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05-30-2016, 07:52 AM   #1
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Pentax K-3 video: external mic trouble

After having read Pentax-Forums for years, I finally decided to become a member myself And I will just start off my career with a troublesome help request...
Increasingly using my K-3 for video shooting I have got stuck with the following: Using 1,5V-powered professional Sony lavalier mikes of ECM-44B/55B type I get great interview sound but also a constant twittering noise rendering all recordings more or less useless. First I thought it is the mikes' fault (since the built-in microphone as well as my 9v-powered Rode Stereo Videomic Pro work flawlessly) until I discovered that any TRS cable or plug connected to the K3's mike port (unless it is the Rode SVMP) makes the camera produce and record that noise. So my request for help is this: Could you proud K3 owners just plug any simple TRS-cable into your camera and tell me what happens? Just switch the K-3 to video mode and pull up the manual recording volume in the video menu. You should hear the noise right away on your headphones but it should also be visible on the level meters. I just have to find out whether this is "normal" or whether it is my specific camera! BTW, turning off shake reduction does not help Of course I understand that any cable may introduce noise to the system, this way the Sony's XLR to TRS adapter cable may be the culprit but then again with the very same cable the lavaliers work like a charme with any audio recorder... Or is it the K-3's 2V-feed-current in the mike port which messes things up here? Or do you know of any trick that should be done to the XLR cable? But please try that little experiment described above and let me know! Thanks a lot

05-30-2016, 06:13 PM   #2
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I just tested it with a PC headset mic and there was no unexpected sound whatsoever.

I also have the SVMP and with it, even when powered off, there is also no hissing noise. No background noise either when I manually set the audio level to 10.

I'd blame the Sony mic. Have you tested it without its own power source?

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05-31-2016, 07:25 AM   #3
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Thanks for trying to check, Adam! I have tried some more mics in the meantime. Some work fine, some have that noise :-( To really check the camera please do the following: Don't try another mikrophone, just plug in some adapter, extension cord or empty TRS-plug. Then put the mic-volume in the menu to 15 and actually record some seconds. That twittering hissing will be ten times louder on the recording, and it is exactly the same noise which I find added with certain microphones like the Sony lavaliers! At volume 10 the hissing will be audible on the recording, too, but it is not yet noticeable during metering preview... Sorry for not making that more clear before :-) Disengaging the Sony's own power source does not help, either. The 44-type simply stops working, while the 55 is less loud and still hissing. Things have actually changed quite a lot over the years: While the SVMP works on my old K-7 as well, the lavaliers and some other hissing companions simply don't... I am just pretty reluctant now to order any new microphone for the K-3 :-(
06-01-2016, 01:08 AM   #4

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I had to look up 'TRS cable' to see what you meant. I just know them as stereo cables with mini-plugs.

Maybe the cable is the problem. Are you using a fancy cable with some electronics in it, like some audio cords feature? Or does your cable have problems with it's shielding? What happens if you use a standard 3.5mm consumer-grade stereo mini plug cable?

Also note that the recommended Pentax mic impedance is 2.2 kilo Ohm ...

06-01-2016, 08:05 AM   #5
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Yeah, I once also started by looking up the terms TRS and TRRS ) The cable is a shielded XLR to stereo mini jack adapter, since the Sony lavaliers as pro audio equipment output to XLR.
I thought this impedance question was more about general compatibility, i.e. the recording volume, and not about side-effects like inserted noise. But this is where my lacking experience in audio/video matters come in... Actually, after checking the specs it looks like my XLR type lavaliers have a (balanced) output impedance of 100 and 250 Ohms respectively... However, the recording quality is great, but maybe the impedance mismatch is indeed the source of the hissing noise trouble... Any audio tech expert here who can confirm this?
The Sony brochure also states that the "naked" lavaliers without power source, intended to be plugged into their wireless transmitters, have an (unbalanced) impedance of 2500 Ohms. Maybe they would actually work better, given the 2V feed current from the camera... Any experienced opinion?

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