Balanced to Unbalanced

[Lambda]

Edit:
C and E are technically the same as D with Extreme Values for the Resistor

A is a Common and calld "Impedance balanced"

Q. How is impedance balancing audio different from normal balancing?

Would impedance balanced and electronic balanced audio provide exactly the same noise reduction as regular symmetrical...

www.soundonsound.com

Q. How do balanced signals work in audio gear?

Could you please explain why audio gear uses balanced signals and how they work?

www.soundonsound.com

B is uncommon directly but might happen if A is used wit a Polarity revers switch or cable (common on X Over or Activ sub/monitors.)

Here is a matrix of typical balanced output and receiver schematics.
This is a highly simplified representation of potential implementations. What is shown here as a transformer-based output could also be implemented electronically. The functionality would be similar, but the transformer version is easier to visualize.

Particularly when implementing this electronically with op-amps, extra care must be taken, as the common-mode voltage will be limited and could introduce additional distortion.

Connections labeled as "Might work" depend on whether the unbalanced gear is truly floating or if ground loop voltages and currents are present.

"Potentially unsafe" means that the connection could short out the balanced output, potentially causing damage.

 

[Devnull]

The noise cancelling properties of a balanced circuit is because the receiver responds ONLY to the difference between the two legs, and the interfering signal is deemed to be equally in both legs so cancels out in the receiver. For this to happen, the source and the receiver have to be balanced, as well as differential. By 'balanced' this means that the impedances and capacitances to signal and to ground have to be identical so that interference genuinely induces equally into both legs, to be cancelled in the receiver.
Now in reality, nothing is ever perfectly balanced, capacitances and impedances will vary, so the cancellation of interference will be limited. Nevertheless, this 'Common-Mode rejection' will typically be at least 60dB especially at audio frequencies, so that represents a pretty impressive reduction in induced interference. There is also a limit to how big the common-mode interfering signal is, as semiconductor input stages won't handle high amounts of interference. Fortunately, there's rarely need for very high common-mode voltage capability, but one can occasionally get caught out. It's another benefit of transformer balancing as these can take hundreds of volts of common-mode without damage, if designed to do so.

A good explanation but I think you left out a critical piece of information. To have common mode rejection the signal conductors must be coupled pair.

 

[Speedskater]

The chart in post #21 looks weird.
The first two, don't look like balanced outputs.
The last 3 have nonexistent ground terminals.

 

[Lambda]

The first two, don't look like balanced outputs.

Tarts the Point. You Never know how a manufacturer implements a "Blalanced" Output (and ASR is not testing it)

Many Devices only have what some call "Impedance Balanced" outputs meaning only one output is actively driven and the other and the oter one is Passive with the same impedance
Some even don't care about this and just ground it.

Nevertheless you get some CMRR

Q. How is impedance balancing audio different from normal balancing?

Would impedance balanced and electronic balanced audio provide exactly the same noise reduction as regular symmetrical...

www.soundonsound.com

Q. How do balanced signals work in audio gear?

Could you please explain why audio gear uses balanced signals and how they work?

www.soundonsound.com

If you absolutely can not have a transformer:

Uses at least 2 resistors in an passive adapter cable.
This would in nose cases present a load bigger then( 300ohm || Unbalanced input impedance ) to the XLR output and would therefore be fairly save for your source as long as you don’t have excessive ground loop voltages.

The first version with the voltage divider gives Consistent -6dB.
the second version is more dependent on the specific output

Other helpful links

Signal interconnections

Signal interconnections

www.paformusic.org.uk

Balanced I/O

Balanced drivers and receivers - the stuff no-one tells you

sound-au.com

Q. What is the ‘Ground Compensated’ output on my mixer?

SOS Technical Editor Hugh Robjohns replies.

www.soundonsound.com

Q. How do balanced signals work in audio gear?

Could you please explain why audio gear uses balanced signals and how they work?

www.soundonsound.com

Q. How is impedance balancing audio different from normal balancing?

Would impedance balanced and electronic balanced audio provide exactly the same noise reduction as regular symmetrical...

www.soundonsound.com

Concepts in Audio Signal Transmission: Part IV

image credits: eatuppizza Part IV: Balanced Signal Transmission What are balanced inputs and outputs, how do they operate, and does it really matter for signal quality? This post will review commo…

naiant.com

Balanced Line Technology

The Douglas Self Site. audio amplifiers, genealogy.

www.douglas-self.com

Differential, Single-Ended, Balanced, Unbalanced, and all that jazz...

