Personal View site logo
AT875R mic phantom powered directly by the GH2
  • balazerbalazer

    Here is a small secret: some microphones that require phantom power with a minimum of 9-12 V will operate happily using the 2.5-v "plug-in" power provided by the GH2's mic port. I have my GH2 set up with the Audio-Technica AT875R, and I am very pleased with the results.

    More details: http://personal-view.com/talks/discussion/3197/at875r-mic-phantom-powered-directly-by-the-gh2#Item_7

    Audio samples: http://personal-view.com/talks/discussion/3197/at875r-mic-phantom-powered-directly-by-the-gh2#Item_11

    Which phantom powered mics will operate on such a low voltage? Electret condenser mics (i.e. permanently charged) are good candidates. You'll also want a mic with high sensitivity, to give a high SNR given the noise of the GH2's pre-amps and the quantization noise of 16-bit samples. I speculate that mics that can operate on a low-voltage battery are good candidates. But ultimately you'll have to test the mic to see how well it works. Here's more info: http://recording.org/pro-audio-gear/30016-phantom-power-is-a-mystery.html

    How do you wire the mic cable? From my testing, the AT875R can be wired with XLR pin 3 unconnected, or shorted to pin 1, which apparently means it is impedance balanced. Here are wiring references:
    http://www.audio-technica.com/cms/site/4ffc7039c199613a/index.html/index.html#unbalancedinput http://www.benchmarkmedia.com/discuss/feedback/newsletter/2008/05/2/helpful-how-tos-how-properly-connect-balanced-outputs-unbalanced-input

    You must lose something by operating the mic under spec, right? Generally speaking, the max sound pressure level before distortion will be reduced somewhat, and the sensitivity will be reduced a tiny bit. Judging by the specs of other Audio-Technica shotgun mics that can operate on phantom power or from a 1.5-V battery, the max SPL is reduced by about 10 dB. Even with that reduction, the max SPL is still quite high - so high that if you are in that environment, you better be wearing earplugs. I tested some loud sounds, and I was getting distortion inside the GH2 with the mic level setting set to 1 (the lowest gain setting) before I got any distortion from the mic.

    Of course the weak point in any GH2 mic connection is the 2.5-mm jack. I got the highest quality cable with a right-angle connector that I could find, and made my cable just the right length to keep it secure and out of the way. The link is unbalanced, so to minimize interference, use a shielded cable and keep it short.

    The GH2's lack of real-time audio monitoring prevents the use of the mic port for any application in which the audio is critical. But you can work around the lack of monitoring to a certain extent. Plug the mic into something that does allow monitoring (e.g. the Zoom H1), and do some walk-around tests to identify problems. I found and eliminated noise coming from my shock mount, cable, and XLR connector. You can also record a short test video and play it back and listen through the GH2's terrible, tiny speaker before shooting.

    The shock mount configuration in my photos is intended to have a very low profile. A more standard configuration would put the shock mount higher and allow for the use of wide-angle lenses. But in my configuration the mic is out of the view of all of my lenses, including the Lumix 20-mm. I swapped and reconfigured the elastic bands to improve the isolation and give a slight upward tilt that keeps the mic out of the lens's view.

    With the GH2 mic level set to 4 (the highest gain setting), speaking in a normal voice from about 3 feet in front of the mic puts the meter at 7 bars, just into the red.

    Compared to the MKE-400, the AT875R has better rejection of off-axis sounds, and the shock mount I'm using performs much, much better than the one built into the MKE-400. I might have been satisfied with the MKE-400, except for its shock mount. Every time my finger touched the camera, you could hear it in the recording.

    Where to get mike:

  • 98 Replies sorted by
  • stoneystoney

    @balazer I heard it workd on 5Dmk2 but didn't know it would work on Gh2. Yes I have the sam mic and would like learn how you did in detail. Thanks!!!

  • John_FarragutJohn_Farragut

    Wow, I have a AT875R and wondered about this. Was thinking of spending money towards a Videomic Pro, but if this works, it will save me money!

    @balazer I found a premade cable. Will this work?

    http://www.hosatech.com/product/443984/XVM-101F/_/Microphone_Cable%2C_XLR3F_to_Right-angle_3.5_mm_TRS%2C_1_ft

    If it does, I will buy immediately and try out. It is not an angled XLR but it will do. And I have a 2.5mm to 3.5mm adapter.

