Balanced and Unbalanced I/O?

M

mbernardo

New member
What does it mean when an input or output jack is "balanced" or "unbalanced"? Will I destroy the equipment if I mismatch the I/O? Does the cable itself make it "balanced" or "unbalanced" or is it the gear connected to the cable?
 
No, I think it'll cause an impedence issue though.

I have one by running unbalanced out of my mixer into the 2 balanced inputs on my 1010lt.
 
mbernardo said:
What does it mean when an input or output jack is "balanced" or "unbalanced"?
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Balancing is a noise reduction/rejection method. The label tells whether that jack has the appropriate circuitry or not.


mbernardo said:
Will I destroy the equipment if I mismatch the I/O?
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Check the manual. Some balanced outputs can be damaged by driving unbalanced inputs unless the cables are wired a specific way. Lots of gear these days can handle either, and will likely be labelled as such. Again, check the manual.


mbernardo said:
Does the cable itself make it "balanced" or "unbalanced" or is it the gear connected to the cable?
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The gear is balanced. The cable is not, but needs to be the correct type for the whole thing to work right. Both pieces need to be balanced as well, or the circuit won't function right.
 
boingoman said:
The gear is balanced. The cable is not, but needs to be the correct type for the whole thing to work right. Both pieces need to be balanced as well, or the circuit won't function right.
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I think perhaps by the strictest definiton, the cable may be balanced. But when it is in the circuit, it becomes secondary. And strictly, it's the connector, not the cable, that needs to be correct.

peace--
 
boingoman said:
I think perhaps by the strictest definiton, the cable may be balanced. But when it is in the circuit, it becomes secondary. And strictly, it's the connector, not the cable, that needs to be correct.

peace--
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It's the cable too. For a balanced connection to happen, the output circuit, the output jack, the plug on the cable at the output end, the cable, the plug and jack at the input end, and the input circuitry all have to be correct. Correct means two signal wires, and ground. The connectors are usually either XLR or TRS 1/4". The two signals are both referenced to ground, but are 180 degrees out of phase, or inverted from each other. The principle at work is common mode rejection. Both signal wires will pick up the same noise signal, in phase. The reciever will flip the - signal to be in phase with the + signal, and at the same time will invert the noise on the - signal to be out of phase with the + signal noise. The summed in-phase signals will add, and the summed out of phase noise will cancel.
 
boingoman said:
Jesus freakin' crap. Wading through that gave me a headache. :p
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gave you a headache? i'm still carrying the headache that i got from that almost a year ago. :D

in a nutshell, this is what i got out of it:
 

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Robert D said:
For a balanced connection to happen, the output circuit, the output jack, the plug on the cable at the output end, the cable, the plug and jack at the input end, and the input circuitry all have to be correct.
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I bought a bunch of TRS and RCA cables yesterday and none of them made references to being "balanced" or "unbalanced" though. Oh well, my equipment is still functioning after hooking them up (LOL). I took electronics when I was in Grade 10 so I can somewhat understand this. I just didn't know what the effects were of mismatching balanced and unbalanced cables and equipment. I'm the kind of guy who'd just go ahead and mix, record, and master without knowing the technical details, meanwhile I'm missing out on a lot of basic fundamentals. Thank you all for your replies.
 
mbernardo said:
I bought a bunch of TRS and RCA cables yesterday and none of them made references to being "balanced" or "unbalanced" though.
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For reference, TRS is a balanced cable (or should I say can send/recieve a balanced signal when plugged into balanced equipment :)), it's got wires connected to three points, hence TRS (Tip, +) (Ring, -) (Sleeve, Ground), similar to XLR. RCA cables are unbalanced. They only have the + and Ground signals, similiar to TS cables (notice not "R")
 
No problem. Glad I could help. To go a little more in depth, here is the wiring relationship of XLR to TRS:

Pin 1 - X/S(sleeve) - Ground
Pin 2 - L/T(tip) - Hot (+)
Pin 3 - R/R(ring - Cold (-)

So XLR = Pins 123
TRS = Pins 231

I hope that makes sense. Many user guides for mixers will often have wiring diagrams of this relationship, or how to wire a balanced to unbalanced cable. It helps to see a picture I think.
 
There are generally 3 Types of Ballanceing being used in most Prosumer audio Gear....

1) "True Ballanced audio" which is the Same Signals being Transmited down both Hot wires but out of Phaze and the Noise get canceled out this way, This is usually created useing an audio transformer for most Tube equipment or useing a Ballanced Line driver or Dual Opamp for Solid state curcuitry....

2) "Impedance Ballanceing" which is a psudo ballanced signal which is created by Tieing Pin 3 to ground with a resistor of the Value of the Output impedance of Pin 2 which gives you the same noise canceling benifits of True Ballanced and be able to run long cables and without the Extra Curcuitry that is needed for True ballanced...This method of Ballanceing is looked down upon by some Poeple but it has been used by Companies like Mackie in some of there consoles and is used by AKG, Neuman and others to Create a Ballanced ouput in there Transformerless Microphones so it seems that it is a good way to create a Ballanced output from a non-ballanced audio source....


3) "Dual Mono/Stereo TRS" which isn"t really ballanced but is what is used in some So Called Ballanced TRS Outputs and is basicly a audio signal on both hot wires that is not out of phaze so there is no noise cancelation...This is what is used in Stereo TRS outputs/Inputs and is not ballanced but the cable can be used for Ballanced signals.....


I am going to be doing some experiments on compareing True ballanced with Impedance Ballancing to see which actually performs better (I hope it is the Impedance ballancing ) ...I am designing a Small compact but hopefully high quality Preamp and since space is a concern I would like to do Impedance ballanceing but I will try both.....


Cheers
 
Cool Minion! Let us know how the impedance balancing works out. Of course, you'll have to have a noise problem to solve to know if you've solved it.
 
Oh dear gawd not this again..... :(

The only serious issue I have heard of is this:
Check the manual. Some balanced outputs can be damaged by driving unbalanced inputs unless the cables are wired a specific way. Lots of gear these days can handle either, and will likely be labelled as such. Again, check the manual.
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So other than that, just worry about matching connectors as much as possible.
Balanced connectors: XLR, TRS 1/4"
Unbalanced connectors: RCA, TS 1/4"

and just as a sidenote--any cable with a balanced connector on one end and an unbalanced connector on the other end, will be in total unbalanced. Connecting any cable between a balanced jack and an unbalanced jack will result in an unbalanced signal path along the cable. Try not to worry about it too much but take notice of your gain staging when you lose a few dbs here or there.
 
Robert D said:
It's the cable too. For a balanced connection to happen, the output circuit, the output jack, the plug on the cable at the output end, the cable, the plug and jack at the input end, and the input circuitry all have to be correct. Correct means two signal wires, and ground.
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Yeah, I was kind of free-forming there. BTW the shield isn't really necessary for balanced operation. Phone lines for example aren't shielded, but are balanced. And not all balancing schemes use two signals. The above-mentioned impedance-balancing circuit has no signal on the cold wire, for instance. The cold wire is hooked straight to ground through a resistor.
 
Minion said:
2) "Impedance Ballanceing"...This method of Ballanceing is looked down upon by some Poeple

Cheers
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Yeah, it gets a bad rap. It works pretty well, though, as long as you realize it has very real limitations, and work within them.
 
boingoman said:
Yeah, it gets a bad rap. It works pretty well, though, as long as you realize it has very real limitations, and work within them.
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Actually I was just reading a couple articles on the net about Ballanced outputs and they state that Impedance Ballanceing is actaully a Good way of createing ballanced output and in some ways better than useing a Dual Opamp or a Ballanced line driver because with a Dual Opamp each outputs output impedance can vary with temperature and Voltage swings which causes bad CMR.....

It is actually a good little article if you are interested in this sort of stuff and has a Link to another article by the Owner of Jensen Transformers backing up what he says (but of cource he says Transformers are the best way to go)...

You can read it here:

http://www.sounddevices.com/tech/balancing.htm



Cheers
 
Hey, Minion,

Thanks for the link. Good article. If you haven't checked out the Jensen sight, you should. Bill Whitlock has a bunch of papers on balancing there. And also lots of schematics of balanced circuits, both electronic and transformer, including one that has a circuit that gets around a couple other issues with dual op-amp differential inputs. It may be applicable to the circuit you want to make, as well.

I read an article once by the guy who started Soundcraft, I'll find the link. He also feels the so-called "impedance-balanced" circuit is excellent, he is a fan. He also discusses why in some cases the dual opamp circuit has better performance in really hostile enviroments with long runs, which explains part of how the single op-amp circuit got a bad rap. Like the dual opamp circuit, it has to do with the opamp's changing impedance causing an imbalance in the legs, since one leg is just connected to a resistor, and does not change. Seems like there is always some kind of trade-off.

I'm interested to see what you come up with. :)
 
Well last Night I etched the PCB"s for my Pre amp design (Just a Rough prototype design) and I etched a seperate PCB for a Dual opamp Ballanced Line Driver....

I still have to drill the Holes in the PCB and Order a few Parts and wait for them to show up but after I get the Pre amp Built (Still have to do the Power supply also) I will Post some of my Results of the Differant Ballancing methods but more Importantly (To me anyways) the Quality of the Pre amps sound ....

Cheers
 
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