I posted this picture over on WBF in the middle of a long semi-fruitful discussion on the benefits and drawbacks of differential operation. Ken Newton suggested sticking with the accepted technical definitions and distinction among differential vs. single-ended and balanced vs. unbalanced that I...

www.audiosciencereview.com

Impedance balancing with active drive vs. Transformer coupled output

Guide on the design principles of output stages for condenser microphones. We address the advantages and draws of using transformers and more.

www.dpamicrophones.com

 

[sergeauckland]

A good explanation but I think you left out a critical piece of information. To have common mode rejection the signal conductors must be coupled pair.

That's inherent in being balanced, i.e all impedances on the two conductors have to be equal. In practice that's most easily accomplished in a twisted pair. It doesn't have to be like that, as originally telephone cables were balanced over long distances without being closely coupled, but I agree, it's a lot easier ro ensure balance if they are.

S

 

[Devnull]

That's inherent in being balanced, i.e all impedances on the two conductors have to be equal. In practice that's most easily accomplished in a twisted pair. It doesn't have to be like that, as originally telephone cables were balanced over long distances without being closely coupled, but I agree, it's a lot easier ro ensure balance if they are.

S

Maybe it's the engineer in me coming out but unless it's stated as coupled/twisted pair the worst case scenario has to be assumed which is 2 uncoupled conductors. Doesn't matter if it's cables between equipment or conductors on a circuit board. The vast majority of TDR, BER and scopes I've used had balanced inputs/outputs that used single conductor coax cables. V+ and V- on two individual cables going into 2 individual physical connections.

As an aside, why has the audio industry bastardized basic electrical engineering terms and concepts? Why are single ended signals referred to as unbalanced? Why are signals referred to as balanced when they most likely mean symmetrical? Why do people assume that in theory an XLR is a balanced symmetrical signal?

 

[Clint Goss]

Thanks ALL for this assistance!

My writeup:
XLR outputs might carry a digital AES/EBU signal (which handles two channels bi-directionally) ...

AES-EBU is not bi-directional.

I got this from a Reddit discussion at

https://www.reddit.com/r/livesound/comments/17q75nw/whats_the_difference_between_aes_cable_and

:

LittleContext: AES/EBU also carries two channels instead of one, and can do so bi-directionally.

... and later ...

guP1on: And riedel performer does 2 ch bidirectional aes3 over xlr

... but this info is superfluous to the purpose of my writeup, so I'll just nix it ... THANKS for that!

A Balanced signal only requires two conductors. The screen is optional at line level, generally necessary on microphone circuits, or very long line level cables but not necessary at line level for shorter circuits or for digital signals.

Thanks. Got it ... I am changing the text to be technically correct, and also align with the common usage for audio:

New text: A two-conductor TS socket does not typically output a balanced signal, since balanced signals are typically transmitted on three conductors.

Transformer Balanced Outputs. Don't forget centre tapped transformer balanced outputs.

Ugh. More complexity. I gotta research this ...

a common misunderstanding of how the noise cancelling works.

Yea, I totally messed that up. Updated the doc to talk about CMR separately, and also ...

To have common mode rejection the signal conductors must be coupled pair.

.. I now mention the use of "typical" twisted-pair cables.

Q. How is impedance balancing audio different from normal balancing?

Would impedance balanced and electronic balanced audio provide exactly the same noise reduction as regular symmetrical...

www.soundonsound.com

Q. How do balanced signals work in audio gear?

Could you please explain why audio gear uses balanced signals and how they work?

www.soundonsound.com

Excellent sources! I've added them. I've also added your citation and a brief mention of Ground Compensated outputs.

Again ... Thanks ALL for this assistance!

 

[Clint Goss]

Here's an updated version, with the suggestions incorporated as well as some general cleanup and corrections:

Balanced to Unbalanced Audio Connections - Feb 28 Second Draft Version

 

[babadono]

I must chime in here...In the first two rows, are we calling them A an B? the driven signal must have an equal impedance to the one that is grounded. The grounded signal should be through its impedance matching network (usually just a resistor) to signal ground. Pin 1 of the XLR connector should be to chassis ground. And then cables connecting balanced to unbalanced equipment should keep chassis of the balanced equipment off the conductor that is carrying the signal ground of the unbalanced equipment. 99.9 % of the time it is the least desirable interconnect to connect pin 1 and 3 of an XLR connector together.

 

[Clint Goss]

In the first two rows, are we calling them A an B?

The "A and B" in this discussion are back to my original image I posted - both shielded coax cables with A floating pin 3 and B tying Pin 3 to ground Pin 1 at the source end.

