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Active crossover star grounding questions
Active crossover star grounding questions
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Old 22nd July 2004, 01:56 AM   #1
Beggar is offline Beggar  United Kingdom
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Default Active crossover star grounding questions

Hi all

Im just routing the grounds on my active crossover circuit, and a few questions about star grounding have arisen. Im not too knowledgeable about star grounding, however afaik it is best if all ground connections route to a single point by their own conductor.

Now with my crossover the circuit layout is too complex to allow for this, thus i wonder should i do...

a) Connect each op-amps signal grounds into their own star, and connect each opamps power grounds (between the decoupling caps) into their own star. Run a conductor between the two local stars, then run a large conductor to a star point for all other opamps. (Like connecting multiple power amplifiers off the same power supply)

OR

b) Connect each op-amps signal grounds together in a star, and run all these to a 'central' signal star, and do the same with power grounds, then connect the 2?

OR

c) Neither a or b, im stupid and someone should tell me what to do?

Also depending on what implimentation of star grounding selected, can anyone tell me where the grounds for the input and output connectors should be routed to, my current guesses are either into the opamp's signal ground their signal goes to/comes from, or directly to the boards main signal star?

I would, as always appreciate any help or suggestions people can give me with this.

Thanks, Nik

P.S. As of late im feeling a bit take take take with this forum, so i apologise for this.
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Old 22nd July 2004, 11:53 AM   #2
moamps is offline moamps  Croatia
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Default Re: Active crossover star grounding questions

Quote:
Originally posted by Beggar
b) Connect each op-amps signal grounds together in a star, and run all these to a 'central' signal star, and do the same with power grounds, then connect the 2?
Hi,
This solution looks much better.
Quote:
..... where the grounds for the input and output connectors should be routed to.....
Both versions are OK, but I prefer second.

Regards
Milan
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Old 22nd July 2004, 01:03 PM   #3
Beggar is offline Beggar  United Kingdom
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Hi ya

Thanks for the answer, i shall indeed proceed with that method

Cheers, Nik.
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Old 22nd July 2004, 03:15 PM   #4
Zodiac is offline Zodiac  United States
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Default Depends on ps

Depends on how you are powering them.

If all opamps are from the same supply then there should be a power supply star as well as a power supply ground star, both stars meeting at the regulator (active regulation) or ps cap (passive regulation)

If opamps are from galvanically isolated supplies then there is no need for star grounding.

I would not have a signal ground. I would choose to run my grounds from opamp to opamp

My 2c

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Old 23rd July 2004, 01:59 AM   #5
jewilson is offline jewilson  United States
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Beggar

Check out this thread http://www.diyaudio.com/forums/showt...0&pagenumber=1

Also look for the applications note on at www.analog.com
and on www.ti.com both companies have good detailed infomation on high performance grounding.
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Old 23rd July 2004, 02:44 AM   #6
sam9 is offline sam9  United States
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Everything I've read with respect to power amps says:

A - Do not use the point where the PS caps meet at this tends to be quite noisy. You can run a connection from that meeting point to the star ground.

B- If you have any auxilary systems such as relays, those should be connected at or near the PS caps, and then go to the star point.

C- Keep power gounds and signal grounds separate, on the PCB but connect them to the same star point. Sub-star points for each of these makes sense.

This would seem to make sense for anything else, not just amps.

--- Also per D.Self ----

D- Connection of the Starpoint to earthing point (i.e., place where the green wire is bolted to the enclosure) is made via the shield on the input signal. I've done it this way with no problems, but it seems weird. It seems to dictate that the shield have a substantial current capability.

E- It's kind of old fashioned and probably pointless, but I have seen cases where a 10-50 ohm series resistor is used on the PCB just before the point where you run the signal ground connect ion off from the board. The idea is that all other ground paths have a lower impedance as seen from the star point. I've never done this and never suffered for not doing it, but I mention it just because it is an option for the paranoid.
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Old 23rd July 2004, 01:26 PM   #7
Beggar is offline Beggar  United Kingdom
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Hi everyone, thanks very much for all your input, i have taken alot of the advice on board.

In the end i went for a signal star ground in the middle of the board supplied by 10 sub stars, (one from each quad opamp) I dont think i could have fitted on the bus style earthing as zodiac mentioned, and as for the power supply I had to connect all the power pins with jumper wires, so i can have a nice earth star ground, and power supply stars. If anyones interested ill post some pics of this 'monster' (mmm affection) when its built.

Cheers, Nik.
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Old 23rd July 2004, 03:00 PM   #8
jewilson is offline jewilson  United States
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Using a star ground.

I normally put the star very close to the power supply caps, that works fine.
If your creating a PCB keep the ground area for small signals returns as wide as possible.

Power returns should not connect to the signal ground except at the star.

Of course the chassis ground is connected to the star.

Treat the input and output signals with their own returns to to the star ground.

Don't dasy chain grounds that's bad.



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