Phono cable and common mode noise filter? - Page 1
Forum section: electronics / beginners

author: FriedMule
author_rank: Frequent Contributor
timestamp: May 31, 2018, 02:07:07 am
content: Hi again:-)I know that balanced signals for audio, often uses XLR plugs and cables with two leads and one shield.But it is wary seldom that you find XLR on a consumer CD player or a tape recorder so I was thinking if it was possible to take the signal from the two phono cable leads and put them through the same filter as you would do with a balanced signal?And in that way, clean the signal for noise the cable have picked up on there way.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: May 31, 2018, 02:18:28 am
content: Yes, but, you still want a lowish impedance ground on the shield, otherwise the common mode (AC, RF) voltage can be ridiculous.For the same reason, you may want common or normal mode filtering, rather than just differential. Basically just split C1 in half (two 440pF, well, use the next common value 470pF), to ground, one from each side.Tim

author: JohnnyMalaria
author_rank: Super Contributor
timestamp: May 31, 2018, 02:46:10 am
content: Not so sure about this. Balanced audio uses one wire for the signal and a second wire for an inverted copy of the signal. At the receiving end, the difference between the two is twice the original signal and, because the noise on both wires is the same, it cancels out.Wire 1 = Signal + NoiseWire 2 = -Signal + NoiseWire 1 - Wire 2 = 2Signal(BTW, what's a "tape recorder")

author: FriedMule
author_rank: Frequent Contributor
timestamp: May 31, 2018, 04:03:04 am
content: Quote from: T3sl4co1l on May 31, 2018, 02:18:28 amThanks so with these small modifications you think that it should have a positive influence on noise that the cable could pick up as antenna?

author: FriedMule
author_rank: Frequent Contributor
timestamp: May 31, 2018, 05:43:31 am
content: I have tried to draw what you said + added a variable pot.What would happen if I lovered the voltage to the TL071?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: May 31, 2018, 02:22:42 pm
content: You managed to ground -IN, it looks like...You need to use a dual ganged pot to adjust the gain of a diff amp, R10 and R11 in sync. Probably not a good idea, because real pots don't track terribly well (+/-5% or worse?), which directly limits your worst-case CMRR to maybe 20dB.Better to use just a little gain at the input, and put a single pot at the output. The resistor values shown give a gain of 0.625 actually, so it's definitely "little gain".Tim

author: JohnnyMalaria
author_rank: Super Contributor
timestamp: May 31, 2018, 02:57:47 pm
content: The purpose here is to send a stereo pair through a balanced line and then use one filter to remove the noise, right?If so, I'm struggling to understand how it will work. In the circuit, +in is left and -in is right (or vice versa). So, for a mono signal, the differential amplifier will simply cancel the L and R (to give L - R). For stereo, components at center pan will cancel. You need an identical circuit but with one signal inverted (say R) so that its output is L + R. Then you have to generate the sum and difference of these to recover the L and R correctly:(L+R) + (L-R) --> 2L(L+R) - (L-R) --> 2RMaybe I'm missing something.

author: FriedMule
author_rank: Frequent Contributor
timestamp: May 31, 2018, 02:59:29 pm
content: Quote from: T3sl4co1l on May 31, 2018, 02:22:42 pmI trust what you say and for me it sounds right.The original circuit is on this page:http://sound.whsites.net/project51.htmCan anyone tell me if this is trash or info and "translate" it to imbecile? :-)

author: FriedMule
author_rank: Frequent Contributor
timestamp: May 31, 2018, 03:01:38 pm
content: Quote from: JohnnyMalaria on May 31, 2018, 02:57:47 pmNo this circuit is only mono! :-)shield/negative and positive lead on one cable pr circuit.

author: JohnnyMalaria
author_rank: Super Contributor
timestamp: May 31, 2018, 03:23:23 pm
content: So where are the two phono cables coming from? I assumed you meant the left and right channels of the CD player/tape recorder. Are you taking one channel at the source end and creating an inverted copy before sending both along a balanced cable? This sounds like a balanced line driver.Thisis an interesting read.

