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    XLR v. regular RCA co-ax

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    deepee99

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    XLR v. regular RCA co-ax

    Post by deepee99 on Wed Dec 12, 2018 1:53 pm

    Could someone explain (in the King's English) why balanced (XLR) interconnects are superior to old-fashioned coax? Isn't the required xformer for XLR yet another bump in the signal chain?
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    Peter W.

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    Re: XLR v. regular RCA co-ax

    Post by Peter W. on Wed Dec 12, 2018 3:13 pm

    Yes and no.

    The real reason for a balancing transformer (XLR) is that it will accept DC-offset sources without trouble. This can be very important when the source(s) are multiple and unknown in quality and output.

    The output transformers in tube equipment eliminate any DC offset in the signal, and the power-transformer does so with the wallplate voltage.

    Early solid-state equipment was often significantly troubled in this way - and so some few had interstage transformers to eliminate it.

    Hope that helped.
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    deepee99

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    Re: XLR v. regular RCA co-ax

    Post by deepee99 on Wed Dec 12, 2018 3:47 pm

    Peter W. wrote:Yes and no.

    The real reason for a balancing transformer (XLR) is that it will accept DC-offset sources without trouble. This can be very important when the source(s) are multiple and unknown in quality and output.

    The output transformers in tube equipment eliminate any DC offset in the signal, and the power-transformer does so with the wallplate voltage.

    Early solid-state equipment was often significantly troubled in this way - and so some few had interstage transformers to eliminate it.

    Hope that helped.

    It did (as usual). Thanks, Peter
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    Peter W.

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    Re: XLR v. regular RCA co-ax

    Post by Peter W. on Thu Dec 13, 2018 4:17 pm

    deepee99 wrote:
    Peter W. wrote:Yes and no.

    The real reason for a balancing transformer (XLR) is that it will accept DC-offset sources without trouble. This can be very important when the source(s) are multiple and unknown in quality and output.

    The output transformers in tube equipment eliminate any DC offset in the signal, and the power-transformer does so with the wallplate voltage.

    Early solid-state equipment was often significantly troubled in this way - and so some few had interstage transformers to eliminate it.

    Hope that helped.

    It did (as usual). Thanks, Peter

    There is, of course, another reason - the transformer serves to isolate a microphone (for instance) from an amplifier (for instance). So a musician is less likely to get shocked (amongst other things) if either is defective. You will see XLR adaptors differentiating between Isolation, Balancing, and Both in their descriptions. Sorry for answering only with reference to balancing.

    wildiowa

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    Re: XLR v. regular RCA co-ax

    Post by wildiowa on Thu Dec 13, 2018 8:04 pm

    You hardly ever see XLRs and low impedance connections in consumer stereo gear. Studio stuff, yes. In our applications, live sound, the low impedance allowed mic runs of almost unlimited length without loss of signal or interference from AC or other sources. With a high impedance mic you were pretty much limited to 25 or 30 feet before you started getting buzzes, hisses and dirty feeds. Low impedance we went a hundred feet or more sometimes. Same appeared to be true hooking up components in the signal chain. It was just a lot lower noise compared to RCAs and 1/4 inch phone jacks. I also thought it was a compatibility issue as 3-conductor XLRs with the male/female ends allowed universal, standard interconnections for pro music and studio apps. I am sure there is a more technical explanation.
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    pichacker

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    Re: XLR v. regular RCA co-ax

    Post by pichacker on Fri Dec 14, 2018 7:53 am

    XLR - A balanced line - has good common mode rejection from external sources and helps eliminate ground loops (hum).


    Last edited by pichacker on Fri Dec 14, 2018 10:44 am; edited 1 time in total
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    Peter W.

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    Re: XLR v. regular RCA co-ax

    Post by Peter W. on Fri Dec 14, 2018 7:55 am

    pichacker wrote:XLR - A balanced line has good common mode rejection from external sources and helps eliminate ground loops (hum).


    Yes, and what comes out of a transformer is "balanced" irrespective of what goes in.

    wildiowa

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    Re: XLR v. regular RCA co-ax

    Post by wildiowa on Fri Dec 14, 2018 10:32 am

    Just think of those rock show with a snake running like hundreds of feet from the stage to the sound board with dozens of low level mics coming in, and sending a processed pre amp level back hundreds of feet to the stage. Not possible with the two conductor high impedance lines. Other high impedance sources like guitar and keys had to kick into a direct box to get a low impedance feed before you could get it to the board. Apparently the grounded shield is independent of the two inner connections that actually carry the signal and that produces some magic. I can also tell you that using a mic in high impedance seemed to have a lot hotter signal than using the same mic in low impedance mode. All this is becoming moot as digital mixers are using Cat 5 cable runs to the board or a guy walking around the venue with an iPad mixing wirelessly.
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    deepee99

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    Re: XLR v. regular RCA co-ax

    Post by deepee99 on Sun Dec 16, 2018 1:24 pm

    Thanks, Gents, you've satisfied my curiosity.
    I would distill it thus: In the relatively short runs <15 feet give or take, that we use for our systems, one is as good as the other, all other things -- component grounding, and the separation of signal lines from close parallel runs of 60-cycle 120 VAC -- being equal, there's no urgent call for the added expense of XLR cabling.

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