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RCA interconnects; why coax construction and not simple 2 wire?

flightops

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I'm not trying to start a heated discussion on cables, I'm just trying to ask an honest "i don't know why" question because I'm not educated/trained in electronics. At least not to the level of understanding the theory/principles behind it in audio systems. Repair, replace and troubleshoot? I'm not too bad at that. Theory/principles? Pretty sketchy there....I'm more technician than engineer when it comes to electronic stuff.

Why do RCA interconnect cables all seem to be somewhat of a coax construction and not a simple 2 wire type?

I get that line levels are low strength signal and the shielding of an outer braid helps reject external "noise" sources like RF and EMI, but is it really that much of a problem if a simple two wire cord is used? Would they really be at risk of picking up RF/EMI in a home audio scenario?

I have cut open a set of the really cheapo rca cable before and they are even core and shield type construction, even if they are very (very) thin wires.

There must be a good reason for it because the cheapies would be even cheaper (IE: to construct) if they were simple two wire cords.

Again, not trying to start something, I honestly just want to understand the "why" of it.....
 
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You touched on the reason, that of shielding from noise. It does make a difference, especially for anything but very short lengths, or in very low impedance circuits like loudspeakers.
The simplest way is to try it. Just make a 1 or 2m long interconnect from lamp cord. I think you'll find the noise levels unacceptable unless your conditions are very benign.

S
 
You touched on the reason, that of shielding from noise. It does make a difference, especially for anything but very short lengths, or in very low impedance circuits like loudspeakers.
The simplest way is to try it. Just make a 1 or 2m long interconnect from lamp cord. I think you'll find the noise levels unacceptable unless your conditions are very benign.

S
so where does the noise come from if the cable is run away from other components or power sources? Does the 2 wire cord behave somewhat like an antenna and pull RF right out of the ambient environment if it has any significant length to it? Sources like the RF that we're all "bathed in" or even cosmic remnant stuff that used to make snow on old crt tvs when on a blank channel?

I may try that lamp cord "experiment" just to help illustrate it to my mind.....
 
In the backside of the gear stack/rack a lot of conductors are used for different AC signals and power wires plus a DC sometimes for trigger switching. I have seen very low level RF signal coming from a 12 foot actuated satellite dish using very thick coax for video and digital audio reception that was corrupted by the AC wires in the peripheral. Shielding is a good method of reducing any crosstalk and reactance from wires to other wires. This specific situation was a very tiny satellite pola rotor down converted signal affected by the AC wires. I am guessing but it does happen. On the flipside we do see where some RCA cable companies use a simple braided 2 wire construction and people seem to be happy with that but myself I always use coax.
 
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Hmmm, now I'm wondering what woudl happen if you slipped a copper braid tube over a two wire cord? Would it shield it or not......might be worth experimenting with, to satify my own curiosity if nothing else.
 
so where does the noise come from if the cable is run away from other components or power sources? Does the 2 wire cord behave somewhat like an antenna and pull RF right out of the ambient environment if it has any significant length to it? Sources like the RF that we're all "bathed in" or even cosmic remnant stuff that used to make snow on old crt tvs when on a blank channel?
60Hz and 50Hz AC energy is all around us emitted by the power lines in our walls and power poles underground etc. It is picked up by low signal level cables. Plus RF energy is there too and I have seen this cause aviation RF frequency to be picked up by a phono operation. So using coax is a better method of grounding out these extraneous energy levels.
 
Hmmm, no I'm wondering what woudl happen if you slipped a copper braid tube over a two wire cord? Would it shield it or not......
Yes, 3 conductor wire including the shield would provide shielding but is not required for low level audio applications.
 
In the backside of the gear stack/rack a lot of conductors are used for different AC signals and power wires plus a DC sometimes for trigger switching. I have seen very low level RF signal coming from a 12 foot actuated satellite dish using very thick coax for video and digital audio reception that was corrupted by the AC wires in the peripheral. Shielding is a good method of reducing any crosstalk and reactance from wires to other wires. This specific situation was a very tiny satellite pola rotor down converted signal affected by the AC wires I am guessing but it does happen. On the flipside we do see where some RCA cable companies use a simple braided 2 wire construction and people seem top be happy with that but myself I always use coax.
I am planing to make some interconnects, but I've got a roll of rg59 copper core and shield for that. Just have to find it in my storage shed.

But it got me wondering why a simple two wire cord is not something you see in rca interconnects. For whatever reason, I've never had that thought before, I just followed the coax "bandwagon"....
 
why a simple two wire cord is not something you see in rca interconnects.
It is used and sold by some companies to good success that follow that trend but coax is preferred in my opinion.
 
