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Unbalanced vs. balanced lines



Unbalanced lines
Unbalanced signal lines are characterized by the fact that the cable and connectors use only two conductors, a center conductor surrounded by a shield. Examples of unbalanced wiring are found in tip/sleeve 1ž4-in guitar cords or the cables used with many CD players and tape decks which terminate with RCA phono type connectors.

In an unbalanced configuration, the shield surrounds a single center conductor. (See Example 1, below) The shield stays at a constant ground potential (as it is connected to ground when plugged into equipment) while the signal voltage in the center conductor varies in a positive and negative manner relative to it.



Example 1
Because the shield completely surrounds the center or “hot” conductor and is connected to ground, it intercepts most of the electrical interference encountered by the cable and passes it away harmlessly to ground.


Very little or no interference will be able to reach the center conductor where it would interact with desired signal. Because the shield is one of the two conductors required to complete the circuit, it must always be connected at both ends of the cable. This may set up a condition called a "ground loop" that sometimes produces hum when the grounds of different pieces of electrical equipment are connected to each other.

Note: A shield that consists of wire that is braided instead of just spun around the center in a spiral will provide superior coverage. Spiral shield is less expensive but can spread apart when the cable is flexed, exposing the center conductor to unwanted hum and buzz.

If outside electrical interference does manage to penetrate the shield, it will mix with the desired signal that is present in the center conductor and be amplified right along with it as noise, buzz, etc. This might not be a huge problem with electric guitars, tape decks and unbalanced microphones when the cable is only a few feet long.

But in environments containing a lot of interference or when an unbalanced signal is sent long distances, such as down a snake, it will become more and more susceptible to unwanted interference. This problem can be alleviated with the use of balanced lines.


Balanced lines
Balanced lines are characterized by the fact that there are two center conductors for the signal, surrounded by a shield. (See Example 2, below) This shield is connected to ground like unbalanced lines but it is not required as one of the signal conductors. Its sole purpose is to provide its line of defense against unwanted interference.



Example 2
A benefit of this configuration is that the shield only needs to be connected to ground at one end of the cable in order for it to work. Having this ground disconnected or “lifted” at one end can eliminate the ground loop problem discussed in the previous section on unbalanced lines.


Exception: the ground must be connected at both ends when transmitting phantom power. Phantom power will not work if the ground is lifted at either end.

The two center conductors of a balanced line act as the sole conduit for the signal and operate in a “push-pull” manner. That is, as the voltage on one conductor becomes positive, the voltage on the other conductor becomes negative by the same amount and at the same time (and vice-versa).

So at any point in time, both conductors are equal in voltage but opposite in polarity. The receiving circuit that processes this balanced signal is called a differential amplifier and this opposing polarity of the voltages on the conductors is essential for its operation.

Now, if any unwanted electrical interference manages to penetrate the outside shield, it will interact with both center conductors equally but with the same polarity. The effect in the differential amplifier is that these same polarity voltages aren't processed and effectively cancel each other out - the noise disappears.

This ability of balanced lines to reject noise and interference makes them popular when it is necessary to send signals over long distances.

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by Al Keltz

I've been sound teching for about 8 years, and that's the most concise and informative description of Bal vs Unbal that I've ever read. Sweet post m8.
-Rob

Always need ballanced cos less distortion more quality :S

I've never really been sold by the whole balanced/unbalanced thing. I got a Delta 1010 soundcard with 10 unbalanced in/outs, with 2 hardware reverbs, 3 hardware synths, all running into an unbalanced patchbay. Alledgedly, unbalanced should introduce a lot of noise, especially with all the unbalanced cable running into my unbalanced patchbay, and then into mymonitors, again using unbalanced cables. Recording even the true analog synth I have, the noise hovers at approximatley -80 to -90db, which is more than quite enough Each to their own I suppose, but unless I start to hear the noise, I'm not gonna shell out any £££ for balanced gear


Edit: the above is assuming u record at a decent volume. Otherwise u will get noise, and it sounds gash

Thanks fgp303! Always wondered about that! hehe. Extremely helpful!

so thats what the difference is
thanks!

Working in a music store, you wouldn't BELIEVE how many people I get asking "how do I go from RCA to XLR?" And then I get to cringe while I ask them "WHY?!?!?! It's an exercise in futility!"

there is no unbalanced boogie man. using unbalanced cables is fine. the sound quality is not inferior honestly it's simply a grounding issue. It's like saying p*rn power outlets give 'dirtier' electricity than p*rn. it's the wrong adjective.

not disagreeing with the tut.... btw

Really interesting post. Thank you

Thanks fgp303 ! Very interesting topic!

now it all makes sense! cheers for that!

good tutorial thanks

Very informative - thanks.

lots of useful information here
cheers

really informative, i had no idea what it meant from the title but now it makes some sense