author: FriedMule
author_rank: Frequent Contributor
timestamp: May 31, 2018, 04:56:34 pm
content: Quote from: JohnnyMalaria on May 31, 2018, 03:23:23 pmMy idea is that it takes two wires from each cable (i.e. left positive and left negative) to transport the left signal from i.e. a CD-player. If these two have the opposite signal, you can use a sort of technic that normally are being used in balanced systems.After the filtration are the signal clean and now we don't care about the balanced part anymore, so we can treat the signal if it was a normal unbalanced signal and can send the signal to amplification.

author: C
author_rank: Super Contributor
timestamp: May 31, 2018, 06:30:43 pm
content: Need to start with the basicsWhen you use a shielded cable like a phono cable or BNC cable. have a shield that is not suppose to carry a signal.This is not fact. The shield does carry the return signal, due to the large conductor size you have little voltage drop.If you connect the shield to ground at both ends then you create a possible DC ground loop or an AC ground loop.It is not good to have something floating so one end should be DC Ground connected.A capacitor can then give a AC ground at other end. This capactor may need adjusted due to things like power supply ac noise.For quality signals you want a differential balanced signal. This gives a no signal point centered between the two signals.One step down is a differential signal. Here you could have one side with 0 signal but still not ground.The better equipment mount the phono plug on an insulator and treat it as a differential input. You then add a capacitor from shield to ground to remove some noise.In this case the shield is carring the signal return current which should be a small voltage change and has noise that the shield has picked up.The differential input looks at the difference. The noise does create a difference.When you use single ended signals there is no magic way to remove noise in the frequency range of the actual signal. You only have what frequency range should be there and filter out the remaining.So converting a single ended signal to differential balanced signal does not give a magic way to remove noise.It can let you have a better filter to remove frequencies that should not be there.Quality is differential from original signal source to end use.Often the best you can do is have as much as possible differential.C

