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Combining 2 audio outputs into 1

Discussion in 'Audio' started by john2k, Sep 11, 2017.

  1. john2k

    john2k

    100
    1
    Jun 13, 2012
    I have 3.5mm audio outputs from two different devices. One is a TV and the other is amazon echo dot. I need to connect them to my sound system on the same 3.5mm input channel. Now from what I have read it is not safe to use audio splitters for this purpose as the output of the two devices might not have resistance protection.

    So question is what is the best way to combine these two outputs? Is there not a simple to make the audio cable with a Y connection and possibly add some kind of resistance to prevent audio from one device going to the other device? A bit like the concept of a signalling diode?

    I came across the following item on ebay: http://www.ebay.co.uk/itm/172859360361

    Has anyone used anything similar? will this do the trick?
     
    Last edited: Sep 11, 2017
  2. AnalogKid

    AnalogKid

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    Jun 10, 2015
    Yes, that will work. Note the warning on the product page about significant loudness reduction

    ak
     
  3. turbogt16v

    turbogt16v

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    Mar 27, 2015
    Last edited: Sep 11, 2017
  4. Externet

    Externet

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    Aug 24, 2009
    If both signals are "low line level" I would join them with a reversed monophonic splitter. If any signal is speaker level, I would not.
     
  5. john2k

    john2k

    100
    1
    Jun 13, 2012
    I've received the device, it's essentially 3 stereo sockets with resistors soldered in parallel to the two combining sockets. I drew up a diagram showing how it's wired. And it seems to work well. Audio volume is low if i try and listen on the headphones but on a soundbar or amplified speaker its perfect.

    I have a question, looking at this diagram, is there some sort of way to add some kind of variable resistance to allow one channel to be priority? and if that priority channel has any audio coming through it I would like the volume of the other output to be reduced more than the priority channel? Because my priority channel is a amazon alexa echo dot which will occasionally need to talk over whatever is playing on the main channel
     

    Attached Files:

  6. Audioguru

    Audioguru

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    Sep 24, 2016
    Your circuit combines signals at the output of an amplifier then the speaker has poor damping of its resonances and then it will sound boomy and maybe screachy. Therefore mixing of the signals with resistors or a mixer circuit should be done at the input of the amplifier.

    When the signals are mixed at the input of the amplifier then a Jfet can be used to reduce the level of one signal when the other signal has priority. The signal with priority needs to have a rectifier and filter circuit to detect its signal and feed it to the Jfet.
     
  7. john2k

    john2k

    100
    1
    Jun 13, 2012
    The device seems to work good, the resistors that are in the unit have a colour band of red, purple, red and gold. What resistor is this? i'm thinking off making the same thing but inline using just the wire instead of a bulky box.

    Also, does anyone know if there is a way for me to amplify one of the lines using either 5v or 12v supply?
     
  8. davenn

    davenn Moderator

    13,214
    1,731
    Sep 5, 2009
    2.7 kΩ
     
  9. john2k

    john2k

    100
    1
    Jun 13, 2012
    When I connect my TV headphone jack to this device it mixes the two sources fine. However, if I turned my TV off whether its in standby or completely turned off at mains, I get a very annoying humming/buzzing sound. If I unplug the 3.5mm cable from the tv then the noise disappears. Is this some sort of ground loop issue?
     
  10. Audioguru

    Audioguru

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    Sep 24, 2016
    The TV is never completely turned off since its on-off remote control receiver is always powered.
    Have you tried reversing the TV's 2-prong AC plug? Maybe your mains receptacle has its live and neutral wires connected backwards (since some 2-prong plugs cannot be reversed)?
     
  11. john2k

    john2k

    100
    1
    Jun 13, 2012
    But I completely turn off the TV at the mains and unplugged it until the standby light turns off. By changing direction of the 2 prongs and changing the polarity I assume that isn't a problem as technically those figure 8 prong connectors can go in either way meaning the TV should be able to take power either way?
     
  12. Audioguru

    Audioguru

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    562
    Sep 24, 2016
    I assume that your electricity is Canadian or American where there is live, neutral and ground connections on each AC receptacle. One of the two prongs on an appliance (your TV) might be larger so that its plug can fit only one way so that the chassis of the appliance can be grounded with a resistor or capacitor. If the appliance has both prongs on its plug the smaller size then it can be plugged in forwards or "backwards" and it works the same both ways (except then its chassis might have hum on it).
     
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