How to power an unpowered microphone

Discussion in 'Camcorders, Action Cams & Video Making Forum' started by Mythobeast, Feb 15, 2014.

  1. Mythobeast

    Mythobeast
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    I purchased a Vixia HFM500 camcorder and a lavalier microphone to do some cheap documentary interviews. I found out once they got here that the microphone isn't powered, and the camcorder won't power an unpowered microphone.

    Is there an inexpensive way of getting power into the mix so I don't have to purchase another microphone?
     
  2. Terfyn

    Terfyn
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    Look at Amazon or Maplin for a Mic Preamp. Or buy a Yoga stereo tie clip mic from Maplins . £34.99 It works very well for both my camcorder and my PC (voiceovers)
     
  3. Chelters

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    Buy a new, battery powered mic from Amazon. Seems to be plenty of them around the £15 mark.
     
  4. rogs

    rogs
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    On the face of it, this doesn't seem to make any sense?... all modern camcorders - like this Canon model - will have 'plug in power' available from the external mic socket.
    It is also extremely rare to find a lavalier mic that doesn't use 'plug in power'. Only dynamic mics will not require any power, and would work here anyway!

    Where an electret lavalier is being used with a mic input that doesn't provide plug in power (like many audio mixers for example) then you would need to power the mic - typically with a 1.5V AA battery fitted in an appropriate inline connector.

    But the vast majority of electret lavalier mics will simply draw their power from the camcorder mic socket.....are you sure this doesn't work?.....
     
    Last edited: Feb 15, 2014
  5. Terfyn

    Terfyn
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    This may bear repeating that as the mic input on your camera will be stereo, it is worth buying a stereo mic rather than a mono one.
     
  6. Trollslayer

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    Maybe it is a dynamic microphone, again can you provide details so we can help you?
     
  7. rogs

    rogs
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    I think that may depend on what you need the external mic for Terfyn..... if you are looking to record dialogue, rather than general 'ambient' sound, then many people prefer a mono track.
    Many mono lavs are pre-wired to give you 'dual mono', by sending the same audio to both camcorder tracks.
    This is true of the cheap Neewer lav mic we've discussed before, for example. Notice the the stereo jack in the picture here:
    Neewer 3.5mm Hands Free Computer Clip on Mini Lapel Microphone: Amazon.co.uk: Computers & Accessories

    Of course you might like to have two mono mics connected... then a cheap splitter cable like this one:
    3.5mm Jack Headphone/ Earphone OR Mic: Amazon.co.uk: Electronics
    might be useful?
    That would allow interviewer and interviewee to both be 'close miked' for better results.....
     
  8. Mythobeast

    Mythobeast
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    Thank you, everyone, for your quick responses. In answer to your questions:

    The microphone in question is a Giant Squid Audio omnidirectional lavalier microphone (Omnidirectional Mono Microphone

    For reference, the camcorder is a Vixia HF M500. I received a message from Canon support yesterday stating "The external microphone will not function if you are not using a powered external microphone." Totally weird, but there you have it.

    The purpose to which I'm putting it is for recording interviews for a documentary. We have an external digital recorder (Zoom H1) which will be recording the interviewee's responses. That works just fine with the GSA omnis. The interviewer will always be sitting right next to the camera, so I was hoping to match the audio intake with an identical microphone plugged into the camera.

    I'll look into a pre-amp, but any solution for more than $100 would make it cheaper to just pick up a second H1 and clip that to the interviewer, just using the camcorder's built in microphones to sync up the sound.

    Thanks again!
     
  9. Terfyn

    Terfyn
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    On the face of it, this doesn't seem to make any sense?... all modern camcorders - like this Canon model - will have 'plug in power' available from the external mic socket.

    I have yet to find a camera with phantom power available as a switchable option.

    I think that may depend on what you need the external mic for Terfyn..... if you are looking to record dialogue, rather than general 'ambient' sound, then many people prefer a mono track.

    If a stereo mic is being used for, say, a voice over (as I do) the fact that both mic capsules are picking up the same audio effectively makes the signal "mono". I have never used a mono mic and rely on the signal location to provide the position in the stereo field. In any case, the video editor will have the facilities to create a "mono" signal if required.

    I note that the Giant Squid lavalier mic has a stereo plug fitted.
     
