[Axiom0617]

I listen on a Sennheiser HD650 using a balanced cable with 3-pin XLR connectors.  Most of the time, I listen through my headphone amp which has balanced input/output; however, I'd like to also be able to listen to stuff from my desktop computer from time to time.  My sound card is a Xonar Essence ST, so it requires a 1/4'' TRS stereo jack to connect to it.
 
My question is, is it safe to connect my balanced cable to the Xonar Essence ST using a 3-pin XLR to 1/4'' TRS adapter, even though the cable is balanced and the Essence ST is an unbalanced source?  Will this negatively affect my sound quality?
 
Lastly, does anyone have any recommendations as to where to purchase the 3-pin XLR to 1/4'' stereo jack adapter?
 
Thanks

 

[Iniamyen]

Yes, the adapter would probably connect the balanced negative terminals to TRS ground (along with the XLR grounds), then the left and right channels would be connected to the left and right channels of the TRS connector. Or vice-versa, it doesn't matter... I am sure it would be safe.
 
Any sound quality differences would be due to your balanced source versus your sound card single-ended output, as the main difference would be a short length of wire in the adapter. That's up to you to decide.
 
Here's one such adapter: http://www.headphone.com/accessories/adaptors/headroom-xlr-to-14.php
 
After seeing the price, I'd make my own.

 

[nikongod]

Edited:
I think I may have misread what the OP wrote.
If you want to plug headphones with balanced terminations into an amplifier with only SE outputs this cable is very easy to make and available all over the place. Pretty much every cable maker sells one or will make one for you.
 
Edit:
The below is what I originally wrote:
it is not safe to ground active outputs on power amps. If the amp does not have output protection, or output resistors (which function as output protection devices in this case), there is the risk of the thing blowing up.
 
So, no, I would not do what the OP describes. 
 
If you want to risk it, I have seen cables built like you describe by a few cable MOTs.