I didn't catch the original message here, what sort of equipment are you 
plugging the head phones and or adapter into?
If it is a high output source such as a stereo receiver then there could be 
some chance of damage, however, without saying martin is wrong because he's 
not, the technical explanations were correct, a lower output source such as 
an MP3 player, or discman, or sell phone or computer sound card is a little 
different than a high out put source that expects a certain load.
soundcards especially are very forgiving, and often have circuits built in 
to prevent under or over loading at the output or input jacks.
most sound cards, and sell phone outputs likely have a resister that will 
become activated if the right channel is shorted to ground, so that anyone 
can plug a mono plug into the jack and not worry about anything.
remember, these things are built to be more or less idiot proof, and i'm 
sure lots of people plug in stereo to mono adapters.
I think most of those adapters mix the left and right channel to the left 
channel without shorting right to ground...and when you plug the mono plug 
into a stereo jack, the jack more than likely has that resister martin 
refered to like the ham rigs to accept the mono jack without causing a 
loading issue.
I too have used stereo to mono adapters on stereo outputs with no 
perceivable negative results.
One thing to look at would be to use a single ear piece settup for mono 
listening only.
this device has a stereo plug that goes into a stereo jack, and mixes 
everything to the left channel and the single ear piece...the resisters and 
so on are usually inside the ear piece...and if not, the left and right 
channels, the tip and ring of the plug are connected together at the audio 
driver in the ear piece to prevent shorting to ground.
nearly any head phone jack will accept a load from 8Ohms to a few hundred 
ohms for different head sets, so the difference in load from having one 
driver connected to both channels, as aposed to having separate drivers 
connected won't matter very much to the output.  the only thing will be a 
slight volume drop.
to be absolutely safe, I suppose building a breakout box with the proper 
resisters and so on to maintain a specific load ont he amplifier would be 
bennificial, but as I said, unless your using a very picky source, it's not 
goig to make a huge difference.
Most modern IC bassed preamps and amplifiers won't even blink at a shorted 
channel at maximum output...or, they'll just shut that channel off, or pull 
back the output to that channel.
But again, this doesn't solve the issue of getting all the left and right 
audio material into one channel either.
your dealing with output power up to maybe 1 watt with most applications 
using headphone jacks, and most of the components inside are over valued 
well above that, so even if you crank the volume, and short everything out, 
nothing will smoke or become damaged.
If its a home stereo receiver, with a 3 or 5 watt output to the headphones, 
then yes, it could cause some issues with full volume and shorting or 
incorrect loading.
just my nickels worth on this.
martin's definitely technically right, I just think that most if not all 
modern devices have short protection and variable loading circuits built in.

73
Colin, V A6BKX
----- Original Message ----- 
From: "Mark" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Monday, April 05, 2010 9:07 AM
Subject: Re: OT Stereo to mono head phones adapter


> Hi
>     I hope that the adapters I bought from radio shack will have the right
> components built in. Now, I am worried.
>
> God bless,
> Mark
> Jesus Is Lord!
> Pendleton Redeemer
> http://pendletonepiscopal.org/
> ----- Original Message ----- 
> From: "Martin McCormick" <[log in to unmask]>
> To: <[log in to unmask]>
> Sent: Monday, April 05, 2010 6:08 AM
> Subject: Re: OT Stereo to mono head phones adapter
>
>
>> Mark writes:
>>>      I need to locate an adapter that takes both speakers of a head set 
>>> =
>>> jack and combines them in to a single "mono" out put for a head set. I =
>>> need this for a person who can only hear in one ear. Any help would be =
>>> appreciated.
>>
>> This sounds very simple at first but don't go too fast.
>> A lot of Y adaptors just connect the left and right channels
>> together which is okay if you are feeding one output to two
>> inputs but if you connect the left and right channels together
>> from a pair of amplifiers, each channel will see the other
>> channel as a rather heavy load. if there are different signals
>> on the two channels. What you are actually wanting is a
>> two-channel passive mixer which would combine the two outputs in
>> to one.
>>
>> You can do this by connecting a series resistor from
>> each channel to a single junction which will be the hot side of
>> the mono headphone.
>>
>> The value of the resistors should be aproximately that
>> of each headphone. When you connect the resistors together, the
>> output level will be down about 3 DB so one may need to turn the
>> volume up a bit, but the series resistors will protect each
>> amplifier output stage from being melted by unusual loads.
>>
>> Martin McCormick WB5AGZ  Stillwater, OK
>> Systems Engineer
>> OSU Information Technology Department Telecommunications Services Group
>