Proper wiring to avoid ground loops

[Newmarket]

No, Its been done for several decades inside equipment all the time. Electronic theory doesn't change when its passing out the XLR jack.

The two things are not mutually exclusive. fwiw longstanding practices (of which I am well aware) do not mean that they are the optimum method. And note that we now have a very different rfi environment compared to some decades ago (when the largest hazard might be the local taxi firm or CB rig breaking into the school PA or whatever

 

[Cqwet Dbdfte]

We live in an ocean of 60Hz E and H fields, which can get thorny. Shielding in, and of, power supplies gets increased attention in newer EMI/RFI emission (conducted and radiated) standards. Measuring leakage currents from power supplies is not so hard and can reveal poorly designed or specified power transformers. Shielded AC power cords are not hard to get nor expensive. If you can wire all your buildings AC power inside EMT, greenfield, -conduit it would help.

 

[JohnRoberts]

We live in an ocean of 60Hz E and H fields, which can get thorny. Shielding in, and of, power supplies gets increased attention in newer EMI/RFI emission (conducted and radiated) standards. Measuring leakage currents from power supplies is not so hard and can reveal poorly designed or specified power transformers. Shielded AC power cords are not hard to get nor expensive. If you can wire all your buildings AC power inside EMT, greenfield, -conduit it would help.

The standard advice to ground both ends of cable shields is not about capturing 60 Hz hum. At very high frequencies the impedance of longer shields rises and diminishes their effectiveness.

[edit- FWIW I have used lots of shielded cables inside consoles only grounded on one end, but those were operating inside a grounded metal chassis with no internal RFI sources. [ /edit]

JR

PS: along the lines of RFI being more pervasive these days than in the past, I was reading an old acoustics text and they characterized a perfect sound absorber as an open window..... Not where I live.

 

[Cqwet Dbdfte]

If Edison won "the war of currents" the 60 Hz hum would not be an issue.

 

[Bjorn Andersson]

Rane Commercial have some very good information in their knowledge base articles about grounding and audio interconnections.
https://www.ranecommercial.com/kb_article.php?article=2127https://www.ranecommercial.com/kb_article.php?article=2107This book by Philip Giddings in my audio installation bible: Amazon.com

 

[RCAguy]

Assuming balanced wiring in a recording studio, shielding is for RF noise; it’s less effective against hum than twisting the pair of signal conductors. NBC radio (high RF and hum fields) had thousands of balanced twisted pair cables with shields removed once inside the copper-lined patch bay room. In my half underground studio, with low RFI, i even run line levels using only cat5 without shields.

 

[Newmarket]

We live in an ocean of 60Hz E and H fields, which can get thorny. Shielding in, and of, power supplies gets increased attention in newer EMI/RFI emission (conducted and radiated) standards. Measuring leakage currents from power supplies is not so hard and can reveal poorly designed or specified power transformers. Shielded AC power cords are not hard to get nor expensive. If you can wire all your buildings AC power inside EMT, greenfield, -conduit it would help.

We do. But what has changed over time is the high RFI frequencies encountered. Try your 5G mobile as a noise source around audio connections.

 

[ccaudle]

If I remove the grounds on xlr pin 1 from both outputs, is that the proper way to break the ground loops in my setup?

To come back around to the original question, if improper equipment design is injecting 60Hz into your audio circuitry, connecting shields at only one end can sometimes help. If you do that the best performance is achieved by connecting the shield at the equipment output, and not connecting at the equipment input.
That can sometimes cause RFI problems to show up, but if you are not in a high RF environment it may not matter.
My preference is to have correct equipment connections so that shield currents do not affect the audio performance, but understandably cutting into your currently working equipment is sometimes not the first choice, especially if just snipping one connection in a couple of cables solves the problem.

 

[MicMaven]

Cool Beans. I am interested in this discussion because I am in an active discussion with a highly qualified amateur radio technician and we disagree over a "Pin 1" type buzzing in a microphone input / cable. He insists there is no such thing as a Pin 1 problem and believes a shielded mic cable is the only cure. I believe, based on experience alone, one can use a multiple conductor UNshielded cable and avoid buzzing in the mic input PROVIDED I ground the whole mess to the transceiver chassis - which sorta, kinda, depends on what manufacturer and model we are dealing with, as some have more problems with this sort of thing than others. In this case, it is an older Ten-Tec rig, and TT rigs have more of this issue than, say, um, Kenwood rigs.

