Ground Loops Demystified publication is now available in e-book format from Speciara web shop at https://speciara.com/products/ground-loops-demystified. The e-books is published by Creator Technlogy Oy.

Eliminate Hum, Buzz, and Noise—Once and for All with Ground Loops Demystified book

Ground loops are one of the most frustrating problems in audio systems—and one of the most misunderstood. Ground Loops Demystified cuts through the confusion and shows you exactly why unwanted hum and interference happen, even in “properly grounded” setups.
Written for musicians, audio engineers, AV installers, and serious hobbyists, this practical guide explains ground loops in plain language, then walks you through proven, real-world solutions. You’ll learn how to identify the source of noise, use the right tools, apply safe isolation techniques, and design systems that stay quiet from the start.

No guesswork. No dangerous shortcuts. Just clear explanations, step-by-step troubleshooting, and professional best practices for clean, reliable audio—at home, on stage, or in the studio.

If noise is killing your sound, this book shows you how to kill the noise. You can buy this 115 page e-book at https://speciara.com/products/ground-loops-demystified

Ground Loops Demystified Quick Start: Fixing Audio Hum the Right Way

In addition to full book you can buy in e-book format, I have also made a Quick Start short booklet on Fixing Audio Hum the Right Way. You can buy the Ground Loops Demystified Quick Start 12 page booklet (9.95 Euros) or get it for you can get it booklet worth of 9.95 Euros in exchange for your e-mail address (join the mailing list).

If you’re hearing hum, buzz, or strange interference in your audio system, you’re not alone with this booklet. Ground loops are one of the most common—and most misunderstood—causes of audio noise. The good news is that most ground loop problems can be identified quickly and fixed safely once you know what to look for. This Quick Start section gives you a clear orientation before diving into the sample chapter from Ground Loops Demystified book.

What This Guide Will Help You Do:
• Recognize whether your noise is likely caused by a ground loop
• Avoid common (and dangerous) “quick fixes”
• Take safe first steps toward diagnosing the problem
• Understand what the next chapter will show you in detail

You don’t need advanced electronics knowledge to get started.
You can now join

I am now giving this Quick Start guide for anyone interested to ready it in exhange for your e-mail address. You can download the Quick Start free by joining to the Ground Loops Demystified book e-mail list. Just write your e-mail address, press join the list. You get a verification e-mail, and when you have conformed your e-mail address you get e mail that gives you the download link. The mail sender is Creator Technology (check your spam folder if you don’t see the mail in your inbox).

You can unsubscribe any time (unsubscribe link included in e-mails sent to you).


Type Common Countries Nominal Voltage Grounded
A USA, Canada, Mexico, Japan 100–127 V No
B USA, Canada, Mexico 100–127 V Yes
C Europe, South America, Asia 220–240 V No
D India, Nepal 220–240 V No
E France, Belgium, Poland 220–240 V Yes
F Germany, Finland, Spain, Russia 220–240 V Yes
G UK, Ireland, Malaysia 220–240 V Yes
H Israel 230 V Yes
I Australia, New Zealand, China 220–240 V Yes
J Switzerland, Liechtenstein 220–240 V Yes
K Denmark 220–240 V Yes
L Italy, Chile 220–240 V Yes
M South Africa, Swaziland, Lesotho 220–240 V Yes
N Brazil 100–240 V Yes
O Thailand 220 V Yes


https://www.iec.ch/world-plugs

After some research on some product information pages and Wikipedia Network Isolator page I found out that there are some special cases where there are sensible reasons to use such extra isolation device on Ethernet network. After some more searching, I also found products designed for industrial applications and audio applications.

PATIENT PROTECTION
Galvanic isolation of the Ethernet interfaces on medical electrical equipment or systems
for which patients must be protected from harmful leakage currents in line with standards.

APPLIANCE PROTECTION
Protection of particularly valuable devices from ripple voltages and surges from the edge of the network.

MEASUREMENT TECHNOLOGY
Protection of electrical measurement and monitoring equipment from external voltages and interference voltages from the
Ethernet cabling.

