Ground Loops 101

[jkeny]

Fortunately, I believe ground loops are fairly rare these days.
What is a much more common issue are leakage currents.
These arise from the ubiquitous use of SMPS in the form of power bricks, wallwarts & internal PSes in computers & other devices often found in the playback chain
These leakage currents similarly find their way into & cause noise issues in signal ground.

But again, the best solution is to ground the the non-positive output from the SMPSes.

PS. I note that the AP grounding recommendation diagram above is the very same one I recommended here for Amir's benefit - obviously it depends on who is the messenger, as my suggestion was rejected as idiotic by some of the same people who praise it above

 

[Empirical Audio]

Fortunately, I believe ground loops are fairly rare these days.

I suspect that many "RF" noise complaints are due to ground loops.

Steve N.
Empirical Audio

 

[Kingrex]

Speedskater hit the nail on the head. It's poorly designed equipment that causes ground issues, provided you built up your foundation power correct. Every audio system I power and can't rid all the noise, its always the gear. Unfortunately owners don't want to deal with that. And to be fair, I had to send my amps to a different manufacturer to have the internal ground issues fixed because the maker of the amps did not know how to do it themselves. The audio owner then buys cheaters or disconnect grounds from plugs. Now that voltage is hanging in the case of your gear. Is only takes about 40 miliamp at 120 volt to kill you. Most tube amps operate around 600 volts.

And, grounding properly brings about a quiet, calm and ease that far surpasses a poorly grounded or ungrounded system. Always ground your gear.

And, a power conditioner won't help fix equipment that is not working properly. If it's humming, it will most likely continue to hum after you put a power conditioner in front of it.

And lastly, a power conditioner will work as intended only if you have a well grounded system and all the behind the wall power is installed correct.

 

[Ron Resnick]

Hmmm. I am skeptical that the manufacturers of our favorite audio electronics don't know how to design and implement a proper ground in their equipment.

I am no electrician, but as a layman I suspect that the need to use a cheater cord to solve a 60 Hz hum is a result of somewhat random and unpredictable interaction between audio components, and among audio components and the existing electrical system and maybe varying lengths of different circuits and existing electrical system's ground wiring and grounding efficacy.

 

[Folsom]

Hmmm. I am skeptical that the manufacturers of our favorite audio electronics don't know how to design and implement a proper ground in their equipment.

I am no electrician, but as a layman I suspect that the need to use a cheater cord to solve a 60 Hz hum is a result of somewhat random and unpredictable interaction between audio components, and among audio components and the existing electrical system and maybe varying lengths of different circuits and existing electrical system's ground wiring and grounding efficacy.

It truly is too complicated to sum up shortly and easily.

Sometimes mixing of manufacturers with different scheme that are both correct is an issue. Sometimes it's shielding... Sometimes you get a bad part you don't know is bad because it doesn't present itself in testing before you sell the piece of equipment.

And as far as the fear factor... Grounding hasn't been around as long as electricity has and yet most people haven't died from it. And ground is a noise source, to think that it's some sorta giant hole you can just throw noise into is ignorance. We try to make it work that way as much as possible, but mostly because we're using it for meeting codes or trying to use it for a shield, not because it actually is inherently a giant hole you can throw noise into.

 

[ack]

It truly is too complicated to sum up shortly and easily.

Sometimes mixing of manufacturers with different scheme that are both correct is an issue. Sometimes it's shielding... Sometimes you get a bad part you don't know is bad because it doesn't present itself in testing before you sell the piece of equipment.

And as far as the fear factor... Grounding hasn't been around as long as electricity has and yet most people haven't died from it. And ground is a noise source, to think that it's some sorta giant hole you can just throw noise into is ignorance. We try to make it work that way as much as possible, but mostly because we're using it for meeting codes or trying to use it for a shield, not because it actually is inherently a giant hole you can throw noise into.

Exactly. With respect to the underlined, I had to deal with it just today, by chance, as a result of trying a few other things. A very small amount of hum was coming out of my amps; lifting their grounds "fixed" it; removing their interconnects "fixed" it. Was it the amps? Nope; I traced it to the Pass XP-25 phono (God, I hate that thing, it will be booted asap).

What we've said before is that all ground paths have to be exactly the same, in order to avoid ground potential and ground-induced noise. Although one can elect to use the exact model and same-legth cords (as I do), this is easier said than done, because there may be many ground paths via power cords and interconnects (involving how the signal ground may be connected to earth ground inside the various components, if at all).

