Balanced versus Unbalanced wiring and the dreaded "ground loop"

[Mmmmqac]

If only we could go back in time and educate manufacturers and designers who left us so many problems to deal with. Unbalanced audio should never have happened, and the XLR connector should have had two pins, not three. And as for ground-lift switches... don't get me started.

 

I have made my share of mistakes, and as I continue to gain more experience and understanding of the laws of physics (particularly concerning electric charge and magnetic fields), I am becoming aware of what those mistakes have been. An excellent series of articles that would be of immense benefit to DIYers were recently republished in Electronic Design News. I include the link here.

 

 

 

[Mmmmqac]

That's strange, the link I pasted changed to EDN's home page. Paste this into your browser instead:

http://www.edn.com/design/consumer/4429968/The-G-word--How-to-get-your-audio-off-the-ground

 

[WRGKMC]

I read that article and have to say its pretty dumb. It's written to make people question circuits and make them think, but its short on reality and full of assumptions are quite amateur.

 

Its best to study the inventors and the obstacles they encountered making their inventions and the common sense used overcoming those obstacles. Some of those obstacles were dealing with the natural science that could only be visualized in a theory, and the other often dealt with them in practical manufacturing methods.

 

The whole reason for having a chassis is to act as a faraday cage and it wound up being the most practical method of blocking EMF which is essential in amplifiers. It also cut the cost of manufacturing and design way down by providing a common conductor to all the components needing a path to ground or negative voltages. Its truly ingenious in fact.

 

As for other designs, Many were developed in the dark dealing with an unseen force which became popular because they worked, and worked well.

 

Its easy for anyone to look back on history and say this invention could have been better or this one is inefficient, but they weren't educated in electricity or the physics of that time. If they had been they would see how wonderful those designs actually were in dealing with the actual problems.

 

Its only been a few decades since man has been able to see electron move through different substances. Prior to that it was 100% theory. We wouldn't have the computers we do today if it wasn't for the electron microscope being able to see electrons move through semiconductors and thereby discover the impurities that slowed the electrons and caused heat.

 

We are limited in electronic designs by the quality and thereby the efficiency of the components used in those circuits. Mathematical Theory alone does not take inefficiency into consideration. Those component inefficiencies have to be added to the theories for the circuits to actually work.

 

If you want one highly efficient component that's closest to working as the theoretical version requires, you may need to manufacture a thousand and test every one to find the one that has the highest efficiency. If the less efficient components aren't put to use in some other circuit, it becomes very expensive harvesting only the most efficient parts and throwing the others away. Instead you have different grade classifications for parts.

 

In the past "Military Grade" components had the highest efficiency and lowest tolerances. This was needed in situations where failure due to quality wasn't an option. You have enough to deal with in war dodging bullets and bombs. Consumer electronics consisted of lower quality components that were still good enough to do the job.

 

The difference between Balanced and Unbalanced is a matter of cost. If you run balanced cables between circuits, you still need shielding to block EMF. If an amp needs a High impedance input, and you run a long line to it, its best to convert the source signal to balanced low impedance so there's less signal deterioration over long wire runs, the convert it back to high impedance once its reached its destination. Doing this adds to the cost. With short runs the amount of fidelity lost sending a signal through an unbalanced cable isn't perceptible so a low cost method works fine in those cases.

 

With todays advancements in digital both of those methods are inferior. It would be better to convert the audio to digital and send a binary signal through a copper or fiber optic cable then convert the signal back to audio once it reaches its destination. At the moment, the cost of doing that is inhibitive, but with the cost of materials like Copper constantly rising its only a matter of time before you connect your TV to your Hi Fi with a Fiber Optic cable that requires no magnetic shielding and does not link the chassis of one unit to another to provide a common ground. If the Audio is sampled at a high enough rate you have virtually no loss.

 

Most stereos and TV's made today already have digital ins and outs to connect them together. You even have Microphones and preamps that have built in converters that can plug straight into a USB port. The technology is there but the process of change seems slow and it comes down to cost. When you do look at it from a historical view, the changes that have come about in the past 50 years has grown exponentially and at some points doubling each year.

 

When you say unbalanced circuits should have never been designed its like saying all the Radio, Television and Audio products shouldn't exist. None of those products would have been affordable to the masses, and all the industries from Broadcasting, Hollywood, Recording music, stores and theaters right on down the line would never have existed. See the glass as half full and you will see the genius in the designs. Then see the half empty glass as opportunities for improvement.

[Mmmmqac]

I read that article and have to say its pretty dumb. It's written to make people question circuits and make them think' date=' but its short on reality and full of assumptions are quite amateur.[/quote']

Are we talking about the same article? The one where Bruno Putzeys wrote about impedance balance vs current balance, supporting everything with real math, then walked us through the design of his balanced pre-amplifier (including real PCB layout), and finished with real plots of noise and distortion?

 

Its easy for anyone to look back on history and say this invention could have been better or this one is inefficient, but they weren't educated in electricity or the physics of that time.

You are correct, but I still wish I had a time-machine so I could visit my younger uneducated self and give him some valuable knowledge. I'm sure Rane feels the same way about the ground-lift switch botch-up mentioned in the comments attached to Bruno's article.

