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  1. xja
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       #1  
    As has been discussed, the T600 often won't send audio out the headphone jack when it is plugged into a line-in input on a stereo (and sometimes certain cassette adapters). It senses the impedance on the tip (left) channel and if it exceeds a certain threshhold (and is not an open circuit), it assumes an earphone/mic is connected....earphone in the ring (right) channel, mic in the tip (left) channel. The threshhold is somewhere just over 1000 ohms, it appears. This is because the mic is about 1400 ohms, while most headphones are under 100 ohms (some are higher) and most cassette adapters are under 1000 ohms.

    When it decides that an earphone/mic is connected, it routes the phone audio out the left channel (to the earphone) and it routes any audio from apps like PocketTunes to the internal speaker.

    Usually the line-in input impedance on a stereo (as well as mixers and some cassette adapters) is well above this threshhold, so the Treo thinks a mic is plugged into the right channel.... too smart for its own good! So to get the Treo to send audio out, you need to lower the apparent impedance that the Treo sees.

    One kludge workaround is plug-in a Y adapter into the audio jack. Connect one side of the Y adapter to your stereo (or whatever line-in you are trying to connect to) and in other side, connect a set of headphones. This way you are putting a low impedance device in parallel, thereby lowering the impedance that the Treo sees.

    If you are a real geek and like soldering, with less than a dollar of Radio Shack parts, you can modify an audio cable to put a 1000 ohm resistor between the left channel and ground and between the right channel and ground. That will lower the impedance below the threshhold and trick the Treo into sending audio out the jack.

    Neither of these solutions are ideal from an audiophile perspective but they do work.

    Hopefully someone (maybe Handspring/PalmOne?) will make such an adapter for us, or better yet, if possible, modify the software to let the user override the impedance sensing (assuming it is not all done in hardware, which is quite possible).
  2. #2  
    Great explanation. I'm thinking about giving the radio shack approach a try. Welcome any other input or observations you have.
  3. xja
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       #3  
    There are many ways to accomplish this in terms of the parts you choose to modify (eg, cables with different connectors)... also, it might be easier to do it with wire and putting the plugs on the end yourself rather than trying to modify an existing cable (easier to work with the wires).

    My only other input if you decide to make your own is that it might not be as easy as it sounds if you don't have experience soldering and working with tiny components and wires, so it could lead to a frustrating experience, so don't blame me!
  4. #4  
    you can also use a ground loop isolator... isolates the device from the amp so that it does not cut out and also an all in one cable solution in situations where you leave the cable in place.....
  5. #5  
    I'm glad I ran accross this posting. I purchased the adapter for the Treo 600 and was very disapointed because it appeared to only be any good if you wanted to hook the device up to head phones.

    Everything else I have plugged it into simply seems to disable the adapter all together and sound comes out through the phone's speaker as normal. I assumed that it was a "feature" to prevent it from being plugged into devices that it could not power, and had pretty much given up on the idea of playing my MP3's through the line-input on my car stereo.

    The ground loop isolator sounds like the better solution for me. Has anyone tried this? How does it work? Can you recommend a specific brand, model or part number?

    Thanks,
    TechDude
    Last edited by TechDude; 12/31/2003 at 07:53 PM.
  6. #6  
    Why does the Treo 300 earbud work to receive audio but the Treo 600 earbud does not?
  7. #7  
    I've used both on my Treo 600 and they both work fine for me.

    What happens when you plug in your earbud?

    Did I understand you correctly?

    Are you saying that using the earbud that came with the Treo 600 does not allow you to hear sound but using the Treo 300 earbud on the Treo 600 will give you sound?

    --TechDude
  8. #8  
    The Treo 600 earbud will not play Pocket Tunes sound UNLESS you hold down the button which apparently (according to the great info in this thread) changes the impedence and allows the music to play through the earbud. I use a small binder clip to hold it down, others use a small loop of velcro that they can slide up over the button when needed. The earbud works fine as is for the phone.
    Charles

    Kyocera 6035-->Samsung I-300-->Samsung I-330-->Treo 600-->Sprint Treo 650-->Cingular Treo 650-->AT&T Treo 680-->AT&T Crimson Treo 680-->AT&T Black Centro-->AT&T Copper Treo 680-->iPhone 3G 8GB-->iPhone 3GS 16GB-->HTC EVO 4G
  9. #9  
    Very good! Thank you for posting the information again.
  10. #10  
    Originally posted by xja
    One kludge workaround is plug-in a Y adapter into the audio jack. Connect one side of the Y adapter to your stereo (or whatever line-in you are trying to connect to) and in other side, connect a set of headphones. This way you are putting a low impedance device in parallel, thereby lowering the impedance that the Treo sees.

