Eliminating ground loops in audio and video systems

UNDERSTANDING, FINDING, & ELIMINATING GROUND LOOPS IN AUDIO & VIDEO SYSTEMS – 2005 Generic Seminar Template is a very good collection of information on ground loop problems on audio and video systems. The writer Bill Whitlock from Jensen Transformers really knows what he is talking about.

gndisolation

Here are some fact points picked from document:

The very meaning of the term ground has become vague, ambiguous, and often quite fanciful. Some engineers have a strong urge to reduce these unwanted voltage differences by “shorting them out” with massive conductors (the results are most often disappointing) or finding a “better” or “quieter” ground. There are several common myths about grounding. Many indulge in wishful thinking that noise currents can somehow be skillfully directed to an earth ground.

An excellent broad definition is that a ground is simply a return path for current. We must remember that current always returns to its source through either an intentional or accidental path.

In all real equipment, there are parasitic capacitances between the power line and the equipment ground. They are the unavoidable. These capacitances allow leakage current to flow between power line and chassis/ground inside each piece of equipment. Any connection between two such devices or such a device and a grounded one will carry this leakage current. We must accept this fact as reality.

For grounded equipment, the effects of leakage current are usually insignificant compared to voltage differences between outlet grounds. Substantial voltages are magnetically induced in premises safety ground wiring by the imperfect cancellation of magnetic fields that surround the two load-current-carrying conductors. Significant ground voltage difference (1 volt is not unusual) will exist between the chassis or local “ground” of any two pieces of safety-grounded equipment. We must also accept this fact as reality.

When a system contains two or more pieces of grounded equipment, whether via power-cords or other ground connections, a “ground loop” may be formed.

Transformer isolators are very good devices in solving ground loop issues, but you need to remember to check performance data for isolators carefully. Beware of products that are not well-specified. They can sometimes solve noise problems, but at the expense of sound quality.

Noise rejection in a real-world balanced interface is often far less than that touted for the input. That’s because the performance of balanced inputs have traditionally been measured in ways that ignore the effects of driver and cable impedances. In real life the ground noise rejection of ordinary differential amplifiers is extremely sensitive to impedance imbalances in the driving source and real-world outputs are very rarely so precisely matched. The CMRR can easily frop from its advertised or “rated” 90 dB down to 65 dB.

The ground noise rejection of ordinary differential amplifiers is extremely sensitive to impedance imbalances in the driving source. With unbalanced sources, their entire output impedance becomes “imbalance” and the noise rejection of differential amplifiers is quite poor.

Electric fields can capacitively couple noise into signal conductors. Grounded shield solves the entire problem well. Braided shields with 85% to 95% coverage are usually adequate. Note that shield ground connections can affect CMRR. Cable capacitances between each signal conductor and shield are mismatched by 4% to 6% in typical cable. The imperfect symmetry and/or mis-matched capacitances will cause signal current in the shield. This current should be returned directly to the driver from which it came. For shielded balanced audio cables, the shield should ALWAYS be grounded at the driver — whether or not the receiving end is grounded. The most widespread industry practice is to ground the shield at both ends. It provides a good guard against RF interference but compromises CMRR to some degree.

Be sure all balanced line pairs are twisted. Twisting makes shielded or unshielded balanced pair lines nearly immune to magnetic fields and makes unshielded balanced lines nearly immune to electric fields. This is especially important in low level microphone circuits.

Effective magnetic shielding, especially at power frequencies, is very difficult to achieve. Imperfections in real cables result in unequal induced voltages that add noise to the differential signal (SCIN = shield-current-induced-noise). Generally, the best cables have braided or counter-wrapped spiral shielding and the worst have foil shields and drain wires.

Bundle signal cables. All signal cables between any two boxes should be bundled. For example, if the L and R cables of a stereo pair are separated, nearby ac magnetic fields will induce a current in the loop area inside the two shields — coupling hum into both signals. Bundling all ac power cords separately helps to average their magnetic and electrostatic fields, which reduces their net radiation. Of course, keep signal bundles and power bundles as far apart as possible.

12 Comments

  1. Tomi Engdahl says:

    Quick Press Mult Video Feed
    http://livesoundadvice.com/connections/quick-press-mult-video-feed/

    Here’s how to hook up one or more passive DI boxes to make a Quick Press Mult. This lets you send isolated audio to multiple video cameras without creating ground loop hum or a level mismatch.

    How to use passive DI boxes to feed audio to multiple video cameras. Allows you to make a Quick Press Mult for any last minute gigs.
    https://www.youtube.com/watch?v=gWpjVvPi4wQ

    Read more about it at http://livesoundadvice.com/connections/sound-advice-quick-press-mult/

    Reply
  2. Tomi Engdahl says:

    Would dedicated lines cause ground loops?
    https://www.youtube.com/watch?v=uWqLbiqKMPY

    Running separate ground and power lines for each piece of audio or video equipment is a smart way to run your system for best sound quality. But are there problems from ground loops and their hum?