author: IDEngineer
author_rank: Super Contributor
timestamp: May 31, 2018, 06:57:59 pm
content: Quote from: FriedMule on May 31, 2018, 04:56:34 pmThat's where the confusion lies: Your separate left and right phono cables are NOT differential pairs. They are single-ended.Let's start with the signals themselves. Each of your two phono cables has a single center conductor and a shield. The shield is most likely tied to ground, and the center conductor is carrying the signal. If you have a multimeter, check continuity between the shields on the left and right cables... I bet they're both grounded, and thus nearly a dead short. These are single-ended signals, measured relative to ground (the shield in both cables).An XLR connector - or indeed, any truly differential signal - has TWO signal conductors in addition to a ground reference. The signal of interest is measured ACROSS those two conductors. In a purely differential environment, those two conductors are all that you need; you don't need a ground reference at all, because the signals on those two conductors are not relative to ground, they are only relative to each other. (In the real world, you probably [but not definitely!] can measure one of them relative to ground but that misses the whole point of differential pairs, as we'll see below.)As noted by another respondent herein, the two wires in a proper differential pair have identical but inverted signals. Imagine the original signal is a 2Vpp sine wave. When the sine wave is at its positive peak (+1V), a scope viewing both wires of the differential pair would show one wire at +0.5V and the other at -0.5V. The voltage difference between them is thus +1V. At the negative peak, the first wire would now be at -0.5V and the second would be at +0.5V, and the voltage difference between them is -1V. Thedifferentialbetween them is swinging a full 2Vpp, but viewedindividuallyeach wire only sees 1Vpp.Why would we do this? Two reasons: Isolation and noise immunity.Isolation is a secondary benefit and results from the fact that, with a purely differential pair, you don't need to connect the grounds of the equipment on either end of the wire. This is especially critical in some audio (and video) environments. The two pieces of equipment could be on different AC power phases, for example, leading to hum problems. The two grounds on either end can be at different voltage potentials (ground is NOT always ground, no matter what they told you in school!) which would cause current to flow in the cable shields, another source of hum and interference. By isolating the grounds, the only electrical connection between the pieces of equipment can be the differential pair itself.Noise immunity is a primary benefit of differential signals. It works because the two wires in the differential pair have signals that are identical except for being exactly 180 degrees out of phase ("inverted" is probably the better, more general term here). The signal of interest is thus the mathematical difference between the wires. Now, imagine that along the way, your differential pair picks up some noise. Let's say it's a 60Hz sine wave from some mysterious, unknown source. Since the differential pair is traveling together - in fact, in the case of XLR microphone cables, the differential pair is actually twisted together - to encourage them to both pick upexactly the same noise. Thus in this example they both now have a nasty 60Hz sine wave. But crucially, that sine wave is thesame on both wires.On a scope, to the naked eye, your signal now looks totally trashed... but what's really happening is that your original signal is differential, while the 60Hz is common to both wires (aka "common mode"). If you have an identical sine wave on two wires and measure across them, what is the voltage? Zero! Because the voltage on the two wires is always the same, you'd measure zero differential across them. (Importantly, think about what would happen if you measured just one wire relative to ground... you'd see a sine wave, right? But measured across the differential pair you'd see nothing at all, because they're always the same voltage.)All of this is wondeful, but how do you use it? Well, a transformer is inherently a differentiator. Hook your differential pair across a transformer winding and you get zero for common mode signals but anything differential generates an associated magnetic field in the core. An opamp configured as a differential amplifier does the same thing: Common mode signals are rejected (because there is no voltage difference to be amplified) while differential signals are recovered. Voila - now your 60Hz is gone.With all of this background: You cannot treat single ended signals as differential signals. They are not the same. Might it work? Sure... a diffamp will usually work with one input grounded, which is what your single ended source would do. But you're not getting all of the advantages that people expect from truly differential signals, and you're working really hard to not get them.Likewise, you cannot simply take the center conductors of the left and right channels and run them into a diffamp. As another respondent noted, at best you'll create a low-quality karaoke machine by removing centered signals (such as the vocals) and the result will sound really weird.The left and right channels are NOT a differential pair and cannot be processed as such. You cannot expect noise reduction with differential processing of single ended signals.If the above was redundant and you already knew all of it, my apologies. Otherwise, hope it helps!

author: JohnnyMalaria
author_rank: Super Contributor
timestamp: May 31, 2018, 06:59:59 pm
content: Quote from: FriedMule on May 31, 2018, 04:56:34 pmWhat you are describing IS a balanced line driver. The technique has been used for decades to connect single-ended equipment in recording studios etc. Traditionally, a single-ended signal is fed through a transformer to generate the + and -. The most important use is for microphones. Consumer phono levels are sufficiently high that unless you have a cable meters long I doubt you'll notice much benefit anyway.

author: C
author_rank: Super Contributor
timestamp: May 31, 2018, 08:04:09 pm
content: That is great IDEngineerQuote from: FriedMule on May 31, 2018, 04:56:34 pmSo your CD-player has a stereo outputA stereo amplifier is two mono amplifiersWith a mono amplifier your speaker that has two connections has signal on one connection and ground return of the other.Differential is having a mono amplifier for each speaker connection.You have one mono amplifier doing signal+ andYou have one mono amplifier doing signal-.A true differential amplifier is better then the two mono amplifiers because it can do the common mode rejection that IDEngineer discussed in his post.So a good stereo amplifier is two differential amplifiers.And good stereo system will have differential inputs or quickly convert single ended to differential.Note that electronics can be better then a transformer for audio.C

author: JohnnyMalaria
author_rank: Super Contributor
timestamp: May 31, 2018, 08:10:15 pm
content: Quote from: C on May 31, 2018, 08:04:09 pmThat's the very subject of the article I linked to. Definitely worth a read.

