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Canon C100 & multiple audio issues

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Rick James
Canon C100 & multiple audio issues
on Nov 18, 2016 at 12:41:35 am

My company has been struggling with multiple audio issues on 2 Canon EOS C100 (mark one) cameras. Camera A has the Dual Pixel Auto Focus update and is running firmware 2.0.7.1.00. Camera B does not have the autofocus update and has firmware 1.0.7.1.00 installed.

Here is a



illustrating the different noise issues. The camera’s have 3 audio issues listed bellow:

1. Unknown distortion on XLR input channel 1 when an external mic is attached (in the top handle grip unit). Sounds like overload, over modulation, clipping (but the audio levels are within good range).

2. When either input is switched to Mic +48 phantom power, there is a constant buzz accompanied by a high-rpm “beating or thumping" sound. The noise only appears when +48 is selected and is heard even when nothing is connected to the XLR inputs.

3. XLR input Chanel 1 presents a “white noise/hiss” sound similar to the common noises produced by a cameras internal mechanisms, only louder. Assuming it is camera noise, it is also present in Channel 2 at a lower level.

HISTORY
Cameras were purchased in late 2014 or early 2015.
Sony microphones from older sony DVCam/miniDVcam’s have been used as the on-camera mic (Sony ECM-NV1 and ECM-MX1)

Distortion in Channel 1 Input appeared in each camera after a firmware update was installed (details unknown).
The +48V buzz in both inputs and the loud white noise/hiss in channel 1 appeared intermittently at first, and gradually became constant (is constant now).

Attempted solutions have included camera reset (using menu option and reset button), update to latest firmware, reinstalling firmware (camera would not accept), using several different combinations of mic’s and XLR cables, trying different audio settings.

Camera’s mic input (3.5 mm plug) works well with no issues. The issues are only with the XLR inputs in the top handle unit.


TEST SETUP
3 different XLR cables used: 6’ low noise balanced *with polarity reversed, 25’ balanced Kopul 3000 Noiseless, 18” balanced Kopul 3000 Noiseless.

7 different microphones used: Sennheiser ME66/K6 super cardio condenser, Audio Technica AT897, Shure SM87A condenser mic, Sony ECM-NV1 and XM1 (from older Sony Cameras), Sennheiser G3 wireless Lav, Sony UWP wireless Lav.


FINDINGS
There is NO DISTORTION when the Shure SM87A mic is connected to Channel 1 with any of the XLR cables, (+48V was turned on in the camera). The +48V buzz and the white noise is still present.

There is NO DISTORTION when the Sony ECM-NV1 connected to Channel 1 with the reverse polarity cable. (+48V was turned on in the camera).

There is NO +48V BUZZ when the Sony ECM-XM1 is connected to Channel 1 or 2 with a balanced XLR cable. (+48V was turned on in the camera).

All other combinations presented the distortion, buzz, and white noise.


CONCLUSION

We need to fix the C100 mic inputs and we also need to figure out what is causing these problems. My understanding of audio signals and electronic circuits is pretty basic but after researching the issues, it seems like there are a combination of possible factors. It seems likely that components inside the preamps in both cameras have become damaged over time. Could this be a result of frequently plugging in powered microphones into the XLR terminal when phantom power was active, or by a combination of activity like misfired cables? AND/OR the usage of the Sony ECM microphones over time possibly reversed the polarity of the C100’s preamps? The Shure SM87A did not present the Channel 1 distortion. I know that most microphones guard against unbalanced cables, etc., but many Shure mic’s add additional protection against voltage fluctuations, reverse voltage, and misswired cables/equipment through a variety of protection diodes and decoupling capacitors that aren’t included in other microphones. The Sony mic’s are wired with their copper shielding split between pin 1 and chassis ground, whereas the XLR cables are only wired to pin 1. Not sure if this has any relevance.

If anyone has suggestions or possible solutions let me know.

Thanks!


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Al Bergstein
Re: Canon C100 & multiple audio issues
on Nov 18, 2016 at 3:27:35 pm

I'd send one in for repair, see what they find. Mine with similar setup do not exhibet this. Canon's repair folks are pretty good and turn around quickly.

Al


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Rick James
Re: Canon C100 & multiple audio issues
on Nov 19, 2016 at 2:26:49 am

Thanks Al. I've heard that about Canon service. We'll be sending them in next week.

Cheers


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