 

We learn so much from making mistakes, but I lament the fact that we are often powerless to undo the mistakes that have taught us so much. Wouldn't you love to live in a world where:

• ground-loops never spoiled our music with hum
  
• XLR connectors didn't confuse us with what to do with pin-1
  
• you didn't have to modify your equipment because somebody else wired the XLR incorrectly
  
• cables between equipment did not mix HF interference into our music?
  

Sure, balanced cables cost more, but look at the advantage! As for the extra components to make an input or output balanced: now that we have learnt that it is only the impedance that needs to be balanced (as opposed to cable pairs carrying mirror-image waveforms) we see we could have done it on consumer goods by adding a couple of resistors and maybe a capacitor.

 

When you say unbalanced circuits should have never been designed its like saying all the Radio, Television and Audio products shouldn't exist. None of those products would have been affordable to the masses, and all the industries from Broadcasting, Hollywood, Recording music, stores and theaters right on down the line would never have existed. See the glass as half full and you will see the genius in the designs. Then see the half empty glass as opportunities for improvement.

 

My bad. I should have been clearer and written "Unbalanced audio interconnects should never have happened... ." I did write it in the same sentence as my thoughts about XLR connectors, but I can see I was not totally clear on what I meant.

 

​If there are some amateurish assumptions the EDN article, and some potential for improvement in the reality department, please bring them to light so that we can all discuss them and learn.

 

Thanks

[WRGKMC]

Are we talking about the same article? The one where Bruno Putzeys wrote about impedance balance vs current balance, supporting everything with real math, then walked us through the design of his balanced pre-amplifier (including real PCB layout), and finished with real plots of noise and distortion?

 

Yes same article. I'd say that article was shallow, superficial and targeted to those who have no electronics background.

 

 

[*]ground-loops never spoiled our music with hum ~~

I deal with those issues by avoiding them in the first place.

Of course my experience dated back to before homes had ground plugs so having a cold chassis was imperative.

 

~~

[*]XLR connectors didn't confuse us with what to do with pin-1 ~~

I know how to wire XLR jacks so its a non issue. In some cases I do wire the leads in reverse to intentionally reverse the microphones polarity. This is done so when micing both the front and back of a speaker, both mic signals are in phase. These would be special cables used only for that purpose.

 

~~

[*]you didn't have to modify your equipment because somebody else wired the XLR incorrectly ~~

Well I did that work for a living and got paid well to fix peoples screw ups so its not surprising others can make mistakes. I see it as job security when you have that many idiots who haven't got a clue.

 

~~

[*]cables between equipment did not mix HF interference into our music? ~~

Well I only get the occasional AM radio bands on guitar circuits when the components have just the right specs to act as a Crystal radio. Had this in fact last night when I built a FuzzRite fuzz pedal. The circuit was just right for picking up a local radio station. The quality of the sound for its intended use is very good however I may just leave it as is. I don't mind the ghosts in the background and can make for some interesting recordings. If it gets annoying I'll probably use a couple of ferrite coils to eliminate it or change the length of some of the hookup wires to tune it out.