author: JohnnyMalaria
author_rank: Super Contributor
timestamp: May 31, 2018, 08:15:21 pm
content: Balanced input and output circuits using commercially available line receiver ICs:https://www.diyrecordingequipment.com/pages/balanced-input-output-assembly-guidehttps://octopart.com/ina134pa-texas+instruments-55433408

author: C
author_rank: Super Contributor
timestamp: May 31, 2018, 08:45:26 pm
content: Good differential amps are differential in & differential output.TI calls these Fully differential ampsC

author: FriedMule
author_rank: Frequent Contributor
timestamp: June 01, 2018, 01:03:13 am
content: As always a giant knowledge you all share!! Thanks, really thanks!! :-)What would you recommend now then, a cap from lead to case/ground, an inductor, ferrite ring or something else, to remove 30khz and up?

author: C
author_rank: Super Contributor
timestamp: June 01, 2018, 01:36:01 am
content: A filter is not magic.When you add something, most times you effect all signals.When you do a 30k low pass filter that is just effecting the higher more then below.So first question is how do you know you have a problem?You can not hear 30k so how do you know it is there and how much are you measuring.I would expect the output of a CD drive to be good.C

author: Marco
author_rank: Super Contributor
timestamp: June 01, 2018, 02:30:23 am
content: Quote from: C on May 31, 2018, 08:45:26 pmIt's not going to make much difference for audio ... his circuit is good nuff. Just use it with twisted pair cable instead of coax.

author: Richard Crowley
author_rank: Super Contributor
timestamp: June 01, 2018, 03:10:21 am
content: Quote from: FriedMule on May 31, 2018, 02:59:29 pmThe original circuit is correct. But you have made an incorrect connection where there was no connection in the original. The wire from GNDREF to the 5K pot does NOT connect to the negative signal node from R9 to R11 and the V- input of the op-amp. In the original circuit this is simply a "crossover" where the horizontal and vertical paths DO NOT connect together. But you have added a "connection dot" which grounds the negative signal completely. This totally kills any differential properties of the circuit.By now, you must have understood that your two unbalanced signals from your unidentified source do NOT represent a balanced source in any way, shape, or form. They are the Left Channel unbalanced output, and the Right Channel unbalanced output. If you combine them together in a differential input circuit such as you have show, you will end up with a monaural audio signal that consists of the Left Channel MINUS the Right Channel. This will sound horrid and will be useless for any practical application.You can add "pseudo-balanced" outputs to a source with only unbalanced outputs by measuring the output impedance and creating a matching impedance for the "negative side" of a balanced circuit. After measurement of the output impedance (which isn't really that difficult, even with minimal test gear), it is simply a matter of a balanced connector (TRS or XLR) and a 2-cent resistor to ground. Many pieces of pro audio gear use this scheme and although I find it slightly sleazy, it is quite effective and I can't argue with that.However you said that you are trying to reduce 30KHz interference noise? That hardly requires (or would be effectively reduced) by using a traditional balanced/differential connection scheme. We use balanced connections mostly to reduce lower-frequency noise (like 50-60Hz mains power hum and overtone buzz). Filtering out 30 KHz would be much more easily done with conventional, simple low-pass filters. I have to wonder how a 30KHz noise could really even be affecting any normal audio path as it is well above the high-frequency pass-band of even "hhigh-fidelity" audio (i.e. 20KHz)

author: David Hess
author_rank: Super Contributor
timestamp: June 01, 2018, 03:29:38 am
content: Quote from: C on May 31, 2018, 08:45:26 pmIf Texas Instruments had not confused instrumentation and difference amplifiers with differential amplifiers, then they would not have needed a fourth catagory.

