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Disconnecting headphone ground before signal

post #1 of 6
7/22/11 at 11:19pm
Thread Starter 

So, TRS plug are designed in a way that the the ground connection is made first and disconnected last.

 

I'd like add a switch to the ground of TRS jack output. Firstly to incorporate a mean to switch between active/passive/no ground, second to prevent signal shorting to ground while plugging/unplugging, and thirdly to turn off the headphone (by leaving it with an open circuit).

 

So, is it a bad idea to disconnect the ground of a TRS jack while leaving the signal connected?

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post #2 of 6
7/23/11 at 5:56am
If you disconnect ground from the jack with the headphones plugged in, then the outputs of both channels will be connected together through the headphone drivers.
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post #3 of 6
7/24/11 at 3:51am
Quote:
Originally Posted by Navyblue View Post

So, TRS plug are designed in a way that the the ground connection is made first and disconnected last.


That statement is untrue and confusing.

 

As you insert the plug into the jack, the plug's left channel contact will touch the jack's ground contact first, then the jack's right channel contact, then finally the left channel contact.  Along the way, the plug's right channel will also make contact with the jack's ground, and then the jack's right channel contact.  In between these transitions, the plug's left and right contacts could cause shorts across the jack's ground, right and left contacts.  When you remove the plug from the jack, the sequence of events is reversed, but the same shorts occur.

 

As digger945 says, disconnecting the ground on the jack side doesn't completely remove the headphones from the circuit, both drivers are in series now, straddled across the left and right outputs (you'll hear the difference signal between the left and right).  But more importantly, doing this won't prevent all TRS jack shorting scenarios (the left and right contacts could still get shorted to each other) when the plug is inserted or removed.

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post #4 of 6
7/24/11 at 8:08am
Thread Starter 

Thanks guys. :)

 

So as a safety precaution, it is a good idea to turn down the volume when unplugging headphones. I assume this applies only when music is playing and it matters less if nothing is playing? And I guess, the same effect can be achieved from isolating the input?

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post #5 of 6
7/24/11 at 8:35am

Always turn the volume down, its just good practice even if not strictly required. 

 

If you mute (pause source or with a mute switch) and leave the volume knob set for inefficient headphones and plug in sensitive headphones the user gets blasted with high SPL, and the headphones could be damaged when you start the music again. Dont do it. 

 

Pausing the music or muting the amp does protect the amp, but does nothing to protect the headphones. Volume down every time protects both. 

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post #6 of 6
7/24/11 at 9:24am
Thread Starter 

Thanks for the explanation. :)

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