 

~~~~

Sure, balanced cables cost more, but look at the advantage! As for the extra components to make an input or output balanced: now that we have learnt that it is only the impedance that needs to be balanced (as opposed to cable pairs carrying mirror-image waveforms) we see we could have done it on consumer goods by adding a couple of resistors and maybe a capacitor. ~~

 

There's more to it. Since the entire frame is ground to all components in a circuits you have to look at the entire circuit as a whole when making changes. If the entire circuit is truly balanced to use differential as noise cancellation, you would still have to shield everything in a faraday cage including your connection cables to protect it from stray EMF. Just walking past or waving your hands over an unshielded circuit causes many strange things to happen. The human body can act as a ground or an Arial to the circuit and just being in close proximity all kinds of weird things to happen from acting like a Theremin or Metal detector to producing static electricity. In audio its all about good shielding. without it you can have all kinds of noise.

 

The big problem of the past in having good balanced circuits was not just added parts but having super low tolerance parts so you had a good balanced waveform. If you drive a class A amp for example with an unbalanced signal, you can get superb results because the transistor or tube is biased at a positive value some place in the middle of its amplification curve. All the wave has to be is symmetrical and you will drive the signal positive and negative extremely well. Many of your best amplifiers use this system because it creates fast transients and sounds really good.

 

I'm a big believer in minimalism. I've learned that the more components you add, the more you rob the signal of its quality. This holds true in analog and digital. Electronic components add noise and rob the signal of its harmonics and details. Its OK if those items are unwanted, but you remove the unwanted at the cost of loosing some of the details that are good.

 

In the case of electric guitar, I'd never use a balanced circuit or cables. I want the signals to be mangled by inferior circuits as a sound effects that gives that instrument its particular sound. Other instruments I want to preserve the highest quality possible so I runs everything from the mic to speakers balanced. Even there it can be a toss up in some cases. Vocals, especially mine may need some white noise to grunge it up. It all depends on the particular work I'm doing.

 

In other cases, I could care less about the sound quality. Watching television for example, So long as there isn't any noticeable hum or noise I could care less if the signal was balanced or not. If its my Hi Fi, then I may choose a digital connect instead of analog if it gives me better sound quality. In some cases it does and others it makes things worse by adding digital artifacts that drive me crazy. I find that more annoying then analog static, tape wow and flutter or even lightening strikes heard on an AM radio.

 

~~

​If there are some amateurish assumptions the EDN article, and some potential for improvement in the reality department, please bring them to light so that we can all discuss them and learn.

 

Thanks[/color]

 

Like I said its superficial. It reads like an amateur with practically no electronics knowledge wrote it and there was no depth to why things are as they are. That may have been the writers intensions, and was meant to be something read by beginners only then he succeeded. I realize there's only so much you can write in a small article like that but there was nothing useful there for even amateurs.

 

It costs manufacturers allot of money to retool factories and do things differently. They don't do it because there are better ways of doing things or is popular. They do it because someone is willing to pay for it.

 

Add to that most circuits are designed on computers using cad programs, today, there isn't much sense in thinking outside the box. These programs are so finely tuned to taking into account the costs of manufacturing, you can be working in the program and see the cost of that build as a running subtotal. May one change that you think is good and you can see the cost to the bottom dollar to manufacture the design. You can even scan the design and identify the areas that are suspect in costing too much and it will make suggestions on changes that are proven to be fault free.

 

I know engineers who work here at Canon that do nothing buy figure out how they can save pennies on production by taking a piece of metal that gets punched out of a chassis frame and using it in another part of the machine. Instead of punching a square hole they punch a rectangle so that piece of metal can be folded into another bracket that holds another part some place of the machine in place without any additional grinding, cutting or shaping. The entire build is a jigsaw puzzle and they have teams of engineers to focus on different areas. Then they have other engineers that makes one groups efforts work with another group so all the parts of the puzzle fit together. Its quite amazing actually.

 

This is a big deal because cost of resources is high and to remain in business requires you budget those resources wisely. They get down to super small things that would seem stupid to the normal citizen. Putting washers on with the wrong side down can cost a company millions. A stamped washer is rougher on one side then the other and when reversed it wears out moving parts more quickly. I had been a tech for 25 years didn't believe it till I got involved in things on a manufacturing level. When you see the data of failures tracked over thousands of machines, all over the world and find something as stupid as a washer is causing the company to loose millions in premature parts failures, you get a sense of why things are done exactly the way they are.

 

In audio, I doubt if many know all caps have polarities which affect the sound quality when installed backwards. In factories they only pay attention to electrolytic caps because they will obviously blow when connected with a reverse polarity. But few know the foil in caps have the positive signal applied to the center of the inside foil wrap. The negative potential is applied to the outer wrap. This limits hum in circuits and has an effect on charging times. All caps properly installed makes an amp run quieter and more efficient. The component will work whether its reversed or not but, its only one small item in a chain of many that can add up collectively degrade the quality.

 

