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Old 24th June 2006, 07:26 PM   #31
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thanks a bunch Nigel, your certainly very knowledgable and extremely helpful. Now, I know this will seem very silly to you, but Im new to this stuff, and I don't exactly know how remove the screen connection from a cable.
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Old 24th June 2006, 07:45 PM   #32
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Quote:
Originally posted by paulspencer
As I understand, balanced outputs mean that additional circuits are added in the signal path to the balanced output jacks. If the unbalanced outputs are used from a unit, then surely these circuits would be bypassed and not in the signal path.
Its the same circuit that feeds both. Its just the ballanced connector has the normal signal plus an inverted version of it.

A DI box is used to feed a line level signal into a microphone input on a mixing desk, not what you need.

You need a ballanced cable between the ultragraph and the amp but do not connect the earth, just connect hot and cold.

Also on the feed to the ultragraph wire the centre pin of the RCA to hot on the ballanced jack/XLR and the shield of the RCA to cold on the jack/XLR.
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Old 24th June 2006, 07:49 PM   #33
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If you're using XLR leads, then there will be three wires inside the plugs, two are normal insulated wires, the third is the screen (or shield) and has no insulation on it. It's this uninsulated wire which should be disconnected.

If you're using 1/4 inch mono jack plugs (there's no reason for you to be using XLR's), there's only two wires, an insulated one to the tip, and the screen to the sleeve - again, disconnect the screen.
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Old 24th June 2006, 07:57 PM   #34
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Disconnecting the earth on a mono jack won't do the same job.

You can only do that with XLRs or TRS (stereo) jacks.
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Old 24th June 2006, 08:00 PM   #35
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Thanks for all the help guys, I really appreciate it.
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Old 24th June 2006, 08:00 PM   #36
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Quote:
Originally posted by BlackCatSound
Disconnecting the earth on a mono jack won't do the same job.
Of course it will, what makes you think it won't?.
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Old 24th June 2006, 08:36 PM   #37
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Hi CARTRulz, these days most everyone in the West wires balanced XLR connectors:

Pin 1 - ground, either circuit, chassis or switchable
Pin 2 - signal positive
Pin 3 - signal negative (not ground!, signal negative has audio on it out-of-phase with Pin 2)

Interfacing from balanced to unbalanced gets complicated because there are so many variables on the balanced side. Unbalanced is easy, centre pin carries the signal, outer 'pin' is system reference or ground. The balanced side has three common types - transformer-coupled passive balancing, instrumentation-type active balancing, and 'generic' active balancing. The first two are true isolated balancing in that impedance between either balanced leg and circuit ground is extremely high, on the order of mega ohms. An instrumentation amp is an active circuit designed to emulate a transformer. For both these types using only Pin 1 (ground) and one of either signal pins won't work. To visualize why, consider connecting an unbalanced source to a transformer input using only pins 1 and 2. Pin 3, the other end of the transformer primary, isn't connected to anything so no current flows (in reality almost no current, physical imperfections like winding capacitance allows a little signal through.) Generic active is sometimes called 'pseudo balancing', both inputs are referenced to ground. It's the equivalent of two unbalanced inputs/outputs, each independent of the other handling a different phase. These factors limit how ground is handled.

Examining unbalanced output to balanced input connections first:

Transformer coupled in - RCA centre pin to XLR pin 2, RCA ground to XLR pin 3, optionally (and likely) connect XLR pin 3 to XLR pin 1 to reduce hum
Instrumentation amp in - Generally same as above
Generic Active in - RCA centre pin to XLR pin 2, RCA ground to XLR pin 1, optionally tie XLR pin 1 to XLR pin 3 to reduce noise

Now the output side, balanced to RCA unbalanced:

Transformer coupled output - XLR pin 2 to RCA centre pin, XLR pin 3 to RCA ground, optionally connect XLR pin 3 to XLR pin 1 to reduce hum, often not required
Instrumentation amp output - Generally same as above
Generic Active output - XLR pin 2 to RCA centre pin, RCA ground to XLR pin 1, do not tie XLR pin 1 to XLR pin 3. Doing so shorts one leg of the output to ground.

The first two output connections preserve the full output voltage swing, the latter loses 6 dB since only one leg is available for use. In reality there is no true 'balanced' connection to unbalanced equipment, you're really just messing around with grounds. My suggestion for unbalanced out to balanced in is: RCA centre pin to XLR pin 2, RCA ground to XLR Pin 1, tie XLR Pin 1 to XLR Pin 3. For balanced output to unbalanced input: XLR Pin 2 to RCA centre pin, XLR pin 1 to RCA ground. Only tie XLR pin 3 to XLR pin 1 only if the output completely lacks bass if left unconnected. And by that I really mean sounds like a telephone, or is very low in level.
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Old 24th June 2006, 08:52 PM   #38
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Ok now heres where I'm very confused. I purchased these the other day"

http://www.amazon.com/gp/product/B00...Fencoding=UTF8

However, I'm still getting hum. Is that becasue its going from ballanced to unballanced? So basically when I follow those directions I'll be making a cable thats staying unballanced to unballanced, which will eliminate humming, correct?
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Old 24th June 2006, 09:07 PM   #39
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Quote:
Originally posted by Nigel Goodwin


Of course it will, what makes you think it won't?.

Because a mono jack in a ballanced jack socket shorts cold and earth together, no matter what the wiring.
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Old 24th June 2006, 11:51 PM   #40
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Ok so heres what I got now. I bought 6 RCA to XLR cables. On the RCA side there is one insulated wire from the pin and one straight piece of metal that goes from the ring and has a wire soldered to that, which then comes in contact with the metal sleve that screws into the head. On the XLR side there are 3 wires. One insulated thats in pin 3, and 2 uninsulated that go to pins 1 and 2. However, this seems to go against what Nigel said, as the insulated wire on the XLR side goes to the pin on the RCA side, which carries the signal, correct? Im so lost, someone please send help!
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