    Comments:

    Flimsy wiring OK between grounds rods? let’s define that a bit more. The NEC requires any bonding wire between ground rod to be a #6 minimum. The most destructive danger with isolated ground rods is lightning. A ground strike can produce thousands of volts and thousands of amps between those two ground rods for a few milliseconds. Think about audio gear grounded to the dedicated ground rod and yet they are still connected to the electrical ground system via the three wire AC cord. That mega voltage and current in a lightning strike will now be across your gear!

    Another great audiophile myth propagated by the likes of The Absolute Sound and it’s cousins is the idea that the Earth is some magical sink hole for electrical noise. Just like you dump dirty water into the ground (or sewer) you can also dump electrical noise into the Earth as well and make it go away. WRONG! The only time the Earth is effective is as a current return for the noise source. That would be lightning and some types of RF radio. Other than that, the Earth has no electrical noise reduction properties. Does your smart phone have an Earth ground, Your car? What about high tech military aircraft with tons of analog sensors? Where’s the Earth ground to get rid of the electrical noise here?

    Yes, that’s how most world electrical systems are designed. But after the component or device’s power transformer or switching power supply, the signal or DC power ground need not be tied to the AC ground. It’s optional depending on many other factors. But in no case may a neutral be substituted as a ground. An likewise it’s also illegal to use a ground as a neutral. That is a common hack when a 240v only outlet now needs 120v as well, the ground becomes the neutral. Older cloths dryers and electric ranges did this but it’s now illegal. They must now have four wire connections.

    I don’t know about other locations. In San Jose and Santa Clara California, your broadband supplier grounds their input boxes to your house ground system/rod. That could be Comcast cable, satellite tv, or AT&T.

    Reply
  3. Tomi Engdahl says:

    Do grounding boxes improve sound?
    https://www.youtube.com/watch?v=zgqYdq0VgKg

    Several accessory companies manufacture and sell extremely expensive ground boxes and this customer wants to know if they work and why. Paul says it doesn’t matter if they work or not, there’s a bigger issue at stake.

    Comments:

    If your worried about ridiculous tweaks like this then it’s not a hobby anymore it’s borderline mental illness and you need take a break from hifi. It’s the same as believing if I put a racing stripe on my car it will go faster.

    sometimes you need to start with the basics. making sure the building grounds are clean and tight at the incoming power to the building, at the grounding rod connection. Also make sure all electrical connections are tight within the breaker panels. Any loose connections on the line side will have the same effect as a loose ground. Another overlooked area is weak ballast in fluorescent lighting.

    Ah, Ground – the subject of much myth, misinformation, and snake oil.

    Great to hear some no-nonsense jargon-free advice, on a wide range of audiophile topics, from a genuine expert not trying to sell, sell, sell. Many thanks!

    The two primary concepts needed for audio are:

    1) Star Grounding. Yes, it’s true, it’s real, and there are very good reasons why virtually every serious recording studio is star grounded.

    2) Ground loops & ripple current. This is a different beast entirely to Mains Ground. Snake Oil salesmen like to conflate & confuse Mains Ground issues with Signal Ground & Ripple Currents. Almost all equipment, no matter how well grounded to the Mains Ground, will introduce mains frequency hum & harmonics thereof into signal ground by way of imperfect power supplies & filtering. The problem is compounded when different devices have a potential difference between signal grounds. The solution is total galvanic isolation – either via transformers or optically via opto isolators or digital optical.

    CAD and Entreq make modern version of these products. All listeners and reviewers seem to like them a lot. Listen for you self. Read the reviews. However Paul has got a point, maybe the grounding do not get perfect, but the current might flow easier and the background noise gets lowered. Paul should try one of these out. It is PS Audios active mains conditioning vs the ground boxes passive way. The alternative is filtering, which weakens dynamics.

    The best combination for most systems aought to be power regenerator, dedicated mains line and ground boxing the components. Costly but improving quietness and dynamics. It is tested with success.

    Paul has more information regarding this on PS Audios forum.

    Esoteric Audiophile
    I spent around 6 months developing “Virtual ground” boxes, It’s a special pseudo-science device that seems impossible to “Do anything”. After all, a nice solid earth ground is hard to beat right? Well, after 6 months of research and development, I created many devices that can totally transform, clean and manipulate AC signals to give

    One misunderstanding in audio circles is the Earth as a ground. The Earth ground has nothing to do naturally with man made electrical systems. The only time the Earth ground comes into the circuit is with lightning and radio. Now we do Earth ground our electrical systems for safety purposes but beyond safety reasons, an earth ground is not required.

    You’re better off building a Faraday shield cage around your sound room and grounding everything to earth ground! Neutral = ground, Ground = safety ground.

    Mark Knopfler’s studio is an actual lead-lined Faraday cage on all six axis’, with proper star grounding on all power and signal grounds.

    I have no issue either with ground boxes, etc. If it truly works than it truly works. The line gets crossed at the point at price. “Snake Oil makers and sellers can use all the pseudoscience and made up words they like, it is up to the buyer to educate themselves even just talking to someone honest in the know will do the job. The line gets crossed for example, at the point of charging $400 for an item that cost all of $24 to make whether it works or not.