    If you are a real geek and like soldering, with less than a dollar of Radio Shack parts, you can modify an audio cable to put a 1000 ohm resistor between the left channel and ground and between the right channel and ground. That will lower the impedance below the threshhold and trick the Treo into sending audio out the jack.
    O.k., I played around with this over the weekend. I tried it with both 300ohm and 550ohm resistors; it seemed to work the same with either. It seems to me the different resistances should not make much difference to the Treo, other than a minor power consumption difference. I did my "permanent" adaptor with the 550ohm resistors, mainly because they were smaller. Anyone see any potential issues with using higher or lower resistance?
  11. #11  
    Originally posted by acourvil


    O.k., I played around with this over the weekend. I tried it with both 300ohm and 550ohm resistors; it seemed to work the same with either. It seems to me the different resistances should not make much difference to the Treo, other than a minor power consumption difference. I did my "permanent" adaptor with the 550ohm resistors, mainly because they were smaller. Anyone see any potential issues with using higher or lower resistance?
    I too would like to know a safe setup before frying the Treo... any EET gurus out there?
  12. #12  
    Anybody can post some picson this workaround? And some detailed instructions on how to modify this? And what parts needed with part numbers possibly? That would be great. Thanx...
  13. #13  
    Originally posted by MoseGiganticus in this thread

    Something i was thnking about when dealing with this impedance issue. Radio Shack make a "headphone extension" cable that has "volume control knob" built in. Check it out:

    Radio Shack Link

    This "volume control knob" is just a resistor pot, so if you plug a cable from your T600 into this, then run this into your car stereo, you should be able to adjust the pot until you get the impedence that the T600 is lookng for. Basically, if you have everything plugged in and the sound is still coming out of the speaker, just turn the knob (there-by increasing the impedence) until the sound starts coming through the stereo. I would imagine that this would be a good way to match impedences too, so that you will get maximum volume output from your T600.

    I haven't tried this, so I'm not sure, but i think it should work for you people who are having probelms. It's a $6 fix (if it does work).
    I guess the only wild card is that I don't know what the resistance range of the pot is, but I could figure that out if someone wanted to know (just test it with my voltmeter).
    I used this cable and it worked great for my car stereo. I'm thinking about soldering a 3/32" tip on the cable so that I don't have to have two adapters plugged into my Treo. But for now, it's a quick, easy, and cheap fix.

    I like this option better than soldering resistiors into a audio cable because it offers variable resistence as aposed to being a fixed resistence that may not work in every application.

    I was pleasently surprised when my Treo was able to feed audio to my car stereo at ALL volumes offered by this cable. I had suspected that it might only work at a certain volume and below, but apparently even at maximum volume there is enough resistence there to trick the Treo into thinking it's plugged into a set of headphones.

    Hope this helps,
    TechDude
    Last edited by TechDude; 02/17/2004 at 08:46 AM.
  14. xja
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       #14  
    A rotary volume pot such as the Radio Shack part you have identified is a good idea and easy solution.

    In case you are wondering why it works: (for geeks only )

    A potentiometer such as this works by having a resistive material across the leads of the source and a knob or slider that contacts the resistive material, in essence tapping the signal at a varying point along the resistive material and feeding it to the load (headphones, cassette adapter, or your stereo line inputs in our case). The resistive material before the contact point INCREASES the impedance of the circuit. The resistive material after the contact point is in essence in parallel with the load. Since it is in parallel, it LOWERS the impedance of the circuit (this is what we need to get the T600 to feed the audio out the headphone jack... ie, we need to get the impedance under approx 1000 ohms ).

    The total impedance of the pot will never be more than the impedance of the resistive material NO MATTER WHAT THE VOLUME IS SET TO (it is less because the load is in parallel with the post-contact resistive material... impedance goes down as the impedance of the load goes down and as the volume is increased) so as long as the impedance of the resistive material is under approx 1000 ohms, it will work for solving this problem. It turns out this Radio Shack rotary pot is approx 540 ohms (at least the one I have), so it works pretty well.

    As for whether having a much lower impedance would have a material effect (as acourvil asked), I can't imagine that it would, considering many headphones impedances are lower than 30 ohms. The impedance levels may affect the power requirements (probably not so much of an issue since we are plugging into stereos with powered amplifiers) and signal quality but I am not familiar enough with the Treo design to know if that would have a noticeable impact. I suspect not.

    Anyway, here are some links on potentiometers for those who just can't get enough!

    http://www.allaboutcircuits.com/vol_6/chpt_3/6.html

    http://www.eatel.net/~amptech/elecdisc/potentio.htm
  15. #15  
    A fellow EE lol
    When the dark clouds gather on the horizon, when thunder and lightning fills the sky, When fate is but a glint in the eye of a fallen Rattler, And hopes are lost friends, When the sinew of the chest grows weary from those hard-charging linebackers, And the muscles in the legs grow tired from those hard-charging running backs ... You must remember that the Rattlers will... Strike, Strike, and Strike again.
  16. #16  
    Quote Originally Posted by TechDude
    I'm thinking about soldering a 3/32" tip on the cable so that I don't have to have two adapters plugged into my Treo
    OK, I'm game - I'll destroy $10 worth of parts from Radio Shack in this endeavor. One question, tho - when I get the 3/32" tip, what's the pinout I should use? What color to tip, ring, and ground?
  17. greenlion's Avatar
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    #17  
    Great info! I enjoy playing around hardware too, but what we really need is software solution, to cut down on the number of adapters that you need to carry around. Hopefully someone out there can come up with something.

    Users will only listen to music over personal headphones -- what a ridiculous assumption to be made by the Treo designers!
  18. #18  
    bump
  19. #19  
    "A rotary volume pot such as the Radio Shack part you have identified is a good idea and easy solution."

    I picked one of these up and it works great. This forum ROCKS!

    James
  20. #20  
    Thanks so much i have been trying to hock up my Treo to my car's AUX input and it was not letting me.
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