You could manufacturer all balanced circuits, but you'd have to show my some data that shows it be superior. If it is, why not save that circuit for the high end gear where you can drive the profits up and make it worth doing. Other then your own personal preferences, its not going to make people dig into their wallets and pay for something unless those differences are perceptible. Most people listen to crappy MP3's so that gives you an idea of their willingness to forgo quality for cost. Back in my day it was AM vs. FM radio. FM cost more and they didn't have any rock or pop stations till the 70's. We're going through the same thing with digital. Stations have digitized and the sound quality is so poor it doesn't matter if you have great gear. You'll never hear the details unless they increase the sampling of the broadcasts to a higher quality.

[Kazinator]

The idea that balanced lines should have only two pins, not three, is wrong.

 

First of all, on a basic intuitive level, suppose a microphone cable has only two conductors. On what basis can you call it balanced? The receiving pre-amp on the other end of the cable cannot by itself perform some magic to make it balanced.

 

The "balanced" in "balanced signaling" means that impedances are balanced, and impedances need a reference: they are impedances to the reference ground. (Cue entry of third conductor ...)

 

What is true is that you don't need a third conductor for every single balanced pair. In a cable which carries, say, 7 balanced lines, you need 15 conductors: 2x7 + 1.

 

A misconception in balanced signaling is that each of the two differential conductors has to carry the signal in opposite and equal polarity. That is in fact false; it's possible for just one of the pair to have that signal (referenced to ground: the extra conductor) and the other member of the pair can just be at 0V: no signal. The balancing still works (including its noise-canceling aspect), because a balanced signal is just the difference between two unbalanced signals. In this assymetric situation, noise is still induced equally in both of these lines. The noise still sees identical impedances in both branches of the differential amplifier and identical, but opposite amplification, which cancels it out.

 

[Mmmmqac]

 

XLR connectors have four solder terminals (the shell, pin-1, pin-2 and pin-3) but the audio cables we are talking about have two cores and a screen. The cable screen connects to the shell, and two pins carry the signal. History has shown us that many people have been confused by the presence of three pins and they connected the cable screen to pin-1 only, and not to the connector shell as well. If XLR connectors had only two pins and three solder terminals, then history would be different and we would not have a multitude of products and installations that trouble us with ground currents getting into places where their noise can be amplified.

 

The purpose of a cable screen is to extend the clean environment (in a noise sense) between circuits housed within different enclosures. In effect it turns two enclosures into one having a hollow conductive conduit between them.The screen is not a "ground reference," and balanced impedance has nothing to do with the screen. A circuit's reference node can be at any potential, it does not matter what voltage it is with respect to ground.

 

Noise that capacitively couples into the screen is kept away from the cores, and conducts via the enclosures to whence it came. If inside the product only pin-1 is connected (and not the shell terminal), then the noise current will find another path to whence it came, possibly corrupting the audio signal along the way.

 

Noise carried by magnetic fields will couple into the entire cable. The differential input to the pre-amplifier will cancel the noise if and only if both lines have the same complex impedance. Noise coupled into the screen will create a ground loop, but we don't care because unlike un-balanced equipment, there is no electrical connection that can carry this current into our amplifier (assuming a pin-1 botch-up has not been made).

 

The impedance presented to the hot and cold conductors in the cable hinders current flow into the circuit nodes that are the "stiffest," or most difficult to change the voltage of by driving a current into them. If we consider a differential opamp circuit, the impedance network for the inverting input has the opamp's output terminal as this "stiff" node. The impedance network for the opamp's non-inverting input has the reference node itself as this "stiff" node.

 

I still recommend the EDN article for DIYers. Perhaps some HC forum subscribers will find it a bit simple, but I suspect many will learn from it. I don't mid admitting that until I read it, I did not fully understand the physics behind why golden-ears claim that cermet and carbon potentiometers sound different.

[WRGKMC]

 

XLR connectors have four solder terminals (the shell, pin-1, pin-2 and pin-3) but the audio cables we are talking about have two cores and a screen. The cable screen connects to the shell, and two pins carry the signal. History has shown us that many people have been confused by the presence of three pins and they connected the cable screen to pin-1 only, and not to the connector shell as well. If XLR connectors had only two pins and three solder terminals, then history would be different and we would not have a multitude of products and installations that trouble us with ground currents getting into places where their noise can be amplified.

 

XLR connectors came after older screw on connectors that were needed to run phantom power. Since most mic connectors are capable of running phantom power using the shield and one of the hot leads, there's no issue running AC and DC on the same line.

 

The purpose of a cable screen is to extend the clean environment (in a noise sense) between circuits housed within different enclosures. In effect it turns two enclosures into one having a hollow conductive conduit between them. The screen is not a "ground reference," and balanced impedance has nothing to do with the screen. A circuit's reference node can be at any potential, it does not matter what voltage it is with respect to ground. ~~

 

Yes I mentioned that several times. The cable and chassis act as a Faraday cage. The screen can do both, act as a shield and act as a DC/AC ground potential. If the quality of the shield is good (90% copper or better) and thick enough the EMF will not get to the core wires.

 

External static and noise travels along the "skin" of the shield. It doesn't mix with the signal or DC potentials in the wire. Its the current in any case that can cause noise by generating a signal in the wire using the "left hand rule". Current being sent through a wire uses the right hand rule. Both of these are complicated topics, and even though I love it, its more involved then what's needed in this discussion.

 

In any case, external the external shield doesn't act like a water hose for EMF and carry magnetic forces through the shied and contaminate the interior. Any current the shield does generate when MMF passes through it, is carried down the outside of the cable as a skin effect so its incapable of generating a signal in the core wire. The stray crosstalk should be blocked by the cores insulation layer. The EMF has to be super strong for it to generate a voltage in the shield and core wires. .

 

