I want to make a couple of line-level cables with male RCA plugs on both ends. They are for powered subwoofers, and need to be about 15 feet long. I do not want to bother with baluns if I can make do with a simple unbalanced line.
All the interconnects that I have ever cut open use a cable that has a stranded center wire and a woven shield. I cannot find that cable anywhere. I do find lots and lots of "RG-6", which has a solid wire in the center, and is a whopping 1/4" in diameter. I also found some with two center strands, also 1/4" in diameter. http://www.parts-express.com/pe/showdetl.cfm?Partnumber=100-282
So... The question is, how best to make the cables? What wire to use?
I tried searching. Everything I found got into the business of baluns or active balanced/unbalanced converters.
All the interconnects that I have ever cut open use a cable that has a stranded center wire and a woven shield. I cannot find that cable anywhere. I do find lots and lots of "RG-6", which has a solid wire in the center, and is a whopping 1/4" in diameter. I also found some with two center strands, also 1/4" in diameter. http://www.parts-express.com/pe/showdetl.cfm?Partnumber=100-282
So... The question is, how best to make the cables? What wire to use?
I tried searching. Everything I found got into the business of baluns or active balanced/unbalanced converters.
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I found this: RG-59/U Copper Braid Shield 100 ft. | Parts-Express.com
It's got a solid center and it's 1/4" in diameter.
URM70 or if you want a little thinner RG58. Both are stranded centre, which I prefer as it's more flexible.
Yep thats the one.
Bud why not using the microphone cable?
Use one conductor to the center and the other one to outside of the RCA plug.
Connect the shield also to the outside of the RCA only on the side where the equipment is connected to the ground.
Thats mostly the amplifier side.
Bud why not using the microphone cable?
Use one conductor to the center and the other one to outside of the RCA plug.
Connect the shield also to the outside of the RCA only on the side where the equipment is connected to the ground.
Thats mostly the amplifier side.
I am going to display my ignorance now. Ready for it? Here it is.
I don't understand that last part about connecting the shield on one end. Neither the pre-amp nor the sub's plate amp is connected to ground except via a two-pronged wall plug. Both are on the same circuit, and the wall plugs have big and little sides. I am guessing you will recommend connecting the shield to the negative conductor on the end that plugs into the plate amp. But I haven't the foggiest idea why.
Any shielded cable will work. It is even less critical since this is for a sub where any capacitance of the cable/HF roll-off is a complete non-issue.
I think the idea behind connecting the shield at one end is to act as a sort of "drain" for any EMI picked up by the shield. Connecting it at one end would prevent currents from flowing on the shield between the components, but since you would have a wire connected at both ends anyways (the signal ground), currents will flow - ground loops - between the components if a potential exists.
See more info here: Sound System Interconnection
I think the idea behind connecting the shield at one end is to act as a sort of "drain" for any EMI picked up by the shield. Connecting it at one end would prevent currents from flowing on the shield between the components, but since you would have a wire connected at both ends anyways (the signal ground), currents will flow - ground loops - between the components if a potential exists.
See more info here: Sound System Interconnection
Dunno about benefits of RF cables at audio or their sevicability when home assembled but Radio Shack currently have an on-line special of 16ft "Monster Cable" standard duty subwoofwer interconnects on sale in the US. $17.99 ea.
As you find, not many parts stores retail quality audio screened cable any more but the major distributors all stock it by the reel. You might not save all that much with DIY on that price, either.
As you find, not many parts stores retail quality audio screened cable any more but the major distributors all stock it by the reel. You might not save all that much with DIY on that price, either.
That might be very interesting indeed, depending on what Monster call "standard duty subwoofer interconnect". AFAIK, at least their higher-grade interconnects are quite awesome.
I would rate the quality of interconnect as follows:
cheap OEM cable < slightly higher-grade application-specific interconnect cable < lower-grade microphone cable < RF cable < higher-grade microphone cable < top-of-the-line application-specific interconnect cable
Monster counts as application-specific interconnect; good microphone cable would, e.g., be (pro-grade) stuff like Cordial.
If this particular flavor of Monster is not that good, it might still make sense to go with RF cable.
I'm not going to go through the pain of explaining the outer shield connection; I will only state that I agree with Geosto's statement.
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Greetz,
MatchASM
I found some on amazon for $4.29 plus shipping. That comes to $13.89 for the pair, total.
But I still want to know how to make my own, and I want to understand the mysteries of ground, neutral, and shield. I think I am starting to catch on regarding that last bit.
I did find coax with a single stranded center wire, but the smallest roll is 500 ft. But as Geosto points out, the mic cable with two stranded center wires is at least as good - if I can reconcile myself with 1/4" cables.
