All cables have two conductors!
RCA cables are coaxial cables, meaning that each cable has a positive conductor (inner) and a negative conductor (outer).
What's better, one conductor or two conductors for an RCA interconnect?
I have a somewhat nice RCA analogue interconnect with one conductor, referred to as a coaxial Cable I guess. But I see higher end RCA cables with two conductors and ground wire. Which is better?
Is better detail provided when connections are made with two conductors?
68 responses Add your response
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To clarify, I understand that there is one conductor, generally copper, and a shield which I guess also is considered a conductor. And then there are cables with 2 conductors, each a separate strand separately shielded. And then a third wire of sorts that acts as a drain or a ground. Is it better to have two separately shielded wires, which I guess can have multiple strands twisted around each other, versus a Single separately shielded copper wire? Higher extremely expensive analog interconnects have two conductors Plus a separate wire serving as a ground. If it don't matter for rca Cable purposes, ie. Unbalanced, why is it done. Presumably because it increases quality, and if so, why? |
Greetings If you have only one conductor that is a coaxial cable which is used for hooking up a antenna to a tuner or your cable TV or communication hookups. It probably would work but interconnect cables (RCA/SE) are 2 conductor with or without shield. Everyone of my RCA cables are 2 conductor. Some have shields some don’t. Try the Cable Company for a loaner RCA/SE cable so you can hear the difference for yourself. Joe Nies |
When shield is used as return any electrical noise current induced in the shield will create voltage difference along it - between source/output and destination/input. Input will "see" the difference between output signal wire and output GND, plus noise voltage between both ends of the shield. |
How would one know? Wouldn’t one have to try both first before answering this question? If two conductors happens to sound better, wouldn’t every cable manufacturer use this configuration? What brand of higher end RCA cables are made with 2 conductors and a ground? So many questions… |
Let me please clarify my statement from my earlier response. Your coaxial cable can also be used for digital signals. Such as from a transport or music server to your DAC. A good coaxial cable is important to have. Once you get into the analog world having a 2 wire RCA/SE or 3 wire XLR/Balanced cable is needed. Such as from a TT or DAC to your pre-amp. Joe Nies |
Interconnects can be a very important components in a system. The better the boxes in your system the more important the interconnects are. With cheap interconnects the actually materials are important and maybe the configuration. But as the cost goes up… as does the effort in getting better sound the less the specific materials and configurations determine the output. It is the effort put in to choosing materials and configuration. There are lots of ways to accomplish great sounding interconnects. In most cases one parameter will not determine the sound. It will be highly dependent on your system and the specific interconnects. |
I did a experiment once.
I tried to measure if I could get any graph or see any benefits or difference between my trippel shielded (stated on the jacket) RCA and new bought but braided sterling silver RCA.
I wanted to see if there were ANY notable diffrence between them and I don't want to make things worse down the road and note that X hours later. I measured with the calibrated microphone and REW with the mic on stand. Then I switched out the triple one to the silver one and redo the measurements again with no other changes at all.
I sat down and compared the two measurements back and forth and really tried to find a difference somewhere/anywhere. I went through all 10-15 different types of graphs that I could find in REW and analyzed them and comparing them back and forth. That could give me any clue on what could be changed between differens shielded/braided or copper/silver.
I did not find anything at all only in one graph for impulse response that the silver had MAYBE a little bit better in that graph. But it's so small that probably needed to run 10 measurements on each cable and analyze those and see if there were any average measurements difference. Now with only one measument of each RCA the difference could be normal variation between measurements that i had noticed. Yes ot were not a big difference!
With all that said i just let the new silver cable be in the system when it anyway didn't had any negative effects.
Another conclusion as far as cable construction, crossection and geometry when they were totally different is that it didn't do any difference in this situation*. *Situation = if you have alot of RF in your place (near a radio station) or if you have low signal level as from TT to RIAA. That is a total different situations. And why some have totally different experiences.