    So much B.S. in the audiophool world.
    Go to any guitar forum or YouTube and search “How to eliminate guitar rig hum”.
    You’ll find actual real world answers from professionals dealing with it every day in different venues with all manner of power supply issues.
    Here’s a hint: transformer isolators

    There are two levels of grounding in any one piece of equipment…
    1) Chassis ground and
    2) signal ground
    Using all balanced signal lines with chassis grounded shielding and keeping all interconnections as short as poss all should be good .
    Signal grounds ( if using RCA unbalanced lines ) should form a Mecca earth structure ( Paul says ‘star’ … same thing ) which should terminate as far down the signal lines as poss ..
    Grounding boxes are a big hoax .. they are a supposed to be a final ‘fix’ for desperate Audio Fools who will part with any amount of $$$’s just to keep themselves from going totally insane !!

    “Grounding boxes are a big hoax…”
    Maybe a little hoax? I’d never heard of them before today.

    Reply
  4. Tomi Engdahl says:

    See how expensive grounding boxed can be https://www.futureshop.co.uk/accessories/grounding/grounding-boxes#page=1
    and then look at this grounding box parody video with some truth in it:

    AUDIOPHILE GROUNDING BOX – DIY
    https://www.youtube.com/watch?v=NOVfFLTXB3k

    Learn how to make an Audiophile GROUNDING BOX at home.

    Reply
  5. Tomi Engdahl says:

    https://forum.audiogon.com/discussions/ground-box-what-s-in-them

    Inside?
    Ifor the manufacturer huge, no wait, mega huge profit and for the buyer… A lot of hope :-). And a piece of metal with some screws and some wire and, very important, the Black Box…inside? All you can imagine…

    https://www.computeraudiophile.com/forums/topic/34650-how-does-the-grounding-boxes-work/

    They don’t work.

    Next!

    They do work. Tremendously well. For audiophiles looking for emotional support they are doing something to clean up their grounding and improve their system. The money spent validates the emotional improvements.

    They don’t work in the following ways:

    1. They don’t provide a safety ground

    2. They don’t extract and store noise from the ground plane

    3. They don’t filter noise

    4. They don’t attract stray currents or voltages (where “they find peace”! :))

    5. They don’t work “like a bit of mother Earth”

    What they might be actually doing:

    1. Acting as an antenna receiving (or even broadcasting) signal

    2. They might form a common ground across devices if more than one device is connected to the same grounding box/connector (resulting in more cross-talk but possibly fewer ground loops)

    3. Their ‘technical’ explanations sound plausible to folks that don’t understand how ground actually works, but sounds like gobbledygook to anyone with basic a Physics education

    Reply
  6. Tomi Engdahl says:

    Here is real expert information:

    Bill Withlock Ground Papers

    An Overview of Audio System
    Grounding and Interfacing
    https://centralindianaaes.files.wordpress.com/2012/09/indy-aes-2012-seminar-w-notes-v1-0.pdf

    Reply
  7. Tomi Engdahl says:

    https://forum.audiogon.com/discussions/ground-box-what-s-in-them

    A few years back a friend of mine bought some very expensive P*D cables, forgot the name but it was something about 3-4k per meter, after a while he wanted better connectors and opened the cable. Guess what he found? Belden computer cables, thin, cheap, surrounded by big foam. He was really mad about that… the question is: Do you really want to know what you have bought?

    Syntax, I remember someone posting pictures of the inside of the Transparent “boxes” that are on their cables and it was just silicone glue and I think a resistor.

    Reply
  8. Tomi Engdahl says:

    https://hifiwigwam.com/forum/topic/92390-grounding-box/

    If you maintain all original earth connections, then adding another one is more likely to induce ground loop hum than cure it.

    This paragraph says it all to me: “If you can effectively remove or drain away the pollutants, stray magnetic currents and impedance fluctuations before they contaminate the sound, there becomes no need for the active synthetic filters & other such devices commonly recommended by many manufacturers. Our ground box’s are surprisingly heavy, feeling very solid and robust. However we do not talk about the specifics of construction, materials or any of the development technology housed within any of our products, especially the range of Ground Boxs.”

    FFS, they can’t even spell ‘boxes’. And if anyone can explain to me how these will ‘drain away pollutants’ I’d love to know.

    Total and complete bullshit, without even bothering to try and explain.

    Very good point Serge but people see what they want to see and hear what they want to hear

    Reply
  9. Tomi Engdahl says:

    #51 – How To: Splitting, Balancing & Isolating Line Level Audio signals.
    https://www.youtube.com/watch?v=tJ50iyMWA7c

    information & resources about transformers and splitting line level audio signals.

    #021 Transformer Isolated Passive Mic Splitters!
    https://www.youtube.com/watch?v=K_gl1RIXVFU

    In this video we take an inside look at passive transformer isolated microphone splitters and how we use them in the real world.

    Reply

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