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How do I get microphone input from a speaker output?

Discussion in 'General Electronics Chat' started by jasonbe, Sep 23, 2008.

  1. jasonbe

    jasonbe New Member

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    How do I get microphone input from a speaker output?
     
  2. Torben

    Torben Well-Known Member

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    Typically if you need to get the sound from, say, a guitar amp which does not have a line out, you set up a microphone near the speaker cone and record that. You may want to run long cables and put the amp and mic' in a separate room. This is done both in the studio and on stage and is very common.

    Otherwise I would suggest that it would be much easier to take the output from before the power amp output stage, buffer it, and run it to a line out jack (which you add). However, I've never seen anybody bother to make this mod (OK, I did see one Hammond organ which had been modded to have a line out, but that's it).

    Does this make sense?

    It sounds from your questions like you're interested in getting into home studio work. What references are you using? If I have time later tonight I'll try to remember to put together some links for you to read which should help get you started with some basic studio techniques.


    Torben
     
  3. jasonbe

    jasonbe New Member

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    I don’t really consider myself a musician. I would like to learn how to program computers. I know that USB headsets can communicate analog microphone and speaker signals to a computer. I would like to learn how to communicate analog signals to a USB headset that could pass this information on to a computer. I have input and output analog signals. I’m considering my analog outputs like speaker signals and my analog inputs like microphone signals. So, when I say that I would like to get microphone input from a speaker output, I really mean that I would like to connect analog output to analog USB headset input, and connect USB headset output to the analog input of another device. Though, I’m worried that the newer microphones and speakers will send and receive complicated signals and won’t be compatible with analog signals. I have thought of just placing the microphone of each device by the speaker of the other device, but I would prefer to make an electrical connection.
     
    Last edited: Sep 23, 2008
  4. dave

    Dave New Member

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  5. Externet

    Externet Member

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    If you mean to electrically connect the audio meant for a speaker into a microphone input jack, obtain a quality potentiometer of any value, 10K will work too; connect its extreme terminals as if it was a speaker and wire the center wiper terminal and ground to the microphone jack.

    Adjust the speaker source for low volume and the potentiometer for a level comparable to as if it was a microphone with no distortion. That will be a position near the start of rotation.
     
  6. Torben

    Torben Well-Known Member

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    . . .and make darn sure you never turn the speaker output up or you'll blow the mic' input and burn up the potentiometer. :)

    Speaker output power can be many Watts. That energy has to go somewhere; a resistor burns it as heat. To bring the signal down to microphone levels a lot of Watts may need to be burned.

    There are potentiometers available to handle many Watts of power but the ones I have seen are not cheap.


    Torben


    Torben
     
  7. Torben

    Torben Well-Known Member

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    So essentially you want to use a USB headset (like a gaming/Skype headset) to emulate a sound card, by replacing the boom mic' with an input jack and replacing the headphones with output jacks? Why not save yourself the headache (and the cost of a new headset) and just use a real sound card or audio interface? The frequency response will probably be better and you will know that the inputs and outputs are correctly designed for their tasks.

    As you note, USB doesn't actually transfer analog signals. The analog signals are digitized and sent over the USB cable via USB serial protocol. For what you describe that wouldn't be an issue though, since that happens inside the headset (or its adaptor) and by the time the wires reach the microphone or speakers it's analog.

    Anyway, perhaps I'm missing something here. It's been known to happen. :) It would be helpful if you could state exactly what you are trying to do (as in, exactly what devices you want to interface with). Perhaps someone can describe a better way to achieve your end goal.


    Torben
     
  8. Externet

    Externet Member

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    Hi Torben.

    I do not understand why you say :

    "Speaker output power can be many Watts. That energy has to go somewhere; a resistor burns it as heat. To bring the signal down to microphone levels a lot of Watts may need to be burned. "

    Can you please explain ?:confused::confused: Do you mean a speaker output connection with a 10K resistor instead of a speaker has to dissipate 'many Watts' somewhere ?

    Miguel
     
  9. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    No, I imagine he was talking about using a potentiometer ONLY - where turning it almost entirely to the top could, potentially, damage both the pot and whatever you're feeding.

    The correct way (assuming you wanted a pot?) it to use a high value resistor to feed the pot.

    Very little power will be dissipated, as the resistor (and the pot) are high values.
     
  10. Torben

    Torben Well-Known Member

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    Yes, that and the fact that I posted that one in a hurry and didn't check my numbers. I blame beer and exhaustion for my incomplete post. Apologies. :)


    Torben
     
  11. jasonbe

    jasonbe New Member

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    Can a sound card or audio interface accept signals with a voltage as high as that of the signals used to power speakers? Can a sound card or audio interface send signals having a voltage as low as signals produced by microphones? I am trying to make an electronic translator for the LBC6K Laser Beam Audio Communicator found at http://www.ramseyelectronics.com/site/default.asp?search=LBC6K&page=search&x=15&y=3 and a computer, but I’d even prefer to communicate the Laser Beam Audio Communicator with one of cypress’ PSoC boards, i.e. a microchip.
     
    Last edited: Sep 24, 2008
  12. jasonbe

    jasonbe New Member

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    Could you give me some type of estimate of how much a resistor will distort the waveform of the audio signals? I’ve heard about attenuators, but I’m not sure what type would be the best for what I’m doing.
     
  13. neoandrewson

    neoandrewson New Member

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    hi,
    looks like a cool device..
    i didnt get this point.. could you explain more about the translator you are planning?
    are you trying to connect two computers (or microcontrollers) at two ends of the communicator? or control the audio using computer?
     
  14. audioguru

    audioguru Well-Known Member Most Helpful Member

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    A high value resistor in series with a pot that is turned down makes a voltage divider. Maybe your speaker output is 7V and you want to reduce it to 10mV (0.01V) to feed a mic input. Then you want the divider to reduce the voltage 700 times. You will be attenuating the speaker signal 700 times.
     
  15. Torben

    Torben Well-Known Member

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    I'm not sure that the questions you are asking are relevant, since the headset microphone and earphone connections will suffer similar limitations as a sound card. Either way you still need some kind of level matching such as that given by some other posts in this thread (and here).

    According to the manual and schematic for the LBC6K this is all easier than you're fearing it will be. On page 19 is the following:

    If you want to shell out for an audio interface with a line out, you should just be able to connect that directly to J1. If you need to come out of the built-in sound card's headphone jack (or, say, the headphone line on your headset, if you want to use that to free up the sound card I/O) then you could try adding, say, a 1k or so pot (maybe a 500Ω pot would be good too) as described in other posts in order to form a voltage divider. Play with the output level on the computer and the setting of the pot until it sounds good.

    For the output (I assume you're planning on using two LBC6K kits to get two-communication going?) from the LBC6K's receiver into the computer, you'd probably be going into either microphone input (either the sound card jack or the mic' lines in the headset) or else into the line in on the sound card or audio interface. Again, it's a headphone output going into a line-level (or mic-level) input, so try the divider or potentiometer until it sounds good.

    Are you ultimately planning on transmitting and receiving analog signals such as audio, or are you wanting to transmit digital data?


    Torben
     
  16. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    It won't, resistors don't add distortion.

    Two resistors in a standard attenuator is all you need, making the bottom one a potentiometer would make the level adjustable.
     

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