You must understand the golden rule about electricity. It travels the path of least resistance, It requires a "difference in potential" to be attracted from one point to another. Items that are electrically neutral, or have no difference in potential, have no attraction.

The reason why normal unbalanced circuits work is any AC noise is attracted to the nearest ground. It shouldn't be attracted to the core wire. If you do get hum its either because the shield quality if poor or the hum is coming from within the chassis.

 

Noise carried by magnetic fields will couple into the entire cable.

 

Noise isn't carried by the magnetic field. The field generates a current. Thing "generator" or guitar pickup. When you pass a wire through a magnetic field the lines of flux generate a current. {Left hand rule}. That current has to be great enough, and sustained long enough to develop lines of flux to generate a secondary current in the core wire. [Right hand rule]

 

Static on the other hand can generate extremely high voltages, 30K plus just walking on a carpet. They may be able to jump across the dielectric of the cable (insulation layers between conductors) and disrupt the signal creating sparking noise. This doesn't happen much however because the shield is usually efficient enough to discharge the voltage completely like a lightening rod. If the Tribo electric charge is great enough to penetrate the core then low voltage components are susceptible to damage.

 

The impedance presented to the hot and cold conductors in the cable hinders current flow into the circuit nodes that are the "stiffest," or most difficult to change the voltage of by driving a current into them. If we consider a differential opamp circuit, the impedance network for the inverting input has the opamp's output terminal as this "stiff" node. The impedance network for the opamp's non-inverting input has the reference node itself as this "stiff" node.~~

 

Have no idea what you mean by stiffness. Maybe this was something some instructor used to explain things and it clicked for you but its not what we use in the industry. Impedance is AC resistance. The change of AC polarity is resisted by the components its connected to. The two main items are caps which take time to charge and discharge, and coils which resist charging due to the lines of flux expanding and contracting. Each of these have opposite effects on the voltage and current. One will make the current lag, one will make the voltage lag (phase delays) in the voltage changes.

 

All the amplification devices need is the correct signal strength to amplify the signal properly. Like any SS amplifying device, and OP amp has an ideal range of operation where its above the floor so the noise isn't heard and below the ceiling where the signal gets flattened. Then its a matter of amplification factor (usually greater then 1:1) and the curve the signal is best reproduced (usually between 50~70% of max)

 

You can place any impedance you want before an amp, but it comes down to current vs voltage. Low current, high voltage travels longer distances then high current low voltage. The source of the signal determines what is best. If conversion is needed to preserve fidelity, then that's what you want to do. The impedance just have to match the amp (or be within a tolerable range) when it gets there.

[Mmmmqac]

I know "stiffness" is only an illustrative term, that's why I put it in quotes then explained it after a comma thus:most difficult to change the voltage of [the node] by driving a current [signal] into [that node]. The term is not uncommon. Have you not heard of "stiffening" a power-supply to reduce sag caused by high load current? And surely an educated man like yourself could have worked out what I meant if he did a bit of deductive reasoning instead of merely quickly skimming over the posts of others before quickly responding.

 

And what do you mean, WRGKMC, by "Noise isn't carried by the magnetic field"? I suggest that YOU think "guitar pickup" (as you suggested to me), and consider the delivery mechanism of mains-hum (unwanted signal, aka, NOISE) into single-coil pick-ups.

 

​In all of your ramblings here you have said a lot, but told us nothing that you consider assumed or unrealistic in the EDN article. Instead you labelled it as shallow, superficial and targeted to those who have no electronics background. Contrary to what you say, it is quite obviously targeted at people with a lengthy electronics background. I say that because Bruno Putzeys concentrates on dispelling old naive ways of thinking about ground --- ways of thinking that people with no background would not need to unlearn.

[agedhorse]

Seems as though there are a few pretty basic misunderstandings between balanced, impedance compensated and unbalanced signal transport protocols.

 

A couple of facts that might highlight these misunderstandings and WHY they are wrong (or in some cases only partially wrong and partially right)

 

1. Balanced wiring requires at least 2 conductors, the screen or shield is not (theoretically) necessary BUT IN PRACTICE, a shield is necessary because balanced receivers do not have good rejection at very high frequencies and the circuitry relies on the shield for this purpose.

 

2. Ground is not ground at all frequencies. HF and RF makes things very difficult to generalize, but at very high frequencies, all kinds of parasitic inductances and capacitances come into play. The techniques used to deal with these play a big part in the design of grounding systems and how shields or chassis (especially located remotely) are connected. This is especially critical when designing with switchmode power supplies or class D amplifiers.

 

3. Impedance compensated signal transport protocols will always have a signal to noise ratio that is 6dB worse than a truely balanced protocol for systems that use active line drivers. This is due to the available drive voltage being doubled (all else being the same).

 

4. Many times, the signal transport protocol (an even the connectors themselves) are chosen based on maintaining legacy connectivity. How would you guys like it if guitars changed connectors every few years like the consumer electronics and/or IT industry does. A guitar that is obsolete after 5 or 10 years would not go over well in the marketplace... I would expect rioting in the streets

 

5. The shell connection is unreliable at best (especially on the cable male end) when mating with the opposite gender connector. The shell is rarely used with the exception of some pretty specific applications. The shell connects with pin 1 at the source end for microphones, whioch extends the shield/screening to the mic body for Faraday shielding of the element and associated electronics. This connection is always done within the microphone itself. (except perhaps Chinese black market copies which target cosmetics rather than performance and functionality it their counterfeits.

 