My question/ point is ... I guess, is whether the cable must be shielded, or whether a twisted pair cable with a sufficient number of conductors can be used and still avoid this sort of ground loop buzzing - or must it be a shielded cable - and if so, then what happens if I ground it at a both ends (meaning I connect Pin 1 of an XLR to the XLR Connector shell and also connect the shield of the mic cable to the shell of an 8-pin Foster plug which connects the shield to the transceiver's chassis.

Sheesh! I hope this makes sense ... it gets complicated pretty quickly for this old ... I do not want to engage my technically minded friend if I am off base - he is pretty long in the tooth, but he worked for SONY and built recording studios in Nashville in his day and knows about the radios ... but I cannot quite dismiss the "Pin 1 Problem" concept as I have had buzzing in the mic input, which was solved by connecting grounds to the chassis. BUT I CONCEDE I am still a rookie at this, so I don't wanna waste either his or my time riding the wrong trail.

THANKS for helping. James - K8JHR

 

[mrtnasty]

[have 60hz hum in my recording setup and I am suspecting it is due to ground loops] -- Years and years ago when I built and wired my music mixing production studio, I was generally worried about inadvertently creating some ground-loops with so many balanced and unbalanced cables going between everything everywhere. I knew that there had to be some kind of solution to this problem without having to resort into inspecting how every cable and piece of equipment was grounded and wired and after researching this issue a bit.....I found the answer.....well, at least for me.

>> BALANCED-POWER << -- While I am more than certain that there will be those on this forum who will probably completely debunk and/or decry the use or validity of using "Balanced-Power", but at least within my mixing studio, my audio is -- DEAD SILENT -- even at high gain levels. I can barely even hear any hiss coming out of my monitors with the faders up on my mixing console and the console's output control set at the 3 o'clock position. DEAD QUIET!!!

I have three 8-channel snakes running from my portable digital recorder rack to the inputs of my mixing console. Then, there is a TON of cabling running between the various console AUX and CHANNEL sends/returns and my signal-processing rack (shown as the bottom image below). And, guess what!!! >> NO HUM!!! <<

And.....I seriously doubt it was just "dumb luck" that I happened to interconnect and wire-up everything correctly!!! (Although that certainly is a real possibility)!!!

> TOP -- Mic-Preamp Rack // BOTTOM -- Digital Recorder Rack
View attachment 119368

>> IMAGE -- View of Earth photographed from the Moon photo-mural (Moon horizon is seen at the mid-woofer level)
>> TOP -- DynAudio BM15A Studio Monitors // BOTTOM -- MACKIE 32*8 Mixing Console
View attachment 119369

>> SONY 1U CD-PLAYER // TC ELECTRONIC "FINALIZER" // SONY CD MASTERING RECORDER
// PRESONUS 8-CHANNEL COMPRESSOR/LIMITER "X3" // TC ELECTRONIC "TRIPLE-C" MULTI-BAND COMPRESSOR
View attachment 119370

>> LOTS OF TC ELECTRONIC SIGNAL-PROCESSING EQUIPMENT (INCLUDING 7 MORE "TRIPLE-C" COMPRESSOR/LIMITERS)
>> The "Balanced-Power" chassis is mounted at the bottom portion of this signal-processing rack and is not shown here:
View attachment 119371

/

Hi, thanks for the reply, but by balanced power do you just mean using a 3 prong power cord? I have that on everything piece of equipment in my signal chain except the audio interface at the end.

 

[Newmarket]

If Edison won "the war of currents" the 60 Hz hum would not be an issue.

I suddenly wish to hear some AC/DC Or is that DC/AC

 

[JohnRoberts]

Cool Beans. I am interested in this discussion because I am in an active discussion with a highly qualified amateur radio technician and we disagree over a "Pin 1" type buzzing in a microphone input / cable. He insists there is no such thing as a Pin 1 problem and believes a shielded mic cable is the only cure.