POTENTIAL DIFFERENCES (BUILDING TECHNOLOGY)
Potential equalisation currents are prevented in computer systems connected via an Ethernet
cabling over greater distances.

AUDIO
Reduction of low-frequency AC voltages (mains ripples), which are caused by the network connection, to an imperceptible level.

Medical applications

Network isolators are used in the medical industry to protect patients against leakage currents. IEC standard IEC 60601-1 (3rd edition) specifically deals with medical electronic and electrical equipment and systems, and classifies non-medical devices as potential hazard sources. Network isolators work to remove this hazard, by electrically disconnecting medical devices from a network. They are often installed in the medical field in conjunction with isolation transformers, which serve to protect the patient from electrical faults. The international standard IEC 60601-1 Medical Electrical Equipment (3rd edition) specifies stringent criteria on the safety and isolation of medical devices. Very many medical institutions use Ethernet isolators for electrical safety and to keep equipment interference free. Medical-grade Ethernet isolators must follow strict regulations concerning the isolation level that an Ethernet isolator provides. Isolators marketed to meet European Medical Device Directive (EN6060-1) typically have isolation level of 4kV or higher.

Industrial applications

Network isolators have industrial applications in overcoming the problems of differing ground potentials across networks, or between network components for example to stop shield currents on shielded Ethernet cable (ground loop currents) and on electrical testing facilities where higher that normal office environment electrical disturbances are present. There are also uses in electronics testing  systems where dangerous voltages are present.

Ethernet Isolator combines intrinsically safe energy limitation and galvanic isolation page tells that the FieldConnex® Ethernet Isolator combines intrinsically safe energy limitation and galvanic isolation into one product. Now Ethernet connections are plug and play in Ex-Zone 1. Intrinsically safe Ethernet Isolator EI-0D2-10Y-10B product provides galvanic isolation according to EN50020 for 10 BASE-T/100 BASE-TX. It contains active electronics and needs a power source to operate.

Audio applications

Ground loops and high frequency noise have known to cause all kinds of issues with sensitive audio systems. Especially people tuning their HiFi systems are interested could Ethernet connection be improved in some way. Because almost all the audiophiles would have experienced of tuning their own audio system with variety of cables or accessories in order to enhance the music sound from their treasured audio systems, some special HiFi equipment manufacturers have seen market for expensive Ethernet isolators for HiFi applications. So called ‘audiophile’ grade ethernet cables have made inroads into specialist audio dealers.

Audio Stream Ethernet Accessories and Cables page has information on several special (expensive) accessories that are claimed to provide improvement when used with HiFi equipment. In Ethernet isolation sector the page lists SOtM iSO-CAT6 Ethernet isolator. SOtM iSO-CAT6 Ethernet isolator product page claims that noise interference created by LAN port has enormous effect to system sound and SOtM iSO-CAT6 may offer certain varying sound improvement (for other views check reviews at 6moons and avrev). SOtM iSO-CAT6 manual says that this product provides isolation 1500Vrms, 0.5mA, 60sec (same level as normal Ethernet cards).

Are the isolators really needed in audio system? Maybe not in most cases (but there can be some special cases where extra isolation can have some effect). By default the ethernet ports are isolated with transformers. However – ground loops from shielding still can exist if you use shielded cables. If you are worried on ground loops on audio system, I recommend to use unshielded Ethernet cables, so you get no ground loop. If you are really paranoid on isolation, isolate the audio with a fiber optic cable. Some people who have written on their experiences have found out no difference on copper, isolated copper or fiber on sound quality. This no difference will also apply to special Ethernet cables: The use of solid core verses stranded or gold verses silver for the conductors for this link in particular is just putting lipstick on a pig. Again, this is digital side… The likelihood of there being a genuine difference rather than a psychoacoustic cause for the described difference is much, much lower given known physics.

