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Old 26th April 2002, 12:19 PM   #1
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Question What are XLR connections??

janez.knez@email.si
As an amateur electronic designs of Aleph seem new to me. For example what is XLR input, which connectors to use with XLR and how do you connect the inputs minus pole if you are using RCA connectors? Has this something to do with BALANCED and UNBALANCED input, and what are they these inputs? I would appreciate if someone could explain this to me and maybe send me a picture of the XLR connectors.
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Old 26th April 2002, 01:43 PM   #2
SteveG is offline SteveG  United States
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<B><I>As an amateur electronic designs of Aleph seem new to me. For example what is XLR input, which connectors to use with XLR></I></B>

an XLR is a type of connector. You see them used on microphones, and other BALANCED inputs and outputs on professional audio and in some home audio.

<B><I>and how do you connect the inputs minus pole if you are using RCA connectors?</I></B>

This all depends on what you are connecting- some equipment can take a balanced or unbalanced input, and some will have to use an audio transformer to convert the signal. On the XLR connector, pin 1 is cable Shield (ground) pin 2 is signal with a + phase, pin 3 is the same signal with a negative phase, so that the pin 2 and 3 carry identical but inverted signals. The amplifying device looks at the difference between the signals on pins 2 and 3, and ignores anything that is the same on both pins 2 and 3- that's how it rejects noise.
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Old 26th April 2002, 07:45 PM   #3
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And so when using RCA connectors in parallel with XLR,
you short pin 3 to 1, grounding the negative input.
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Old 26th April 2002, 08:15 PM   #4
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It is worth pointing out that the rules for converting balanced inputs are DIFFERENT than the rules for converting balanced outputs.

NEVER short pins to turn a balanced output into an unbalanced output.

It is common mistake (myself included) to confuse the "+" and "-" symbols on a typical XLR pinout drawing with polaraity. (as in battery positive and negative)

In this context: "+" means non-inverting and "-" means inverting. Both signals "float" above ground.

The web has many sources for those that need in in-depth explainations for balanced technology.
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Old 19th July 2002, 07:42 PM   #5
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I have finished my Aleph5 and I was wondering if anyone know how to connect the PCB pads for the XLR connections to the Neutrik XLR connector. Which pins correspond to GND, INV, and NON-INV ?
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Old 19th July 2002, 07:43 PM   #6
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I'm silly... I missed the information in the first post.
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Old 19th July 2002, 09:34 PM   #7
jleaman is offline jleaman  Belgium
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ive started my aleph 5 boards also .. ill post a pic tomorrow..

jason
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Old 19th July 2002, 10:19 PM   #8
sam9 is offline sam9  United States
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Default Suggest you read this

Look at www.rane.com/pdf/groundin.pdf

Until this article was pointed out to me I though XLR connectors were just a better way to connect equipment. They are but its not that simple. The author maintaind there are numerous ways manufactureers implement XLR connectors but only one of them is correct. Unfortunately, the one right method is not so common.
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Old 21st July 2002, 03:18 PM   #9
djk is offline djk
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"NEVER short pins to turn a balanced output into an unbalanced output."
With true balanced outputs you can short either pin 2 or 3 to ground. The voltage will double, and the gain remain unchanged, just like it would with a transformer balanced output. An example of this would be the Madisound electronic crossover. With pseudo balanced outputs you can loose 6dB of gain, or the whole signal ! The Rane electronic crossovers are an example of a pseudo balanced output.
Older equipment had pin 3 'hot', newer equipment has pin 2 as 'hot'. Consult the owners manual to be sure.
Use pin 2 'hot' (non-inverting or +) for new construction.
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Old 21st July 2002, 05:46 PM   #10
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djk,

I stand by my original post, never short one of your (+ or -) outputs to ground. In the case of the most common 3 pin XLR usage;

Pin 1: Gnd.
Pin 2: Non-inverting. AKA High, "+," plus or hot
Pin 3: Inverting. AKA Low, "-," minus or low

MY Balanced to Unbalanced configuration:
XLR -> RCA
Pin 1 -> RCA Ground
Pin 2 -> Hot or RCA center pin
Pin 3 -> Lift

I assume what you mean:

XLR -> RCA
Pin 1 -> Lift
Pin 2 -> Hot or RCA center pin
Pin 3 -> RCA Ground

That would probably work. You would get the extra gain you mentioned. It would make your system too prone to ground loops and other sources of noise. Throw in a patchbay where you try to mix and match balanced and unbalanced, watch out.

My first suggestion is the scheme that is standard practice for proffesional audio and video applications. Add in that the equipment most likely to be used in the above example will have more than enough gain, you won't miss the extra 6dB lost in your example.

Aud_Mot
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