6. Simplistic articles can often be taken as misleading to those who do not deal with this kind of stuff on a professional level, There are a lot of details left out that it is assumed the readers, being skilled in the art of the topic (and it's historical context) have.

 

[Luthier-Atlanta]

Ouch my head hurts after that read gent's. Great info!

[Mmmmqac]

5. The shell connection is unreliable at best (especially on the cable male end) when mating with the opposite gender connector.

Good point. As I understood the EDN article and the IEEE standard, we need to be connecting pin1 and shell terminals everywhere (inside devices and both ends of cables), and to fix cable heating due to high ground-loop current by running a Parallel Earth Conductor, NOT by "lifting" the ground. Have I got that right?

Now, if we had a Go-back-in-time-atron, we could organise a connector with reliable shell connection to become the standard.

 

 

[agedhorse]

Note than many panel mount XLR connectors no longer include a shell connection. Therefore, the shell is becoming an unnecessary legacy afterthought.

 

The "proper" way would be for the power system safety grounds to be the hard grounds and the signal grounds being loosely connected (which is how many manufacturers do it) but this begins to fall apart when rouring signals over longer distances and to buildings that have different earth bond connections. At this point, it's almost universal that (audio) transformer isolation becomes the accepted industry standard with one end or the other being at least loosely connected to the respective ground/earth.

 

The problem is that different implimentations work better (or are safer) for different applications. There is no universal "best way".

[ewizard]

This has recently come up in another sound forum I frequent. The argument was whether we should follow the IEEE standard that states we should have pin 1 connected to the XLR shell, or leave the shell unconnected? Depending upon which camp you desire to be in and what you feel is the true issue, is yours alone to decide. The facts are simple though when lined out.

 

The IEEE standard requires that the shell be connected to ground via pin 1. This connection is usually made with either a wire or the shielding itself. Most XLR cable is only 2 conductor with a drain shield ( or jacket ). There are others that use 3 conductor with a drain shield. In either case the pin 1 connection and shield become one.

 

The other method, which many prescribe is the more appropriate way, is even simpler yet. Simply the shell of the XLR is left out of the circuit and pins 1-3 have there own dedicated wire. Pin 1 is ground and is almost always connected to the shield/drain wire. This is from a sound engineers standpoint the superior method.

 

So why does it matter? In either case you have a balanced connection, so why does having the shell as part of the circuit matter? Ground loops is why! If the XLR shell is part of the circuit then you can never " LIFT " pin 1 to eliminate possible ground loop issues. The problem is that different equipment connected to different power sources can have different paths to ground. The difference when connected through the cable to other parts creates the ground loop potential. With the XLR shell and pin 1 being hard wired together, a simple pin 1 lift cannot eliminate the problem. Now with a simple XLR cable that has the XLR shell out of the circuit, a pin 1 lift can be utilized and since no path to ground exists at that point, problems can be reduced or eliminated.

 

The other big argument is RF interference and noise introduction. The IEEE standard is superior at elimination of those ailments, but there is usually no problem these days with acquiring a clean RF free signal between products. Why is that? It's because the runs are usually too short to have the introduction of RF and noise introduced. Not to mention most products are well designed to eliminate the potential of RF noise pollution.

 

RF and noise are usually a non issue. The workaround that has been toyed with and implemented by many is simple. Instead of connecting the shell at both ends per IEEE standards, simply only connect the male XLR end shell to pin 1. This adds the benefit of RF and noise rejection while still leaving the ability to do a pin 1 lift. Basically the drain wire connects to pin 1 at what is the chassis ground to most units. This extends the RF and noise rejection onto the XLR line. The upside is that you can still implement a pin 1 lift if grounding is an issue. Not a cure all, but the best of both options.

 

As for balanced lines as an end all be all, I don't see it. You need a preamp circuit that is designed to sum the signals, which in a guitar amp can add some costs and in general as mentioned before, it just isn't needed. The current system isn't perfect, but it also isn't totally inept.

[xiaoluoj]

high current low voltage. The source of the signal FIFA 15 Ultimate Team Coins determines what is best. If conversion is needed to preserve fidelity, then that's what you want to do. The impedance just have to match the amp (or be within a tolerable range) when it gets there.

[WRGKMC]

 

And what do you mean, WRGKMC, by "Noise isn't carried by the magnetic field"?

 

Definitely not. A magnetic field is converted to an electrical voltage by wire when either the magnetic lines of force cut through a wire or the wire cuts through the lines of magnetic force. This sets the electrons in motion through the wire.

 

The magnet in a pickup coil only senses the string movement cutting through the lines of force and generates a signal in the coil by magnet field disturbance.

 

 

The magnet's force in a pickup has no effect on RF noise like AC hum. The core can be non magnetic iron or not even have a core and you'd still have that noise generated in the coil. The Coil is what produces the noise spikes, not the magnet. Because you have many winds of wire concentrated together, say its 500 turns wrapped in the same direction, the passing of a single magnetic line of force cutting through the coil generates a signal 500 times greater then it does cutting through a single conductor and if it happens quick enough the coil will remained charged as the electrons drain off.

 

An iron or any permeable metal core intensifies the strength or the coil because it focuses the EMF to more wires in the coil by acting as a conduit. It doesn't matter if the core is permanently magnetized or not, it doesn't draw in EMF like a vacuum cleaner. Its only the fact that it is a Ferris metal channels the EMF to more wires in the coil and therefore generates a stronger signal.

 

Much of this has to do with the number of winds the coil has and if its close to being in phase or out of phase with the RF signal. Since 60HZ AC is within the audible hearing range, its difficult to block it from amplifier circuits without rolling off your bass frequencies. There are also AC harmonics at 120hz, 180hz, 240etc up into the treble frequencies that will generate auditable signals when preamplified if those waveforms do reach the core conductors.

 