How Ethernet Isolators Work

An Ethernet isolator separates the electrical currents of multiple devices: it allows the Ethernet data signals to pass without allowing the two circuits to physically contact each other. The Ethernet isolator is basically just several 1:1 Ethernet transformers put between the RJ-45 connections (two needed for 10/100 Mbit/s Ethernet, four needed for 1 Gbit/s Ethernet). Typically all those transformers are built into one transformer module similar to ones used in Ethernet cards and switches. Such isolator consists of a small PCB at the back panel with two RJ45 connectors and a LAN transformer in between. This would provide an additional 1500V to 4000V of isolation depending on the transformer chosen.

Network isolators are commercially available in various designs. Medical-grade Ethernet isolators must follow much stricter regulations concerning the isolation level that Ethernet isolators for industrial uses.

Ethernet isolators are typically constructed using the same technique as normal Ethernet port. Ethernet specification needs magnetic transformer coupling between RJ45 connector and electronics. Most modern Ethernet ports with MDIX functionality (auto-detect direct or cross-connect) use 1:1 transformers optimized for Ethernet frequencies (frequency range depends on line speed) and impedance (100 ohms)  for all used signal pairs.

Transformers offer a very good common mode rejection: A transformer only “sees” the voltage accross its windings, not the common voltage both ends of the winding are driven to simultaneously. You get a differential front end without a deliberate circuit, just basic physics.

An Ethernet isolator could be basically built using one such transformer module (contains 2 or 4 transformers in one case) that is just wired between two RJ45 connectors. Standard Ethernet transformers provide typically 1500Vrms isolation. If higher isolation level is needed, a suitable special transformer with improved isolation specification needs to be manufactured. For example medical isolator can isolate the data AND the shield up to 5.000V. The nic transformers only isolate the data up to 1.500V. Here is picture of MI 1005 E Medical Built In Isolator showing that there is just transformers (inside black box in the center) and two RJ45 connectors.

Isolation is a very good idea on communications systems that are linking lots of different hardware over a wide area: You don’t want fault current/voltages in the mains wiring or devices to spread onto your communications wiring.

Ethernet transformer links:
http://www.haloelectronics.com/products/lan/ethernet/
http://www.mouser.fi/new/molex/molexRJ45jacks/
http://www.mouser.fi/new/halo-electronics/halo-ethernet-transformers/
https://www.eeweb.com/company-blog/microchip/migrating-from-the-lan9115-to-the-lan9210/

Links to more information:
http://www.diyaudio.com/forums/pc-based/154048-ethernet-galvanic-isolation.html
http://www.bb-elec.com/Learning-Center/All-White-Papers/Ethernet/Power-over-Ethernet-PoE.aspx
http://hackaday.com/2010/10/26/ethernet-connection-using-capacitive-coupling/
http://www.youritronics.com/magnetic-less-ethernet/

Some product links:

I have found those with Google search. I have not used any of those or recommend them.
http://industrialcomponent.com/baaske/2006633.html
http://industrialcomponent.com/baaske/ethernet-isolation.html
Ethernet Data Isolator – 10BASE-T/100BASE-TX
http://industrialcomponent.com/baaske/2006633.html
L-com 10/100/1000 Ethernet Data Isolator (EN60601-1 Compliant) provides isolation up to 4 kV
Bourns 360 V dc 3kA 1500 Isolated Ethernet Protector, Wall Mount Mounting is an Ethernet surge protector product that also promises to provide 5 kV isolation for 10/100/1000 Mbit/s Ethernet.
EMO EN-100C :: Network isolator for PCB mounting is intended for integration on the PCB of the device being protected. The devices in the EN-100-series meet the requirements of IEC 60601-1 (3rd edition) and IEC 60601-1-2 for medical settings
Phoenix Contact Network isolator – FL ISOLATOR 100-RJ/RJ – 2313931 is a passive passive network isolator for electrical isolation in Ethernet networks up to 4 kV and speeds of up to 100 Mbps.
https://www.mtl-inst.com/images/uploads/datasheets/is_ethernet/9468-ET.pdf
http://www.mmcchina.com/Upload/whitepaper/MMC_Whitepaper12EN.pdf
http://industrialcomponent.com/baaske/ethernet-isolation.html
http://industrialcomponent.com/baaske/2006633.html
http://www.baaske-medical.de/media/content/Datasheet_MI1005_MI1005E.pdf
http://industrialcomponent.com/baaske/2006633.html
https://www.dustinhome.fi/product/5011222413/rj45-network-isolator-6kv
https://www.dxengineering.com/parts/dxe-iso-plus-2
https://www.phoenixcontact.com/en-pc/products/network-isolator-fl-isolator-1000-rj-rj-2313915

