What are "true" balanced connectors

Galvanic isolation isn’t a requirement for a balanced circuit.

True.

The transformer output, unless it is center tapped, is only differential, which is where the value is anyways as far as common mode noise rejection is concerned.

Yes, but it proves my point: The + and - are not necessarily referenced to ground. This is something which has just come about because we now use inverting op amps to drive the (-).

Balanced means that the + and - amplitudes of the signal are referenced equally to ground. 

Not a requirement when using transformers which are not center tapped, as was the case for many decades. In the old days, you'd use a single amplifier output, to drive one side of a transformer, and the resulting output had no reference to ground, only to each other.

It is only in modern times that we can use multiple op amp stages as the sender and receiver. And still, the receiver does not rely on any ground reference.

Best,
E

Sleepwalker:

Balanced signals used to be transmitted by transformer outputs and inputs which were galvanically isolated.

Best,
E

Each signal is actually referrenced to ground,

Not universally true.

Best,
E

sleepwalker is correct.
A "true balanced input" means the + and minus of the input are differential, and not referenced to ground.

A "true balanced" amp means that both outputs are driven. Most amps only drive the red output.

The Parasound A21 as well as several of the Yamaha P2x00 amps from way back are examples of amps with XLR inputs, but they are not balanced.

By comparison, a true balanced situation is when the (+) and (-) and ground are separate, and the (-) carries the opposite of the (+) signal.

By reading both the (+) and (-) and summing them electronically you can cancel out noise picked up along the way.


This is not the same as having a truly balanced preamp or amplifier, that's a whole other story. :)

XLR bridged : Same electrical properties as an RCA connector. The XLR connector is there for convenience only.

It will work, but you loose the fantastic noise cancellation possible by a true XLR cable.

This "bridge" is done by shorting the (-) and ground pins together.