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?
@jumia Specifically I was using Mogami Neglex 2534… 2x blue, and 2x clear, and the shield. The Mogami is in a brown jacket, so that the WAF abides it laying on a brown wood floor. I usually order from Markertech and use the Nuetrik ProFi (RCA) or their XLR ends. |
I dunno @jumia - I needed an XLR to RCA and was not about to pay money and time awaiting a cable. And it even sounds OK. The soldering looks a bit rough, but once the end is screwed on, you cannot see it. |
Finally I appreciate the help. OK so you combine the two connectors before attaching to the RCA. Makes sense and I guess you have to mix them together. At least the two conductors had a peaceful journey from the preamp and then all hell broke loose when they reach the RCA connector. Blue , I believe is the ground connected to the Shell on both sides of Cable as mine have been done and recommended this way. And the shield is out of the picture by stripping it back Not sure why the hell every comment above made this issue so damn complicated Great job holmz |
^Twist them together.^
I put together some XLR to RCA yesterday. On the Neutrik XLR:
On the DAC I split the power and shoved a ferrite core on, with the +V in the one direction and the -V wound the other way. |
@jumia Simply by careful soldering. |
I like Mogami too. I have their 3173 Cable as a interconnect between amplifier and preamp. This is a little thicker than the 2549 and also has a drain wire Plus 2 conductors. In this situation the drain wire is connected to both sides. Still breaking in and thus far it’s a wonderful cable and very inexpensive. |
Since you are only concerned with single ended RCA interconnects with coaxial cables, I will share my experience with you. For many years I used a fine 75-ohm Belden #9259 oxygen free single center conductor coaxial cable with a bare copper braided shield over a polyethylene foam dielectric. This was my principal preamplifier output to my mono block power amps input for many years. I really had no complaints. Due to a change in my room arrangement, I was forced to construct new & longer interconnects. I was unable to acquire an adequate amount of the Belden #9259 cable without purchasing an entire roll. I did however receive a timely tip from a respected analog guru. He recommended Mogami W2549 coaxial cable which has 2 OF center conductors + bare copper braid. You can experiment with it in 2 methods: 1) solder 1 center conductor to the RCA + cup, the other center conductor to ground & the bare copper braid as the shield or 2) solder both center conductors to the RCA + cup & the bare copper braid as ground. Interestingly, the company that I purchased the cable from (Redco) actually terminates them per method 1 (above). However, I chose the second method. I made my main pre to power amp interconnects 25' long. 2 more pair 1 meter long and a 4th pair 2 meters. After about 300-400 hours of "run-in" I was more than pleased. Doing this project requires some good tools, materials and diligence or alternatively, pay someone or business to do it. If you are a DIY person, you may wish to select an RCA connector with a crimp connector option for the braid so that you only have to solder the center conductor(s). I found that soldering the braid to the ground of the RCA connector to be the most difficult part of the process, mostly because the RCA's that I chose didn't leave me much real estate to work in. I was not able to compare these particular Belden vs Mogami coaxial cables in my system fairly, but I am very pleased and settled with this decision & execution. The Mogami cable is exceptional in every aspect with vivid detail and dynamics. I hope this has provided some limited comparative insight. Best luck
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@jumia At one RCA connector shield and negative/return wire are both soldered at the base of the connector while signal/positive wire is soldered to center pin. On the other side only two wires are soldered while shield is left unconnected/floating. |
Recent answers Have been amazing. The RCA connector - isn't it designed to accommodate one conductor and then gripping the shield where it is soldered at the base of the connector. So how does the RCA connector accommodate 2 connectors(positive and negative) and a ground wire. I really like atmaspere’s answer including discussion about the shield carrying the signal. It made a lot of sense to my simple mind.
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There is no standard for balanced differential amplification using an RCA connection. If such a thing is used expect a bit of the Wild West. |
Simple answer to your question is it depends.
There are two standards for RCA. Single ended RCA which uses one wire for signal (the inside pin) and usually is shielded (the outside ring) but the shield is not required for functionality. The second standard is Differential input RCA which is balanced like XLR and uses two wires to send signal on wire one and inverted signal on wire two. No shield is used.
Both cables will work on any equipment but generally, you will get better results using the correct cable with each standard. |
Big Volta’s “V” is for DC Volts. little Volta’s “v” is for AC volts.
Back to the OP’s question… (On an XLR we would solder it to the -180 side.) It is kind of like 1/2 a transformer, if we look at it like a twisted pair, so I would suggest that one attaches it somewhere. I use the negative side, but the center pin seems like a valid choice. |
@kijanki I try to always use caps in the spelling too. @jumia Look at it this way. If the signal is passing through the shield as it does when only the shield and center connection is present, then the construction of the shield and any noise to which its subjected to will affect the sound, some of it possibly in the form of added intermodulation distortion as the noise is impinged on the signal. When the shield is separate from the signal this won't happen so it sounds better. The actual technical description is more complex as you know; this is the Cliffnotes version. |
@atmasphere AFAIK we should write symbols of units named after person with capital unit letter V, kV, A, kA, kHz, kW etc. but spelled out units with lowercase : volts, amperes, ohms, watts. Multiplier doesn't change that, so it will be kilovolts, kiloohms, kilowatts, kilohertz. The only exception is when unit contains two words like degree Celsius. |
So I’ve inquired about one conductor versus 2 conductor as part of an RCA interconnect. There has been a substantial response from very very smart people. Unfortunately, somehow the brilliance is having trouble leading to a point where someone can understand what is being said. brilliant people herein don’t really do a very good job explaining things Beyond extremely technical jargon. This thread of information is a testament to how challenging it is for brilliant minds to communicate in a manner that can be understood by us average mortals. Truth be told this discourages people and is an unattractive aspect of this hobby of sorts. Do these really brilliant people know that most people reading the comments have no idea what they’re talking about. It’s really really hard to understand. I have always considered True genius to be the ability to explain a very complicated situation to the masses. Otherwise what’s the point. |
@deludedaudiophile To be clear no direct line can be drawn between single-ended and balanced lines as they are mutually incompatible. A phono cartridge in most tonearms is a balanced source, but usually its operated single-ended, leaving you with that weird ground wire that has to be hooked up to avoid buzz. When you run it balanced the ground wire is gone, instead there is the shield of the tonearm cable with a twisted pair inside, much like the tonearm tube itself. FWIW dept.: the use of capitals is to honor the people that did the early research; Hertz, Ohm, Volt, etc. are all names of people but 'kilo' and 'mega' are not- they are multipliers. So you see kOhms, kHz, kV or mV (milliVolts). Anything else is either ignorance or being sloppy, and yes, I've been there. |
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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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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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). |
kHz would be it, but I needed to make the K lower case as the spell check caps it. |
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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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. |
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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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). |
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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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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@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. |
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. |
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. |
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. |
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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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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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. |
@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. |
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. |
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! |
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. |
Interesting @crustycoot . That journalist no doubt discovered what was already being used industrially and in the scientific community no doubt for decades prior. |
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. |
@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. |
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. |
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. |