Sources:
http://www.tech-faq.com/ethernet-isolator.html
http://electronics.stackexchange.com/questions/180415/ethernet-3000v-isolation
http://www.mouser.fi/new/halo-electronics/halo-ethernet-transformers/
http://www.diyaudio.com/forums/pc-based/154048-ethernet-galvanic-isolation.html
http://www.6moons.com/audioreviews2/sotm2/1.html
http://www.avrev.com/home-theater-accessories/acoustics-eq-room-tuning/sotm-iso-cat6-lan-filter-and-tx-usbhub-review-3.html
http://www.computeraudiophile.com/f22-networking-networked-audio-and-streaming/audiophile-ethernet-cables-13798/
http://www.computeraudiophile.com/f22-networking-networked-audio-and-streaming/ethernet-cables-audiostream-test-17713/
http://electronics.stackexchange.com/questions/27756/why-are-ethernet-rj45-sockets-magnetically-coupled/27762
http://www.diyaudio.com/forums/pc-based/154048-ethernet-galvanic-isolation.html

Antenna isolator is very convient way to solve antenna connection related ground loop problems. Unfortuantely isolator has some drawbacks: attenuation and possible poor suscpectibility to RF interference.

Here is the picture of one commercial antenna isolator:

The circuit inside main details pretty much resembles the simple circuit shown at Building your own antenna isolators page with some RF filter added to the center:

Another type of antenna signal isolator is RF transformer based antenna isolator as shown at Building your own antenna isolators page:

Read more at https://www.epanorama.net/documents/groundloop/antenna_isolator.html and https://www.epanorama.net/documents/groundloop/antenna_isolator_building.html

It was originally posted to YouTube under name
Where does that noise come from?

A friend called from a big computer festival Assembly 1999 that was starting. It was one of the biggest this type of event in Europe with thousands of people coming with computers. Some of my friends was running big screen and video streaming for the event.

They had all the stuff rented and set up for the event by the AV contractor. Everything worked flawlessly on the previous day. But on the first day the audio and video system started picking up lots of noise. The audio signal had mains humming in it, and video signals had “humming bars” on them. As more computers get powered up on the hall, the worse the noise becomes. We are not talking about few computers, there was over two thousand computers on the hall.

Same event 2010

I walked in to the even with my tool-set. Solving the audio problems involved sorting out the lines that picked most noise. Most of the audio connections were analogue (both balanced and unbalanced) and most video connections used composite video interface. I walked in to the event with necessary tools. A combination of audio signal isolation transformers and “ground lift” on some balanced audio lines made situation OK.

Video signals were a tougher problem. There were some very long video line runs from the main video mixer to different locations (projectors for big screen, smaller screen etc..). Those long video lines seemed to have lots of noise in them. I measured form 100 mA to 1 ampere mains AC current on coaxial cable shields on the cables with most humming bars! Disconnecting some of those longest lines made the video system to work noise free, but what to do because we can’t live without connections to video projectors.

The main program on the event was starting on the next day, so this problem needs to be solved so that everything works flawlessly or at least “well enough” by tomorrow. I know I would needed some type of video signal isolation devices for those problematic video lines, but our equipment supplier did not have them. It was already quite late night, so it was impossible to try other sources.

