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Author Topic: Wiring for RCA connectors  (Read 2519 times)

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Offline aysvideo

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Wiring for RCA connectors
« on: May 18, 2015, 03:30:26 AM »
I'm getting ready to build several pairs of RCA interconnects, using some mil spec cable I have.  From what I can see on various diagrams I've found online, the positive lead goes to the tip, and negative to the sleeve.  The wire I'm using has 2 conductors and a shield.  Both conductors have white insulation around them, with one of them having a blue stripe. 

I guess it doesn't really matter, as long as I'm consistent, but generally speaking, would the conductor with the blue stripe be used as the positive?  Also, am I correct in assuming that on an RCA connector, the shield just gets clipped, as opposed to a 3 pin XLR, which uses the shield on one of the three pins as a ground? 

I've done XLRs before, but this is my first time doing RCAs, so any advice is welcome.  Thanks in advance,

Randy

Offline tgakidis

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Re: Wiring for RCA connectors
« Reply #1 on: May 18, 2015, 05:06:55 AM »
Your can go either way below:

Shield to ground
Blue & white to tip

Shield & white to ground
Blue to tip
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Offline aysvideo

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Re: Wiring for RCA connectors
« Reply #2 on: May 18, 2015, 10:59:08 AM »
Thanks, gentleman.  Also, I wasn't planning to use these for video.  The reference in my user name is there because i was in the video biz for many years, but not any longer. 

Offline DATBRAD

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Re: Wiring for RCA connectors
« Reply #3 on: May 27, 2015, 06:38:25 PM »
There is one more way if you want to take advantage of the shield. This will require you to build them directional. Just wire each conductor to tip/sleeve as you suggested in your original post, and trim the shield totally flush to the insulation, and this will be the source end. Then, unweave some of the shield at the other end, make a small pigtail, twist it together with the negative conductor, and solder to the sleeve termination. This makes the shield active, without signal traveling through it. Even the highest grade milspec for twisted pairs using a silver clad copper woven shield is not ideal for using as combined negative and ground. Best to use only for ground. Good luck!
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Offline DATBRAD

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Re: Wiring for RCA connectors
« Reply #4 on: May 28, 2015, 12:12:08 PM »
That still will have any interference on the shield common with the signal return path.  There's not anything to be done about that with an unbalanced connection--there is no signal negative here.  That scheme has some merit where the receiving end is balanced.  See diagrams 20 and 17 here:

http://www.rane.com/note110.html

Jon, thanks for sharing that Rane info, another strong argument for the merits of balanced connections. If you read down towards the end of the paper, it mentions special cable assemblies when unbalanced connections at each termination are involved. Disconnecting the shield from one end "lifts" the ground, preventing a ground loop. Now conventional wisdom has the shield tied to ground on the source end so not to create a dipole antenna. Usually, the higher power component of the two is the one to tie in the shield. Preamp to power amp, tie in at source, D/A to preamp, tie in at output end. 2 conductor cable allows the shield to work with unbalanced connections, and without any noise added to return signal since it's not on the shield. Really, trial and error with the particular components the OP is using will be the best way to know what works, as long as it's not messing around with A/C ground, please don't do that.. Later....
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Offline DATBRAD

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Re: Wiring for RCA connectors
« Reply #5 on: May 28, 2015, 08:50:17 PM »
I think its warranted to distinguish between DC powered components and A/C powered. An unbalanced twisted pair with shield connected at both ends creates a second audio path that absolutely will create a ground loop with A/C powered components, in the form of audible 60 cycle hum. Shielding is going to help block RFI, but does a poor job with EMI. That is why balanced and shielded cables are the best. There is a ton of information online about the One-End-Open Shielding technique. It's been around as long as I can remember, and I'm 52 so that's a long time, lol....Enjoy the bench work guys !!!! Ltr.....
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Offline DATBRAD

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Re: Wiring for RCA connectors
« Reply #6 on: June 03, 2015, 09:53:39 PM »
Jon, My mention of the twisted pair is only because the OP mentioned having 2 conductor woven shield milspec. Come to think of it, I can't recall ever building anything with that wire for totally unbalanced use, maybe a few times for interfacing balanced and unbalanced.

At Luminous we get custom orders for the shielded version of the Monarch II fairly often, always requesting the drain wire  terminated at one end only. Our dealer in Indonesia orders 5 meter versions, RCA-RCA, used in audio systems at some high end custom limo shop there he deals with. For those we use 22AWG solid core silver clad copper twisted pair with foil wrap and attached drain wire. I was told the application has something to do with differential amplifiers used in 12V car systems.

During training on unbalanced shielded interconnects, I was taught that a true shield captures the stray EMI and RFI, and to achieve this the bare shield drain wire connected to the shield is grounded at one end of the cable only. That way all of the captured signals are "drained" to ground at one point. The result is protection from induced voltages on the conductors inside the shield, something a shield connected at both ends will not do with an unbalanced connection.

If the shield drain wire were grounded at both ends, that provides a path for current to flow between the two ground points. If the ground points are not at the same potential, current can flow in the drain wire, which is in contact with the shield, inducing voltages on the conductors inside the shield.

Induced voltages are a real threat to low-level analog signals run over long distances in parallel with higher voltage and higher current-carrying wires, that is one of the main reasons shielding exists. In live sound and sound reinforcement applications, multiple sections of cable, many unbalanced, are used for low-level analog signals which pass through multiple components, effect racks, and the console itself. It's a common practice to terminate only one end of the shield drain wire of each section of cable, so that the captured stray influences are taken to ground at one place only.

I just happen to reside in the camp of people that follow the one-end-open shielding philosophy for unbalanced interconnects. In a nutshell, I agree with the concept that a shield drain wire terminated at both ends becomes a current carrying conductor, inducing unwanted voltage on the conductors it is meant to protect, and a shield allowed to "float" at both ends does nothing at all.

I didn't invent the concept, it's older than I am, but I do prescribe to it 100% I guess we should agree to disagree on this one.....

Great discussion!

Edit to add: That Analog Devices paper is great, and if you back up from page 15 you referenced, read the bottom of page 12 through page 13. It briefly touches on the one-end-open shielding application.
« Last Edit: June 03, 2015, 10:03:41 PM by DATBRAD »
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