What is a star ground?

Okay, that's another one of my "what a newb!" thread titles, since I know on a technical level what a star ground is. What I don't understand is why they are used exclusively in the audio world. Is it to alleviate ground loop issues?

-- Darren, asking all the stupid questions since 2003

Star grounding is used in all cases where precise operation on small signals is important.

Not stargrounding runs the risk of drawing current through a non-ideal ground rail resistor, and thus changing the ground reference.

Clean ground is the important thing when working with small voltages.

Jakob E.

So basically, you have to make a decision on where your single ground point will be, and then make sure all of your grounds run in parallel straight back to that point? Is this specific only to a single device, or is this something you need to worry about for an entire studio full of devices?

Thank you very much, Jakob, for the explanation!

Thank you, Chae.

I'm beginning to get a picture of how this works, now, I think.

Steel has resistance. So a chassis used as a ground will develop voltages in the metal due to ground currents.
If you mix in shield currents(dirty noise) with your audio currents in the chassis, you get the noise from the shield in the audio.

You can do lesser versions of the star ground, like using two ground points intead of one.
when you start using a zillion ground points you can run into problems.
Fender never used start grounds because they prototyped until they didn't have to. But if you don't have the time to solve a ground problem, then the start ground is the bom.

Try to solder your start ground directly to the chassis, a big lug for instance, where everythng can be tied in. less resistance and better performance over time. no coroding due to disimilar metals.
cj

I dislike the term ground loop. I like to use the terms potental difference. A "ground loop" is caused by two "ground" points having a voltage difference between them and electricaly connected current then "flows'.

Years ago I read a good intel writeup on grounding. remember in the macroscopic world we llive in, the current that "flows" "thru" the circuit has to sum up.

FWIW when I build high gain effect petals I single point ground and power. I do this in tube guitar amps as well.

IIRC current flowing in a shield reduces it effect as a shield

Good writeup is at www.geofex.com look for start grounding an amp

Thanks Consul for starting this thread, i've just started designing some boards for my hamptone project and i was wondering what advantages there would be to using two layers, the signal and a power plane with really thick traces on the power plane and a star ground layout to minimize interaction. Will this make a noticable difference in PSRR? Or it a bit overkill? I'd really like to see how a very low noise psu should be designed/layed out. I'll post some test layouts later...

The best explaination I've found on this is here:

http://www.aikenamps.com/TechInfo.htm

Look under "Advanced" then star grounding.

Some of my favourite links for grounding/interconnection/balanced/unbalanced knowledge:
From Rane website:

Rane sound sys interconn. Note 110:

http://www.rane.com/note110.html

http://www.rane.com/pdf/note110.pdf


considerations in gnding and shlding audio devices

http://www.rane.com/note151.html

http://www.rane.com/pdf/note151.pdf


system problems and equip manuf.

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


grounding and shielding with computers

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




From Jensen website:


Interconn bal and unbal AN003

http://www.jensen-transformers.com/an/an003.pdf


Hum and buzz in unbal interconns an004

http://www.jensen-transformers.com/an/an004.pdf


AS032 Build the Hummer to find Pin 1 Problems

http://www.jensen-transformers.com/as/as032.pdf


AS085 Proper grounding inside equipment

http://www.jensen-transformers.com/as/as085.pdf

Lots of reading...

...but useful!

Mark

Wow! Thanks all for the links. It'll take me a while to plow through those.

Dang RF! That's a good looking project!

There are a lot of Star Grounds on Hollywood Blvd. also.
Just don't step on Brando! :?
:guinness: :guinness: :guinness: :guinness:

Generally the best place to run a star ground to is the power supply point that is referenced to ground. This could be the negative side of the filter cap in a single power supply, the junction of the two filter capacitors in a dual supply. This is typically the lowest impedance as far as a ground reference. Many manufactureres put a ground buss between the filter caps just so there is a place to tie all the grounds back to.

Something I just thought of...

You know that copper tape you can buy? Could you run that around on the inside of a case and run your grounds to it? Given how much better of a conductor copper is, do you think that would work?

If you look at power amp design with bipolar supplies, usually the ground point between the main resevoir caps are linked separately away from the signal ground (as in the + and - of these caps first join together, then get taken to the star ground). This may not be necessary with devices that only deal with line level signals, but is probably good practice nonetheless.

As far as the ultimate star ground implementation goes, don't we already break the rules by joining all the grounds at one particular device, and then taking all the grounds of all the devices and joining them together? Take star ground to its ultimate implementation, and all them green wires that join together in your device should really be taken outside of it, and bonded together at one huge massive ground point along with a million other ground wires from all your other kit...innit!!

Or, we could just use balanced lines between all pieces of gear??

Bjorn

:sam: :sam: :sam: I had one of these in a restaurant in Kensington today...damn they're good!

Just think of your chassis as a buss bar in a mixer, where everthing gets summed.
Whatever that means. Too much Monster Energy. Unleash the Beast!
:wink: