JPF Home Page Forums Musician Gear and Techniques General Technical Forum Balanced/Unbalanced Eplained

I've seen so many questions about this mystery. I thought that I'd try to explain.....
Balanced and unbalanced, the lowdown

A balanced connection consists of three wires, hot (+), cold (-), and ground. The hot and cold are identical signals, but of opposite polarity (often erroneously called "phase.") The signal is the difference between these two. The main advantage to this connection is that any noise induced in the cable will be equal, and of the same polarity, on each conductor. Therefore, the noise cancels when fed to a balanced input. Unbalancing, either by using an adapter or by feeding an unbalanced input defeats this noise cancellation. All low-impedance microphones use balanced connectors.
An unbalanced connection uses only two wires, signal and ground. These are normally used for consumer audio gear, though many fine devices use unbalanced ins and outs. As long as the cables aren't longer than about ten feet, this works just fine. Price is the main consideration for using unbalanced topology when designing equipment.
There is some confusion about levels and connection types. While generally any balanced device operates at +4dBu and most unbalanced devices operate at -10dBv, the level has nothing to do with whether or not the equipment is balanced. Those levels are simply standards, +4dBu is the professional standard and -10dBv is the accepted level for consumer gear.
So, what happens when you plug a balanced line into an unbalanced input? Well, the first thing is that you lose 6dB of signal due to the fact that one lead, usually the cold lead, just got grounded. Normally this is no problem as the unbalanced device operates at a lower level anyway. However, the same might not be true when plugging an unbalanced line into a balanced input. Most times this is no problem, but I have some boxes in my studio which will not tolerate this and hum loudly in protest.
Bonus Section:
Phantom power is the most popular way to provide power to condenser microphones. It consists of applying a DC voltage (nominally 48V, but most will operate anywhere from 12 to 52V) to both signal leads (pins 2 and 3 of an XLR cable.) Since the same voltage is on both leads, it has no effect on the signal and no voltage is across the coil of a dynamic mic (though it can destroy older ribbon mics.) The purpose of phantom power is to bias the condenser and to power the impedance-matching preamp in the microphone. This voltage is normally supplied by the mixer via the mic cable.
I hope that this has answered a few questions and we can get back to making great music.
Peace

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"Take 276, you know this used to be fun."
John Entwistle

Yeah.

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Later,

Pat

My basic understanding of balanced cables, with both hot and ground wires contained inside the shielding is to allow longer cable runs to prevent spurrious electricial noise from entering the cable as well as to prevent serious frequency loss in the longer runs. Balanced cables of course are mostly used in Pro settings such as recording studios. All electricial signals are developed between the input and ground. There of course is no difference in so named balanced or unbalenced cable. The Electronics Industry of America set the standards long ago and when you buy equipment it is ready to use. You would have to take an Electricial Engineering College course to get an in depth understanding. I can't remember exactly but if memory serves me right, cable runs of over 25 feet on dymanic microphones will begin to see a measurable frequency loss. Condensor Microphones, of which are powered, (amplified) because of the very small electricial output can have much longer runs without measurable frequency loss. Cable design is also important as the cable can act as a capicitor of which lowers max frequency in the circut. But this is all taken into consideration in design and manufacture so is not really a concern usually. I don't know if studios have a way to test their equipment but they may.

Cool. Thanks for the explanation. I've been comtemplating getting the shure 86 condensor mic to replace my 57 as a vocal mic. It sounds warmer, but i didn't have a clue as to why.

-lafe

Thought we should move this up for folks. = )

Y'know, I should have posted this a long time ago.

Rane Note 110: Sound System Interconnection...

http://www.rane.com/note110.html

Given that this was bumped, hence is current, it should receive a bit of refreshing.



Balanced circuits are "balanced" because both the inverting (-) and non-inverting (+) inputs are equal impedances to ground.

It isn't signal symmetry that provides noise rejection of balanced inputs, but noise symmetry, which is why we use twisted pair of cable for balanced audio connections as opposed to untwisted conductors, or triax cable.

When these balanced cables are exposed to external noise, the twisting works to ensure that both the inverting and noninverting inputs have equivalent noise, so that it can be cancelled by the polarity inversion.

With regard to a few other issues mentioned in this thread:

1) There really is no such thing as a "balanced cable".

2) In short runs of cable, between balanced (low impedance) sources and (high impedance) destinations, you can pretty much use any decent quality twisted, paired shielded cable, and achieve a good result. Cables that have 100% braided shield, provide the best RF rejection.

3) You really don't need to worry about issues of high frequency roll off unless you are:

a) Using high source impedance devices (some microphones)
b) Running extremely long distances (thouasands of feet), using a high capacitance cable.

4) There is no industry association that certifies cable for use as a balanced audio interconnect. The AES (Audio Engineering Society) develops standards and practices for audio equipment. They are not always adhered to by the industry.

http://www.aes.org/publications/standards/

The Rane notes, as referenced by Patrick Bryant are good sources of information.

Also read the application notes authored by Bill Whitlock, at the Jensen Transformers website,for in depth tutorials on audio interfaces, noise interference, and power and grounding practices.


http://www.jensentransformers.com/apps_wp.html