Question: Is 50 Ohm cable adequate, or must it be 75? I found some 50 Ohm with a single stranded center wire that is not quite so thick. RG58, I think it was called. But again, only in humongous rolls.
The impedance, 50 or 75 ohms, refers to the cable's characteristic RF impedance (effectively, a resistance the cable exhibits only at the frequencies it's intended for) well into the MHz. Subwoofer audio is around 100Hz and below, so the only real significance of the cable is its braid shield to screen EMI from the hot signal wire and prevent environmental electrical noise transferring to the signal. All the subjective benefits some associate with RF cable used for audio are quite irrelevant down here. If it's available and well shielded, it will work fine. If it's not well shielded, you will soon hear about it as increased hum and noise.
The Sub's plate amp will have a connection of the outer (cable braid) connection to the amplifier input earth reference point. That's not usually chassis earth at all but some small resistance above it. It is earth as far as signal impedance, say 10k ohms, is concerned. If you look at amp. or sub-amp. schematics here on the appropriate threads, you will see those details. Signal requires a separate return current flow path and that is also the shield braid's job. So get signal current flowing and connect both conductors at both ends, inner wire and outer braid, just like the commercial leads.
The common trap to avoid in earth wiring, even with this routine use, is to avoid duplicating earth connections between units and forming "hum loops". These can be very difficult to trace internally, if not using standard wiring practices.
Regarding cable purchase, I believe Element 14 or RS components now supply cut lengths. Here, major parts retailers sell cable in cut or small (30 and 100m reel) quantities. $4.29 for 15ft leads? Buy several to sell to your friends at a profit, even if it is c**p! 😱😀
try this place....
there stuff is pretty good....
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there stuff is pretty good....
HDMI Cable, Home Theater Accessories, HDMI Products, Cables, Adapters, Video/Audio Switch, Networking, USB, Firewire, Printer Toner, and more!
i'm wondering what possible point there could be to this, I see it all the time. it doesnt even make any sense with balanced XLR interconnects, unless your grounding scheme is stuffed, let alone with RCA where the ground and case/shield connection are one and the same. can you explain how the currents that hit the shield do not flow in the ground wire that is connected to the very same point (which is connected at both ends)?
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Voodoo!
and what does that mean Digitaljunkie? or are you having a laugh? there are no 'sides' RCA has only 2 terminals and the 'return' is connected at both ends with the ground wire, so connecting the shield at only one end is meaningless. just because its called a drain, doesnt mean that currents flow only in one direction and then dribble out onto the ground.
the shield lift at one end was developed in studios for XLR interconnects to solve ground loop issues with equipment they didnt always have full control over. given proper grounding, doing this is IMO bad practice, but with RCA interconnects its literally meaningless and I see otherwise logical people superstitiously doing it without thinking about what they are doing.
the shield lift at one end was developed in studios for XLR interconnects to solve ground loop issues with equipment they didnt always have full control over. given proper grounding, doing this is IMO bad practice, but with RCA interconnects its literally meaningless and I see otherwise logical people superstitiously doing it without thinking about what they are doing.
BTW digitaljunkie, that rant wasnt directly at you, I figure there is a good chance you were having a laugh, although I dont get the joke 😕
If you think about it, one could say that an unbalanced RCA interconnect has 4 connections, two on each end (or perhaps, 'side') of the cable.
Anyhoo, in communication and navigation radios on aircraft, a single-ended connection (but not, an antenna lead) will be 2-conductor twisted pair in a braid shield. signal and ground will have their own conductor, and the shield will be connected to ground, only at one end of the connection. The shield will not be connected to the (usually) component that is further away from the avionics power buss.
So the braid is acting as a 'shield', blocking, or reshaping any spurious RF from getting into (or out) of the cable.
isnt everything you said just then beside the point? XLR has a separate 3rd and 4th conductor too, but we are not talking about XLR, we are talking about RCA which no matter how you look at it has 2 conductors; your 2 ends of the cable thing is meaningless as they are the same and any shield connected at one end or not will be directly connected to ground at both ends
Do you want your signal to travel though a nice massif conductor that go's strait to the other side of the interlink? Or do you like your signal running trough the woven shield?
In my opinion dose the first option sound the best.
The extra shield is in this cable is noting more than a bonus.
Dose it help to keep out the EMC i relay don't know bud if it helps why not.
In my opinion dose the first option sound the best.
The extra shield is in this cable is noting more than a bonus.
Dose it help to keep out the EMC i relay don't know bud if it helps why not.
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