Help with amplifier input

Discussion in 'The Projects Forum' started by droggie, Dec 29, 2012.

  1. droggie

    Thread Starter Member

    Oct 21, 2012
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    I am working on the schematic attached below and want to know if I am able to use the headphone jack (pictured) as an input and if so do I need to worry about polarity? I see three prongs. Are they all supposed to connect to the same point or are they are to be connected separately?
     
  2. tubeguy

    Well-Known Member

    Nov 3, 2012
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    A headphone jack accepts a stereo or TRS plug.
    You can use it for a mono input by connecting the side terminal to ground and the tip terminal to signal input,

    You only need to use two of the terminals. to find the tip, insert a mini-plug and test for tip connection with an ohm meter or continuity tester.
     
    Last edited: Dec 29, 2012
  3. droggie

    Thread Starter Member

    Oct 21, 2012
    137
    1
    So just connect one of the sides to ground and the top tip to in input? I have a multimeter, is there any way I can test it? I do not know what a mini plug or test tip is.
     
  4. tubeguy

    Well-Known Member

    Nov 3, 2012
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    A mini plug is the plug that fits this jack...
    These are also called 3.5mm or 1/8 inch plugs.
    You will need one to use this amplifier... ? :)

    An educated guess would be the shorter of the two end terminals would be the tip.
     
  5. droggie

    Thread Starter Member

    Oct 21, 2012
    137
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    I get it. Then touch both probes to each tip and which ever one beeps, that will be the one that connects to the input?
     
  6. Audioguru

    New Member

    Dec 20, 2007
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    I think the jack might be a mono jack with a switched contact.

    The small value of the input capacitor cuts bass frequencies below 160Hz.
    The small value of the output capacitor cuts bass frequencies below 426Hz when the load is an 8 ohm speaker.
     
  7. droggie

    Thread Starter Member

    Oct 21, 2012
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    So it is still usable for the circuit correct?
     
  8. Audioguru

    New Member

    Dec 20, 2007
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    You must determine which two terminals you need.
    The tip is for the audio wire and the sleeve is for the ground wire.

    Don't you care that the small values for the capacitors cuts bass frequencies?
     
    Last edited: Dec 30, 2012
  9. droggie

    Thread Starter Member

    Oct 21, 2012
    137
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    I never thought of it. Couldn't I just replace the two caps with a higher value caps like 100uf? I've gotten two readings of continuity: one on the tip, which I was told is ground and another on the bottom which I was told is input signal. If that is not correct, how can I determine which pins I will need?
     
  10. Audioguru

    New Member

    Dec 20, 2007
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    Why don't you CACULATE the value of a capacitor instead of just wrongly guessing?

    For an 8 ohm speaker at 20Hz at -3dB (half power) the calculation is simply 1 divided by 2 x pi x 8 x 20. The answer is 1000uF. Then 20Hz will be at half power and the low frequencies will begin dropping at about 100Hz.

    The input capacitor feeds the 10k volume control so for -3dB at 20Hz the capacitor value should be 0.8uf. Use 1uF.

    The tip of the plug is the input signal. The barrel of the plug is ground.

    Here is a stereo 3.5mm plug and jack. They have an extra contact for the second channel.
     
  11. droggie

    Thread Starter Member

    Oct 21, 2012
    137
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    So I can solder the to the input and active bottom tip to ground correct? My use for this amplifier is to connect it to an iPod.
     
  12. Audioguru

    New Member

    Dec 20, 2007
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    This text does not make sense in English.
    The tip of the plug is the active audio and the sleeve is the shielded ground wire.
     
  13. droggie

    Thread Starter Member

    Oct 21, 2012
    137
    1
    tip* I finished the circuit. How can I increase the overall frequencies of the circuit?
     
  14. droggie

    Thread Starter Member

    Oct 21, 2012
    137
    1
    Every time I change tracks I have to re insert the mono jack into the input. Is this where the second pin comes into play?
     
  15. Audioguru

    New Member

    Dec 20, 2007
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    If you increased the values of the input and output capacitors like I said to do then the bass response should be better. But you need a woofer that can produce deep bass frequencies.
    If you have a half-decent speaker with a tweeter then the high frequencies should sound good.
     
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