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But I see higher end RCA cables with two conductors and ground wire. @jumia Can you show an example of such cable? |
I’ll second what @kijanki wrote. I have never encountered RCA connectors used with coaxial cables. I would expect coaxial cables to use BNC connectors, as I think someone else mentioned. The higher end cables, such as those that came from the factory with my Musical Fidelity turntable, are marked with a directional arrow, which I’m assuming points in the direction of the signal. It also denotes, for me, that the shield is only connected at the phono stage, not the turntable. The turntable does not have a three-conductor line plug 🔌 (which is a good thing to me), it uses a wall wart. The other thing to consider when selecting cables (aside from whether or not it is shielded), is its impedance rating in Ohms. Cables using the same connectors have different impedance ratings for use in either analog or digital applications. I can’t recall the values off the top of my head, but they will each ‘work’ in place of the other, but the energy transfer is not optimal and shouldn’t be considered for permanent installation. The same distinction holds true for XLR connectors; analog applications (I.e. ‘balanced’ connections) cables have impedance ratings which are different than those cables used in digital cables (I.e. AES/EBU connections). More experienced or knowledgeable members are free to correct or explain further the reasons for the difference I describe. If you’re purchasing cables, I would avoid coaxial cables using RCA connectors, if you are contemplating making your own, I would buy at least two-conductor shielded cable (I like Mogami), and consider using four conductor cable (twisted pair) together with the best connectors you can find. I have found good prices and fast delivery from B & H Photo, but would probably consider using one of the specialized cable companies mentioned on this forum the next go-round. Hope this helps
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Blue Jeans Cable recommends coaxial cables for subwoofer, stereo audio, digital audio, etc. They state that, “The most important attributes of a line-level unbalanced audio cable are (1) shielding, and (2) capacitance. Heavy shielding protects audio signals from interference from outside sources. LC-1 Audio Cable uses a heavy double-braid shield, with one bare copper braid laid directly over another for extreme high coverage and high conductivity to ground; this is the identical shield configuration to Canare LV-77S, which tested best in our review of audio cable hum rejection characteristics (LC-1 hadn't been designed yet so wasn't tested at that time). By shrinking the center conductor to 25 AWG and foaming the polyethylene dielectric, we were able to get capacitance down to an extremely low 12.2 pF/ft, much better than LV-77S at 21 pF/ft. Capacitance can be important, particularly in long cable runs, because it contributes to rolloff of higher frequencies.” |
https://www.conch-house.com/best-rca-cables-audiophile/ these are assorted RCA cables. All have a positive and a negative. I’m not sure I’ve ever seen a a RCA cable that doesn’t use both. All the best. |
optimize and oldrooney I learned a bit from both of your responses. I have a purely digital system (can't afford analog). My integrated amp has three connection options (no XLR go figure) so for the fun of it, I have my CD player connected via line stage, coaxial, and optical. Switching between the three my 75 year old ears cannot distinguish the difference between optical and coaxial through my system, the analog line stage as you would expect is inferior to both. I was under the impression XLR was the best followed by coaxial, optical, and then line. |
@tcotruvo, coaxial cable is also the cable of choice in almost any scientific application. My understanding is it is better for electrostatic noise rejection but there may be circumstances where shielded twisted pair is better for magnetic. I am going off memory here. It depends on the shape of the noise field. Primary reason for not using co-axial is it is difficult to work with and maintain its properties. I would expect you would have to have pretty long runs before cable capacitance became important. I am sure there are some bad tube products that could have issues. |
A French audio journalist named Jean Hiraga wrote the paper that proposed using 2 identical twisted wires with a shield that was only connected at one end as a way to assure the waveform being conducted was treated with the same impedance for both positive and negative polarities. This idea was picked up by Noel Lee and his team at Monster Cable and marketed as “Balanced Bandwidth”. They added the prescription that the cables were directional based on which end the shield was attached, and put arrows on the cable. This approach has become entrenched and is accepted as received wisdom by many cable manufacturers today…but not all. Prior to this, virtually all RCA interconnects were coaxial…meaning a center conductor was wrapped with a shield of braided copper separated by a foam dielectric. |
