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I am about to buy a pair of headphones which, by reputation, are best used in balanced mode. The convention these days is to use a 4 pin XLR connector for balanced 'phone connection. I think (but am not sure) that it is wired pins 1, 2 L+, L- respectively and 3,4, R+ and R-. That is the normal setup but I am unsure that it applies for cans. Could anyone confirm?
What I am trying to do is construct a splitter cable to feed L and R 3 pin XLR outputs to a 4 pin XLR for the headphones. This obviously leaves me with a pin short at the 4 pin receive end as there is nowhere for the shield/ground to go. Ideas?
Follow Ups:
some balanced connections use 2 XLR connections (L, R) some use a single XLR connection. You should know the amp and earphones to find out compatibility. Cardas has all connections.
You really do not need any shielding on a headphone cable, just use pins 1 and 2 on each 3 pin plug and wire them to the appropriate pins on the 4 pin plug (you have the convention correct).
If any of your cabling does have shields, pin 1 on each XLR jack will have a connection to the chassis, and most 4 pin XLR plugs have a tab that's not a pin but rather the shell of the plug itself, and the shielding can terminate there.
...except making a 3-pin XLR to 4-pin XLR adapter.
But, I am sure you will find this link useful and your answer is probably in there. I doubt that your headphones use a shielded cable because there is nothing to ground in the headphone. If you do have a shielded cable going back up to the headphones that should be connected to the 4-pin XLR body and you can connect that to the 3-pin XLR ground pins using the shield of the adapter cable you are making. If you have un-shielded cables then forget the ground.
Regards
13DoW
Since our preamps can drive headphones in precisely this manner.
The trick is, ignore pin 1 on the 3-pin XLRs. The output of a balanced source should occur between pins 2 and 3 since ground is ignored and is not part of the signal (if not then its not really as balanced as the manufacturer is claiming). At this point the hookup is obvious.
Thanks Ralph. I only wonder about ignoring Pin 1 on the 3 pin XLRs. Obviously I cannot connect the shield at the 4 pin end in any case but should I not connect the shield to ground at the only available point, Pin 1 on the 3 pin XLRs ?
Pin one, if driving a headphone, simply should not be involved. Just don't hook it up.
Think about a traditional output transformer being used to go between a tube and the balanced line. The output transformer will have two wires for the secondary of the transformer. They go to pins 2 and 3. Pin 1 is tied to the circuit ground and the transformer may not have any connection there at all (some have a center tap, but its well-known that the use of a center tap degrades common mode rejection ratio, so you really don't see them unless the designer didn't know what he was doing).
You can see from the above that the output occurs between pins 2 and 3 because that's the output of the transformer. That's how balanced line is supposed to work. This means that between two channels you have 4 connections so you just hook them up.
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