author: David Hess
author_rank: Super Contributor
timestamp: June 01, 2018, 03:41:57 am
content: For what it is worth, if you are suffering from ground loop induced noise, then running the single ended signal with or without a shield (1) into a high impedance input difference or instrumentation amplifier at the receiver can improve the situation considerably. The instrumentation amplifier does not care if the source is single ended or differential.There are better ways to handle this but it requires no modification to the source. This assumes however that there is a separate ground connection between the source and input to limit common mode excursions which will usually be the case when grounded power cords are used on both sides.(1) A lot of cheap audio and video cables just have twisted pair instead of coaxial construction.

author: FriedMule
author_rank: Frequent Contributor
timestamp: June 01, 2018, 03:57:07 am
content: Quote from: Richard Crowley on June 01, 2018, 03:10:21 amThe changes did I make after this comment:Quote from: T3sl4co1l on May 31, 2018, 02:18:28 amQuote from: Richard Crowley on June 01, 2018, 03:10:21 amTo a start, I did not know if it would work so I asked here as my first question and got this answer:Quote from: T3sl4co1l on May 31, 2018, 02:18:28 amQuote from: Richard Crowley on June 01, 2018, 03:10:21 amcould you please explain it more, maybe with a small shematic?Quote from: Richard Crowley on June 01, 2018, 03:10:21 amI was trying to filter as you write, but got the answer that is was impossible, that I only could filter HF.

author: Richard Crowley
author_rank: Super Contributor
timestamp: June 01, 2018, 04:24:12 am
content: Quote from: FriedMule on June 01, 2018, 03:57:07 amSorry, either I don't really understand what/why you are asking about this, or those other responses, while technically correct seem rather oblique to what I thought you were asking.QuoteThis shows RSwhich is the Source Impedance of the existing unbalanced output. Frequently there is actually a series resistor in the output path as shows, and that could be assumed to be the source impedance if you can't actually measure it.They simply create a "fake" ("impedance-balanced") "cold" output with the SAME output impedance as the active "hot" output. Then whatever noise is induced into the balanced path along the way will be picked up equally by the "hot" + side and thhe "cold" - side of the balanced audio connection. That gives maximum advantage to the differential input circuit at the destination end to reject the common-mode noise picked up by both the hot and cold sides of the balanced circuit.QuoteBut 30KHz is exactly "HF", so your responses are very confusing. Do you REALLY mean 30 Kilohertz, or do you mean 30 Hertz? 30 KHz is almost trivial to filter out without even giving a second thought to balanced connections. While 30Hz is very definitely why we use balanced connections.

author: Richard Crowley
author_rank: Super Contributor
timestamp: June 01, 2018, 04:49:24 am
content: And always remember that a "impedance balanced" output, and even a "real" balanced output by themselves do almost NOTHING to reduce pickup of noise and interference. It is the differential/balanced INPUT of the destination gear that does all the heavy lifting.This diagram shows the larger view and how the destination input circuit interacts with the source output circuit...https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcR-AtAyyBBuI_IN-ALsYLhM3vVGcaNNwEa13HoOVlq9QfPBgLY2

author: Brumby
author_rank: Unknown
timestamp: June 01, 2018, 06:08:38 am
content: With all the talk about the circuitry, I hope the cabling is not forgotten.To get the benefit of balanced line signal transfer, please make sure you use the proper balanced line cabling - the twisted pair inside a single shield. One cable per channel.Don't try doing this with two standard shielded cables - the sort you get in a set of stereo RCA leads - and just using the centre conductor of each as your differential lines with the two separate shields (connected however you like). If you have an electrically noisy environment and/or long runs, you will never get it to work properly.

author: FriedMule
author_rank: Frequent Contributor
timestamp: June 02, 2018, 03:59:10 pm
content: First I am wary sorry that I first reply now, but had some family busyness to help with.I'll try to explain it better.:-)The whole idea is to use standard of the shelf music sources that do not have balanced output. And then connect them to my amplifier. Unfortunately does my old amplifier get noise in what I think as the whole spectrum, 50hz and up.So my thought was simply to take each channel's positive and negative leads, filter the common noise and thereby have a clean signal. When the signal is cleaned, I just want to amplify it.

