bias maybe) by having a resistor between my audio commons etc. and earth.  The top of the resistor is my audio common reference and the bottom is my artificial -tve of a couple of volts.

I use what was called "transmission grounding". Both inside a chassis and if I'm hooking up various bits in a system, like inside a desk or a rack of pre amps with an external supply. 
As for shields on signal lines, I lift them at inputs.  You can terminate them at R.F. with a little RC network and, sometimes I do, sometimes I don't. 

OK, about the shields... Are you talking about shielded cables inside the box?  Or XLR pin 1s?

mitsos said:

OK, about the shields... Are you talking about shielded cables inside the box?  Or XLR pin 1s?

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Both. 

Pin 1 of my input XLR on the back of the chassis goes to chassis (I don't know how the other guy might wire his cables that plug into and out of my box) but my XLR cable I'm plugging into it will have the shield lifted.
Again, you could supply them with a ground lift switch for line inputs to cover yourself in case they don't lift shields on cables. You could also have the ground lift switch terminate at R.F.

http://www.groupdiy.com/index.php?topic=29106.0

There's a link contained in that thread to the rane note on grounding. It's very informative.

Winston O'Boogie said:

Pin 1 of my input XLR on the back of the chassis goes to chassis (I don't know how the other guy might wire his cables that plug into and out of my box) but my XLR cable I'm plugging into it will have the shield lifted.
Again, you could supply them with a ground lift switch for line inputs to cover yourself in case they don't lift shields on cables. You could also have the ground lift switch terminate at R.F.

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hmm, so you have pin 1 of the cable attached only on the female side? Are you talking line signals only? Can't do this with phantom power mics can you? I haven't gotten into mic building and schemos much but if you're sending them DC they should have a ground reference, that's why the assumption.

The rane and other articles are at:

http://pin1problem.com/

"hmm, so you have pin 1 of the cable attached only on the female side?"

Yes. 

"Are you talking line signals only?"

Yes.  I wasn't clear enough on that.  I did put line in italics but that gets missed most of the time.

"Can't do this with phantom power mics can you?"

No. Phantom mics need the connection for power return and shield, dynamic just needs it so you have somewhere to shunt crap on the shield.
If it's just your studio you're using stuff in, you could lift it on valve mics if you're external supply is wired right.

If you want to do the other guy who might use your stuff a favour, put a ground lift switch (with the R.F. shunt)
on the back of the chassis for all your line ins. 


Cheers.   

Thanks winston for clearing that up! 

If anyone has any ground tips/strategies to help out the new guys and other electronically impaired folks (like me, for example).

777funk said:

I think most people like star grounding near the input jack. But other than that I don't know much.

What rules do you use in your projects?


thanks! and interested to see what others have found. This can apply to both tube and solid state stuff.

Click to expand...

I don't use rules for grounding, I use my brains. Redraw the full schematic diagram replacing the ground with actual low value resistors. That will tell you what you should not do...

Winston O'Boogie said:

http://pin1problem.com/

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I was at Neil Muncy's place a few weeks ago... his basement is wonderland for techy-people