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Thread: Microphone Troubleshooting

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    Microphone Troubleshooting

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    I have a (very) small home studio with a Yamaha MG82cx mixer feeding my HP desktop running Audacity.

    Last Christmas, my wife got me an MXL 990 condenser mike. It's performed well enough for my needs up until lately.

    It still seems to work decently at low volume levels, but as input increases, it quickly saturates and starts clipping the signal.

    I checked all cable connections and the cable wires themselves and found no issues. I removed the connector covers to expose the soldered connections to enable voltage readings. Without the mike attached, phantom voltage is a solid 48vdc. As soon as the mike is connected to the cable, phantom power measured at the mixer drops to 30 - 35vdc. On the chance that the phantom power in my mixer had gone bad, I connected a separate phantom power supply, with the same results.

    Something is causing that mike to load down phantom power.

    Is there any way to troubleshoot the mike's internals, or is the only way to salvage this mike a rebuild board?

    Thanks in advance.

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    The phantom power specification calls for 6.8k resistors in series with the 48V supply in the mixer so a voltage of 30-35V with the mic connected is perfectly normal.
    JRP Music - Audio Mastering and Restoration
    http://www.jrpmusic.co.uk

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    Are you in a part of the world that presently may have high humidity in the air? Mic capsules don't particularly like moisture on them which can cause a variety of problems. Moisture from your breath can also get onto the capsule.
    You might try drying out the mic by putting it in a plastic ziplock bag with a couple of packets of desiccant such as the image below. I have a couple of mics that seem more prone to moisture than others and usually they come back if dried out a couple of days like this.
    Attached Thumbnails Attached Thumbnails damp-mic-jpg  
    Mark.......

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    Regarding the measured phantom power, I did some checks a while back with loading of mics on phantom as in the link below. Your measurement is in line with what I had gotten. .....(ignore the CAD M179 values, as it had some functional problems and I had to replace an IC in it)
    Phantom Power for Oktava MK-219 Mic
    Mark.......

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    Oh, you *might* say it gets a bit damp around here, just a bit south of Seattle. <g>

    I keep all of my mikes in plastic bags with desiccant packs. Absolutely necessary around here. And I never use the mike without a sock to (hopefully) block moisture and help a bit with plosives. The way I see it, it's excellent advice no matter where you might be.

    Still, it's been a while since I regenerated my desiccant packs. Maybe I should try that and see if there's any improvement....

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    Hmm, the spec for the MXL gives LESS than 3.0mA from 48V but the figures suggest a current pull of 3.8 to 5mA?

    This could indicate a problem with the electronics in the mic or the drain could be within tolerance. Try the drying out procedure first but if there is anything wrong with the mic I suspect it will be the capacitor capsule and changing that I think I would leave to the mnfctr?

    Just seen "sock"! Do you mean the actual foot covering? If so get a proper pop shield!

    Dave.

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    Dave,

    I believe we're thinking along the same lines concerning the current draw. I'm thinking I'll make up a short test cable that will allow me to take current readings. But simple things first. Verify dry.

    As for the sock, yes, I mean a foot covering.

    I also have a "proper" pop shield.

    Using a sock or handkerchief over the mike has been around since mikes were invented, I do believe. <g>

    I like doubling up on moisture shielding. It's like chicken soup. It might not help, but it certainly won't hurt!

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    Quote Originally Posted by Bard Skye View Post
    Dave,

    I believe we're thinking along the same lines concerning the current draw. I'm thinking I'll make up a short test cable that will allow me to take current readings. But simple things first. Verify dry.

    As for the sock, yes, I mean a foot covering.

    I also have a "proper" pop shield.

    Using a sock or handkerchief over the mike has been around since mikes were invented, I do believe. <g>

    I like doubling up on moisture shielding. It's like chicken soup. It might not help, but it certainly won't hurt!
    Don't make up a short test cable if you think the resistance of a standard one is significant? It is not, 5mtr XLR-XLR cable would only add tens of milliohms to the phantom power path.

    If you mean a test cable such that you can insert an ammeter? Again, don't bother, you have current sense resistors already. Check the phantom voltage off load then with mic connected. Ohms law will tell you the current. Don't forget, the juice is fed from TWO 6k8s in parallel so it is volts drop over 3k4.

    Dave.

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