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Adding headset to radio with no 3.5 radio out

Discussion in 'Automotive Electronics' started by Merritt Davis, Jan 17, 2017.

  1. Merritt Davis

    Merritt Davis New Member

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    I have a nice double din radio in my motorhome with bluetooth but it has no way to listen to headphones. It does no work with bluetooth out, only in and it has no 3.5 mm jack. It is a Kenwood DDX9703s model and on the back it has a jack labled AV-out/audio out but when I called Kenwood they said this jack would not work.

    The radio must have seperate grounds for each speaker as well. So, what do I do to be able to listen to headsets while the family watches TV in the back? I do not drive with the headsets by the way. I would prefer a bluetoot set up but I want to be able to listen to my CD/DVD player or anything else that plays on my speakers. I have a 1000 watt amp fed by the low power outs (still have the high power outs but it says not to use both at the same time) and I have a 1000 watt base woofer amp.
     
  2. Merritt Davis

    Merritt Davis New Member

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    I did some checking on line, how would it work if I put in a 2 way rca switch to a rca bluetooth transmitter? I could connectd the stereo channels to the splitter, switched to A amp, B bluetooth. When I switch I can also disconnect the amps turn on so only the bluetooth gets power.

    My only concern is the ground, the bluetooth is designed for marine applications and has a seperate power supply. Is there any concern as to gounding, or does the bluetooth not connect the grounds together? If so, how can I prevent the radio from damage?
     
    Last edited: Jan 17, 2017
  3. alec_t

    alec_t Well-Known Member Most Helpful Member

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    Wouldn't it be simpler just to get a small second radio?
     
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  4. dave

    Dave New Member

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  5. spec

    spec Well-Known Member Most Helpful Member

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    Hi MD,

    Here is a suggestion for discussion:

    Connect an audio power amplifier to the AV output jack socket from the Kenwood and then you will be able to connect a jack socket to the audio power amplifier output to plug your headphones into.

    The audio power amplifier would need a power source which could be 110V or 240V AC, 9VDC upwards or a battery.

    If you had 12V available that would be fine.

    spec

    http://www.ebay.co.uk/itm/AUX-Mini-...544909?hash=item2a69cb1b4d:g:6N0AAOSwmtJXV-8g
    http://www.ebay.co.uk/itm/12V-Mini-...423577?hash=item25c8f70bd9:g:m50AAOSwRH5XLFOX
     
    Last edited: Jan 17, 2017
  6. Merritt Davis

    Merritt Davis New Member

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    I do not have an audio out, only in unfortunately
    I want to listen to movies via bluetooth from my car sterio, much bigger screen and I watch DVD's
     
  7. spec

    spec Well-Known Member Most Helpful Member

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    Oh I misread your post.

    spec
     
  8. Les Jones

    Les Jones Well-Known Member

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    Hi Merritt,
    In post #1 you said that you have "AV-out/audio out" This will not drive the headphones directly as it reasonably high impedance. (Headphones which are normally about 32 ohms impedance need to be driven from a reasonably low impedance source.) The AV out should drive the amplifier suggested by spec.

    Les.
     
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  9. spec

    spec Well-Known Member Most Helpful Member

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    Hi MD,

    Below is an outline schematic showing the simplest approach I could come up with to connect your headphones to the Kenwood DDX9703s.

    You can leave the circuit permanently connected to your Kenwood and if you connect a double pole single throw switch in series with the speakers you could turn the speakers on and off at will. The headphones will be powered all the time.

    Alternatively, with a double pole double throw switch you could select either speaker or headphones.

    If you have any interest in this approach we can do a practical circuit with component types etc and showing speaker switching.

    spec

    2017_01_18_ISS1_ETO_HEADPHONE_CONNECTION_V1.png
     
    Last edited: Jan 18, 2017
  10. Merritt Davis

    Merritt Davis New Member

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    This looks promising Spec, What type of transistor would I use? How clean do you think the signal will be to the earphone?
    I assume this would tap in at the speakers which are 250 watts each peak. Will I need to reduce the power?
     