  10. Mythobeast

    Mythobeast
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    Yes, but I believe that it's faux stereo - same signal on both channels.
     
  11. Terfyn

    Terfyn
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    The Zoom does have phantom power switchable from inside the unit. I have noticed that there is considerable improvement in performance of a standard mic with this switched on.

    I'll look into a pre-amp, but any solution for more than $100 would make it cheaper to just pick up a second H1 and clip that to the interviewer, just using the camcorder's built in microphones to sync up the sound.

    Not necessary if, as I suggested, you buy a powered mic for a third of the cost. I use two electret condenser mics, both made by Yoga, one is the lavalier mentioned before and the other is a hand held mic with the battery inside the handle.
    I use the "tie clip" mic for both camera and PC voiceovers. The hand held is usually mounted on a spare tripod close to the sound source.
    Although modern SD card based cameras do not make any motor noise, the sound of the operator can often be picked up by the on-board mics, so a remote mic is a better option. The camera is away from the subject to gain the shot but the mic should be close to the subject to gain the sound.
     
  12. rogs

    rogs
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    That would be my preferred option......
     
  13. rogs

    rogs
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    Just to be clear..... The Zoom H1 only has 'plug in power'.
    If you need 'phantom power' (48V or 24V) then you would need to go for the Zoom H4, with its XLR inputs....
    You normally only require true (48V) 'phantom power' for professional condenser mics.
    Most electret (lavalier) mics only require 'plug in power' (typically 1.5V) for the internal capsule FET preamp...
     
  14. Terfyn

    Terfyn
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    Its "horses for courses" I use my Zoom H2 for ambient recording and the plug in mics for sync'd sound if possible. I split the audio track from the video in the editor and work on them separately. The problem with the Zoom is that the sound made by handling can become a nuisance so, for me, pinning a Zoom to an interviewee is not an option. I would use a mic on a low table or on a stand.

    Just to be clear..... The Zoom H1 only has 'plug in power'.
    If you need phantom power (48V or 24V) then you would need to go for the Zoom H4, with its XLR inputs....

    The Zoom H2 has switchable power available at the mic input. Only 2.5v but it makes a considerable difference.
     
  15. rogs

    rogs
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    Yes it would.... If the mic needs 'plug in power' you need to switch it on!. Without it, an electret mic will not work at all! :)

    (the 2.5V is nominal... it will be fed through a series resistor, so the actual voltage presented will vary from mic to mic).
     
  16. 12harry

    12harry
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    Just my hapenthworth:
    I've had electrets that work in one audio device and not others . . . on checking with a DVM it seems some gear outputs a slightly lower voltage.
    For VO's I use one of those Budget tie-clip mics (5 for £6 as I recall, sugested a while back, here.). Purists may believe their £XXX tie-clip mic will be better (and the cable might be ), but the greater failing exists in the Artiste, as in my case.
    At those prices I have some spares and any that fail the "lower-voltage" device are colour-coded so I will normally avoid them.
    For serious music recording I'd be inclined to use moving-coil mics which (as others mentioned) avoid this power issue altogether.
     
    Last edited: Feb 16, 2014
  17. rogs

    rogs
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    The 'voltage' is largely academic with electret capsules. The microphone capsule manufacturer will specify a 'maximum' voltage that can be applied to the device (typically 10V), and often a 'typical' voltage (usually around 2V.)
    They will also specify a typical current drain (usually around 0.5mA)
    Add to that a variety of 'plug in power' voltages, supplied by different camcorder manufacturers, and a selection of input impedances (which will also affect the actual applied 'plug in power' DC voltage) and you have a recipe for confusion.

    Measuring the 'plug in power' voltage with a DVM makes for even more confusion.
    A modern DVM has a very high input impedance on DC voltage ranges - in the order of 10Mohms or higher - and so presents virtually no load to the 'plug in' power.
    The plug in power 'voltage' will read higher than when a microphone is atually connected.....

    All of which makes very little difference to the actual performance on an electret mic capsule, in practice.

    The reason that some mic inputs have 'switchable' plug in power is to allow dynamic mics to be connected without any problems. In fact, most modern low impedance dynamic mics will use an output transformer, which will essentially ignore the plug in power. A high impedance dynamic mic, without an internal matchng transformr may be affected by a plug in power voltage across the capsule.
    However, as most camcorder mic inputs are designed for electret mics, using a less sensitive dynamic mic will simply result in a 'noisier' soundtrack recording, as the gain has to be increased to compensate.