  • balazerbalazer

    It doesn't say how that cable is wired, so I don't know if it will work. My guess is it probably will.

  • John_FarragutJohn_Farragut

    @balazer I will try out. It's not expensive. If it doesn't work, I can always try to create own one. I do hope it does work.

  • sshssh

    @balazer Thank you very much, very helpful!

  • balazerbalazer

    The cable is wired with XLR pin 2 to the tip and ring of the 2.5-mm connector, and XLR pins 1 and 3 to the sleeve of the 2.5-mm connector. It also works to leave XLR pin 3 disconnected.

    The particular XLR connector that I used had looseness between the connector part and the housing, allowing it to rattle sometimes. I corrected the problem by putting some silicone rubber bands underneath the housing cover, so that the connector is squeezed tight against the housing.

    Here's a painstakingly detailed video showing how I reconfigured and mounted the shock mount.

  • balazerbalazer

    A related idea: say you've got a mic that can operate on a single 1.5-V battery or phantom power, but the voltage regulator circuit in the mic won't accept phantom power as low as the 2.5 V provided by the GH2. I think you could build a simple circuit with a DC blocking capacitor to direct the GH2's plug-in power to the battery terminals, and connect the signal lines to the XLR connector with the DC bias filtered out. Here's a wiring reference: http://www.rcrowley.com/CamAdapt.htm

    Maybe it's easier to just use a battery, but I do see value in getting rid of an extra battery and an extra power switch. Having an extra battery and power switch, and not having a LED indicator to show you that the mic is turned on (and most battery powered mics don't), means there's a good chance you'll forget to turn it off when you're done shooting, which means you might have a dead battery next time you go to shoot. Also, there's a chance you'll forget to turn the mic on when you begin shooting. A well-stocked videographer will always have spare batteries in his bag.

  • sshssh

    @balazer You explained it so thoroughly, even I can do it! Can't thank you enough. Would you be so kind to post a quick audio test (built-in/mke400/AT875R)?

  • stoneystoney

    @balazer Thanks a lot for the good stuff. About the xlr cable, would something like this work?

    http://www.amazon.com/gp/aw/cr/B000068NZG/

  • balazerbalazer

    I have uploaded short test videos of the AT875R, MKE-400, and the GH2's built-in mic. The camera was 3.5 feet away. The audio is original, all recorded in the GH2. (download the source files) The GH2's recording level was set to 4, and the MKE-400's boost setting was off.

    http://minus.com/mGH2_mic_tests/1g

    stonebat, that cable isn't wired correctly for the GH2 and AT875R. It's meant for connecting a stereo mic to a stereo input. The mono-to-stereo cable is the one that's more likely to work. The stereo-to-stereo cable would probably work, but you'd only get sound in one channel.

  • John_FarragutJohn_Farragut

    @stonebat I have bought the Hosa XVM-101F (that's the mono to stereo version), but it may take a week before it arrives. Will report if it works once I have it.

  • sshssh

    @balazer You are the best!

    MKE400 produces high frequency hiss that is not present with AT875. Would setting MKE to "vol +" and lowering GH2's mic level help?

  • balazerbalazer

    ssh, I've added a boost/no-boost MKE-400 comparison.

    http://minus.com/mGH2_mic_tests/1g

    Using the MKE-400's boost setting seems to reduce its noise somewhat.

  • sshssh

    Yeah, lower, it but it is still there. Sennheiser is cheating, AT875 is a clear winner.

  • gamebgameb

    @balazer Great topic! Great inspiration! AT875 sounds much better than the MKE400. Was never a real fan of it neither of the Rode Video Mics. Since a long time I am thinking about a really good sound solution for the GH2. I am working now with an azden mic support which is not very high, so its fine for me and for now I was using a normal length shotgun with a 1.5V battery. The shorter version of that mic is not so directional, I prefer the longer one. Regarding the mono-stereo issue: If you solder a "bridge" between the two channels of the 2.5 stereo plug, you a have the mono signal on both GH2 channels. A few month ago I tried the classic interview electrovoice 635A (omni-directional) dynamic mic into the GH2 (I think with a low to high impedance matching adapter cable, not sure) and it sounded very nice. So I thought to try out the Beyerdynamic M201TG (which is even 1 inch shorter than the AT875), but with very directional characteristics - off-axis noise rejection - and see how that sounds for voice recording. The M201TG is one of the best mics since ever, don't know if its good for our purposes. Does anybody have this mic and can test it?

