What are "true" balanced connectors


Hello All,

I am considering buying an Odyssey Stratos amplifier. I noticed it is described as having XLR (bridged) inputs

My very limited knowledge of balanced circuits is telling me this is not a "true" balanced configuration...

Am I right on this?

Any help will be much appreciated

Jim
luynes
PM Ralph Karsten (atmasphere).
He will set you straight. His products are truly balanced according to the specifications.

Bob
Well Bob, I wasn't looking for a "commercial"...

All I need to know is what an XLR bridged input means

Jim
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.


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. :)

The Odyssey Stratos amp is not a true balanced amp.  The inputs are there strictly for convenience and if you look inside, you will see they are connected to the RCA jacks.
Balanced inputs are not defined by whether two channels of a stereo amplifier are bridged or not. The concept of balanced inputs is that the input is a differential receiver, where the signals on each wire are equal and opposite polarity. Thr differential receiver subtracts these two signals to reproduce the original signal. The benefit over single ended signalling is noise rejection. If the cable is exposed to a source of electrical noise, that noise will be induced with the same polarity and amplitude on both signal bearing conductors, and since the differential receiver subtracts the signal on both conductors, it cancels out the noise, which is common on both sides of the differential pair. This is how the term “common mode noise rejection” was coined. 

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.
Each signal is actually referrenced to ground, but the differential receiver only uses the two signal bearing wires to convert the differential signal back to single ended for further handling. 
Each signal is actually referrenced to ground,

Not universally true.

Best,
E


@luynes 
You wanted the right answer and I told you.
That Ralph is a designer and not an armchair EE, isn't the issue.
Now you have conflicting answers, and not the definitive one,
I guess you'll never know for sure. Good Luck
B

Thank you Erik!

YOU gave me exactly the specific answer I needed

Thank you Sleepwalker.

You gave me an answer to the broader question regarding what a balanced connection is. That your explanation may not correlate 100% with Erik's is irrelevant to me (beyond my pay grade!) ;-)

No Bob, you did not give me anything close to the "right answer" - Read my question(s) - then read your original reply -  then tell me if you still think you gave me the "right answer." I do not have conflicting answers. I now know EXACTLY what I needed to know about the Odyssey amp I was considering to buy...

I wish members would not use this very useful resource as a platform for "sales pitches"...
Sorry stereo5!

I also need to thank you for giving me a clear and direct answer to my original question!
@erik_squires 

 Each signal is actually referrenced to ground,

Not universally true.
 
I should have said referenced to -signal- ground. That is the balance point that both signals share in common. 

Sleepwalker:

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

Best,
E


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


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
@luynes
You don’t have a clue as to what the ’balanced’ spec is.  This is evident in your original post.
I just pointed you to a person who has experience with Balanced Topology. 
That you find that unacceptable is your problem.
And, if you wanted to know if the amp was truly balanced, why not contact the manufacturer directly, instead of soliciting guesses from those that don't even own the unit?
B
@erik_squires 


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

Best,
E


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

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 (-).
The plus and minus halves of the signal can float with respect to ground.  Or not.