Interesting @crustycoot . That journalist no doubt discovered what was already being used industrially and in the scientific community no doubt for decades prior. |
Twisted pair exposes both wires evenly to electric and magnetic fields causing identical induced noise currents that cancel. It is extremely efficient, as long as the pitch of the twist is much smaller than wavelength of the offending electrical noise. Shield works great at higher frequencies where, in spite of being non-magnetic, shields by means of skin effect (noise currents flow on the outside - shield). Shielded twisted pair is the best combination. |
Learning as we go: after some googling and contemplating there is one area that needs clearing up. The OP was enquiring about various RCA analogue cable designs I believe. I'm sure there can be sound differences between them, single channel coax 75 ohm unbalanced or 110 ohm balanced (3 pin) are among them. One connector, one channel. A coax with RCA connectors is "probably" an s/pdif digital only cable. The single RCA connector has a stereo digital protocol and cannot be used as a single channel analogue cable. As a side note: My Oppo 203, used as a transport, uses one of these single s/pdif to connect a Bifrost 2 DAC. Unfortunately the s/pdif-optical output is not working correctly (verified using an optical cable) A center vocal track is slewed to the right channel, while using an HDMI cable out of the Oppo dac is perfectly centered. Any advice to correct this would be very appreciated as for 2 ch cd output the off centered output is noticeably more resolved with lower background noise. Bummer! |
Kijanki ... You need to go back and review a bit. Twisted pair is good for magnetic and perhaps low frequency EMI. Coax is superior for RFI (with proper RF shield) and is in general better for electrostatic conduction as you have no field differential between the shield and the inner conductor. Even for magnetic coax can be very good. |
@kijanki got it right in one. @deludedaudiophile , you are ignoring in your response that an RCA cable with a twisted pair and shield is in fact a coaxial connection. If the cable is very long this doesn't work so well, but in the shorter connections that are seen in household hookups it works just fine. For longer connections of course balanced is the way to go. |
I am not ignoring that it is a coaxial cable because it is not a co-axial cable -- the axis of the conductors is not consistent in a twisted pair with shield. Much of the benefit of a coax is the symmetrical arrangement of the shield w.r.t. the center conductor. A shield around a twisted pair provide electrostatic shielding, but the question was RCA, and the two conductors (as noted by Kijanki) do not see the same electrical impedance which will defeat the benefit of twisting (at least for magnetic I/F) which works where both conductors see the same impedance hence induced voltages cancel. There is probably a reason why oscilloscopes probes, which are single ended, use coaxial cable and not shielded twisted pair. |
I suspect that reason for oscilloscope to have plain coax is capacitance. Twisting wires reduce inductance but increases capacitance - important with scope’s high input impedance and very high measured frequencies. Unfortunately this coax arrangement creates errors. When you short probe and touch tested circuit with shorted leads it will show small amount of noise (in spite of being shorted). It is because current flows from the circuit thru the shield (finding return to GND) causing voltage drop, that shows on the input as signal - exactly what we try to avoid in interconnects by using two wires inside of the shield.
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So what happens if you Connect the ground to the connectors on both sides of the RCA cable? If one side of the ground is not connected to the other side within the cable wouldn't the impact of a ground wire only connected on one side become an antenna? Isn't it Better to let the ground flow back into the component and let that take care getting rid of the ground activity.
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All those examples you gave Kijanki are differential connections where the impedance in each leg is the same. EMI induces a current. The equal impedance means those equal and opposing currents generate equal and opposing voltages which cancel.
The op stated RCA which is not a differential connection. Ground and signal connections have different impedance hence the induced voltages from the equal and opposing currents do not cancel out.
