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Author Topic: Galvanic isolation of all three pins in XLR vs ground lift  (Read 1201 times)

Miguel Dahl

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Galvanic isolation of all three pins in XLR vs ground lift
« on: August 21, 2018, 02:09:45 pm »

This might be a stupid question, but I'm curious about the difference.

If running a signal line to several active speakers, where one of them is powered from a different outlet with a different ground potential. Is there a difference in using a galvanic isolation between all three XLR-pins and just "lifting" pin 1? on the signal feeding the speaker on a different ground potential relative to the ground potential to where the signal originates from?
« Last Edit: August 21, 2018, 02:23:09 pm by Miguel Dahl »
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Pete Erskine

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Re: Galvanic isolation of all three pins in XLR vs ground lift
« Reply #1 on: August 21, 2018, 02:58:58 pm »

This might be a stupid question, but I'm curious about the difference.

If running a signal line to several active speakers, where one of them is powered from a different outlet with a different ground potential. Is there a difference in using a galvanic isolation between all three XLR-pins and just "lifting" pin 1? on the signal feeding the speaker on a different ground potential relative to the ground potential to where the signal originates from?

Depends on the input.  if it is transformer isolated no problem.  It is much more likely that you will need to have an isolation transformer in the line.
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Pete Erskine
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Miguel Dahl

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Re: Galvanic isolation of all three pins in XLR vs ground lift
« Reply #2 on: August 21, 2018, 03:11:28 pm »

Depends on the input.  if it is transformer isolated no problem.  It is much more likely that you will need to have an isolation transformer in the line.

Thanks, but I feel it didn't answer my question regarding what "answer I seek", the difference between a 3p iso and just a pin one iso.
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Pete Erskine

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Re: Galvanic isolation of all three pins in XLR vs ground lift
« Reply #3 on: August 21, 2018, 03:42:21 pm »

Thanks, but I feel it didn't answer my question regarding what "answer I seek", the difference between a 3p iso and just a pin one iso.

A transformer is a 2 pin iso.  Lifting pin 1 just disconnects the ground but if your equipment is NOT transformer isolated, pin 1 does not really isolate it, particularly if it is and electrally balanced I/O.

If you have transformer and pin 1 lifted it is a 3 pin iso.
« Last Edit: August 21, 2018, 03:44:23 pm by Pete Erskine »
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John Roberts {JR}

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Re: Galvanic isolation of all three pins in XLR vs ground lift
« Reply #4 on: August 21, 2018, 04:25:25 pm »

This might be a stupid question, but I'm curious about the difference.
perhaps...  do you have a problem?
Quote
If running a signal line to several active speakers, where one of them is powered from a different outlet with a different ground potential. Is there a difference in using a galvanic isolation between all three XLR-pins and just "lifting" pin 1? on the signal feeding the speaker on a different ground potential relative to the ground potential to where the signal originates from?
If the active speakers have a well designed input there will be no difference, if they don't the answer is not to float the ground (pin 1), but maybe see if the speakers float in the canal out back.

JR 
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Jonathan Johnson

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Re: Galvanic isolation of all three pins in XLR vs ground lift
« Reply #5 on: August 22, 2018, 12:37:07 pm »

perhaps...  do you have a problem? If the active speakers have a well designed input there will be no difference, if they don't the answer is not to float the ground (pin 1), but maybe see if the speakers float in the canal out back.

JR

OK, let's assume that we've got balanced in/out, and they are well-isolated, so there's no impact on the audio. If there is voltage potential between the two grounds -- "pin 1" -- could you conceivably get a current flowing on the shield? What is the likely current? Could it be high enough to lead to undesirable heating of the shield?
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John Roberts {JR}

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Re: Galvanic isolation of all three pins in XLR vs ground lift
« Reply #6 on: August 22, 2018, 02:06:46 pm »

OK, let's assume that we've got balanced in/out, and they are well-isolated, so there's no impact on the audio. If there is voltage potential between the two grounds -- "pin 1" -- could you conceivably get a current flowing on the shield? What is the likely current? Could it be high enough to lead to undesirable heating of the shield?
sure... mike probably has pictures of melted stuff over in the power forum from rogue ground currents.

JR
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Jonathan Johnson

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Re: Galvanic isolation of all three pins in XLR vs ground lift
« Reply #7 on: August 22, 2018, 03:49:56 pm »

OK, let's assume that we've got balanced in/out, and they are well-isolated, so there's no impact on the audio. If there is voltage potential between the two grounds -- "pin 1" -- could you conceivably get a current flowing on the shield? What is the likely current? Could it be high enough to lead to undesirable heating of the shield?

My point being that there may be reasons other than sound quality to isolate or lift pin 1.
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John Roberts {JR}

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Re: Galvanic isolation of all three pins in XLR vs ground lift
« Reply #8 on: August 22, 2018, 04:01:01 pm »

My point being that there may be reasons other than sound quality to isolate or lift pin 1.
If the safety ground is drawing excessive current you have a larger problem that needs correction.

JR
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Jordan Wolf

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Re: Galvanic isolation of all three pins in XLR vs ground lift
« Reply #9 on: August 22, 2018, 10:11:32 pm »

sure... mike probably has pictures of melted stuff over in the power forum from rogue ground currents.

JR
Indeed, this Sticky is all about that, due to a RPBG and the snake wiring was the fuse.
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