  11. spec

    spec Well-Known Member Most Helpful Member

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    Hi MD,

    Those parts are not transistors; in this case 'TR' stands for transformer- A sloppy schematic from me.:oops:
    It would all depend on the quality of the transformers that you use. But without spending a fortune on transformers there is no reason why the sound should not be excellent.

    Below, there is a link to the type of transformer that may be suitable- I have not analyzed the transformer in detail. It is just a guide to the type of transformer that would be required
    The power from the Kenwood is not really relevant, strange as that may seem. The drive to the transformer is essentially a voltage drive rather than power.
    Maybe maybe not. It greatly depends on the impedance of your headphones and their efficiency (sensitivity). If you could post details of your headphones or a link to the specification, that would be handy.

    The signal to suit your headphones can be easily adjusted; this is no big deal.

    By the way, this circuit is passive and needs no power supply.

    spec

    LINKS
    (1) http://uk.farnell.com/vigortronix/vtx-101-001/transformer-audio-6-3-6-3-1-1/dp/1674300
     
  12. Merritt Davis

    Merritt Davis New Member

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    I will be hooking a bluetooth to the end of the line so I can use my bluetooth headset. I miss read the schematic before, I thought you were using transistors but I see you are recommending amplifiers. With this set up do I need to worry about grounding since the radio uses a floating ground.
     
  13. spec

    spec Well-Known Member Most Helpful Member

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    Oh, I see.That means that the transformer is less critical.

    Not amplifiers, but transformers- perhaps the schematic symbols threw you.

    You always need to attend to grounding, but with this circuit the Kenwood ground and the ground marked on the schematic are completely isolated so there would be maximum grounding flexibility.

    spec
     
  14. Merritt Davis

    Merritt Davis New Member

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    Are there any other transformers that will work, I cannot find one in the states from that company. By the way, I very much appreciate all your help with this.

    Hammond Manufacturing - Transformers 101F ?
     
    Last edited: Jan 18, 2017
  15. spec

    spec Well-Known Member Most Helpful Member

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    No Probs about help.

    There are many transformers that would be suitable, especially as the transformers will be connecting to the blue tooth transmitter rather than the headphones direct.

    But you can buy the Hammond transformers from Element 14 (Farnell) http://uk.farnell.com/vigortronix/vtx-101-001/transformer-audio-6-3-6-3-1-1/dp/1674300

    spec
     
  16. Merritt Davis

    Merritt Davis New Member

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    I think I found a supplier in the US in the meantime for the correct transformer. Hopefully my last question, on the schematic it shows 4 speakers hooking to the transformers correct? Or is it just two showing left and right. There is a little plus symbol to the left of the text which makes me belive this set up is for 4 speakers but of course I only need a left right for the bluetooth.
     
  17. spec

    spec Well-Known Member Most Helpful Member

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    No just two speakers- ignore the little plus marks and other small artifacts- they are just a result of the circuit capture application that I am using and my laziness.:cool:

    The transformer is not 'correct'. It is just an example. Anyway a different transformer, but possibly from the same range, will be used to interface to the Bluetooth transmitter.

    spec
     
  18. Merritt Davis

    Merritt Davis New Member

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    I did find the matching transformer to the one you spec'd. Does it matter which is + or - going into the transformer?
     
  19. spec

    spec Well-Known Member Most Helpful Member

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    Not radically, but take + = A and - = B.

    spec
     
  20. Merritt Davis

    Merritt Davis New Member

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    After looking at it closer that makes sense. I have the parts ordered and should recieve Monday. All I need to pick up is a 3.5mm female jack and I am good to go. Thanks again :)
     
  21. Merritt Davis

    Merritt Davis New Member

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    Ok, news flash. After contacting Kenwood a dozen times I finally got them to confirm the AV/Audio output is designed to be used with a rear monitor/headset. I think if I use the right cable (audio video) I can simply plug my bluetooth into the audio portion of the rcas with and RC to 3.5mm adapter. What say you?
     

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