.. I have seen this cause aviation RF frequency to be picked up by a phono operation. So using coax is a better method of grounding out these extraneous energy levels.
Interesting that you would mention that. I live fairly close to an army military base where they use secure burst transmission to communicate between ground units and things like APC's and I'll sometimes get a digital tone/pulse sequence when playing records. I've often wondered if that was the source of those digital sounding tones. I've always just accepted it as something I have to deal with because I have no idea how to shield it out. I already use decent quality RCA cables (well, as far as Ii know they are) between deck and preamp and preamp and receiver.

Could also be something aviation as the air base I used to fly out of (I was military SAR before retirement) is 30 mins up the road and they fly secret squirrel and sub hunters out of there too. Crypto communication stuff, as well as our more common uhf/vhf/hf aviation radios we used on the chopper.

Now that I think of it, it could be localizers, DME equipment or any other number of aviation nav aids I infrequently pick up as that tone.

Only happens when running the phono decks though and not often. Maybe once or twice a month at most.....no idea how to stop it as with the assumption it was something military came the assumption I wouldn't be able to shield from it...
 
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Interesting that you would mention that. I live fairly close to an army military base where they use secure burst transmission to communicate between ground units and things like APC's and I'll sometimes get a digital tone/pulse sequence when playing records. I've often wondered if that was the source of those digital sounding tones.

Could also be something aviation as the air base I used ot fly out of is 30 mins up the road and they fly secret squirrel and sub hunters out of there too. Crypto communication stuff, as well as our more common uhf/vhf/hf aviation radios we used on the chopper.

Now that I think of it, it could be localizers, DME equipment or any other number of aviation nav aids I infrequently pick up.

Only happens when running the phono decks though......
I experienced actual voice COMs from a overhead small aircraft. I could hear the talking. It happened several times until I changed out the gear for a new Technics amp and turntable. But that's not to say that digital bursts cannot use a different RF spectrum
 
You touched on the reason, that of shielding from noise. It does make a difference, especially for anything but very short lengths, or in very low impedance circuits like loudspeakers.
The simplest way is to try it. Just make a 1 or 2m long interconnect from lamp cord. I think you'll find the noise levels unacceptable unless your conditions are very benign.

S
Does twisted pair make a difference as opposed to lamp cord?
 
I actually have that downloaded but it's slow going for me getting through it.

I have a few.....ummm......"remnants"....from 30 years pf military service that make maintaining a stream of concentration for any significant period of time, shall we say...."challenging". Anything techincal/theory is even more of a challenge.

I'll get there, it's just slow going.
 
Does twisted pair make a difference as opposed to lamp cord?
I'm no expert, but from what I remember reading is the twist is generally not desirable as it makes the length longer overall, which increases impedance, which degrades the line level signal. Don't quote me on that though. As I mentioned, I'm certainly no expert.

We do it on data bus wiring, but that's likely a bit different principle than audio cabling as that's shielding communication data between things like ADU's, radios, FCU's, etc.....IE: digital information, not analog.
 
I actually have that downloaded but it's slow going for me getting through it.

I have a few.....ummm......"remnants"....from 30 years pf military service that make maintaining a stream of concentration for any significant period of time, shall we say...."challenging". Anything techincal/theory is even more of a challenge.

I'll get there, it's just slow going.
Just ask here and we'll give you the abbreviated version if that works for you. :D
 
I'm no expert, but from what I remember reading is the twist is generally not desirable as it makes the length longer overall, which increases impedance, which degrades the line level signal. Don't quote me on that though. As I mentioned, I'm certainly no expert.

We do it on data bus wiring, but that's likely a bit different principle than audio cabling as that's shielding communication data between things like ADU's, radios, FCU's, etc.....IE: digital information, not analog.
In an interconnect is that important? Seems some of the fancier cable stock does twisted, tho. I remember when we installed twisted pair wiring in our office network, tho :)
 
I experienced actual voice COMs from a overhead small aircraft. I could hear the talking. It happened several times until I changed out the gear for a new Technics amp and turntable. But that's not to say that digital bursts cannot use a different RF spectrum
I've never picked up light aircraft and there's a municipal strip nearby. But the military stuff? I know from operating it myself it can punch out some serious power when you need it.....which I'm guessing it might be.

Now that I think about it, it might be an HF call identifier I'm hearing infrequently. Kind of sounds like it. Each of our aircraft has a distinct one and "tones it out" first on highest power when we would "key up" on HF. It's how the HF ground stations would identify us by tail numbers before we even spoke....

But we were using HF phone patch a lot less when I was wrapping up. Aircraft had gotten sat com sets integrated into the radio suite, so there was less and less HF coms needed....
 
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In an interconnect is that important? Seems some of the fancier cable stock does twisted, tho. I remember when we installed twisted pair wiring in our office network, tho :)
Someone else will have to chime in on that. Answer is "above my pay grade"......IE: I don't know.....;)
 
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