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Old 8th June 2003, 10:31 PM   #1
Prof is offline Prof  United Kingdom
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Wink Should I come down to Earth ?

My Gainclone is now a day old, still sprawled across my living room floor, but producing nice sounds ! The tweaker in me has now started to kick in, and my attention now turns to earthing. With no input, I get a slight hum from my speakers, quite normal, I believe, for a Gainclone (especially a naked Gainclone !). As an experiment I connected the power ground star point to mains earth and the hum quietened to virtually nil. Now, my NAD CD player is not earthed, it has a two core mains lead, so it just "floats". I have measured the chassis voltage of the CD player at about 50V AC, the Gainclone ground is also about the same (with the CD player disconnected). This volatge is obviously just "leakage" , so no harm in connecting to earth, or is there ? I would of thought that earthing the amp (and eventually, the metal case of the amp) would "shield" the circuitry from RF interference, a good thing ? However, I`m concerened about problems that I may get when I eventally connect my Satellite Decoder, Television and XBOX. These appliances have switch mode power supplies with chassis grounds that do carry a little more "oomph" ie. their grounds float at a higher voltage with respect to earth, and can actually provide a little current if connected to earth. Should I avoid earthing anything, or is there an advantage in doing so ? Maybe I could connect to earth through a resistor and/or capacitor. Can anyone with any knowledge on this matter please advise ?
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Old 9th June 2003, 03:48 AM   #2
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Search on "ground loops".

The best way to deal with a ground loop is to eliminate it if you can implement a single-wire-ground situation, where removing 1 wire would isolate you from your mains ground.

In your case, that get difficult because of your satellite receiver. I have personally used resistors to limit the current flow in the ground loop as a successful crutch, so keep that in your pocket if you need it.
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Old 9th June 2003, 04:14 AM   #3
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Default Re: Should I come down to Earth ?

Quote:
Originally posted by Prof
I have measured the chassis voltage of the CD player at about 50V AC, the Gainclone ground is also about the same (with the CD player disconnected). This volatge is obviously just "leakage" , so no harm in connecting to earth, or is there ?
An actual earth ground has no particular relevance to your audio equipment.

Quote:
I would of thought that earthing the amp (and eventually, the metal case of the amp) would "shield" the circuitry from RF interference, a good thing ?
Neither the amp nor the case require any earth ground connection in order to be effective at shielding. If that were the case, then the sensitive instrumentation on aircraft and spacecraft could never be effectively shielded. At least not without a REAAAAAALLY long extension cord.

Quote:
However, I`m concerened about problems that I may get when I eventally connect my Satellite Decoder, Television and XBOX. These appliances have switch mode power supplies with chassis grounds that do carry a little more "oomph" ie. their grounds float at a higher voltage with respect to earth, and can actually provide a little current if connected to earth. Should I avoid earthing anything, or is there an advantage in doing so ? Maybe I could connect to earth through a resistor and/or capacitor. Can anyone with any knowledge on this matter please advise ?
The only reason you'd want to connect to the earth ground (i.e. the safety ground) is for safety reasons. That's basically its only purpose.

se
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Old 9th June 2003, 06:59 PM   #4
mothman is offline mothman  United States
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Steve,
What happens to stray voltages on the chassis.Am I wrong in thinking that an 'earth' connection also functions as a drain?
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Old 9th June 2003, 07:34 PM   #5
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Quote:
Originally posted by mothman
What happens to stray voltages on the chassis.Am I wrong in thinking that an 'earth' connection also functions as a drain?
What exactly do you mean by "stray voltages"? Stray voltages from what? And what's the reference point for the voltages (seeing as a voltage is just the potential difference between two points)?

The earth connection really only functions as a drain as it regards such things as lightning. That's basically all it's there for so that if lightning happens to strike the power lines, it provides a path to ground seeing as lightning is due to opposing static charges between the earth and the clouds.

se
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Old 9th June 2003, 09:00 PM   #6
mothman is offline mothman  United States
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I do understand the 'safety ground' function and it having nothing to do with the 'amp ground'and I guess 'stray voltage' is a term flung around to confuse novice guys like me.I thought airborn or a connected component could channel nasties into the amp circuit or maybe it was reading too many of Jonathan Skull's columns that corrupted me.
Seriously though assuming my amp is properly grounded(and I believe it is)and my case is connected to 'Earth Safety Ground'is directly connecting 'Amp Ground' to this point,to get the shielding benefit of the case OK?..You don't really wanna leave the amp floating do you?
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Old 9th June 2003, 09:16 PM   #7
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you got it!!!!
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Old 10th June 2003, 06:17 AM   #8
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Quote:
Originally posted by mothman
I do understand the 'safety ground' function and it having nothing to do with the 'amp ground'and I guess 'stray voltage' is a term flung around to confuse novice guys like me.I thought airborn or a connected component could channel nasties into the amp circuit or maybe it was reading too many of Jonathan Skull's columns that corrupted me.
Hehehe. J10's cool. He and I go back to the old The Audiophile Network BBS (a.k.a. TAN) back in the mid-80s (that's where JA recruited him from to write for Stereophile, along with several other TAN members). But alas he's sold his soul to Monster Cable.

Quote:
Seriously though assuming my amp is properly grounded(and I believe it is)and my case is connected to 'Earth Safety Ground'is directly connecting 'Amp Ground' to this point,to get the shielding benefit of the case OK?..You don't really wanna leave the amp floating do you?
Floating with respect to the chassis? Not really. Technically you're better off making the chassis part of the amp's reference ground. Just that once you bring the safety ground into the picture, you open yourself up to ground loop and other problems.

So basically you trade a margin of safety for a margin of potential noise problems.

Of course you can use a line level input transformer and just eliminate any ground loop and interchassis current problems altogether. That's what I've been doing for years.

se
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Old 11th June 2003, 09:59 AM   #9
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Prof,

I suppose that laying on the floor you have one transformer (you don't specify if one or two) and the two channels of your GC.
Join the two channels together (get them close) and run a wire from the star ground of left channel to the star ground of the right channel.
This wire must be very short, so you have to get the two cannels toguether.
Then, from a middle point of this wire, connect to the ground wire of your transformer (or if you use two bridges, the ground point).
For now, forget the mains earth.
Turn it on and listen.
Silent?
If not, you have a problem with ground loops on your implementation.
You can try also connecting only one channel and see how does it behave.
If there's noise with only one channel connected, you have a ground loop.
If it's silent and the noise only appears whent both channels are connected, it's because you have long wires to the ground point, and you easilly solve this as I describe above.
I hope this helps.
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Old 11th June 2003, 11:35 AM   #10
DRC is offline DRC  United Kingdom
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Prof,
I would always recommend connecting a metal chassis to earth/ground for safety - even with 'double isolated' electronics - as you should not discount the possibility of the case coming into contact with mains/live (externally) - with an earth connection it should at least blow a fuse / open an RCD somewhere !!

The real question is do you connect the 'center tap' of your PSU to earch as well ? If you do not you risk some other piece of connected equipment raising the potential of this point WRT ground and generally swinging it around !! My choice would be to connect to ground (through a resistor ?) but not to make it to difficult to change, if, and when, nessesary ...

My most recent experience of 'ground loops' occured after my cable TV intallation was upgraded with a cable modem. This resulted in severe interferance breaking through the shields from a DVD and PC (no problems prior to modem). Nothing I tried could eliminate this totally (ferrites/earthing/un-earthing/messin' with the cable TV shield/hasselling the cable co/etc/etc) and I eventually had to resort to optical links . Sometimes no amount of fiddling with earthing will fix a problem ....

Dave
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