"Balanced" Inputs and Outputs

[Chris D]

Okay, all... I feel silly asking this, but I'd just be foolish to let my longstanding ignorance go any longer on this question:

What exactly are "balanced" inputs and outputs? I assume there's more to it than just a different connector. How are they different?




CHRIS
Luke: "Hey, I'm not such a bad pilot myself, you know"

[David Meek]

From another "I'm not sure about this" kinda guy, I can say two things about balanced connectors:

1) They generally give you better quality sound
2) They generally raise the price of a component a good bit over the same unit without them

C'mon poobahs, where are you? Enlighten us. :




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[Kevin P]

Ok, I'll take a stab at it:

Balanced connectors have three conductors, two for the signal and one for the shield/ground. In essence the signal ground is separated from the chassis/shield ground, resulting in better noise/RFI rejection. In a pro environment (stage, studio, etc.) this is important since the cable runs are longer and there are lots of sources of RFI. Balanced connectors are usually XLR, which is a more robust connector than RCA.

Unbalanced basically means there's only one signal wire and a ground, which is also connected to the shield. These are the common RCA connectors used in home gear.

For home use, there's little difference in performance between balanced and unbalanced. Also, a lot of balanced home (and pro gear for that matter) can operate in a "quasi-balanced" mode where the grounds are still connected but isolated, which makes it possible to connect unbalanced gear to balanced gear. The BFD is a good example of this. It can be connected with a half RCA half XLR cable with no ill effects.

KJP




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[Brandon B]

To embellish:

The two signal lines in the balanced cable carry the signal 180 degrees out of phase with each other, one the original signal and the other flipped. Any noise or interference picked up by the lines will be in phase on both lines. When you reverse the flipped signal and add it to the original, the now-out-of-phase copy of the noise cancels itself.

Then there is the matter of true balanced components, where the audio signal path is fully duplicated throughout the entire component (obviously expensive and not usually found in components untuil you get to true top end stuff, like Ayre, etc.).

BB

[brucek]

chris,

I'll give you my quick take on this subject.

Balanced connections will provide superior isolation against external interference and will reject any noise that may jump a ride on an interconnect cable from any number of sources. Radio Frequency interference (RF), noise from dimmers or fluorescent lighting, AM/FM radio transmissions and lots more can end up interfering with your audio signal.

Very basically, balanced outputs use three wires instead of the two used in unbalanced interfaces (or single ended as it's known). Generally they use an XLR connector instead of the 'RCA' connector you're used to having on your system. Balanced connections will run higher levels over the line compared to single ended.

One of the three wires is signal ground, the same as you're use to in RCA single ended cables.
The other two wires carry the audio signal, each being 180 degrees out of phase from each other, like a mirror image. These two signals usually come from matched op amps, transformers, or a differential amplifier in various configurations - one amp which is inverting and one which is a non-inverting amp. You may call these two signals plus and minus.

When the plus and minus signals arrive at the receiving end they travel into a 'difference' receiver which obviously only allows signals that are 'different' to pass.
The audio signal is completely 'different' because it's out of phase and therefore passes easily through the receiver.

Now here's the beauty of this arrangement. If there is noise picked up on this balanced XLR cable in its travel from pre-amp output to amplifier input, then that noise is picked up equally on both the 'plus' and 'minus' wires. Because these two signals are the 'same' they are rejected by the difference amp. This is known as common-mode rejection you may have heard of.
So, any noise is cancelled and any audio signal is freely passed. Beautiful arrangement.

In a single ended arrangement, noise is picked up on the single audio wire with reference to ground and is then amplified. Yuk.

This sort of arrangement has to be well done with matching input impedances and high quality components because as you can see, there is a lot of chance for distortion in the difference amp if it isn't a good one. If one channel handles the signal differently than the other, then you can introduce distortion in the signal. Today, usually single chips take care of all this rather nicely though. Even so, you usually see these types of inputs and outputs only on upper end equipment.

Generally, balanced connections are a must in a recording studio where you have miles of cables criss-crossing each other. It would be a disaster to use single ended in these applications. But in any case, they are always a recipe to have a quieter system. Running long interconnects is a good reason to use balanced if you have it available. But, at home with our one meter cables and fanatical placement of each cable, I wouldn't get too exited about balanced connections (good as they are).

brucek

[Lex]

About the only thing left to discuss, is the differences in True balanced, and standard xlr connections. I can't profess to be the expert here, in fact, I was like a sponge trying to soak up the great info these guys posted here.

I can tell you that standard xlr or balanced works exactly like described. But true balanced, does work a little differently, as the shield (if present), is only connected at one end (output end) on a true balanced configuration. But it's been said you can try it both ways, connected at output, or at input. I'd like desperately to fully understand this difference. I do know, you only find true balanced on ultra-high end equipment. I've only had a couple of customers ask for true balanced. I can tell you, that it does work, you don't have to have all 3 pins connected on all XLR connections. My own gear is true balanced, so I've heard this work with my own ears. Determining a distinction in the sound, I haven't.

Lex




Cable Guy DVD Collection

[Chris D]

Wow... more info than I could have hoped for on this. Thanks! Interesting subject.




CHRIS
Luke: "Hey, I'm not such a bad pilot myself, you know"

[Lex]

That's right Chris, on some forums, they might say, umm, those are the big fat black connectors on cables. uhh, does that help ya?

But not here, here you get the goods! B:

(The preceding was perhaps an exaduration of actual events. But we still like to make ourselves feel good sometimes, even if at others expense, lol.) :LOL:

Lex




Cable Guy DVD Collection