ProSoundWeb Community

Please login or register.

Login with username, password and session length
Advanced search  

Pages: [1]   Go Down

Author Topic: How to test XLR output is truely balanced?  (Read 746 times)

Peter Wu

  • Newbie
  • *
  • Offline Offline
  • Posts: 3
How to test XLR output is truely balanced?
« on: January 12, 2021, 08:28:31 pm »

Given an XLR balanced audio output, how can you test whether it is truely balanced output or not?

If it's an output from a mixer it most likely is truely balanced. But if it's output from a mic or some adapters (e.g. 1/8" to XLR adapter), I'm not so sure and would like to be.

Logged

Scott Helmke

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 1656
Re: How to test XLR output is truely balanced?
« Reply #1 on: January 12, 2021, 09:30:20 pm »

Use an XLR to 1/4" TRS adapter and plug in a pair of headphones.  If you hear the signal in both ears, then the output is balanced.  If you just hear it in your left ear then it is only "impedance balanced". 
Logged

Kevin Graf

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 337
Re: How to test XLR output is truely balanced?
« Reply #2 on: January 13, 2021, 08:34:32 am »

And just why would an "impedance balanced" output stage not be a balanced output stage?

Bill Whitlock (retired Jensen Transformers) wrote the book chapter on balanced interconnect systems and "passive/impedance balanced" is one of the systems.
Logged
Speedskater

John Roberts {JR}

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 16688
  • Hickory, Mississippi, USA
    • Resotune
Re: How to test XLR output is truely balanced?
« Reply #3 on: January 13, 2021, 09:39:42 am »

Given an XLR balanced audio output, how can you test whether it is truely balanced output or not?

If it's an output from a mixer it most likely is truely balanced. But if it's output from a mic or some adapters (e.g. 1/8" to XLR adapter), I'm not so sure and would like to be.
First we need to agree about a definition of what "truely balanced" means, it can mean different things to different people.

Passive impedance balance is a completely competent modern solution.

Do you have a problem you are trying to resolve, or avoid?

JR
Logged
When in doubt do what's right.

Ivan Beaver

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 9091
  • Atlanta GA
Re: How to test XLR output is truely balanced?
« Reply #4 on: January 13, 2021, 11:49:00 am »

Given an XLR balanced audio output, how can you test whether it is truely balanced output or not?

If it's an output from a mixer it most likely is truely balanced. But if it's output from a mic or some adapters (e.g. 1/8" to XLR adapter), I'm not so sure and would like to be.
As JR says, it depends on what you call "balanced".

It could have differential drivers, or impedance balanced or transformer balanced.  They would all be balanced, but vary in output level, isolation etc.

One test is to put in a sine wave, turn it up a bit.  Measure from pin3 to pin 1 and from pin 2 to pin 1.  If you get a voltage reading each way, then it is truly balanced (not just impedance balanced).  If you only get a voltage reading in one position, it could be balanced, or unbalanced.  Now measure the resistance from that pin (that did not read a voltage) and see if it is around 0 ohm or around 100 ohms.  If it is 100 ohms, then it is impedance balanced.
If it is 0 ohms, then it is unbalanced
Logged
A complex question is easily answered by a simple-easy to understand WRONG answer!

Ivan Beaver
Danley Sound Labs

PHYSICS- NOT FADS!

John Roberts {JR}

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 16688
  • Hickory, Mississippi, USA
    • Resotune
Re: How to test XLR output is truely balanced?
« Reply #5 on: January 13, 2021, 02:05:56 pm »

As JR says, it depends on what you call "balanced".

It could have differential drivers, or impedance balanced or transformer balanced.  They would all be balanced, but vary in output level, isolation etc.

One test is to put in a sine wave, turn it up a bit.  Measure from pin3 to pin 1 and from pin 2 to pin 1.  If you get a voltage reading each way, then it is truly balanced (not just impedance balanced).
I am repeating myself, there is nothing wrong with impedance balanced... and "truly balanced" is not a technical term...

