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Ground Loops explained


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HQPlayer (on 3.8 GHz 8-core i7 iMac 2020) > NAA (on 2012 Mac Mini i7) > RME ADI-2 v2 > Benchmark AHB-2 > Thiel 3.7

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The Douglas Self link didn't work for me, but there is a coverage of this area in Chapter 18 of "Audio Power Amplifier Design Handbook 5th ed - D. Self"

 

How a Digital Audio file sounds, or a Digital Video file looks, is governed to a large extent by the Power Supply area. All that Identical Checksums gives is the possibility of REGENERATING the file to close to that of the original file.

PROFILE UPDATED 13-11-2020

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Timely subject - if one didn't have many alternatives due to existing wiring (older two prong/no ground), can the use of a GFI wall outlet be an option (with no ground)?

 

Not ideal but would it provide the "same" protection of a normal three prong outlet?

My rig

 

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Some more Bill Whitlock (Jensen Transformers) pages:

 

"Pesky Ground Loop Problems Plaguing You?"

 

Although ground loops often involve power line safety ground connections, disabling them is both highly dangerous and illegal...

AV: Pesky Ground Loop Problems Plaguing You? - Pro Sound Web

 

"Further Eliminating Ground Loop Related Problems With Proper Use Of Isolators"

 

A properly installed isolator virtually eliminates hum, buzz, or other noises caused by ground loops.

AV: Further Eliminating Ground Loop Related Problems With Proper Use Of Isolators - Pro Sound Web

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Timely subject - if one didn't have many alternatives due to existing wiring (older two prong/no ground), can the use of a GFI wall outlet be an option (with no ground)?

 

Not ideal but would it provide the "same" protection of a normal three prong outlet?

 

No, no, and no. The way to fix poorly grounded power (if you cannot get the ground itself to be correct), is to use balanced power. This is a transformer system, that effectively isolates the power you are using from the infrastructure.

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No, no, and no. The way to fix poorly grounded power (if you cannot get the ground itself to be correct), is to use balanced power. This is a transformer system, that effectively isolates the power you are using from the infrastructure.

 

Yeah probably poor choice of words using the "same protection" inference.

My rig

 

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Timely subject - if one didn't have many alternatives due to existing wiring (older two prong/no ground), can the use of a GFI wall outlet be an option (with no ground)?

 

Not ideal but would it provide the "same" protection of a normal three prong outlet?

 

The GFI detects assymetric currents in the hot and neutral and if there's an imbalance of 30mA or more, the GFI trips. Kind of difficult to put in words, always need a drawing, say a lamp's frame hot connects with the frame. Since your 2 prong wall outlet doesn't have an third ground conductor, there's no return path, so the lamp frame is live.

If you are insulated enough, you won't detect the voltage when you touch the frame. But odds are you aren't insulated very well and you stand on earth, or touch a water pipe which is grounded, the current will go through you to ground. The GFI will pick this imbalance and shut the power off.

 

That's the safety aspect.

 

For audio, if an amplifier has a two prong plug and the wall outlet is two prong, 99% of the time, the amplifier is double insulated and incapable of creating a situation with the lamp. If the amplifier comes with a three prong connector, and a 2 prong wall outlet is only available, you can't use this equipment. A three prong device must be connected to ground for the safety certificates and compliance to be intact.

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No, no, and no. The way to fix poorly grounded power (if you cannot get the ground itself to be correct), is to use balanced power. This is a transformer system, that effectively isolates the power you are using from the infrastructure.

 

A balanced transformer requires a ground connection at the secondary. A two prong wall outlet does not provide this connection and can't be used.

AS Profile Equipment List        Say NO to MQA

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If I understand the video correctly, there can't be a ground loop if two pieces of equipment a plugged into the same outlet.

 

Am I right?

 

Even if it is the same outlet, an unbalanced RCA connection can create a ground loop by definition. The shield voltage is really small but can't be eliminated unless there's a transformer.

XLR bonds two components via the shield only and doesn't carry a signal.

AS Profile Equipment List        Say NO to MQA

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If I understand the video correctly, there can't be a ground loop if two pieces of equipment a plugged into the same outlet.

 

Am I right?

 

 

Nope, as soon as two equipment are electrically connected, you can have a ground loop. Balanced power is the only true solution. (Ok, optical interconnect is the other one)

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Even if it is the same outlet, an unbalanced RCA connection can create a ground loop by definition. The shield voltage is really small but can't be eliminated unless there's a transformer.

XLR bonds two components via the shield only and doesn't carry a signal.

 

 

Nope, as soon as two equipment are electrically connected, you can have a ground loop. Balanced power is the only true solution. (Ok, optical interconnect is the other one)

 

 

Not what I was hoping to hear, but I really appreciate the help.