A ground connection is a different path to neutral (they are 'bonded' at the fuse box) plus a link to earth ground for a faster safety route. But, lifting the ground in order to break a ground loop is not anathema either (because of that bonding) - older equipment like my Revox or Nak Dragon just don't have a separate ground wire - and may even lead to proper star-grounding. The problem with lifting the ground is that, in the event of a ground fault, very high current, as high as 150A, may run through the interconnects instead, and that may be a problem.

But is lifting the ground a real concern? Nordost, among others, don't think so. Here's a response I received recently from a dealer:

If you use the Nordost [QRT QB8 MARK II power distributor] then everything is floated (without using cheater plugs) except for one socket where the preamp is plugged in.​

Referring to the Nordost manuals, like https://www.nordost.com/downloads/QBASE Instruction Manual_web.pdf, one will notice that their power distributors have one outlet marked as "Primary Earth", and they want you to connect the preamp to it, effectively making it the star-ground host of the entire system. Here's one of their diagrams and notice where the preamp is connected:



The real problem, in my mind, with lifting grounds, is potential sonic impact; and I hear it with my amps as glare in some frequencies, so I no longer do it there.

-ack

 

[Alrainbow]

This article is to help show what causes those pesky ground loops many of us have had to deal with at one time or another. Essentially what happens is that a signal is created between two ground points in the system. The gain from source to speaker can be very high and amplifies the “ground” signal, leading to that familiar raspy buzzing sound.

Consider the system shown below. Please note this is not meant to be technically rigorous but to illustrate how ground loops can form. Red lines are positive signal wires, black lines are negative signal wires, and dashed green lines show the current flow. The source (CD player, BD player, turntable, cable box, etc.) is connected to earth ground but the preamp and power amp “float”. This shows a system where only the source has a three-prong plug. The signal current can only flow one way and terminates at the single (source) ground terminal. Ground noise affects only the source, but since all components reference the source, the noise is suppressed. Any ground voltage at the source moves its (+) and (-) outputs equally. With no other ground connections the preamp and power amp follow. No ground loop, no nasty ground loop hum.

View attachment 25505

Now consider the case when all components have three-way plugs or are otherwise grounded. Now there are three ground loops formed: source to preamp, preamp to amp, and source to amp. Any ground leakage or noise current in any component can circulate among these loops. The currents through the resistors cause voltage fluctuations that affect each component. Since some of the signal current now goes into the ground loops, instead of the straight signal path shown above, the voltage induced is seen as signal by the components. They cannot tell if it is “true” signal voltage or voltage caused by ground currents. Since the ground current is often 60 Hz leakage from transformers or unbalanced loads that is the source of the 60 Hz (and harmonic) buzz commonly associated with ground loops. Note that any ground noise can cause this effect, whether 60 Hz power line signals or EMI/RFI.

View attachment 25504

A simple simulation can illustrate the severity of the problem. Vsrc may be a turntable, CD player, cable box, etc. It is not used for these simulations thus its amplitude is zero. Notice the source ground, Gsrc, is connected to earth ground by another signal VGsrc. This represents the induced ground signal and is coupled to the source ground pin Gsrc through resistor R3. VGsrc is a 1 uV, 60 Hz signal representing induced ground noise. The preamp and amplifier (represented by ideal gain stages Epre and Eamp) are also connected to earth ground through resistors R4 and R5. Finally, signal grounds are connected through R1 (source to preamp) and R2 (preamp to power amplifier). The preamp has 60 dB of gain, the amplifier has 30 dB, and the 8-ohm load R6 represents a loudspeaker.

View attachment 25503

This example shows R1, R2, and R3 small (1 u-ohm), shorting the source, preamp, and amplifier grounds to the induced signal source VGsrc. They represent ideal cables and ideal source chassis ground. R4 and R5 are large (10^6 ohms) to float the preamp and power amp (e.g. two-prong power plugs). Because there is no low-impedance path to ground from the preamp and power amp, no ground loop is formed, as shown earlier. You can see this is the plot below; the signals are near 0 V at all points (f = femtovolt = 10^-15 V; u = microvolt = 10^-6 V). The top plot shows the source (blue), preamp (red), and amplifier (green) output signals. The bottom plot shows the ground signals at the source (blue), preamp (red), and amplifier (green). Even with only 1 micro-ohm there is some signal generated by the ground signal but it is very tiny (< 100 fV, or 0.000000000000001 V)

