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Old 7th March 2014, 09:45 AM   #21
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I don't know if you've heard of the UKs Compliance Club..

Its a journal of EMC/EMI related material ,with many contributions over the years by Keith Armstrong and other such luminarys. A must have resource.

There are over 100 originally printed issues that you can download in pdf form , and earthing,grounding and shielding of PCBs and ancilliaries are its bread and butter.

EMC Information Centre

You may have to register to gain access , but its free and they do not spam given email addresses.

Rob
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Old 7th March 2014, 10:17 AM   #22
Bonsai is offline Bonsai  Taiwan
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Firstly, have you checked that your input sockets are not shorting to the chassis (disconnect the input wires and measure).

Both the 0V and the PE must connect at one place only on the chassis

For the small signal stuff you have two options

1. Place a 10 ohm resistor between the signal ground and the power ground on the PCB. The input signal ground connects onto the PCB ground only.

2. The second option it to leave the 10 ohm resistor in place, but run a connection from the input socket ground to the star ground on your PCB.

These techniques usually solve most problems. However, not all consumer equipment is faultless.
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Last edited by Bonsai; 7th March 2014 at 10:31 AM.
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Old 8th March 2014, 02:50 AM   #23
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Quote:
Originally Posted by MrSleepy View Post
I don't know if you've heard of the UKs Compliance Club..

Its a journal of EMC/EMI related material ,with many contributions over the years by Keith Armstrong and other such luminarys. A must have resource.

There are over 100 originally printed issues that you can download in pdf form , and earthing,grounding and shielding of PCBs and ancilliaries are its bread and butter.

EMC Information Centre

You may have to register to gain access , but its free and they do not spam given email addresses.

Rob
Wow, LOTS of good stuff here. They suggest connecting a CM choke just like I described. Reading through the articles will help to give you a sense of what the dangers of EMI are, what is susceptible and how to immunize your circuits/appliances.
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Old 10th March 2014, 01:17 AM   #24
BigE is offline BigE  Canada
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I am unfamiliar with the terms signal ground and source ground. Would this sit inline on a single ended input?
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Old 10th March 2014, 01:24 AM   #25
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Source ground is the ground at your source's output. Signal ground is the ground at your amp's input. This is for unbalanced connections. Balanced connections would need a 3-winding CM choke, but they are expensive, exotic and it's arguable whether they would improve a balanced connection.
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Old 10th March 2014, 09:15 PM   #26
BigE is offline BigE  Canada
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Thanks.
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Old 12th March 2015, 12:07 PM   #27
AndrewT is offline AndrewT  Scotland
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Could a ferrite toroid do this duty (post20) as effectively?
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Old 12th March 2015, 12:21 PM   #28
AJT is offline AJT  Philippines
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a ground loop is formed when two points that are supposed to be zero volts actually have a voltage difference between them or that there is an opportunity for loop current to flow due to a complete circuit....

so look at your construction and see it this is possible in your build and then act accordingly....
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Old 12th March 2015, 06:14 PM   #29
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Could a ferrite toroid do this duty (post20) as effectively?
Plenty of CM chokes are a ferrite toroid with two windings. If you mean the bare toroids intended for blocking EMI on cables, then probably, but I don't think it would be easy to get a high enough inductance. The 60Hz inductance needs to be high enough at 60Hz to break fault currents through the coil so that the magnetizing current isn't large enough to saturate the ferrite.
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Old 13th March 2015, 04:41 AM   #30
benb is online now benb  United States
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Originally Posted by KatieandDad View Post
I'm baffled.

If you build a solid amplifier with a star 0V it will work flawlessly.

I've also got a pre-amp with a solid star 0V and it works flawlessly.

Connect the two together and you invariably end up with a loop.

I've got a commercial CD player which I'm not going to modify.

I thought breaking the loops in the pre might do the trick but it hasn't.

The question is where to break the loops.
It's not the star "0v" that's the solution or the problem. Needless to say, it's more complicated than a star ground.

It's other things (capacitive coupling between power transformers, and actual capacitors across the line, neutral and ground connections where the power cord comes into a unit, for two things) that make "ground" on Component A not the same as "ground" on Component B.

This guy (Bill Whitlock of Jensen Transformers) explains it really well, after taking several pages to explain why you do NOT want to use a "ground lift" thing on anything. He also sells audio isolation transformers which indeed solve the problem, though they're not the only (legal) way:
http://www.bennettprescott.com/downl...g_tutorial.pdf
There was a link to a "blue wire" connection earlier in the thread, and there's also circuits where that "blue wire" is replaced with a 10 ohm resistor. This resistor drops most of the voltage difference between two components' "grounds" and allows the input to effectively function as a balanced input which cancels out the difference between the two chassis.

Here it is, post #57 of that same thread:
3 stage LIN topology - NFB tappings?

Here's your homework: Look over all this and tell us why that 10 ohm resistor fixes the problem.
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