author: IDEngineer
author_rank: Super Contributor
timestamp: June 02, 2018, 05:38:52 pm
content: Quote from: FriedMule on June 02, 2018, 03:59:10 pmRead this entire thread again, and consider these points:1) If "my old amplifier get noise in what I think as the whole spectrum" means your amplifier is noisy, nothing you can do to its input signal will fix that. You can test this by shorting the inputs to the amplifier; does it still have what you consider excessive noise? If so, the source of the noise is within the amplifier itself and you can't fix that by manipulating the signals from "standard of the shelf music sources".2) Your "standard of the shelf music sources" apparently do not have native differential outputs. The left channel, by itself, has no noise-free reference you can rely upon. So how would your magic filtering circuit "know" what is noise (to be removed) and what is signal (to be preserved)? That's what true differential signals do for you: Give you a way to distinguish between the signal and everything else.Here's a thought experiment: You are given a signal comprised of a square wave at 1KHz and a triangle wave at 1KHz and told to filter it to (using your words) a "clean signal". No other information is available. Describe what your circuit will do to "clean" this signal. You can't, because you don't have enough information. Is the square wave the signal and the triangle wave the noise? Is it the other way around? Now, consider your left (or your right) signal. Without a reference, how does your circuit "know" what to retain and what to reject?

author: C
author_rank: Super Contributor
timestamp: June 02, 2018, 05:55:03 pm
content: You need to understand that when noise is added to a signal it is very hard to remove.Music is generally thought of as 20hz to 20khz.So 50hz & 60hz power is in the music band.So if you already have some noise, you try to prevent adding more noise.On some audio systems you find a large ground lug. This is to be connected to all parts of the system with large wires. The intent is to remove the differences between each part's ground.For you CD this is the medal chassis.Then for each stereo source you have a 3 or four wire connection.With the ground bonding above the signal return should not be carrying much ground noise.There still could be a difference in potential for the signal returns.A differential input can work with this.When you do use a differential input then you want each phono jack isolated.Here your old amplifier might not use the differential inputs.Think of each channel of a source asMusic source + noise1Music return + noise2at the output.Noise1 is not the same as noise2. With out that ground bonding, noise2 changes.The best you can easily do is not add more noise to the source output connections before it gets to your old amplifier's input connection..Better connections is an important step.You could twist the two pair output from the CD.If the twisted pair picks up some common mode noise a differential receiver will remove it.For shielded phono cables it is a different story. The shield is limiting the changes to center conductor while picking up noise.This looks like a signal change to the differential input.Here the best you can do is to have a low resistance AC connection to your OLD amplifier ground. But this is also adding more noise to your old amplifiers ground. That ground bonding is an attempt to reduce this.If you filter out power supply noise, you are also removing music.You fix this by not allowing power supply noise in.Good cables and differential receiver connected to your old amplifier is two options.C

author: JohnnyMalaria
author_rank: Super Contributor
timestamp: June 02, 2018, 06:48:53 pm
content: Quote from: FriedMule on June 02, 2018, 03:59:10 pmSo the noise you want to get rid of is neither created by the CD player nor picked up by the cables. It is generated by your amp.Forgive the comparison, but it is like distilling tap water and using that to flush the toilet.

author: IDEngineer
author_rank: Super Contributor
timestamp: June 02, 2018, 06:58:23 pm
content: QuoteQuoteAnyone else here starting to feel like this guy just needs to buy a better amplifier?

author: FriedMule
author_rank: Frequent Contributor
timestamp: June 02, 2018, 07:47:01 pm
content: Quote from: IDEngineer on June 02, 2018, 06:58:23 pmLOL hmm yes that is what I have to do, or build one myself:-)But it sounds like that it is not possible to filter out external common mode noise if there are only + and - wire on each channel? In a DIY amplifier.

