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Stero to Mono

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nuckolls.bob(at)aeroelect
Guest

Posted: Mon Jun 08, 2009 4:32 am Post subject: Stero to Mono

At 06:40 AM 6/4/2009, you wrote:




Greetings... I'm a bit confused on this subject after reading this 

thread and similar threads in other lists. I have the same objective: 

plug my iPod into my Xcom 760's audio in. The Xcom's documentation 

says to use a 3.5mm mono jack in combination with a stereo-to-mono 

adapter plug. My thought was to eliminate the adapter plug by simply 

jumping the left/right channel pins on the jack itself, and this does 

indeed give [seemingly] good results with both channels clearly 

heard. But lately I've read that this may damage the iPod, and I 

should be using resistors/capacitors and/or the adaptor, as though 

the adaptor had some components built into it's small, moulded little 

case. I'm relatively sure that this adaptor plug is doing nothing but 

physically joining the left and right channels from the stereo plug 

into a single tip on the mono plug, and is in no way electronically 'magic'.



Not wanting to damage my iPod, I'd be interested to know the science 

behind all the posts saying 'don't do it' (wire the left and right 

together), use the adaptor plug. Thanks!



     The roots of this thread go back a few years. The

     first adaptation I recall of a common commercial

     stereo music product into an OBAM aircraft was for

     a builder wanting to adapt a compact automotive

     AM/FM radio to his airplane. In fact, he had pulled

     a non-working ADF and was plugging the hold with the

     automotive receiver. He missed the ADF's ability to

     turn the AM radio stations.



     This was before car radios featured low-level audio

     output/input jacks. The only outputs were intended to

     deliver WATTS of energy to speakers. Voltage levels

     at the speaker output of such radios were much higher

     than necessary to service the headphone level inputs

     to intercom systems in tens of milliwatts.



     The task then had several considerations. The output

     stages of the radio were designed to deliver energy

     to low resistance loads (4 ohm speakers). If not

     similarly loaded in this new application, audio quality

     at low output levels might suffer (cross-over distortion).

     So the first thing we did was "load" the radio with

     some handy but relatively low value resistor . . .

     10 ohms, 1 watt was common.



     After that, the too-high output voltage needed to

     be attenuated to levels appropriate to headphone

     input levels at the intercom. At the same time, the

     right-left stereo signals needed to be mixed in a

     manner that provided a summation of the two signals,

     not a conflict.  By conflict, I mean that simultaneous

     positive and negative going transients in program

     material do not cause large currents to circulate

     between the right and left amplifier output stages.



     The risk for damage to the system is low. The strongest

     effect for these circulating currents is distortion

     of the audio. It's common practice to first reduce

     the potential for circulating currents between the

     two outputs by artificially raising their output

     impedances (series resistors) and then setting the

     system losses with a downstream load (parallel

     resistor) to set volume.



     In this example



http://aeroelectric.com/Pictures/Schematics/WalkmanAdapter.gif



     only mixing resistors are called for but if the

     signals from the audio source proved too strong, a

     resistor on the order of 10 to 100 ohms could be

     paralleled with the output to bring the level

     down to size.

        Bob . . .



         ---------------------------------------

        ( . . .  a long habit of not thinking   )

        ( a thing wrong, gives it a superficial )

        ( appearance of being right . . .       )

        (                                       )

        (                  -Thomas Paine 1776-  )

         ---------------------------------------

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jd(at)lawsonimaging.ca
Guest

Posted: Mon Jun 08, 2009 5:37 am Post subject: Stero to Mono

Robert L. Nuckolls, III wrote:

 	  Quote: 	
		   

     The roots of this thread go back a few years. The

     first adaptation I recall of a common commercial

     stereo music product into an OBAM aircraft was for

     a builder wanting to adapt a compact automotive

     AM/FM radio to his airplane. In fact, he had pulled

     a non-working ADF and was plugging the hold with the

     automotive receiver. He missed the ADF's ability to

     turn the AM radio stations.

 

---------------snip -------------
	




Thanks so much for this inclusive explanation, Bob. In my particular case, 

though, I *think* it's safe to assume that the modern Xcom 760 radio is designed 

with iPod/CD player input in mind, and that any attenuation/gain/amplification 

is done on the radio's c.b. The fact that the manufacturer states to simply use 

a 3.5mm mono jack along with a stereo-to-mono adapter plug from the iPod 

headphone out, enforces this assumption, in my mind.



My question, really, is if shorting the ring and tip pins on a stereo jack 

installed on my panel is the electrical equivalent of using the adapter plug. 

Which begs the question: do those adapter plugs contain any sort of electronic 

components at all? Since the price of these critters ranges from $1.00 at the 

Dollar store to $9.95 at the Source (Canadian Radio Shack, gold plated), perhaps 

the high-end ones do, but I doubt it. The sound is good the way I've got it 

(jack pins connected), hearing both channels mixed, good volume. Just don't want 

to put my little iTouch at risk, as some have implied I may be doing...



Thanks, again!



-- 

Regards,  J.

Sonex C-FJNJ, Jab 3300, Prince P-Tip

http://cleco.ca



+-------------------------------------------------------------+

|  J. Davis, M.Sc.            | (computer science)            |

| *NIX consulting, SysAdmin   | email: jd at lawsonimaging.ca |

+-------------------------------------------------------------+



and now... Deep Thought #35, by Jack Handy



When you go in for a job interview, I think a good thing to ask is if they

ever press charges.

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nuckolls.bob(at)aeroelect
Guest

Posted: Mon Jun 08, 2009 6:25 am Post subject: Stero to Mono

 	  Quote: 	
		  Thanks so much for this inclusive explanation, Bob. In my particular 

case, though, I *think* it's safe to assume that the modern Xcom 760 

radio is designed with iPod/CD player input in mind, and that any 

attenuation/gain/amplification is done on the radio's c.b. The fact 

that the manufacturer states to simply use a 3.5mm mono jack along 

with a stereo-to-mono adapter plug from the iPod headphone out, 

enforces this assumption, in my mind.


	


    Yes, we're talking headphone levels for

    signal strength in both the aviation and

    the pocket entertainment world. These voltage

    levels are on in the ballpark with votlages

    that are exchanged between component systems

    on their line-in/out jacks.

 	  Quote: 	
		  My question, really, is if shorting the ring and tip pins on a 

stereo jack installed on my panel is the electrical equivalent of 

using the adapter plug. Which begs the question: do those adapter 

plugs contain any sort of electronic components at all? Since the 

price of these critters ranges from $1.00 at the Dollar store to 

$9.95 at the Source (Canadian Radio Shack, gold plated), perhaps the 

high-end ones do, but I doubt it. The sound is good the way I've got 

it (jack pins connected), hearing both channels mixed, good volume. 

Just don't want to put my little iTouch at risk, as some have 

implied I may be doing...


	


     The only way to see if there are components

     included inside the adapter is to research

     it from outside with test equipment. I suspect

     they have none.  Modern integrated circuits

     are quite tolerant of "circulating currents"

     so if you're satisfied with the audio quality

     then no further action is necessary.

        Bob . . .



         ---------------------------------------

        ( . . .  a long habit of not thinking   )

        ( a thing wrong, gives it a superficial )

        ( appearance of being right . . .       )

        (                                       )

        (                  -Thomas Paine 1776-  )

         ---------------------------------------

- The Matronics AeroElectric-List Email Forum -

Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:

http://www.matronics.com/Navigator?AeroElectric-List

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