In the PDF I am developing, I am distinguishing between a QnD (Quick and Dirty) approach that does well-enough (e.g. at a gig) and a more involved but better approach you might use in a studio. I am trying to get the benefit of a cross-coupled source (no loss of 6dB) and other benefits from a more careful wiring.

 

[Lambda]

the driven signal must have an equal impedance to the one that is grounded.

i would say "the grounded signal must have an equal impedance to the one that is driven"
For simplicity it is not shown but you can and must assume an impedance for the driver. and thats why the the grounded signal has a resistor as impedance matching network

 

[sam_adams]

In the PDF I am developing,

You should study this paper:

Bill Whitlock - Balanced Lines in Audio Systems: Fact, Fiction, and Transformers (Google search—top hits)

I will add, that if you are concerned about signal compatibility when doing gigs, transformer-based interfaces are going to save you a lot of grief and blown equipment when you cannot guarantee that what you will be connecting to is compatible with the devices that you have.

 

[babadono]

The "A and B" in this discussion are back to my original image I posted

Sorry I was referring to the "chart" at the top of this second page posted by Lambda.

 

[Sjkrabbe]

I frequently need to send a balanced XLR signal to an unbalanced destination. This needs to be done on the fly in my performance rig (Ableton Push 3 and a Sylphyo wind controller rendered through several hardware modules), depending on the house system at the venue and the gear of other performers that are running through my rig.

My major confusion is: How do I tell whether to tie pin 1 to pin 3 at the XLR source end?

Some manuals I have warn that doing it wrong can cause distortion or even damage the output stage of the source device. An example of this warning is in the manual for my RME Babyface Pro FS:



OK, so that implies that if the manual says that the XLR output is servo-balanced, then Pin 1 should be tied to Pin 3.

All other gear I have encountered, at best, describes the output stage variously as:

• Cross-coupled
• Transformer-balanced
• Active
• Passive
• Electronically balanced
• Servo-balanced

... or are simply silent on the design of the output stage (maybe this is "none of the above"??)

Could someone identify, for the above terms (and maybe any others that I've missed), whether to tie Pin 1 to Pin 3 at the source end??

Also: What would you suggest if the documentation is silent on the design of the output stage?

For reference, I think these are my choices for wiring adapter cables:

View attachment 430226

As I understand it, Case C, using a twisted pair cable and routing the negative / cold / Pin 3 to the shield of the destination will get at least part of the Common Mode Rejection (20-30dB) that a fully balanced connection would (60dB). I am hoping I could use Case C in any situation where Pin 3 can be tied to Pin 1.

The main reference for this is: Rane Technical Staff, 2015, Rane Note #110, Sound System Interconnection, Figure 4, Cases 3 and 5.

Thanks for any feedback you could provide!

I always do this - in stead of shorting pin 1 and 3 - I put a 47 k ohm resistor in between them - So it is not shorted and it is not floating. Since I havent seen this solution elsewhere, I wonder if there is something wrong in doing this? To me it seems to work, and soundwise I haven´t heard anything wrong

 

[sergeauckland]

In practice, pin 3 is still floating, as 47k is pretty much an open circuit compared with the output impedance of the XLR output.

S

 

[Sjkrabbe]

In practice, pin 3 is still floating, as 47k is pretty much an open circuit compared with the output impedance of the XLR output.

S

thanks - but I guess this prevents an eventual "singing" output of a more unstable output stage, if badly designed??

 

[babadono]

I always do this - in stead of shorting pin 1 and 3 - I put a 47 k ohm resistor in between them - So it is not shorted and it is not floating. Since I havent seen this solution elsewhere, I wonder if there is something wrong in doing this? To me it seems to work, and soundwise I haven´t heard anything wrongView attachment 434337

Like all these situations..it depends...on output topology. I would always use twisted shielded pair wire. YMMV

 

[babadono]

In practice, pin 3 is still floating, as 47k is pretty much an open circuit compared with the output impedance of the XLR output.

S

But you have just given another connection between signal and chassis ground...again dependent on output topology.

 

[Lambda]

But you have just given another connection between signal and chassis ground...again dependent on output topology.

https://www.audiosciencereview.com/...anced-to-unbalanced.60943/page-2#post-2238167 has most output topologies.
What output topology are you missing? And with what output topology would a ~600Ω resistance from pin 1 to 3 cause problems?
As shown in #24, this would work with all outputs I can think of, with the exception of an impedance-balanced signal where only the negative line is driven.

 

[sam_adams]

https://www.audiosciencereview.com/...anced-to-unbalanced.60943/page-2#post-2238167 has most output topologies.

It would be most helpful to our viewers at home if you indicated the source of those images in the linked post.