Fortunately I had one prototype of video “humbugging” transformer with me. It was a common mode choke built by winding thin 75 ohm coaxial cable over a suitable toroid transformer core. This device reduces the amount of current flowing on coaxial cable shield and reduces the noise pickup. I built the device based on some old documentation (someone sent me old document from BBC on hum bugging transformers). I tested this DIY “humbugging” transformer on one of the video lines, and it worked very well. The amount of noise on that video line was reduced to point that it could no longer be detected on the big screen.

The problem is that there were also other lines that seemed to need the same kind of treatment. I went to home lab, trying to gather whatever parts I could find to build more such devices. I ended up building three more on the night from the part I could find – I even managed to find nice plastic cases for them. Next morning I came with my brand new “humbugging transformers” to the event. They worked and saved the show next day. What I made looked pretty much like this inside (this is a later made version that uses the same box).

In the end the video equipment provider that rented most of the video gear for the event end up buying my boxes after the event at decent price. I ended later making some more for this company. I ended up making more on then when needed for some video companies. Quite often when I first rented few of them to solve an emergency, they wanted to buy them for themselves.

They have performed very well on many video systems to solve ground loop problems. There are passive hum suppressor transformers that will very effectively remove the hum from the video signal, but do not affect the video signal otherwise. Those special transformers act like a common mode coils, which stop the annoying ground loop currents on the shield of the coaxial cable, but provide a straight path for the signal inside the cable. This type of device is capable of passing the signals from DC to tens of MHz without problems. The hum suppressor transformer both reduces the current flowing on the cable shield and compensated the voltage differences that would otherwise be between cable ends and eventually get to the signal.

You can find more information on my ground loop noise reducing boxes at
https://www.epanorama.net/blog/2009/09/06/build-humbugging-transformer/ and https://www.epanorama.net/blog/2009/09/15/build-video-isolator/ and https://www.epanorama.net/blog/2010/08/12/audio-isolation-transformers/.

I ended doing more audio and video tricks to keep this event running,

USB isolation works by creating a new ground for the USB device so that it doesn’t have to share ground with your computer (and other devices that you might have connected in your house). This will prevent ground loops. It will also protect the USB device and host from electrical shocks or static electricity shocks. The USB isolators effect a potential decoupling of all USB connections and separate the ‘normal’ PC system from the critical application.

I have thought of getting USB isolator for some time, but many of them seem to be quite expensive (many cost nearly 100 Euros). Then I saw this promising looking Isolator USB to USB Optocoupler Isolation Module Coupled Protection Board ADUM3160 Isolation Voltage 2500V board for around 10 Euros.

Features:

12 Mbps support USB 1.5 Mbps at low speed and full speed does not support pure high-speed equipment
Support USB control transfer, bulk transfer, interrupt transmission, synchronous transmission/etc
Power supply: from the USB port to the PC host
Avoid driving, it is more convenient to use

Specifications:

Compatible with USB2.0
ADUM3160 isolation voltage: 2500V
Power module: isolation voltage 1500V
Using the environment: – 40 ° to 85 °

Support Equipment:
-Full speed equipment: USB flash drive, digital camera, card reader, mobile hard disk, U aegis,, USB hub, AVRJTAG, AVRISP, AVRISPMKII, S – Lab, JET51, J – Link, FET430UIF, PICKIT2, XDS100, LPC cc-link, ICD2, USB serial port (FT232, CP2102, PL2303, CH341 chips).
-Low speed devices: Keyboard, mouse, USBASP, USBHID equipment, USBCDC equipment.
Tested part does not support the USB wireless network card, see USB flash drive.

With those specifications this product looks pretty promising.

In my testing I have found that this product corresponds to the description. It is small and simple. It does what it says. The ground is isolated very well. I tested the isolation with insulation resistance meter at 500V DC, and the device withstood that test nicely and meter showed open circuit. Those are the good things.

There are also some disadvantages and limitations on this product as well.

First is that there is no case that comes with this so I had to make my own because I did not like having open USB hardware laying around potentially making short circuit. That was known when I bought this cheap board instead of somewhat more expensive similar device with plastic case.