Twisted pairs makes total sense in balanced audio connections. It will be better than non twisted for single endednbut coax is likely to be superior. |
In single ended connection we are passing signal and reference point (analog ground). There is a loop from the output to input and back by return - analog ground. Induced electrical noise currents in both wires flow in the same direction and cancel. This would work perfectly if there is no other path for return, like when chassis on one side is not earth grounded (II class) or when it is grounded but analog ground is floating on either side. Analog ground is often connected to chassis ground with the large resistor. That would diminish effectiveness of twisted pair a little but still, twisting would help and perhaps that’s why many manufacturers twist single ended wires inside of the shield. |
You are looking at this more theoretically than practically. Excuse me as my expertise is physics (and managing EEs) not day to day EE and a lot of time around semiconductor processing equipment, some of it quite noisy while trying to do precision measurements. We are not passing a reference point. We are connecting the reference point on two pieces of equipment and making them the same. The impedance on the ground connection is not the same as the signal connection. An equal induced current on the ground creates a small voltage only related to the ground circuit. Induced current on the signal creates a voltage a factor of the impedance . You are making the assumption there is not a relevant secondary path for ground, for instance totally disconnected or a large value resistor. How large is a large value? How large does that resistor need to be to ground so that it is not there? Poked around enough in tube amps to know that resistor may not be very large at all. What if there is a capacitor? 10 nanofarads? That is only 16K resistance to ground at 1KHZ. |
@deludedaudiophile So, you are not EE. Well, I am - designing low level electronics for 40 years. Sorry I cannot explain it to you better. We agree to disagree. |
I have a PhD in materials science and close to 2 decades in semiconductors, semiconductor processing, and associate equipment, including forays into process measurement and control ... well exposed to signals in noisy environment. Doing much of the same in batteries now. I understand the overall issues quite fine and could probably derive a lot from first principles. I understand your argument, I don't agree with all of it and I think you have poorly argued some points specifically as it may apply to real world applications including equipment ground connections and how they relate to loop resistance or impedance. Given the indeterminate ground connection and how that related to the loop resistance all due to the signal connector, I believe you are making erroneous conclusions about what would be common mode noise injection. A speaker connection is balanced from the standpoint of the speaker, but if you induce noise on the speaker cables, it is not balanced at the amplifier input hence why the amplifier circuits for sensors and bridges, both often floating, are still fully differential circuits.
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So it appears there are no clear Views on whether the ground wire should be connected to each RCA connector. So you have 2 connectors connected to the RCA connects ans a ground wire connected to both RCA connects. So it is on this very point there is no clear rationale or consensus as to how the ground wire should be handled.
Personally I think this is really sad and should really frustrate those trying to choose the best interconnect.
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Speaker by definition is balanced. Noise currents induced in both wires cancel at the speakers, since there is no other return path. If you question that, then perhaps you should read what Benchmark Media posted on their website in regarding to headphones being always balanced:
The same happens when analog ground is floating on one side - no additional return path, hence inherently balanced connection with single ended output. Analog ground is likely to be connected to chassis ground to reduce noise coupled from the chassis ground to circuitry, but it is often done with resistor of 100k or more. It is because connecting analog ground to chassis on both ends directly or thru large capacitor creates perfect ground loop (earth ground - chassis - analog ground - interconnect - analog ground - chassis - earth ground). That is why Benchmark amp doesn't even have single ended input. This additional return path, possibly thru (two) 100k resistors creates some unbalance, but doesn't completely null usefulness of twisted pair in SE connection and that is why manufacturers use it. For speaker wires it is no-brainer since it reduces noise, reduces inductance (important) and increases slightly capacitance (not-important). |
As I clearly said, from the speaker standpoint, the speaker itself is balanced, however, if you are considering noise on the speaker cables induced back into the amplifier, it most definitely is not balanced because the impedance on either cable is not the same as the other. That should have been clear when I discussed a similar circuit such as a bridge or other similar sensor (or consider it a phono cartridge), that while not grounded itself, is potentially grounded at the phono stage end. Someone else on this thread, if I am not mistaken, makes a differential input phono stage? If you have two AC connected pieces of equipment, then the ground on either side is never floating even if one piece of equipment has no ground connection due to parasitics. Now obviously those will be lower than if there is a direct ground connection. I was quite clear this would be dependent on implementation. 100K is pretty similar to the loop resistance of single ended RCA connection. I threw a question at some EEs. They said more likely the connection would be a capacitor, at least in the test equipment they develop(ed). I go back to my example of 10nF being 16K at 1kHz. This does null benefits of twisted pair and since the question was twisted pair or coax, it negates potential advantage of coax and swings it towards coax. p.s. bringing up KHz or kHz is pedantic. It is like complaining about spelling / typos in a technical discussion to deflect from the content.
