I am going to be putting in a female XLR port for a dj to plug into in a bar that needs to be balanced over an audio cable. The DJ will be sending out balanced audio and I will need unbalanced for my system. It will be run over audio wire that is intended for single ended unbalanced audio. The wire is 2 pairs of 2 conductor wire each with there own drain. I think that the wire's name is 22-2p. I will edit this post tomorrow to put in the correct name. This wire will then be connected to a Creston Pad-8. The Pad-8 only has rca unbalanced connections. The Dj wants to be able to play his music through our existing system by becoming a new source on the Pad-8. I am not very familiar with working on balanced audio so I'm just looking for any advice. Will I need to buy an adapter, or will the existing wire be able to be connected a certain way on both ends so that it will work? What do I need to look out for to prevent a hum or buzz being introduced into the system?

-Thanks for any help

GWB. Pin1= ground, Pin2=white (red+) pin3 = black (-).

drain=pin1, red(white)=pin2, black=pin3 at the XLR. Wire pin1 ( drain ) to sleve ( grond ) and pin 2 to tip or posative.

I would try the following before going to converters. If the distance is short this should work ( no noise or hum ). Otherwise you will need balance to unbalanced converters. Sonance used to have a relatively inexpensive converter. But pin 1 to shield and pin2 to tip should work.

Alan

John,
in a balanced connection, there are two wires carrying the signal and neither is connected to ground. Just as Audible Solutions says, if you connect on of those to ground, it should work, especially for short runs.

If you do run into hum or buzz, it will most likely be because there is ground current between the chassis with the balanced connection and the chassis with the unbalanced connection. In that case, I would recommend a transformer connection; see Jensen Transformers for a full list of product and wonderful tutorials on hum, hum elimination, and I think even on balanced lines.



Aan, I have no idea whatsoever what GWB means. AWB was the Average White Band out of Australia, whose big hit "Put It Where You Want It" helped them tour the world. But GWB?

The second paragraph is indeed the approach John should use.

George Washington Bridge. I guess you need to be from NY.
G= ground = pin1.
W=white=pin2
B=black=pin3

The acronym was taught to me by a RF engineer at HBO and refers Ground ( shield or drain ), White and black conductors or what you would find in standard microphone ( 1 pair sh) cable.

G= pin1, W=pin2(+), B=pin3(-). "-" does not refer to ground or negative but to the out of phase posative of a balanced circuit. I know you know this Ernie but others reading this might do with the repetition.

If John is using 2 pair shielded he will have one pair of drain, white, wh/black conductors, and an other pair with drain, red, and red/black. White and red are pin2 while the blacks are pin3. drain is pin1. Do not use pin3 an the unbalanced end.

Alan

Some of your answer depends on what is driving the XLR output jacks on the equipment. It could be transformer driven, but more likely these days it is an op-amp in a differential configuration.

If you can find the spec sheet on the mixer board (or whatever you are using for a feed), see if it is OTL (output transformerless) or if it uses transformers.

If OTL (might also be stated as "Active output"... Pin 1 to shield, pin 2 to tip and leave pin 3 floating..... don't ground it... Pin 3 is also an active output... just the negative side of the signal. It is not needed in this case. Pin 2 will carry the full signal. If it has transformers on the output... you will need to ground pin three to complete the circuit path through the transformer.

In my experience, a better way to handle this situation is to put an adaptor on the AMPLIFIER end of the wiring. Once you convert the system to unbalanced, the signal is much more likely to pick up hum and other noises... including CB radio and other unpleasant surprises... Nothing like hearing a trucker running a 1,000 watt linear amp on his CB cursing over a churches sound system... then having that rebroadcast over a radio station. One learns quickly that way.

Unbalanced lines have two things going against them. There is no out of phase cancellation of noise picked up along the wire path... and they are usually high impedance circuits which invite more noise to enter them. The only reason you find them in consumer electronics at all is that they are cheaper. Professional equipment always operates with balanced lines.

What I did with commercial radio stations was this:

Feed the full blown balanced line over to where the amplifier is located. Radio Shack sells a plug in Balanced to Unbalanced line adaptor. Use that on the AMPLIFIER input, and your signal will stay cleaner along the path. It won't become unbalanced until it actually enters the Amp and at least it has some shielding there.

Normally I wouldn't recommend Radio Shack for much of anything but I have used many of those adaptors in radio stations before and never had a moments problem with them. It's kind of hard for them to screw up a simple transformer which is all that will be inside the shell you buy.

Ernie touched on one other important item.... hum because the source and the amp are not at the same ground potential. The best way to handle this is to have an electrician make sure that the source and the amplifer are on the same circuit. If that is not an option.... run a ground wire along with the rest of the wiring and connect it to metal on both pieces of equipment. Normally the shield connection would do that for you... but there are some pieces of equipment that float grounds.... and you need a solid ground connection in this case.

This message was edited by Warren on 08/23/04 21:58 ET.

Just in case anyone is having trouble understanding how/why there can be two signal wires in addition to ground, it's the same thing as bridging amplifier channels, except on a smaller scale.

One channel carries the signal as normal, and the other channel has the identical signal with the polarity opposite (180 deg, out of phase), meaning when one output goes +, the other one goes -.

The result is that the output, taken from one amp's + terminal to the other amp's + terminal, has twice the overall voltage with the same input signal, which doubles the speaker's current level.

The result is a quadrupling of power, if the amp is capable of doubling its power into a load of half the impedance. That, and the amp's - terminals are (or can be) tied together.

Since current is not really relevant in line-level signals, the main benefit is less noise because (a) of the higher signal-to-noise ratio and (b) because the shield is not a signal-carrying conductor.

In what is often called "true balanced circuit topography", the + and - signal pathways are carried by "mirror" circuitry. Again, the result is that ground is never a signal reference.

In most balanced circuits, either polarity's signal actually could be referenced to ground (like a pair of amps) and two signals could theoretically be had at the same time, one + and one.

So, one can use either the + (pin 2) OR the - (pin 3) as a signal output, as long as pin 1 is used as the ground. Just keep in m ind that the two hots are of opposite polarity (phase).

This message was edited by Larry Fine on 08/23/04 22:23 ET.

The balanced (XLR) standard used to share two pinout protocols up until recently. Japanes manufacturers had pin 3 for hot while the British / American standard had pin 2 hot. I think now there is a standard. X = screen, L= line, and R= return.

You can get away with unbalancing a line by tying pin 1 to pin 3, but in some cases, you might want to lift pin 1 at one end. (mic. levels don't apply to this, only line level signals). A balance out[put from a DJ mixer is probably a =4Db signal, while the input you are feeding will probably be a -10 Db input. To do it correctly, a balancing transformer for each channel should be used

[Link: radiodesignlabs.com]

This message was edited by teknobeam1 on 08/23/04 23:38 ET.

Is this a fixed in place board? Or for the DJ of the night type setup? Most DJ boards have a line level output that will be closer to the correct output level for the input of a PAD8. you may want to consider running line as some cheap boards only have line level out. If it's a fixed board then you can run balanced back the the pad8 but I would build a pad for it to take down the signal or preferably a transformer solution. The best thing about an isolation transformer is that you won't have to worry about ground loop hums. Rapco makes some decent transformers thant are a step above Rat Shack but not on the level of Jensen. I use them for backround music but Jensen all the way for anything decent.