There are two popular ways of getting rid of the 60hz EMF noise. One is to get rid of it through phase cancellation, i.e. using a balanced line and differential preamps. The other way is to prevent the noise form ever reaching the signal carrying wires by using a grounded shield. It doesn't matter whether that shield also carries half the signal like it does in an unbalanced application so long as the wire resistance and capacitance is low. Most balanced circuits will use both systems. A balanced line and a shield so you have the best of both worlds.

 

How the signals are routed through those wires for a given amp circuit or whether the sleeves of XLR connectors are grounded or not is optional. I have several mixers, EQ's, Compressors and such that have XLR inputs and on the other side of the connector you have a high impedance wire with a shield and core going to the preamp channel the same wire connects to the High impedance 1/4" input. There is no balanced transformers inside and no difference between the two connectors inputs.

 

 

​In all of your ramblings here you have said a lot' date=' but told us nothing that you consider assumed or unrealistic in the EDN article. Instead you labelled it as [/color']shallow, superficial and targeted to those who have no electronics background. Contrary to what you say, it is quite obviously targeted at people with a lengthy electronics background. I say that because Bruno Putzeys concentrates on dispelling old naive ways of thinking about ground --- ways of thinking that people with no background would not need to unlearn.

 

I'm sorry if my opinion disturbs you but it is my opinion. I should just note I was a technical writer myself for 10 years working for major manufacturers like Ricoh Canon, Mita and others. The manuals would come from Japan poorly interpreted by the engineers and my job was to take what we called Japalish and convert it to English. Often times this involved rewriting a great deal of the manual so it was technically accurate and easily understood by the technicians who repaired the gear. Technologies were mostly digital but also dealt heavily with Lasers, static electricity, audio, basic electric, power supplies, mechanics like motors, relays switches of every kind, Matrix signals and a list a mile long of all kinds of new technologies.

 

The main point is I would have to confirm every word written in the manual, every spec, every adjustment, every circuit, every voltage, every part functioned exactly the way the prototype machine we received did. Because the machines are so complex service techs rely heavily on the manuals and the slightest error could be disastrous.

 

When I got done proof reading the manual it was passed to another individual who would go through it again and not only check my corrections but find their own. After that it was given to an ordinary technician to use and go through all the normal checks and adjustments to see if he came across any errors, all to get the technical writing not only correct, but easy to read and understand by even the poorly educated technicians.

 

So when you asked me if the article was good, I gave you "my" honest answer. Its not necessarily bad, it just misses the mark in many areas from an educational aspect.

 

 

My belief is this, and its very simple. If you rely on only one source of your knowledge, and assume that source is complete its easy to have a fixed opinion on what you believe.

 

I had several great electronics instructors when I got trained and later worked with several who had their doctorates in the field. The first really truthful thing you can believe is electronics is a life long education process. You can not get what you need to fully understand things by reading one article. Read 200, 300, everything you can get your hands on by as many different authors as possible and you may begin to develop a more complete understanding of the topics and theories involved. Even then new things come along all the time that force you to revisit the technology you know so well.

 

Once again, I read that article and none of that happens for me and I see where its lacking. Nothing personal here, it just doesn't have the mojo. The guy may be an electronics wiz but he didn't write much of an article there. (in my opinion)

[Mmmmqac]

A magnetic field is converted to an electrical voltage by wire when either the magnetic lines of force cut through a wire or the wire cuts through the lines of magnetic force. This sets the electrons in motion through the wire.

 

The magnet in a pickup coil only senses the string movement cutting through the lines of force and generates a signal in the coil by magnet field disturbance. The magnet's force in a pickup has no effect on RF noise like AC hum. The core can be non magnetic iron or not even have a core and you'd still have that noise generated in the coil. The Coil is what produces the noise spikes, not the magnet.

 

:)I am finding that forums are a difficult means of communicating technical ideas. We can only see where the other person misinterprets us, and we don't detect their misunderstanding until considerable time has passed. For example: When I misinterpret things written here, I will have no clue that I have it wrong. The writer also does not yet know that I have it wrong. However, when I write a response that makes little sense to the person whom I have misinterpreted, then it is obvious to them that I didn't get what they meant.

 

I must have come across as a {insert your favorite adjective implying low IQ} when I wrote that noise can be carried by magnetic fields. I knew what I meant. You probably thought you knew what I meant too. Judging by your generous help quoted above, I sense that I inadvertently painted a crazy picture in your mind of magnets establishing some kind of conduit for noise to slide along... or maybe that a magnet's force could move or alter the path that noise travels. But I must admit, I could be misinterpreting my own misinterpretation.

 

What I actually meant by "carried" was: If a varying current flowing in a wire makes a varying magnetic field, and then the magnetic field induces a signal in a second wire, in essence the signal was carried from the first wire to the second wire by the magnetic field that was established by the primary current flowing in the first wire. Like the way wires conducting mains currents make alternating magnetic fields that then induce low-frequency currents in microphone cables, or the way hearing aids work in theatres with induction loops.

 

My belief is this, and its very simple. If you rely on only one source of your knowledge, and assume that source is complete its easy to have a fixed opinion on what you believe.

 