View attachment 25502

Now observe the results when R4 and R5 are also 1 micro-ohm, essentially shorting signal and earth grounds through tiny resistors. This represents the case when all components have three-prong plugs. The resistors act as voltage dividers to couple the signal grounds at each point in the chain. The 1 uVpk ground signal has been amplified to about 10 mVpk (about 6 uW) at the speaker. That would be about 36 dB SPL from a pair of 90 dB/W/m speakers 6’ (2 m) away. Still small, but what if the ground signal was 100 uV? That does not seem like much, but then the voltage across the speaker would be about 1 Vpk or about 62.5 mW. With a pair of 90 dB/W/m speakers the volume (SPL) six feet away would be about 75 dB, definitely audible (I would say loud!), and that is with no room gain. We have a ground loop; the signal ground goes one way, and chassis ground another, providing two places for the signal to flow. Now ground is not really ground so any ground signal is amplified, to our detriment.

View attachment 25501

Clearly small leakage or noise currents in the ground loops can cause very audible problems (as we know). Note cables typically have resistance of milli-ohms, not micro-ohms, and components may be plugged into different circuits so the ground path can be very long. Larger (parasitic) resistor values and additional ground signal sources will generate larger and potentially more complex noise as the signals interact among the components and with the primary signal from the source. Even low-level noise can often be noticed by its absence when the system is modified to eliminate ground loops.

HTH - Don

How does this work out on a real balanced system not a fake one ? Some pre amps have isolation input transformers how sore this effect the overall ground path

 

[Alrainbow]

In the end it’s all about perfect balance in voltage potential In think. If a given device remains isolated by its input transformer most of this might solved I’ve read is this true

 

[ack]

Sometimes it's shielding...

And a bit more about this... indeed, some of the hum I fixed today had to do with the Shunyata interconnects on my Alpha DAC (evident on its own preamp input). I twisted them around each other, and it was gone. Apparently, the shield does not provide 100% coverage

 

[DonH50]

How does this work out on a real balanced system not a fake one ? Some pre amps have isolation input transformers how sore this effect the overall ground path

I would describe my presentation as "simplified" and not "fake" but whatever. I picked situations and values I have measured in the real world. There is a range of "balanced" implementations from fully-differential to quasi-balanced to basically three-pin single-ended circuits marketed as balanced.

Disclaimer: I am not an expert on transformers, not a designer f them (in general, save for some RF transformers and baluns not relevant here).

Without knowing how the transformer is implemented in-circuit I could not say exactly the impact. A transformer can provide galvanic isolation to break a ground loop through the safety ground connection, probably the most common problem in an audio system. So, if the signal is differential, it can pass through the transformer without "grounding", and the input transformer will break a ground loop. A transformer is also a common way to convert from single-ended to differential and vice-versa. Again, that can isolate the signal ground at one side from the other, breaking a ground loop. You can buy transformers preconfigured (wired) to do exactly that.

There are caveats, of course. Sometimes the transformer shield is grounded along with the signal at one or both sides, providing a "sneak" path for ground currents. Real-world transformers have shunt capacitance that can allow RF noise through, and common-mode rejection at low frequencies is not perfect due to physical configuration and because it is difficult to get the two sections to be perfectly symmetric. Any imbalance will reduce common-mode rejection.

Transformers have some other quirks that have come up in the audio world. Standard EI (the core and winding actually looks like "E I" compared to say a toroid) transformers generate a fairly significant EM field so have given way (mostly) to toroidal transformers in audio components. The EM fields of a toroid wrap fairly tightly around the circular core so you can pack components closer without risk of hum pickup. But, toroids do not have an air gap, leading to lower efficiency (more loss) and more chance of hysteresis and saturation that can cause distortion in the output waveform. For various reasons the signal through a transformer does not behave the same in both directions (remember AC -- audio -- signals go positive and negative) and the larger the signal the more prominent the difference. That adds distortion to the signal, albeit it should be minute for a properly designed transformer for the application. The lack of an air gap also makes toroids more sensitive to DC on the incoming line, or noise that "looks like" DC, leading some to add DC-blocking circuits to their power connections (typically as part of a noise-suppressing power strip).

For phono step-up transformers, tics and pops can cause the transformer to saturate, which causes distortion and ringing that can last after the actual noise event on the record. Again remembering this is not my field, my past experience with them is that mitigation usually involves greatly oversizing the transformer to handle peaks well beyond (10x or more) the expected cartridge output, and adding capacitors to band-limit the input to reduce the magnitude of such peaks hitting the transformer. The capacitors also add RFI suppression

Note Ethernet also uses transformers to isolate the ground from the signal path which is why ground loops are rarely a problem for an Ethernet connection. Typical RF TV and satellite cables do not so the cable box is often a source of ground-induced noise. Some USB connections include ground isolation, and I'd hope any good DAC with a USB input isolates the power supply and ground from signal ground, but measurements (and hearing) show some do not.

