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Old 25th October 2003, 04:44 PM   #1
Bricolo is offline Bricolo  France
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Default XLR Mic, how can I convert it to assymetric?

Can I simply connect the cold pin to ground?
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Old 25th October 2003, 05:10 PM   #2
OliverD is offline OliverD  Germany
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Yes, that's one possibility.
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Old 25th October 2003, 05:29 PM   #3
Bricolo is offline Bricolo  France
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OK, thanks

BTW, did you recieve my mail?
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Old 25th October 2003, 06:06 PM   #4
Duo is offline Duo  Canada
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In a mic like that there are of course three pins. On being ground, one + and one -. Don't confuse the - one simply to be negative.

Both the + and - pins are used for the same signal, only, the + pin shows the signal as it normally is, and the - pin is 180 degrees out of phase, basically an exact replica of it, but upside down (reverse polarity).

I believe that if you ground the - pin, you will be grounding out the element in the mic and therefore cause problems with the signal coming out of the positive pin. If you leave the ground grounded, and just don't connect the - to anything, then you should be fine. And just use the + pin for the signal in your system.

hope this helps
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Old 25th October 2003, 06:20 PM   #5
OliverD is offline OliverD  Germany
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Actually the mic capsule is connected to (+) and (-) while the microphone body is connected to ground. This makes a balanced connection. It is also the reason why just using the (+) line together with the ground connection will not work. You can safely tie the ground and (-) lines together to make it unbalanced, although I don't recommend it for long lines. A transformer at the mixer/amplifier end would be better.

The approach will also work with most phantom powered microphones. Normally the phantom power is provided common mode at both (+) and (-) line, but all microphones I know will work fine if they get power only from one of the signal lines. The ground line in this case works as both return path for the supply and shield.
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Old 26th October 2003, 01:42 AM   #6
Duo is offline Duo  Canada
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In the case of any XLR equipment I've seen, a reference to ground from either signal line will work.

Perhaps not im some mics, but it should still work.
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Old 6th November 2003, 08:35 AM   #7
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Grounding pin 3 (-) and pin 1 (ground), connecting pin 2 (+) to the unbalanced input and applying no phantom power will work fine with all dynamic microphones, but whether it is possible to apply the phantom power asymmetrically for capacitor microphones with phantom power depends very much on the internal construction.

For example, some AKG types (C535EB, C452EB) have a centre-tapped transformer between pins 2 and 3. When you connect pin 3 to ground and pin 2 to a 48V supply with a 3.3kohm or 6.8kohm series resistor, the transformer secondary simply shorts the phantom supply.

Perhaps it would work if you connected pin 1 to ground, pin 3 to a large capacitor to ground, pin 2 to the 3.3kohm resistor to the 48V phantom supply, and then AC coupled pin 2 to your unbalanced input.
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Old 6th November 2003, 11:38 AM   #8
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Only safe solution is a transformer. These exsist as just an xlr-rca converter.

If it is a dynamic mic, then you might get away with grounding pin2. But other mics may not like this.

Why would you un-balance a balanced mic?
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Old 23rd January 2004, 04:34 PM   #9
marz.tv is offline marz.tv  Sweden
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If it's about dynamic mikes, it's common for bands to have different cables... you know, one balanced xlr-to-tele *unbalanced* for that old PA input (and yes, that cable is soldered with the out of phase signal connected to the screen) --- and another 'proper' xlr-to-xlr cable for plugging the mike into the balanced mixer.

I think most 48v phantom supplys are made to be able to short out through the (usually 6.8k) resistors, so it's not really a safety issue anyway.
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