I had several great electronics instructors when I got trained and later worked with several who had their doctorates in the field. The first really truthful thing you can believe is electronics is a life long education process. You can not get what you need to fully understand things by reading one article. Read 200, 300, everything you can get your hands on by as many different authors as possible and you may begin to develop a more complete understanding of the topics and theories involved. Even then new things come along all the time that force you to revisit the technology you know so well.

 

Once again, I read that article and none of that happens for me and I see where its lacking. Nothing personal here, it just doesn't have the mojo. The guy may be an electronics wiz but he didn't write much of an article there. (in my opinion)

 

Thanks for explaining.

[onelife]

A magnetic field is converted to an electrical voltage by wire when either the magnetic lines of force cut through a wire or the wire cuts through the lines of magnetic force. This sets the electrons in motion through the wire.

 

I hate to be a nit picker here but I think it is an important distinction.

 

When a coil of wire passes through a magnetic field, an electric current is generated in the coil not a voltage as stated above.

 

I believe it is important to understand the difference when applying the fundamentals of Ohm's law in electromagnetic circuits like guitar pickups and other audio applications.

 

The current only generates a voltage (potential difference) when it passes through a resistance such as the volume pot on an electric guitar. For a given (constant) amount of current, the voltage is directly proportional to the amount of resistance. This is why using a 500K pot for the volume control on an electric guitar will produce a noticeably higher output level than using a 250k pot.

 

 

The volume pot acts as a variable voltage divider - which is where I believe the confusion may have come from.

 

[WRGKMC]

 

What I actually meant by "carried" was: If a varying current flowing in a wire makes a varying magnetic field, and then the magnetic field induces a signal in a second wire, in essence the signal was carried from the first wire to the second wire by the magnetic field that was established by the primary current flowing in the first wire. Like the way wires conducting mains currents make alternating magnetic fields that then induce low-frequency currents in microphone cables, or the way hearing aids work in theatres with induction loops.

 

Thanks for explaining.

 

I get what you're saying but the current first has to generate a field, and that field has to be strong enough and be properly aligned with the second wire to induce current flow in that wire.

 

A single wire produces a very weak magnetic field in comparison to the current it may be carrying. The current flow in the second wire is going to be thousands of times weaker unless you're dealing with coils, and iron cores like transformers to efficiently couple the magnetic fields of the two.

 

The two single wires basically act like a transmitter and receiving antenna. The signals in both must have some kind of circuitry that acts like a diode to get the current moving in one direction. A wire connected to nothing will produce no current so there's allot of hypothesis here.

 

It takes allot of EMF to produce a signal in a coil too. There are all kinds of external emf noise hitting pickups all the time some with waves so small (microwaves) they even pass through the shielding of the cables. We just don't hear it because the frequencies are so high. We're only concerned with the ones that are within the hearing spectrum of 20~20Khz (possibly a bit higher to allow for harmonics. There aren't that many sources of noise within that range besides AC power lines and Amplitude modulated radio signals. Relay arcs, static electricity, Motors, Transformers do produce many waves strong enough to travel distances and infect an amplifier.

 

Magnetics is a very cool topic. Its one of those unseen mysteries that was only provable in recent years since they have been able to take pictures of the electrons using a nuclear microscope. Solid magnets are very much like Crystals in many ways and how the electrons pass from atom to atom is very unique when compared to other minerals. Magnetism and gravity are very similar too.

[WRGKMC]

 

I hate to be a nit picker here but I think it is an important distinction.

 

When a coil of wire passes through a magnetic field, an electric current is generated in the coil not a voltage as stated above.

 

I believe it is important to understand the difference when applying the fundamentals of Ohm's law in electromagnetic circuits like guitar pickups and other audio applications.

 

The current only generates a voltage (potential difference) when it passes through a resistance such as the volume pot on an electric guitar. For a given (constant) amount of current, the voltage is directly proportional to the amount of resistance. This is why using a 500K pot for the volume control on an electric guitar will produce a noticeably higher output level than using a 250k pot.

 

 

The volume pot acts as a variable voltage divider - which is where I believe the confusion may have come from.

 

 

I do have a habit of doing that sometimes even though I know better. Thanks

[onelife]

Magnetics is a very cool topic. Its one of those unseen mysteries that was only provable in recent years since they have been able to take pictures of the electrons using a nuclear microscope. Solid magnets are very much like Crystals in many ways and how the electrons pass from atom to atom is very unique when compared to other minerals. Magnetism and gravity are very similar too.

 

I still have a hard time getting my head around how magnetism actually occurs even though I have a good understanding and working knowledge of electromagnetic physics and its applications.

 

Magnetism is just one of those things I have had to learn to accept and deal with.

[WRGKMC]

Yup its one of those things that have been a mystery to man since he first discovered it.

I doubt we know how much it actually affects us considering the entire earth is one big magnet.

Many animals rely on it for navigation so it must influence us somehow. I do draw the line on magnetic

bracelets and shoe inserts having any medical benefits. As a whole it must have some influence on out

evolution and who knows how it affects brain waves which are chemical electrical.

[Mmmmqac]

There is a simple thought-experiment that shows magnetic-fields and its associated attractive and repulsive forces are actually an illusion due to relativistic time-dilations. I'm not sure, but I think magnetic attraction/ repulsion is considered a fictitious force, just like centrifugal force is. Nevertheless, I am still sticking with Lenz's Law for simplicity's sake.

[Camron70]

In particular, considering that this is a D-I-Y forum, we will be protective of the rights of patent and copyright holders, and any infringing material will have to be deleted immediately according to Rule 5 of the Terms of Use which say:

 

 

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watson