author: C
author_rank: Super Contributor
timestamp: June 02, 2018, 08:15:02 pm
content: Quote from: FriedMule on June 02, 2018, 07:47:01 pmThe problem here is that you have to have common mode noise toto filter outA single ended signal be it on a phono jack or BNC does not have common mode noise. Here you have signal + noise that is not common mode.The center conductor caries signal + noise.The shield caries return signal + noise.The shield being exposed picks up environment noise.No common mode noise here.C

author: JohnnyMalaria
author_rank: Super Contributor
timestamp: June 02, 2018, 08:23:56 pm
content: Quote from: FriedMule on June 02, 2018, 07:47:01 pmPlease can you tell us:1. What is your CD player2. What is your amplifier3. What are your cables4. What is the type of noise (hiss, clicks, pops?)

author: Richard Crowley
author_rank: Super Contributor
timestamp: June 03, 2018, 02:54:23 am
content: Various types of noise between audio gear is a very common problem. And there are several rather simple and very effective methods of resolving these issues.However @FriedMule has jumped from a sparsely-defined problem straight into solution-space, asking about an impossible implementation of a method (balanced line) rarely seen in consumer audio gear. Rarely seen because there are always better (simpler/cheaper) methods of solving the problem.@JohnnyMalaria has posted the questions that need answers if we are going to offer @FriedMule any practical advice. A recording of the noise (and the relative signal level for reference) is a necessary requirement for analyzing the problem. A review of how everything is powered and physically arranged might also prove useful.

author: IDEngineer
author_rank: Super Contributor
timestamp: June 03, 2018, 03:07:58 am
content: I'm still waiting for the results of this incredibly simple and quick test:Quote

author: Audioguru
author_rank: Super Contributor
timestamp: June 03, 2018, 03:30:24 am
content: Cheap shielded audio cables have a very poor shield that does not shield noise. Expensive Radio Shack cables are exactly the same ones sold cheaply at The Dollar Store.

author: SL4P
author_rank: Super Contributor
timestamp: June 03, 2018, 07:01:21 am
content: I haven’t seen a single mention of the word ‘phase’, which is critical to the success of balanced circuits.The source and propagation of the +/- legs must be phase coherent, or the CMRR will be negligible.https://en.m.wikipedia.org/wiki/Coherence_(physics)All this isn’t rocket science, but does require understanding and discipline to implement correctly for maximum benefit.

author: IDEngineer
author_rank: Super Contributor
timestamp: June 03, 2018, 04:26:51 pm
content: Quote from: SL4P on June 03, 2018, 07:01:21 amAnother excellent point, and one of the reasons diff pairs are often twisted - to insure they follow the same path and have the same length for phase coherence. However, if you review the technical level of this thread, it will become apparent that phase coherence isn't the largest issue on the table.

author: Loboscope
author_rank: Regular Contributor
timestamp: June 04, 2018, 09:09:20 am
content: In Home-audio-applications noise picked up by a cable is nearly never a problem, at least it is very seldom. Because the length of the cables is very restricted, there are nearly never severe sources of noise that will introduce noise into cables and normally there will be no levels less than line-levels. If there will be noise anywhere, I would first check the source and the amplifiers, as it has been mentioned by several posters before.The balanced system for cables, inputs and outputs has been introduced for and is widely used by professionals, for example on stages, in studios, broadcast etc.For example an open-air concert of a symphonic orchestra + choir: At least 40-60 microphones will be used (very low output signal level!), the cable length will easily add up to 1 km of even more. There will be lots of power cables too, for example for the lights, DMX-cables will be found too, etc. etc.So you can imagine, that there will be tons of possible sources of noise that will introduce noise into the mass of audio-cables with mostly very low signal levels. So it is indispensable to have a cable-system that will be as immune as possible against this external sources of noise.But even here, the symmetric audio-lines will not be capable to eliminate noise that will be introduced by a source, for example a defect microphone.But at home, as I said, the will be simply no need for balanced systems. A proper shielded cable will do its job as I think at least in 99% of all cases.