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  1. Member bakonfreek's Avatar
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    Okay, so I bought an el-cheapo shotgun mic which has a 3.5mm plug on it. I bypassed the little controller board (it had a switch for use with either mobile phones or cameras and used a model specific battery pack) and tacked a cable to the thing. Now, it works with my Sony FDR-AX33 and my Zoom H6 (both of which provide the plug-in power necessary for the condenser), but there's an interesting problem which I have no idea the cause of.

    The Zoom H6, when running on proper DC (or rectified and REALLY well filtered AC), will record from this mic no problem and it sounds surprisingly good given the crap wiring I did on the inside of this thing. It only runs into problems when I am within about 6 inches of a badly designed fluorescent light power supply (or something similarly messy). The Sony FDR-AX33, however, will record a 60Hz hum/buzz no matter what I try. This is not something that goes away. If I run it on AC, buzz. If I run it on the camcorder's battery pack, buzz. If I dial the level back manually, the buzz gets worse (or the signal to noise ratio gets worse--yay, relative metrics). Even going as far in the general direction of away from civilization as my gas money can carry me from Omaha, Nebraska, buzz. This buzz will not go away with a low cut nor with more notching than any sane person would use (later mention makes me believe that this isn't exclusively line power interference).

    There has to be something specific to this camcorder (and camcorders with similar guts--my HDR-CX760 does the exact same thing) that causes this, but what?

    Remember, my Zoom H6 is entirely immune to this unless I have it running on a messy power supply and even then, that hum can be cut with the built in 60Hz low cut. I can't find any helpful documentation (nobody else seems to either have or notice the hum/buzz on battery power), but then again, my "Google-fu" is pretty weak.
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  2. Member Cornucopia's Avatar
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    filtering it out, while it may be necessary, should be seen as a LAST RESORT, but I'd look into the specs of the shotgun mic to see if you've properly shielded it in your modifications first.
    What's the model? Is it balanced or unbalanced? (probably the latter if it's cheap). You may need to redo your wiring in order to reduce your EMI/RFI (leave as little exposed/unshielded as possible). Pix?

    Scott
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  3. Member bakonfreek's Avatar
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    I'm guessing unbalanced. The terminals on the microphone module seem entirely different from the ones in the XLR shotgun mic I have strapped to my HVX, but this is ultimately a guess on my part.

    I still don't get how the Zoom H6 has no problem with the mic while the FDR-AX33 does. Both are tested with just plugging in and (in the case of the H6) enabling plug-in power.

    As for model information, I don't really have much to go off of. It's a module out of one of these el-cheapo DigiPower units from Walmart, but the actual microphone component itself has no identifying marks on it.
    Last edited by bakonfreek; 6th Mar 2020 at 02:04. Reason: add mic information
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  4. Member bakonfreek's Avatar
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    Image
    [Attachment 52247 - Click to enlarge]


    Here's a photo of how it is inside of the shell. I put a bunch of PlastiDip over the exposed wiring where I did my bit (attached a TRS cable in place of the TRRS cable that came with the mic), but the wires coming from the mic were on it when I bought the module and it was potted lazily with some compound which looks like PlastiDip but is softer.
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  5. Member Cornucopia's Avatar
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    With that amount of (electromagnetically) exposed cable, and no shielding in sight, I am not at all surprised that it is getting EMI/RFI. Adding a shielding wrap may help, but since it isn't integrated into the construction, it won't be bulletproof.

    Have a few hunches about the Plug-in-Power also (polarity bias?), but no real way to gauge & test now that system has been modified.

    Can you test compare both record systems with a known-good dynamic mic (which doesn't need P-I-P)?

    Scott
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  6. click on the “Menu” button then select the “Camera/Mic” button. At the bottom of the list you will see the “Audio Rec Level” button. You can adjust the level as needed.

    ..

    ...

    In some cases, manually adjusting volume level can help reduce the
    Hum. Auto gain off.

    ....

    Of course, if it's as wonky/broken as the cx, no hope.
    https://youtu.be/dOlhzY7QMXo
    ...

    Grounding.
    https://cdn.shopify.com/s/files/1/0247/3799/files/preventing_hum_and_rfi.pdf


    ...

    https://www.shure.com/en-US/support/find-an-answer/condenser-mic-for-minidisc-recorder...-plug-in-power

    You bypassed whatever came with the Mic.
    Could be a lot of other issues resulting in the hum.
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  7. Member bakonfreek's Avatar
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    Essentially what I bypassed on the mic's circuit board is a switch to swap the output between either the sleeve (for use on phones, originally used a TRRS connector) or T/R. The actual signal originally passed through a low value resistor (1.5 ohm--1R5 noted on the resistor). It also tapped off a 3V CR2 cell to power it if used with something like a Canon Vixia camera.

    I tested both the H6 and the FDR-AX33 with a dynamic mic. The H6, as expected, did fine. The Sony, well, that was a mess (as with most consumer grade Sony camcorders I have access to which don't have any proper attenuator or "micref: low" option, the levels were way hot).

    _______________________

    click on the “Menu” button then select the “Camera/Mic” button. At the bottom of the list you will see the “Audio Rec Level” button. You can adjust the level as needed.
    I did that before the initial post,

    If I dial the level back manually, the buzz gets worse (or the signal to noise ratio gets worse--yay, relative metrics).
    the buzz seems to be part of whatever noise the signal is competing with. Said buzz is also not audible on a dedicated audio recorder. I wouldn't be surprised if it was just crap audio hardware in the Sony. I haven't had great experiences trying anything external on these things, but usually it's just levels being way too hot. This one doesn't seem related to levels though.

    I also tested using a Panasonic VX870 that I have lying around. No buzz on that, but it has other problems which make it impractical for use.
    Last edited by bakonfreek; 6th Mar 2020 at 11:57.
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  8. https://electronics.stackexchange.com/questions/29379/pull-up-resistor-over-a-microphone

    Might need to stick that resistor back In to bring the Mic back into operating specs. (You'll need to find the model parts spec sheet for the mic module).

    Because you're powering from the camcorder, the voltage is likely different than designed, so you'll need to adjust the resistor value.

    ...

    Otherwise, since you have the excellent h6n, just use that.
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