HTH - Don

 

[DonH50]

I am not on WBF much lately so missed the recent posts.

On "cheater" plugs, I have used them as a temporary trouble-shooting device, but usually measure with a voltmeter to make sure there is not a deeper (and more dangerous) problem. The safety ground (ground wire on a plug or wall outlet) is there because certain component failures or wiring errors can make the chassis "live" with full wall voltage on it. If something else is grounded in the system, it may blow a fuse (good) or burn a ground wire in two (bad, as this leaves the chassis "hot"). I have seen that happen many times over the years including a power supply failure last year in an expensive piece of test equipment that shocked me and burned up a $30k probe.

Truly dangerous situations are less common with consumer components now since so many are "double insulated" with no internal path from external chassis to the power line.

If the cheater plug works, then consider that the problem is (highly likely to be) a ground loop, and search for the root cause and a proper fix. Often that is as simple as a power line or cable ground isolator from Amazon, a parts supply source, or local store. Those are relatively inexpensive, safe, and very easy solutions to a ground loop.

FWIWFM - Don

 

[Kingrex]

Ron, your favorite high end gear might start out perfect, but over 5, 7, 10 years they start to fail. It only takes a small leak to cause noise. Part of the problem for us tube guys is turning the equipment on and off. The inrush is far worse than leaving a well ventilated amp running 24x7. Over time capacitors leak, solder joints can loosten and oxidize. Electronic break down over time.
A good friend with very well know well built SS amp could not get rid of out the speaker noise. He would not accept it was the gear. After having a manufacturer upgrade done recently his system is totally silent. Something was amiss in his equipment.

ACK, I agree in that good grounding is not just safty. It's far better overall performance. You can hear a well grounded system. There is a quiet and ease. Longer listening and less fatigue.

And everyone else noting miswiring of connection cables, RF, EMI noise etc. Not enough can be said about good cable management. Its hard to keep all rhe signal and power cables isolated behind a rack.

 

[DonH50]

<elided>

Its hard to keep all the signal and power cables isolated behind a rack.

It's usually quite a pain. My current console I wired in the back with power on the floor or down low, audio across the middle, and along the top since it had to get to the TV and cable box on top of the console. The console is wooden so I used screw-in hooks and fabric cable ties to clean it all up. The lowest shelf for power, middle for audio, top for video/digital (HDMI, SPDIF, Ethernet). Power cables I shoved against the wall behind to reach the outlets, and speaker cables I ran a foot or two in front of the power cords mostly under the console, exiting out the sides and curving away from the power cords to reach either the speakers or tucked along the side walls (no power cords there) to reach the side and rear speakers.

When it all fit in one rack and was audio only I ran power cables up the back on one corner and signal lines on the other corner. Power amps were on the bottom or to the side so speaker cables were separated from low-level and power cables.

It all sounds nice and neat, and usually was for a day or two, until I needed to tweak something and entropy won out again.

 

[Kingrex]

It's usually quite a pain. My current console I wired in the back with power on the floor or down low, audio across the middle, and along the top since it had to get to the TV and cable box on top of the console. The console is wooden so I used screw-in hooks and fabric cable ties to clean it all up. The lowest shelf for power, middle for audio, top for video/digital (HDMI, SPDIF, Ethernet). Power cables I shoved against the wall behind to reach the outlets, and speaker cables I ran a foot or two in front of the power cords mostly under the console, exiting out the sides and curving away from the power cords to reach either the speakers or tucked along the side walls (no power cords there) to reach the side and rear speakers.

When it all fit in one rack and was audio only I ran power cables up the back on one corner and signal lines on the other corner. Power amps were on the bottom or to the side so speaker cables were separated from low-level and power cables.

It all sounds nice and neat, and usually was for a day or two, until I needed to tweak something and entropy won out again.

I somewhat simiar. I run into issues as I leave behind the rack to my amps. My power cord and interconnect are too close. Then the speaker cable has to go somewhere and it crosses power and interconnects. And behind the rack a little of the same. Power cords have to climb up to gear and interconnect have to also go up and down and across to lace stuff together. At one time I thought of getting an aluminum sheet and making a divider for behind the rack. Stuff the power behind it against the wall and interconnects by the gear. But wait, how much noise are my server and dac putting out to pollute my signal cables. And it all grinds to a halt as I contemplate.

And darned if I didn't end up turning my system on and off 3 times today.