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Even if it is the same outlet, an unbalanced RCA connection can create a ground loop by definition. The shield voltage is really small but can't be eliminated unless there's a transformer.

XLR bonds two components via the shield only and doesn't carry a signal.

 

XLR, or more to the point, balanced signal is not bonded. There are three wires, one signal, one signal that is a reverse polarity of this, and the shield. When the signal reaches it's destination, the signal that was reversed is re-reversed to match the original signal. Any noise that has been introduced through the cabling during it's run, is now eliminated. (Assuming that equal amounts of noise have been added to both the original signal and the reversed signal.) Usually, this process is done via transformer, so that there is also no direct connection (or loop) via the shield.

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If I understand the video correctly, there can't be a ground loop if two pieces of equipment a plugged into the same outlet.

 

Am I right?

I haven't had a chance to watch the video, but I wonder though, how many current designs using RCA connectors have the sockets directly connected to the grounded case as in the Douglas Self main diagrams ? My own DIY gear certainly doesn't and no recent designs from Silicon Chip magazine do either. My S.C. DAC for example with it's earthed case, sees it's "earth" via the preamp which has only the C.T. of the secondary windings connected to it's case,and then finally from the 15W Class A PA via 10 ohm "earth lift" resistors .

 

How a Digital Audio file sounds, or a Digital Video file looks, is governed to a large extent by the Power Supply area. All that Identical Checksums gives is the possibility of REGENERATING the file to close to that of the original file.

PROFILE UPDATED 13-11-2020

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Before I get jumped on about the lack of IEC mains earth on the Preamp, I should have also mentioned that both Preamp and 15W Class A get their power from a separate 2U rack case with 3 transformers . The 15W has a dual secondary winding screened toroidal transformer and 2 separate Regulated PSU PCBs. The 0 volts is connected to chassis and the DC outputs go via 1M long cables to the 15W Class A. The preamps uses 2 separate 18-0-18 30 VA transformers which supply 18-0-18 VAC to the Preamp. The secondary windings C.T's are not connected to earth in the main PSU case.

There is no audible hiss or hum (younger ears) right against the speakers at normal listening levels.

Any genuine improvement suggestions are welcomed.

Alex

 

How a Digital Audio file sounds, or a Digital Video file looks, is governed to a large extent by the Power Supply area. All that Identical Checksums gives is the possibility of REGENERATING the file to close to that of the original file.

PROFILE UPDATED 13-11-2020

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This part:

When the signal reaches it's destination, the signal that was reversed is re-reversed to match the original signal.

 

*************************

The shield has nothing to do with the signal.The signal is the difference between conductor 'A' and conductor 'B'.The noise is the same between conductor 'A' and conductor 'B', so the noise doesn't get amplified

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The GFI detects assymetric currents in the hot and neutral and if there's an imbalance of 30mA or more, the GFI trips. Kind of difficult to put in words, always need a drawing....

 

I think that you give a pretty good description by using asymmetric.

 

I have seen really bad internet articles that say it is about current, but that is the job of a circuit breaker, not the ground fault. GFI is about differential in current.

 

EG, a guitar amp plugged into a GFI. The GFI wants the same amount of current in both the hot and neutral, as stated. If any current goes to say, the guitar strings, and then to the microphone through the guitarists lips, this is bad. So if more than the mentioned 30mA goes to the mic/sound system, instead of the guitar amp plug, the GFI will trip.

 

So back to the Foggie post, most hum in systems from bad power comes from a differential, but in voltage, not current. If there is a voltage difference across the hot and neutral, and the hot and ground, that is where the problem comes in, and the GFI will do nothing for it.

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The shield has nothing to do with the signal.The signal is the difference between conductor 'A' and conductor 'B'.The noise is the same between conductor 'A' and conductor 'B', so the noise doesn't get amplified

 

"When the + and - arms have identical ratios, the bridge is "nulled" and zero voltage difference exists between the lines - infinite common-mode rejection. If the impedance ratios of the two arms are imperfectly matched, mode conversion occurs. Some of the ground noise now appears across the line as noise."

diferential.jpg

But this only works if the two signals are out of polarity with each other. (the plus arm, and the minus arm, referenced in the quote from the article.)

One is "adding" and the other is "subtracting". Then you get no signal difference.

 

"A good, accurate definition is "A balanced circuit is a two-conductor circuit in which both conductors and all circuits connected to them have the same impedance with respect to ground and to all other conductors. The purpose of balancing is to make the noise pickup equal in both conductors, in which case it will be a common-mode signal which can be made to cancel out in the load." "

 

So to me the important part is impedance matching, instead of voltage matching.

Making transformer balancing better than active circuit balancing, at rejecting noise.

differential copy.jpg

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