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Impedance between what and what?. Induced noise current flows in the loop output - speaker wire - speaker terminal - speaker impedance - speaker terminal - speaker wire - output impedance - output. In this loop noise currents will cancel, even if you earth ground it at one point (as long as it is one point only). It is just simple loop with pickup (induced current) proportional to area between wires. |
I absolutely guarantee your fellow engineers will write it as KHz. I just did a quick scan of emails from my engineers and I can find many instances of it. It is probably why I do it. Most of these are MSEE and some PhD. I am working on engineers from 3 continents and who knows how many different backgrounds. w.r.t speaker wires feeding back into the amplifier, or a bridge or phono catridge, you keep saying loop. If there is a ground connection. it is not a loop. This is the mistake you keep making. It is not a loop. It is not about the induced currents being different. It is about where they go once the meet the single ended piece of equipment, i.e. the amplifier, the phono-amp, the bridge amp (which would never be single ended). At the amplifier the resistance, I guess ideally impedance, must be the same so that the induced voltages are the same, or they do not cancel. If you have a ground connection, or simply a difference in termination, as any single ended piece of equipment will be, then you will have an induced voltage difference from common mode injected currents. Let’s go back to our speaker connection. I have common mode current that goes towards the speaker. Both see the same impedance at the speaker (it is a floating speaker after all). The voltage on both sides of the speaker, for argument/illustration raises the same amount, hence no change in voltage across the speaker. If the current goes the other way, one side sees the impedance of the amplifier. The other (ground) sees the the impedance of the amplifier, but also sees a parasitic path through through that ground and out to "somewhere". Now you have a differential voltage caused by the common mode noise. This is common mode. There is still the superior symmetric coaxial structure for rejecting the generation of differential currents from electrostatic fields and even for magnetic fields, the coaxial structure provides rejection. Let’s approach this from an engineering perspective. My search, though limited, resulted in a consensus that for single ended connections, which we are talking, and which you cannot hand wave away a ground connection that is a resistance/impedance significant with respect to the termination resistance/impedance, that coaxial cables are superior for rejecting external EMI. If I am wrong, and what you say is true, there should be ample evidence of this on the web one would prefer with measurements. Here are some measurements done by an engineer who posts on ASR (not Amir/a mod). I also have another posts from a cable company where they talk about most RCA connections being fully grounded (I know I saw that in the past when playing around with tube equipment). That throws out that big resistor to ground in all cases argument and makes the case strongly for my system dependent argument.
