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Absolute beginner question about stereo jacks

Discussion in 'General Electronics Discussion' started by fredfish, Feb 10, 2014.

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  1. fredfish

    fredfish

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    Feb 10, 2014
    I know this is very (VERY) basic and I feel a bit of a fool but here goes.

    I am going to put together a small junction box that will take an audio feed from my computers line out via a 3.5mm lead in to a 3.5mm socket.

    I want 2 outputs (one for headphones and one for the speaker system) each with a switch for on / off - so the permutations would be socket A and B Off, socket A and B On, socket A On and B Off, socket A Off and B On.

    I have 2 x 3.5mm sockets and the 2 switches.

    I realise that the jack sockets have 3 terminals (left, right and ground) and the switches have 2 terminals (in order to cut the signal to any line it is connected to).

    My question is - do I just place the switch in the Ground line? I am guessing that if I place the switch in either the left or right lines from the jack that I will just eliminate the signal on that channel?

    How do I configure it all?

    As you can tell I am a bit confused. :confused:

    TIA

    John
     
  2. Harald Kapp

    Harald Kapp Moderator Moderator

    11,446
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    Nov 17, 2011
    Switching the ground is not a good idea as some current will flow between left and right channel even in the supposedly off position of the switch and your outputs will never be completely off.
    Use dual throw switches and switch bot left and right channel.

    There is another issue with your setup: When both outputs are on, the loads are paralleled. This will double the load to your PC's audio output. At least the volume will go down in that case. In a worst case scenario the output of the PC is overloaded and turns off.
    It is a good idea to insert a simple amplifier into each output (A and B). You can buy inexpensive modules or kits for this. It is then easy to turn an output on or off: just turn power to the respective amplifier on or off.
     
  3. fredfish

    fredfish

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    Feb 10, 2014
    Harald - Thanks for your response, I told you I was confused!

    I take both of your points - I realised that there would be a likely drop in both channels volumes but I hadn't realised it could be to that degree, or cause those problems - thanks for the advice.

    The switches I have aren't "dual throw" switches - would switches like this do the job? http://www.rapidonline.com/Electronic-Components/DPDT-Standard-Toggle-Switch-75-0185

    Another alternative would be to have a toggle switching system. So EITHER A is active OR B is active. I assume that would overcome the drop in signal levels. I also assume that is fairly easy to wire up? (suggestions welcome).

    Cheers

    John
     
  4. fredfish

    fredfish

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    Feb 10, 2014
    I suppose (taking Haralds suggestions in to account) I might be better off with a rotary switch. Would I be correct in thinking that one of the switches on this page would work - if so which one would be best?

    http://www.rapidonline.com/FFSearch...es&filterCategoryPathROOT=Switches&keywords=*

    My preference is to buy from this company simply because they are located in my town and I can go and collect any items.

    I realise that the minimum is a 3 way switch with this selection and I only need a 2 way. As I only need a 2 way would a toggle (as I originally thought) be the simplest way?

    I know - so many questions for such a simple project. But I really would appreciate some pointers.

    Thanks again.

    John
     
  5. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    If you can live with either-or, a dual pole toggle switch is perfect. You will, however, be unable to activate both lines or deactivate both.
    2*DPST switches give you highest flexibility.
     
  6. fredfish

    fredfish

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    Feb 10, 2014
    But would have the potential drop in signal? Is that correct?
     
  7. fredfish

    fredfish

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    Feb 10, 2014
    I am more than happy to have a stab at a set up that includes a couple of mini amplifiers (such as the ones here http://www.rapidonline.com/Education/Stereo-Amplifier-Kit-Class-Pack-of-5-70-0198).

    However those would require the box to be a "powered" system rather than a passive system.

    Sorry for all of this - really I am mainly doing my thinking out loud!

    Thanks for your input - it is much appreciated.

    Cheers

    John
     
  8. Harald Kapp

    Harald Kapp Moderator Moderator

    11,446
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    Nov 17, 2011
    Yes.

    Yes to this too. Other wise you'd generate power from nothing :D
     
  9. fredfish

    fredfish

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    Feb 10, 2014
    The mist is beginning to clear - thanks for your help.

    Right now I am off to create power from nothing - now where did I leave my Alchemy kit, I can turn some lead in to gold at the same time :) :)

    Thanks again

    John
     
  10. BobK

    BobK

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    1,688
    Jan 5, 2010
    Paralleling them will not lose much volume as long as the amp can handle the combined impedance. If you have typical 32 Ohm headphones and an 8 Ohm speaker, the combined impedance is 6.4 Ohms, which is not that much different than 8 Ohms. I would expect a small drop in volume, not drastic.

    Bob
     
  11. fredfish

    fredfish

    7
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    Feb 10, 2014
    Thanks Bob. I appreciate the advice. I had decided to try it without the amps first (I have just returned from purchasing some Dual Throw switches). If all is well I will stick with that - mainly because I want to avoid powering the box if I can.

    Thanks again for the advice.

    Cheers

    John
     
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