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Microphone and camera using same power sounds like crap

Discussion in 'Audio' started by JohnWin, Feb 16, 2018.

  1. JohnWin

    JohnWin

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    Nov 24, 2016
    Hi,

    I'm building a camera shoulder rig and want everything (camera, monitor, light, microphone) to run off of the same battery. So I made a power distribution box with step down voltage regulators.

    Everything works great except for the microphone. It's making some weird pulsing sound. I'm assuming it's the power feeding back thru the output. The reason I think that is because if I power the camera with its own battery the mic works fine. the only time the problem occurs is when the mic and the camera are both working off of the same power supply.

    I've tried putting a capacitor between the + and - and also tried using a diode different places inline. But those were shots in the dark and didn't work.

    Any ideas would be great! Please dumb it way down tho.
    Thx!
     
  2. Harald Kapp

    Harald Kapp Moderator Moderator

    9,230
    1,861
    Nov 17, 2011
    A capacitor alone will help only so much. You need a filter with a series impedance, e.g. an unductor that blocks higher frequency noise but passes DC. You can buy off the shelf modules e.g. in the car accessory section of your favorite store (e.g. like this one) or roll your own (see e.g. here).
     
    JohnWin likes this.
  3. JohnWin

    JohnWin

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    Nov 24, 2016
    Thank you so much! I'll see if I can get one for the local auto store. Hopefully one with directions in English. Thanks again!
     
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,178
    2,690
    Jan 21, 2010
    Are you using switch mode regulators? They can be very noisy.

    Even with this, you can also have problems caused by ground currents.
     
  5. AnalogKid

    AnalogKid

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    Jun 10, 2015
    Please post a schematic and photos of your regulator box.

    ak
     
  6. JohnWin

    JohnWin

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    Nov 24, 2016
    I'm not sure what switching mode regulators are. So idk. I'll attach a photo.
     
  7. JohnWin

    JohnWin

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    Nov 24, 2016
    Ok I uploaded a photo. I'm not sure it worked tho. I don't see it.

    I don't have a schematic. There's really nothing to it. Just an input from a battery going to step down voltage regulators then to there connectors. Oh an there's a switch.
     
  8. Audioguru

    Audioguru

    2,573
    581
    Sep 24, 2016
    You never said the part number of the voltage regulator, its input and output voltages and the input and output capacitor values.
    You say there is more than one voltage regulator. Why?

    When posting, there is a button that says, "Upload a file" which is where you browse the schematic on your computer, click on it and click the "open" button.
     
  9. JohnWin

    JohnWin

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    Nov 24, 2016
    Ok the part # of the voltage regulators is LM2596 DC-DC HW-411 They are the variable type. I get them on ebay and use them all the time. I use one for each voltage I need. On the rig I have a camera which takes 8.4V, monitor 12V, and the microphone at 1.5V. So there are three regulators.

    I don't have a schematic or photos of it at their own URL i can use. Honestly there's not that much to it. I think the problem is im powering the camera and the microphone from the same source but thru there own regulators then plugging the mic into the camera which is grounding them together. IDK tho.. I hope the module @Harald Kapp suggested works.
     
  10. AnalogKid

    AnalogKid

    2,297
    646
    Jun 10, 2015
    Switching regulators are inherently noisy, both through connecting wires and through radiation. The way the regulator inputs and outputs are wired is critical to their noise performance. Photo?

    ak
     
  11. JohnWin

    JohnWin

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    Nov 24, 2016
    That's interesting. Its a big pile of spaghetti too. But the connection are staight foward. the inputs of the three regulators connect to the + and - of the battery. And their outputs go straight to the device via a connector and cable.

    I've got to run into town but will be back in a few hours. I'll post the pic when I get back. Do you know a good place to host the pic so it has a URL? Thx!
     
  12. AnalogKid

    AnalogKid

    2,297
    646
    Jun 10, 2015
    A big pile of spaghetti is the worst possible wiring plan for anything even remotely involving audio.
    Use the "Upload a File" button to upload a file.

    ak
     
  13. Alec_t

    Alec_t

    2,663
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    Jul 7, 2015
    Are you using a star ground system? If not, ground currents from the camera and supplies may get superimposed on the microphone signal.
     
  14. JohnWin

    JohnWin

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    Nov 24, 2016
    image.jpeg

    Hopefully there is a photo attached here
     
  15. JohnWin

    JohnWin

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    Nov 24, 2016
    No, I don't know anything about a star ground system. But that sounds exactly like whats happening. I'll look it up. Thanks!
     
  16. Alec_t

    Alec_t

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    702
    Jul 7, 2015
    Do you have a spec for the mic? Normally an electret mic rated for 1.5V would get its supply via a load resistor from a higher voltage source and that supply would be decoupled by a capacitor.
     
  17. JohnWin

    JohnWin

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    Nov 24, 2016
    Here are the specs for the mic:

    • Transducer Principle: Back Electret Condenser
    • Directivity Characteristic: Cardioid
    • Frequency Response: 50Hz-16KHz
    • Sensitivity: -32dB±3dB(0dB=1V/Pa at 1KHz)
    • Sensitivity Tone Up: +10dB
    • Bass Filter: 60Hz 10dB/octave
    • Output Impedance: 2000Ω±30%
    • Power Requirement: 1.5V AA battery
    • Net Weight: 160g

    That load resistor and decoupled by capacitor sounds like the way to go. I just don't know how to do it. But now that you've given me the keywords i can try to figure it out. I'm assuming it would be best to come off the volt reg for the camera which is 8.4v? Or would it be better to come directly off the battery? Thank you so much for your help!

    I went to three different stores looking for that Auto Filter Module today. Nobody had them. So i guess I'll order one online. I can try the resistor capacitor thing while I wait for it to arrive.
     
  18. JohnWin

    JohnWin

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    Nov 24, 2016
    I don't think it's the regulator because when I put its own battery in the camera the mic works great. And its still on its regulator. t really seems to me that it has something to do with them both being on the same power supply.
     
  19. dave9

    dave9

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    171
    Mar 5, 2017
    Based on those specs I saw a mic listed the same, claims 100 hours playtime.

    http://www.takstar.com/en/product/detail-16-79-15-289

    This suggests a couple dozen mA current at most. With that in mind, I'd run a linear regulator (LM317 or whatever, with a small uF cap after it) to the mic from the camera 8.4V and if that wasn't quiet enough, skip the camera step down board and run it straight from the main battery output instead.

    Frankly I'd want a linear regulator anyway, would not run a mic off a SMPS.
     
  20. Audioguru

    Audioguru

    2,573
    581
    Sep 24, 2016
    You can't hear the 150kHz noise from the switching regulator but it might beat with the frequency of the second or third regulator or any digital encoder or decoder you are using.
     
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