    For camcorders with external mic inputs, it's almost certainly best to stick to electret mics!......
     
  18. MarkE19

    MarkE19
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  19. 12harry

    12harry
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    Rogs Post#17, I used a DMM since the electret worked OK on one device, but not the other. It seems that low voltage was indeed the culprit.
    I'm well aware the DMM is high impedance. Not sure that really matters - If I wanted to measure (the voltage under load), I would plug-in the electret... but the voltage measurement appeared to provide the answer to the puzzle.
    I marked the mic as I believed it is an odd one, since the other four were happy working into either socket. Of course there could be other reasons, but it did at least provide some insight. . . which I though might help others.
     
  20. rogs

    rogs
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    That certainly sounds like an 'iffy' mic Harry.....
    As I say, the voltages involved are nominal... and are not normally very critical....most electret capsules will work from a single 1.5V AA battery supply.
    Yes , measuring the voltage with the mic plugged in would give a better indicator as to what was happening -- but it would mean taking the mic apart, or at least using some kind of 'splitter' lead...

    What is probably more important here is making sure that people are clear on the differences between 'phantom power' and 'plug in power'.

    'Phantom Power' (normally 48VDC -- sometimes 12 or 24V) is required for powering both the pre-amp and the capsule bias of a professional condenser microphone. It should not be used with 'electret' condenser microphones (it may well destroy them)

    'Plug in Power' is a low voltage, low current DC supply (tyically between 1.5V - 5V). It is designed to only power the internal FET pre-amplifier of an 'electret' condenser microphone. The higher capsule bias voltage is already 'flashed' into the mylar capsule of an electret microphone, during manufacture.

    So -- a conventional professional condenser mic will not work with 'plug in power' (although it won't do it any harm)
    An 'electret' condenser microphone may work with phantom power .. but probably only for the few seconds before it is destroyed!
    These days, almost all cheap 3.5mm jack lavalier microphones are electrets, and need 'plug in power'.
     
    Last edited: Feb 23, 2014
  21. Terfyn

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    So -- a conventional professional condenser mic will not work with 'plug in power' (although it won't do it any harm)
    An 'electret' condenser microphone may work with phantom power .. but probably only for the few seconds before it is destroyed!
    These days, almost all cheap 3.5mm jack lavalier microphones are electrets, and need 'plug in power'.

    Still waiting for my Zoom H2 to destroy my mic!:thumbsdow
     
  22. rogs

    rogs
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    You could be waiting for a while!:)... the Zoom H2 only has a 2.5V 'plug in power' option for electret mics. It doesn't include a true 'phantom power' option, so no likelihood of any mic damage.

    The Zoom H4, on the other hand, offers both 2.5V 'plug in power', plus 24V and 48V true 'phantom power' options, for use with 'proper' condenser mics, via the XLR mic connectors.
    So that device could be set to destroy both electret - and dynamic mics - if plugged into the XLR inputs with the wrong menu settings (i.e. 'phantom power' on)....
     
  23. 12harry

    12harry
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    Yep, thanks for that clarity, I did mark the offending mic with nail varnish and bought some more at the bargain price...these all appear to be unfussed by the slightly lower voltage.

    Also, it is likely that pro-style condenser mics with XLR connectors, will probably require 48v "Phantom power" although these days I would expect them to work from slightly lower voltages too. However the H2 is clearly aimed at the budget electrets ( although some of these are far from Budget prices ).



    [Not Electrets]
    ...I managed to get two m/c XLR mics quite cheaply and so far they appear to work OK, even for music. As you know m/c mics also have higher SPL capabilities, so they could be useful for recording drums, etc. The only real inconvenience is making an adaptor to 3.5mm jack - something I may do quite soon. In the meanwhile the mics work through a beautifully made sm preamp, which has a mono phono output. The 5m XLR cables are terminated in 1/4 inch jacks - Standards, Huh!
     
  24. Mythobeast

    Mythobeast
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    Just to satisfy anybody's curiosity, I decided to go with purchasing a second digital recorder for the other microphone. This also justified purchasing a clap-board so that we could better sync up the camera with the three audio sources.
     

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