That does not compute... The Pin 1 problem is about properly dealing with shield noise currents. Pin 1 further implies a 3 conductor (+,-, and ground) interface.

Unbalanced 2 conductor interfaces lack the differential processing capability to reference signals between different 0V signal grounds.

I believe, based on experience alone, one can use a multiple conductor UNshielded cable and avoid buzzing in the mic input PROVIDED I ground the whole mess to the transceiver chassis - which sorta, kinda, depends on what manufacturer and model we are dealing with, as some have more problems with this sort of thing than others. In this case, it is an older Ten-Tec rig, and TT rigs have more of this issue than, say, um, Kenwood rigs.

My question/ point is ... I guess, is whether the cable must be shielded, or whether a twisted pair cable with a sufficient number of conductors can be used and still avoid this sort of ground loop buzzing - or must it be a shielded cable - and if so, then what happens if I ground it at a both ends (meaning I connect Pin 1 of an XLR to the XLR Connector shell and also connect the shield of the mic cable to the shell of an 8-pin Foster plug which connects the shield to the transceiver's chassis.

With a proper differential input and suitable shield ground bonding to chassis ground to avoid ground contamination, the answer to your question depends on the source impedance of your signal, impedance balance of that source and termination, and twist of your twisted cable.

For the differential input stage to subtract out hum picked up by the wiring that hum must be identical*** in both signal leads.

Sheesh! I hope this makes sense ... it gets complicated pretty quickly for this old ... I do not want to engage my technically minded friend if I am off base - he is pretty long in the tooth, but he worked for SONY and built recording studios in Nashville in his day and knows about the radios ... but I cannot quite dismiss the "Pin 1 Problem" concept as I have had buzzing in the mic input, which was solved by connecting grounds to the chassis. BUT I CONCEDE I am still a rookie at this, so I don't wanna waste either his or my time riding the wrong trail.

THANKS for helping. James - K8JHR

Pin one problem has been pretty well investigated in recent decades. It wasn't always so there can be plenty of legacy gear with variable results.

JR

**** the hum rejection improvement delivered by starquad is because of the superior very symmetrical wiring wrap that insures similar noise pickup by both conductors.

 

[Cqwet Dbdfte]

I suddenly wish to hear some AC/DC Or is that DC/AC

Dirty deeds (done dirt cheap)?

 

[JohnRoberts]

If unbalanced paths were not created by arbitrarily grounding everything you wouldn't have an issue, nor if unbalanced connections exist in the first place.

95% or more of audio paths inside (my) large console designs are unbalanced single ended within local audio blocks. Interfaces between these different audio blocks are treated 2-conductor differentially (not balanced). Only input and output connectors require 3 conductor balanced considerations.

This is a mature topic and should be well understood by product designers by now.

JR

 

[JohnRoberts]

I think we talked about it about 12 years ago on an another forum when someone was having issues with an Audent interface and Rick pointed out the sudo-balanced circuit Soundcraft came up with for their direct outs that everyone else copied for the wrong application. Like those monitor controllers.

over the decades I have spoken to many people on multiple forums.

Perhaps you are thinking of "impedance balanced" outputs. FWIW they work fine into true balanced inputs.

JR

 

[MicMaven]

That does not compute... The Pin 1 problem is about properly dealing with shield noise currents. Pin 1 further implies a 3 conductor (+,-, and ground) interface.
Unbalanced 2 conductor interfaces lack the differential processing capability to reference signals between different 0V signal grounds.

Thank you for tackling my question Mr. @JR.

Perhaps I was not clear enough (the frequent rookie mistake of failing to provide enough information) - I am using multiple (6 or 8 conductor cable) and not a two-conductor, un-shielded cable. I think I know the answer for shielded 2-conductor-with-shield cable ... I wonder about using 6 (insulated) conductor un-shielded cable (not using all the conductors for mic audio, using them for PTT and other jazz) and using a conductor for mic ground that is connected end to end but is not a braided shield.)

