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Completely baffled: problems with XLR mikes

Discussion in 'Pro Audio Equipment' started by scape, Mar 9, 2008.

  1. scape

    scape Guest

    I am utterly baffled.
    I have been trying to get some lavalier microphones to work with a standard mixer than accepts an XLR jack.
    I have tried 2 different sets of mikes, and 2 different mixers, and I can't seem to get any sound out at all.

    The set up:
    2 x lavalier microphones (a 'set') with mini XLR plug
    -> mini XLR plug to XLR
    -> plugged into mixer Edirol M-100FX
    no sound

    I have tried switching phantom on and off. It doesnt seem to make any difference. I have played with all the faders, trims, mute etc. I have checked one set of mikes for loose soldering.

    In my good few years of AV work, I must be either completely mad, or coincidently have bought 2 dud sets of mikes in a row!
     
  2. bent

    bent No Bad Vibes! Well-Known Member

    It helps to know the make & model of the mic you're talking about...

    There are many different ways to wire many different lavs...
     
  3. scape

    scape Guest

    I would have supplied the information if I knew, sorry about that.

    One set of lavalier mikes are unbranded, bought from a bulk supplier. Here is the spec:
    Technical Data
    Frequency Range 20Hz - 16kHz
    Sensitivity -65±3dB
    Max. SPL 110dB
    Impedance 2.2kΩ
    Power supply 1.5 - 9V
    Dimensions ⌀5mm x 10mm
    Weight 5g

    The other set I bought off ebay (perhaps a mistake) and they seem to be a homemade job (albeit a very high standard) from individual components.
    I got a leaflet with this set and it says the following:
    Type: electret condenser
    Max SPL: 110db
    Freq range: 50hz - 18khz
    Impedance: 1k (k ohms I assume)
    Sensitivity -50db ~ -60db +/- 3db @ 1khz
    Operating voltage: 1.5 - 9v

    Now I've noticed both of these mikes are asking for an op voltage of 1.5 - 9v. The homejob leaflet expalins that "this electret microphone requires phantom power of 1.5 - 9 volts ... All modern [equipment has] phantom power as standard"

    The last time I checked, phantom power came in 24volts or 48volts? At least, this is all I've ever seen on mixers and audio recording units. Perhaps this is the stumbling block.
     
  4. BRH

    BRH Active Member

    Mini XLR or TA5F needs to go to a adapter for power.... something like this.

    http://www.trewaudio.com/store/product.php?productid=888&cat=0&page=1
     
  5. scape

    scape Guest

    When you say 'mini xlr' do you mean a 'lavalier microphone'?
    The end could be anything, like the ones i bought off ebay. They started out as a 2.5mm jack... i changed it to an XLR.
     
  6. If these mics had a 2.5mm jack on them to start with i'd guess that a fault has occured when you changed them to XLR connections. Maybe check over them again.

    From the specs above it appears they are electret condensor mics so they should have an internal charge already so there should be no need for an external phantom power supply.

    Have you tried plugging another type of mic that you know works into channel 1 or 2 of the Edirol Mixer? This will pin point whether it's the mics or mixer, although it sounds like it's definately a fault with the mics.

    What was the make/model of the other mixer you tried these mics in?
     
  7. scape

    scape Guest

    I followed several tutorials and consulted a couple of books when re-wiring to XLR. I am fairly confident I have got this right. Also, the store-bought unbranded lavs have premoulded mini XLRs on them, so if there was a problem with the wiring in the modified ebay lavs, in theory the unbranded lavs should have worked.

    Yeah, that's what I thought.

    Yes, I have tried plugging in an Optimus omnidirectional dynamic mic into each channel of the mixer, and they work perfectly fine. This is why I'm trying to establish its either a fault with both sets, or I'm doing something fundamentally wrong.

    So far I have tested the 2 sets of lavaliers (4 in total) in the Edirol as above, a Stanton M304 (DJ Mixer) and a Zoom H4 static recording unit.

    Interestingly, when experimenting with the settings on the Zoom H4, the unbranded lavs momentarily 'spring to life' when switching between phantom 48v mode, and phantom off mode. I am wondering if a capacitor is decharging during this process, and as the voltage drops past 9v the lavs operate for a moment, then stop working again. This lasts around half a second.

    So it seems I need to put in a phantom 'converter' or something, but these seemingly cost a fair amount in relation to what I am trying to achieve... plus a deadline is looming; I was hoping for a quick fix.
     
  8. RemyRAD

    RemyRAD Guest

    The problem you're having with these is that they were actually designed to plug into a wireless microphone pack. Such as the Lectrosonics, Shure, Sennheiser, etc.. They are not designed to be plugged directly into a console with phantom power. The adapter won't work. They do not accept phantom power.

    This is how they are wired and how you are supposed to use them:

    It is a common ground with unbalanced audio output on one wire (whichever is indicated in the paperwork). The other wire gets +1.5 to +9 volts average but can survive well beyond 18 volts. These Chinese capsules are available at your local Radio Shaft for $3.98 or something like that. They used to be $.89. You might get one unbelievably good sounding. You might get one unbelievably bad sounding. Either way, this is unbelievably stupid sounding from an equally unbelievable Moderator. But that's what happened here. Furthermore, it is not a balanced output capsule. You would need a transformer or an active device such as an Op-Amp or 2 to create a differential balanced output.

    The microphone actually has a tiny field effect transistor & tiny capacitor as you surmised. Its current drain is so low that it will flash into life for a few seconds when it is making and breaking connections that have any voltage on them at all. A single AA battery will last for a few hundred hours on virtually any back electret microphone with a simple FET impedance converter. The more sophisticated higher output, quality oriented units such as the venerable Shure SM 81 have more sophisticated internal circuitry and require more current. That's why those don't accept a AA battery. But they will work on virtually any Phantom voltage from 5 to 48 volts. I wouldn't run them on a voltage that low but you can if you need or want to. 48 volts is a necessity for unpolarized capsules. Not for the electronics within per se. An original Neumann U87 uses a single 2N3819 N channel FET. That hardly requires any current but the capsule needs 48 volts to polarize it. Even the cheap Chinese NADY condenser microphone doesn't utilize a pre-polarized capsule and requires a full 48 volts.

    So now that you know this, how much money did you waste on these $.89 capsules and why?
    Ms. Remy Ann David
     
  9. scape

    scape Guest

    :shock:
    :?
    ok.

    I think the best way to take this is like this:

    I would like to have 2 lavalier microphones somehow plug directly into a mixer. Any suggestions as to how this can be done would be greatly appreciated. Not wireless, just a direct connection.

    I'm confused about this common ground business - the ebay mics only had 2 connections, and the unbranded ones have a 3 pin mini xlr plug on the end - so one assumes this has 3 connections.

    At the end of the day I just want something that works. I want 2 tiny weeny micrphones in a small space to be heard by a mixer which will take a normal sized XLR plug. I don't care what needs to go between the physical mic and the xlr plug on the mixer, just the absolute cheapest option (so no wireless folks!).

    Soon this will all be too late anyway...
     
  10. bent

    bent No Bad Vibes! Well-Known Member

    Without the make and model you're asking us to do guesswork - and most of us don't like guesswork.

    When it comes to lavs there are far too many different wiring schemes and voltages to take into consideration.

    Can you at least post a pic of the elements and the connectors for each mic you have this problem with?

    We might be able to identify them that way.
     

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