Balanced versus Unbalanced Output

[skibum]

Hello,

I am trying to understand the difference between balanced and unbalanced signals.

I think I have this part right:

Balance signals do not use ground for the return signal (like unbalanced do).

In a balance signal one line is the signal, the second line is a copy of that signal but inverted and the 3rd line is ground.

I can understand how you can do that using an Opamp. But I also read about doing that with a Transformer. Not sure how that would work. Can anyone explain that to me?

I see on some DAC chips (like the PCMxxxx) there is a way to invert the output data. Is that what that function is there for?

I am working on building my first DAC and I am using a TDA1543. I would like to have balanced and unbalanced outputs.

Using an opamp to invert the output signal seems like the easiest option to obtain a balanced output but I really do not want an opamp in my output.

What other options are available to me?

Any suggested reading out there for me?

Thanks,

Skibum

[Speedskater]

That third line which is XLR pin #1 is chassis not audio ground, it is not part of the of the balanced circuit. The signal is between the other two lines which are symmetrical about audio ground.

Rod Elliott has two nice papers:

Balanced Interfaces
Balanced Line Driver with Floating Output

[qusp]

in a properly balanced output there really isnt a signal ground; as this would imply some part of the signal being referenced to ground, which it isnt. The only ground in a fully balanced build is power supply ground, which of course is ultimately the reference for all.

[DF96]

Why do you want balanced output? This only brings advantages if you have long cable runs.

A transformer can invert a signal just by swapping the output connections.