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Ground/Return conductor in Headphones

post #1 of 4
Thread Starter 

 

 

Question: What happens when the S conductor in a typical TRS jack of a device is not properly grounded or does not make contact with the S conductor in a TRS plug of a pair of headphones?

 

My guess: What one would "hear" is the equivalent of the side channel in a mid-side mix, with no stereo separation. Is this correct? I think my thought process below is logical, but I don't have much formal knowledge of electrical theory, so I need some confirmation or to be corrected by someone who really knows their stuff.

 

My thought process: Since the T and R conductors have shared ground through S, they are electrically connected. With the S as a dead end, the signal through T will try to return through R and vice versa. The result would be serious attenuation because of added impedance, and cancellation whenever the amplitudes of both signals are the same. The resulting signal would be the difference of the channels, and identical in both T and R channels save polarity. Since our ears won't care about the polarity (when we have headphones on at least), we would hear the same sound in both ears.

 

Motivation for this question: I have a new portable audio device, and everything coming out of its audio jack sounds like the side channel in a mid-side mix. Obviously I will return the device, but being a nerd, I am trying to figure out what the problem is.

 

Added complication: The device actually sports a combo jack. However, if my understanding of how TRRS jacks work is correct (that the ground is the second R if not still the S, both of which would touch the S in the plug), this shouldn't matter.

 

(edited post title to be more informative)


Edited by arbeil - 10/23/11 at 12:52pm
post #2 of 4
Thread Starter 

Pardon the bump, would anyone be willing to take a stab at this please?

post #3 of 4

without a gnd connection you would only hear the difference between R,L drive V, antiphase, 1/2 amplitude in each driver

post #4 of 4
Thread Starter 

Thanks, jcx.

 

This makes me fairly certain there is something wrong with the ground connection in the jack of my portable device.

 

Could you please clarfiy what you mean by "drive V"? I am not using active headphones...

 

When I do connect the jack with the line-in of an active speakers, the difference signal goes away and everything sounds correct. Does this mean that putting an amplifier into the signal chain gives the signal an alternate ground? I don't even know if 'ground' is the correct word in these cases because portable device does not have a power connection and the ac-dc wall-wart of the active speakers doesn't have a third prong.

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