What's the benefit of a balanced floating line driver anyhow?

[Edmond Stuart]

-29dB output CMRR as you define it, roughly means that the output impedance of one leg is 10 Ohm higher, at least at the frequency that you used for your measurement.
[..]
Hans

Hi Hans,

No, it's not (necessarily) 10 Ohms higher.
A made a mistake by dropping the wrong schematic to measure the CMRR . That one was according to the called "BBC method". My apologies for the confusion.
Instead, I measured (read: simulated) the CMRR differently by looking at the "leakage factor" from a common mode signal (imposed on one of the outputs) into the differential output voltage. This happens to be the same as the ratio between Zo with respect to ground and the common mode Zo, being 49 respectively 1400 Ohms (hence 29dB). IMHO, this is a better figure of merit to quantify the "buoyancy" of a floating driver.

Regarding your last comment, that was exactly my point.

Cheers, E.

 

[rdf]

What's the benefit of a balanced floating line driver, provided that it is connected to a balanced line receiver?

Maximum possible control over the signal current flow between multiple interconnected devices. In standard unbalanced 'hifi' circuits interconnected devices will see low impedance between them, potentially through their power connections as well. How important is it? Dunno...

 

[jan.didden]

Y
So I still wonder what is gained with quasi (read: more or less) floating outputs.

BTW, in my first post I should have clearly stated that I meant quasi (thus electronically achieved) floating outputs, thus not by means of a transformer. Sorry guys for any confusion. 😱

Cheers, E.

Edmond, just for my own clarification: you are talking about a balanced connection where on the source side one phase is actively driven and the other impedance-matched to a passive reference like ground?

Jan

 

[Edmond Stuart]

Hi Jan,

No, I mean a fully balanced/symmetrical connection, i.e. both legs active, thus not one of them tied to gnd.

Cheers, E.