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kHz would be it, but I needed to make the K lower case as the spell check caps it. |
What do you mean current goes the other way? It is the same current - not two different cases. If it cancels at the speaker (no current thru speaker) it means net current in the loop is zero. It will also be zero on the amplifier side (no current in the wires). Impedance in the loop is the same for both wires - you cannot separate them - wires are in series. Presence of the speaker doesn't change anything - we can short it. It is the same wire where two induced currents flow in the opposite direction. What might flow to ground is differential current that is zero. Draw two exactly same current sources of opposite polarities in series and close the loop with resistor. Current in the loop, as well as voltage across resistor will be zero. You can ground it at any point and it won't make a difference - it is floating circuit (no reference to anything). Only connecting it at two points will unbalance currents (alternative path). |
Your thinking is flawed @kijanki. You have an erroneous understanding of how noise induces (or does not) induce current into these circuits and hence have drawn incorrect conclusions about what the result will be. If the noise is flowing in a loop, through the speaker (or cartridge), it is not common mode noise, it is differential. Let us change the problem to a phono cartridge and a pre-amp. By your understanding, even if one side of the phono amp input is grounded, the system is "differential", and hence will receive the full benefits of twisted pair wiring. That is wrong. I noted that @atmasphere who supported you above uses a true differential input on the phono inputs to his preamplifier (for improved noise rejection). The flaw in your logic is that with common mode noise, the current does not (have to) flow through the turntable cartridge (or speaker as the case may be). A simple case is electrostatic coupling which capacitively couples a current onto both wires (common mode). No wire "loop" is required to induce current as the parasitic capacitors forms the circuit. However, since you have one side of the phono pre-amp "grounded" the current in that wire flows into the ground (or some portion of it depending on whether hard ground, resistor, or capacitor. The current in the other wire flows into the loading network, offset by whatever current did not flow to ground (from the other side) but also flowed into the loading network. The result is of course a noise voltage. Coax has superior electrostatic noise rejection compared to even shielded twisted pair. Without a proper fully differential system, there is no benefit of twisted pair. For audio I would assume we can ignore RF antenna coupling onto both wires (common mode), or at least we can ignore the effects which could be similar to electrostatic coupling. If we include them, again, the single ended connection defeats any benefit of twisted pair wiring as above, while the twisted pair has less rejection than coaxial, even shielded. For magnetic EMI coupling, there would need to be a differential current generated at the point of interference as a complete electrical loop, for practical purposes, would need to exist to have a magnetically induced current. A twisted pair does, obviously, reject magnetic coupling of EMI, but so does a coax (through arguably a different mechanism) and it does it rather well. In most practical cases, because the differential current from magnetic interference happens at the point of interference and not at the load/receiver, the balanced connection does not matter for magnetic interference. (note the experiment link I provided that showed in that case superior rejection of magnetic interference with coax).
@jumia , this is not touting my horn, but questioning the competence of many cable companies, but I expect few of them, based on the technical quality of their communication, have the understanding to either refute or agree with what I write. Some of them I am sure do have that understanding.
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A shielded RCA cable (not coax) is 2 conductors, one for ground, and one for signal, plus a 3rd "conductor" which is the shield. The shield will extend the full length of the cable, but only connect on one end. The shield is effectively a Faraday cage preventing RF energy from getting into cables inside of it. Yes, the shield is potentially an antenna. However, if it is connected on only one end, any RF energy should be shunted harmlessly to ground.
If you connect the shield on both ends, and the RF energy generates a large current in the shield, then it could induce a difference in ground voltage which will (or could) show up in the signal on a single ended system. That would also require the stars to align such you had a huge amount of RF and that your audio system converts the RF into something audible. More likely is an electrostatic conduction path which the shield will provide some protection for, or not and/or a magnetic path for which it may provide protection or not. There is more complexity than this and it would take far too much space to put here so I found you a good link. (and RF is obviously both electric and magnetic field).
Most fields have a lot of lore, pass down through the ages, repeated, reinforced, and wrong. Just look at this hobby! Electrical Engineering is no different (and nor is physics). What works in one situation may not work in another, hence rules of thumb often cause bruised thumbs.
This particular link takes a very hard line on cable shielding (not system level noise). From a practical stand point as an end user, you cannot ignore system level noise in order to perfect shielding, but your takeaway should be that unless everything is designed properly (his examples of mil-spec and FAA), then there is no 1 correct way for every instance, only a correct way for your particular instance. I know most of this paper will likely be over your head, but I think perusing it will give you a feel for what the issues: https://www.emcstandards.co.uk/cable-shield-grounded-at-one-end-only
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