Um... clear as mud, I suppose ... Or, perhaps I am way off base ! (Not the first time, but I do try hard!) James

 

[JohnRoberts]

Yes, but a lot of people don't understand they have to lift pin 1 so the input is forced into that mode. Especially on one of those combination style inputs they like to install on small interfaces.

no they don't and lifting pin one can defeat a safety ground path.

UL stipulates that any chassis connections labelled as "ground" must pass a ground bonding test for modest (single digit) voltage rise with 50 Amp test current injected.

Some people dislike my old Peavey stories but I had one fixed install product fail the ground bonding test when the PCB trace evaporated. I could have passed the UL test by labelling the I/O connection 0V or anything other than "ground". Instead I had my PCB artist beef up the ground trace so it could pass the 50A.

When in doubt do what's right.

JR

 

[MidnightArrakis]

Hi, thanks for the reply, but by balanced power do you just mean using a 3 prong power cord? I have that on everything piece of equipment in my signal chain except the audio interface a

[do you just mean using a 3 prong power cord?] -- NO!!! -- "Balanced-Power" is more than - just - using a 3-prong power cord. The diagram below shows what "Balanced-Power" is and note the "AC Polarity" symbols. "Balanced-Power" works in principal the same way as a balanced audio signal does, only at a significantly higher voltage potential.

The following items are at play here:

A) Your audio equipment is being isolated from the mains AC by a transformer. This helps reduce the amount of AC noise that is getting to your equipment as well as just isolating your gear from "the outside world".

B) The primary-side 120VAC is "unbalanced-power" (just like an "unbalanced" audio cable) and contains lots of unwanted artifacts. The secondary-side is 60VAC consisting of opposing voltage polarities, which just like an audio signal, cancels out any common-mode noise. Your equipment is still receiving 120VAC, only it's getting it "differently", i.e., "more cleanly". Read the article link shown further on down for more detailed information.



-- How Does "Balanced-Power" Help To Solve Ground Loop Humming --

Read more at: ePanorama.net - How does balanced power help to solve ground loop humming

> Ready for all of the "shredding" comments!!!

/

 

[ccaudle]

"Balanced-Power" works in principal the same way as a balanced audio signal does,

The biggest effect is when used with equipment which has 3-wire power, unbalanced audio connections, and rfi filtering caps on the power entry. The symmetrical voltage on the power leads can partially cancel the leakage through the filter caps and reduce the leakage current into the chassis.

This is probably the most relevant part from that ePanorama page linked above:
"If you have chassis leakage problems, it can be a miracle. If you don't, it doesn't do any better than any other isolation transformer."

 

[ccaudle]

He insists there is no such thing as a Pin 1 problem and believes a shielded mic cable is the only cure.

No such thing as pin 1 problem in general, or that it is not relevant in his particular case?
The first would definitely be incorrect, the second we do not have enough information to judge yet.

I believe, based on experience alone, one can use a multiple conductor UNshielded cable and avoid buzzing in the mic input

This is for amateur radio use? That is likely in a high RF environment, so if you use unshielded cable you may need pretty severe RF filtering.

still avoid this sort of ground loop buzzing

Don't fall into fuzzy thinking. A microphone is a floating source, it has no connection to power line or safety earth, or to any other powered equipment at all, so there is no loop.

Buzzing is either capacitive or inductive pickup of power line frequencies, or is demodulated RFI.

If the problem is caused by capacitive pickup of relatively low frequency interference, then shielding is really the only effective solution. If the problem is caused by RF interference, then either shielding or good RFI filtering could work.

but I cannot quite dismiss the "Pin 1 Problem" concept as I have had buzzing in the mic input, which was solved by connecting grounds to the chassis

Connecting "grounds" to the chassis (explain what exactly you mean, that term is ambiguous), or connecting shields to the chassis? Shields should of course always be connected to the chassis; the pin 1 problem is caused when cable shields are also connected to the circuit reference node (aka "circuit ground") which causes shield interference current to flow through the audio circuit. You can have a pin 1 problem with or without cable shields (unless you have a true floating source with only the two signal wires into a differential input).

Is there some particular reason you are trying to avoid a shielded microphone cable?
It sounded like the connector on the radio side connects shield to chassis and not to the circuit common, so there is no pin 1 problem if your description is correct.