  • balazerbalazer

    Those are dynamic mics, with lower sensitivity. I think you need a really good pre-amp to get good results with them for anything except loud or close subjects. Did you get a loud enough signal from your Electro-voice 635A into the GH2?

    The mono-to-stereo cable wiring I described earlier gives you sound on both channels. You can't use the stereo-to-stereo cable and bridge the two channels. That would short XLR pin 2 to pin 3, which means you'd get no sound.

    The wiring I described is suitable for most mics that require phantom power. But technically, my cable wiring is not supplying phantom power, since it doesn't put the same voltage on pins 2 and 3. So it might not be a good thing to try with a dynamic mic. The current could damage a dynamic mic. For a dynamic mic, I think you need a blocking capacitor. This wiring should work: tip and ring to a DC-blocking capacitor and then to XLR pin 2; sleeve to XLR pin 3. Connecting just the tip or ring instead of both gives you a little more sensitivity, and sound on just one channel. I don't know if there are any issues of impedance matching with the GH2 and dynamic mics.

    My whole exercise was to find a good mic that would work well with the GH2, rather than finding a way to adapt any good mic to the GH2. To use any good mic, you really need a pre-amp with more gain and less noise, and phantom power at 12 or 48 volts.

  • gamebgameb

    The signal from the 635A into GH2 was perfect. I just don't use it because I don't use these kind of classical interview situations with an omni-directional mic, where the interviewer holds the mic in his hand. But thats why I thought. Lets try the M201TG.

  • gamebgameb

    This is what you need for dynamic microphones: http://www.ebay.com/itm/Pearstone-LMT100-Low-to-High-Impedance-Matching-Transformer-1-5-/110825168019?pt=LH_DefaultDomain_0&hash=item19cdb1dc93#ht_1363wt_1111

  • balazerbalazer

    I don't think impedance conversion is required to use these dynamic microphones with the GH2. They are low impedance microphones. You just need to block the DC voltage. The bigger issue with dynamic mics is their low sensitivity. Used with the GH2 and without an external pre-amp, they will only be suitable for loud or close subjects.

  • AfricaGH2AfricaGH2

    I own a AT4073a, do you think this will work?

    I have an existing 3.5mm TRS to XLR cable, wonder if it's wired correctly, guess I could use a multimeter? I miss my XLR audio on my HMC40!

  • balazerbalazer

    The AT4073a is not an electret mic. You could try it, but I would expect the performance to be significantly worse, if it works at all.

  • John_FarragutJohn_Farragut

    @stonebat I have received the Hosa XVM-101F (that's the mono to stereo version), and it works! The cable is just long enough to put the AT875R on a Rode camera shock mount. Seems to give plenty of level too for short distances (meaning standing directly in front of the camera).

    It's this cable, but I bought it on eBay: http://www.hosatech.com/product/443984/XVM-101F/_/Microphone_Cable%2C_XLR3F_to_Right-angle_3.5_mm_TRS%2C_1_ft

    Yes, it is not an angled cable, so it does stick out much, but at least it works! Because it stick out, you can't practically use the EVF without bumping the cable. I will make my own angled cable later when I have the time. The AT875R is one of the best buys I've ever made! So versatile and good quality.

    @balazer The wiring of the Hosa cable is exactly as you described: The sleeve to XLR pin 1 and 3, and tip and ring to XLR pin 2. Thanks for letting me save some money!

  • zcreamzcream

    @balazer I just looked at your video. I am pretty sure that the mic will be seen if use any of the 12mm, 14mm or 20mm pancake lenses. Have you tried using any of these lenses for video ?

  • stoneystoney

    @John_Farragut Cool. Thanks man!!! Let me think about the sticking part, too.

  • John_FarragutJohn_Farragut

    Let me think about the sticking part, too.

    @stonebat Well, silly me. You can of course suspend the mic further forwards, suspending the XLR plug itself (although the XLR plug is just a tad loose, so I will have to see if it picks up any sound). That way, you have much more clearance. There's still a little bit bumping possible, but much less! It would be even better if the cable went upwards. Here are some pics:

    Hosa1.jpg
    1024 x 768 - 135K
    Hosa2.jpg
    1024 x 768 - 134K
Add a Comment