What are XLR connections??

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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.
 

SteveG

Account Disabled
2002-01-07 7:20 pm
Newton Falls, Ohio
<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.
 
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.
 
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.
 

djk

R.I.P
2001-02-04 4:23 am
USA
"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.
 
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
 

djk

R.I.P
2001-02-04 4:23 am
USA
"Nelson Pass: And so when using RCA connectors in parallel with XLR, you short pin 3 to 1, grounding the negative input. "
"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. "
Actually the gain would remain unchanged from a balanced connection.
"MY Balanced to Unbalanced configuration:
XLR -> RCA
Pin 1 -> RCA Ground
Pin 2 -> Hot or RCA center pin
Pin 3 -> Lift"
This would cause a loss of 6dB from a balanced connection.
"Throw in a patchbay where you try to mix and match balanced and unbalanced, watch out."
I agree, your method for hooking Pin 1 -> RCA Ground cannot get rid of a ground loop. Electronically balanced inputs cannot get rid of a ground loop. Only a transformer can provide galvanic isolation. Or an optocoupler.
What gives the best bang for the buck is cross coupled electronically balanced outputs with transformer inputs.
"My first suggestion is the scheme that is standard practice for proffesional audio and video applications. "
I agree, 99% of those guys don't know what they are doing. Electronically balanced inputs using 1% resistors only have 40dB CMRR. Even if you trim the low frequency CMRR with a pot, and trim the high frequencies with a cap, the transformer will perform better. You will still have hum because of the input off-set current of the op-amps and the high end will sound like an electric shaver if you are in a high RF environment. If you really want it clean and quiet, use a transformer. The ground loop issue can be fixed with a transformer at either end, but the RF can only be fixed at the input.
 
djk,

Your quote from Nelson Pass pertains to INPUTS. This goes back to my original post: Outputs and inputs and should be treated differently.

There are other methods to interface unlike inputs and outputs. The 3 choices I know of, using a balancing bridge type circuit using passive components, using active electronics, and the use of transformers. Depending on your budget would dictate which method to use. For most readers of this forum, I suggest using the correct lift or ground method.

The other parts of your answer (1% restistors, transformers, etc) do not offer anything to contradict my original post: outputs and inputs are different. CMMR and trimming has nothing to with it is a bad idea to short amplifier outputs.

Aud_Mot
 
Thats a very good question. We don´t really take time to think what everything mean.
RCA is also called Cinch or RCA phono, I think it comes from the brand name RCA that used thiese lugs for phonographs, so there you go RCA Phono plugs.

XLR means ground (X for short), Left, Right. Thats what they were used for before stereo came a long. They are also known as Canon from the brand that made them popular.
 

djk

R.I.P
2001-02-04 4:23 am
USA
"it is a bad idea to short amplifier outputs."
I agree, and I'm sorry you don't understand the issues involved here. If the outputs are truely balanced you can connect either output to ground and the difference between the two will not change. I gave examples of both properly and improperly designed equipment.
 
I can't resist...

djk,

I looked at the link you posted above.

It is a schematic for a device with a balanced input and 2 balanced outputs. Where (or how) does this schematic that it is OK to short outputs?

Looking at the schematic provided, I would never short pin 2 to pin 1 or short pin 3 to pin 1.

If I wnated to fid this device to an unbalanced input, pin 2 to hot (or "+"), pin 1 to gnd, Pin 3 open, no connection.

Regards,

Aud_Mot
 
Ummm...... REALLY !

I repeat you can´t short any input pins when they have signal.
On the IC101 in the frontend, if you short 2 or 3 of the XLR in the input when these pins have signal from a previous stage you will short the output of that stage.

If you short the outputs of this device, the opamps are gonna have a hard time driving those 100 Ohm resistors.

Using a transormer is a whole different thing. When you use a trafo and you short one side nothing happens to the primary because it is still floating. Its isolated from the secondary.

If you have a single ended signal in the input you feed it into 2 or 3, depending on what polarity you want, and the other then you can short to pin 1 without any problem.
 
I would not say it is OK to short part of a transformer secondary. At least not in most cases.

Some variables: the design of the transformer, circuit driving the primary, how dynamic the of a load the other phase is.

Loading it with a resistive load might be OK.

Letting a phase "flap in the wind" with an infinate (no connection) load. Might work.

Secondaries reflect thier load back into the primary and affect what the primary driving circuit "sees." Some sort of symetery of loading between phases might be needed.

I do not know of any hard rules when it comes to transformers, but shorting a phase of secondary would be last on my list. Mainly because I do not see a need for it.

Aud_Mot