JR
Quote
If you only get a voltage reading in one position, it could be balanced, or unbalanced.  Now measure the resistance from that pin (that did not read a voltage) and see if it is around 0 ohm or around 100 ohms.  If it is 100 ohms, then it is impedance balanced.
If it is 0 ohms, then it is unbalanced
Logged
When in doubt do what's right.

Peter Wu

  • Newbie
  • *
  • Offline Offline
  • Posts: 3
Re: How to test XLR output is truely balanced?
« Reply #6 on: January 13, 2021, 03:31:39 pm »

As JR says, it depends on what you call "balanced".


Sorry for using a non technical term.

For me, truely balanced means if I attach a very long cable between this output and a mixer, it would not pick up noise. Or should I say the noise it pick up would cancel out.

So impedance balance works for me. If I bought (or am given) a new piece of equipment, I want to make sure it won't create noise problem with long cable run before I put it in use.
Logged

John Roberts {JR}

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 16688
  • Hickory, Mississippi, USA
    • Resotune
Re: How to test XLR output is truely balanced?
« Reply #7 on: January 13, 2021, 04:15:05 pm »

Sorry for using a non technical term.
OPs get a pass...
Quote
For me, truely balanced means if I attach a very long cable between this output and a mixer, it would not pick up noise. Or should I say the noise it pick up would cancel out.
Impedance balance with a proper balanced differential receiver should cancel out any common mode noise.
Quote
So impedance balance works for me. If I bought (or am given) a new piece of equipment, I want to make sure it won't create noise problem with long cable run before I put it in use.
In theory there is a slight benefit to having both legs hot due to 6dB more signal but in practice this is not a real concern for anything other than extreme environments.

I can not offer a simple measurement to confirm the balance of a given output, but it is safe to ASSume that most modern XLR outputs are at least impedance balanced since that only cost the manufacturer pennies. 

JR

PS: for TMI back last century I tested the CMRR of some star-quad mic cable by looping it over a fluorescent light fixture...  and comparing it to standard mic cable... It passed with flying colors.
Logged
When in doubt do what's right.

Mike Caldwell

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 1972
  • Covington, Ohio
    • Mike Caldwell Audio Productions
Re: How to test XLR output is truely balanced?
« Reply #8 on: January 13, 2021, 04:49:36 pm »

Sorry for using a non technical term.

For me, truely balanced means if I attach a very long cable between this output and a mixer, it would not pick up noise. Or should I say the noise it pick up would cancel out.

So impedance balance works for me. If I bought (or am given) a new piece of equipment, I want to make sure it won't create noise problem with long cable run before I put it in use.



How long is the "very long" cable?

Steve M Smith

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 3378
  • Isle of Wight - England
Re: How to test XLR output is truely balanced?
« Reply #9 on: January 14, 2021, 02:54:42 am »

For me, truely balanced means if I attach a very long cable between this output and a mixer, it would not pick up noise. Or should I say the noise it pick up would cancel out.

That requires a differential input stage to benefit from the noise cancelling common mode rejection properties of balanced line. The signal does not have to be equal and opposite on both lines, They just have to present the same impedance. The input stage will do what it always does and amplify the difference.

I have some ART DI boxes which work like that. The circuits on pins 2 and 3 are identical, but the input to one of the circuits is grounded whilst the other goes to the input socket. They work fine as the impedance is the same on both output pins.

Now measure the resistance from that pin (that did not read a voltage) and see if it is around 0 ohm or around 100 ohms.  If it is 100 ohms, then it is impedance balanced. If it is 0 ohms, then it is unbalanced

Or it could be actively impedance balanced - see above.


Steve.
« Last Edit: January 14, 2021, 02:59:38 am by Steve M Smith »
Logged

ProSoundWeb Community

Re: How to test XLR output is truely balanced?
« Reply #9 on: January 14, 2021, 02:54:42 am »


Pages: [1]   Go Up
 



Page created in 0.06 seconds with 23 queries.