Other this is the lack of documentation of dip switch function. From the discussion on the product page I read that the DIP switch is for USB bus speed selection. This device support USB Low and full speed data rate: 1.5 Mbps and 12 Mbps. Automatic speed detection would have been nice, but I can live with this manual selection although getting it to work sometimes might need some manual testing which setting is the right. The switch like it is in the pictures selects the isolator to operate at full speed data rate of 12 MBps. If low speed is needed, the DIP switch should be moved to “ON” position.

There is a limitation how much power can go through this device. You can expect to get 1W MAX (0.2A @ 5V) on isolated DC/DC side for USB power. That’s considerably less than typically available from computer USB port, and may not be enough for some power hungry hardware.

This device support only USB Low and full speed data rates 1.5 Mbps and 12 Mbps. It does not support USB 2.0 Hi-Speed 480 MBps, which means that some fast USB device do not work with it.

Circuit analysis:

When looking at the circuit board, I found out that the main active components in it are:
ADUM3160 USB isolator chip
B0505S-1WR2 isolating DC/DC converter
PC817 opto-isolator

The USB data signal isolation on this device is based on ADuM3160 component which is a USB port isolator based on Analog Devices, Inc., iCoupler technology. The chip uses high speed CMOS and monolithic air core transformer technology. ADuM3160 promises isolation voltage 2500V.

ADUM3160 data from https://www.analog.com/en/products/adum3160.html#:
USB 2.0 compatible
Enhanced system-level ESD performance per IEC 61000-4-x
4.0 V to 5.5 V operation
Low and full speed data rate: 1.5 Mbps and 12 Mbps
High common-mode transient immunity: >25 kV/μs
Evaluation Board and User Guide available
16-lead SOIC wide body package
Safety and regulatory approvals
UL recognition: 2500 V rms for 1 minute per UL 1577
CSA Component Acceptance Notice #5A
IEC 60950-1: 400 V rms (reinforced)
VDE certificate of conformity
DIN V VDE V 0884-10
(VDE V 0884-10):2006-12
VIORM = 560 V peak

B0505S is the DC/DC converter module used to convert USB 5V to isolated 5V for the other USB connector. B0505S is 1WR2 DC-DC Power Supply Module 5V to 5V Isolation Chip DIP-4. The product page at https://www.banggood.com/B0505S-1WR2-DC-DC-Power-Supply-Module-5V-to-5V-Isolation-Chip-DIP-4-p-1526388.html?rmmds=buy&cur_warehouse=CN says that the B_S-1WR2 family is specifically designed for applications in the board power system that require a set of voltages that are isolated from the input supply. This product is suitable for to:
1. The input power supply voltage is relatively stable (voltage variation range ±10% Vin);
2. Requirements isolation between input and output (isolation voltage ≤ 1500VDC);
3. The output voltage stability and output ripple noise are not high.

PC817 is a very common opto-isolator chip. It can provide up to 5000V isolation and operate up to 80 kHz frequency. In this circuit the opto-isolator seems to be just transfer the speed selection information from one side to another. The data PC817 sheet is available at https://learnabout-electronics.org/Downloads/PC817%20optocoupler.pdf

Ground loops can be introduced when different components in audio systems are connected with standard audio cables, and these loops can cause annoying interference. Grounded audi components generally carry significant currents in their ground returns.

Texas Instruments Application Report SLOA143 – October 2009: Ground Loop Break Circuits and Their Operation tells that in many cases, the interference can be reduced significantly with a “ground loop break” (GLB) circuit including a low-value resistor and differential amplifiers.

Ground Loop Break Circuits and Their Operation paper explains this approach and how to design a GLB circuit. The following schematic illustrates a GLB line input. The circuit uses a low value GLB resistor, Rgbk, typically 5 to 20 ohms, plus two differential amplifiers.

The resistance inserted in series with the audio cable shield is called a “ground loop breaking resistor, Rgbk.
More properly it’s a “ground noise reduction” resistor. The resistor can be inserted at either the source or the receiver.