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In Reply to: RE: Amp/Balanced headphones posted by PAR on July 26, 2017 at 06:44:36
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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