Thread: Epic MX DSMC 1 Power crosstalk interference noise

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  1. #1 Epic MX DSMC 1 Power crosstalk interference noise 
    Hello
    I have a run and gun setup using an Epic MX, a sound devices 302 and Micron Explorer 100 radio mics rece.

    I use a Hawkswood GC-2 D-TAP distributor to power all 3 elements.
    https://www.hawkwoods.co.uk/Cine/P/GC-2

    All the cabling is of good quality

    Attached are pictures of the set up

    My issue is that the when I attach the epic power cable to the D-tap distributor with the 302 & radio mics attached, I get a pronounced clicking sound on the audio channels, even when the radio mic receivers are turned off. When I have a separate battery for the epic from the audio elements, the clicking disappears. After much investigation with Sound Devices, Hawkswood and Micron, it seems that the Epic has an oscillation issue that is leaking into the audio circuit.

    Does anyone have any idea if and how I can rectify this issue?
    Any thoughts most welcome

    Thank you
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  2. #2  
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    The most common cause of this type of noise is a ground loop between power and audio grounds. Does the 302 have a ground lift switch to isolate audio ground from power ground?
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  3. #3  
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    Do you get the noise if your Micron receiver is not connected? Might check what cables you are using there if not.

    PoweringExternal Powering(A) RECEIVERSExternal Powering from 7.5 - 16V dc can be supplied by a separate mains unit or from the camera, mixer or tape recorder batteries, providing they are not +ve earth. Always use recommended MICRON combinational cables (these cables are fitted with in-line dc-dc regulator and additional filtering). For powering through the 4-pin Hirose connector, a combination lead is required e.g. AOCPH-HR4(B) TRANSMITTERSIt is recommended that external power only be applied via a MICRON TLP lead, as this lead includes a 9V voltage regulator and dc filtering. For powering through the 4-pin Hirose connector or the 6-pin Lemo connector a combinational lead is required e.g.TLP07CF-6 or TLP07CF-MHR4It is recommended that the internal batteries be removed when the unit is externally powered. Alkaline and lithium batteries are the most suitable because of their long life and reliability. They have a long shelf life and can be relied on to yield their full rated capacity. A conventional 9V transistor radio battery is NOT recommended.Battery Life: 6 to 7 hours continuous minimum expecte
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  4. #4  
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    You can also try floating the shield (pin 1) on the XLR connector at the mixer output end. If there is a common ground connection via power, this is not needed. Having both grounded creates a ground loop.
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  5. #5  
    Hello David
    Thank you for the reply. Sound Devices 302 does not have a ground lift switch . The 302 manual quotes :

    The external DC supply is isolated (floating) from the circuitry to minimize ground loop and interaction among devices sharing the same DC source.

    A DC external source does not have this circuitry.
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  6. #6  
    Quote Originally Posted by David Rasberry View Post
    You can also try floating the shield (pin 1) on the XLR connector at the mixer output end. If there is a common ground connection via power, this is not needed. Having both grounded creates a ground loop.
    David,
    If I understand correctly, you suggest that i unsolder the pin1 = Ground and leave 2 & 3, the idea being that the ground could be supplied by the camera ?
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  7. #7  
    Quote Originally Posted by David Rasberry View Post
    Do you get the noise if your Micron receiver is not connected? Might check what cables you are using there if not.

    PoweringExternal Powering(A) RECEIVERSExternal Powering from 7.5 - 16V dc can be supplied by a separate mains unit or from the camera, mixer or tape recorder batteries, providing they are not +ve earth. Always use recommended MICRON combinational cables (these cables are fitted with in-line dc-dc regulator and additional filtering). For powering through the 4-pin Hirose connector, a combination lead is required e.g. AOCPH-HR4(B) TRANSMITTERSIt is recommended that external power only be applied via a MICRON TLP lead, as this lead includes a 9V voltage regulator and dc filtering. For powering through the 4-pin Hirose connector or the 6-pin Lemo connector a combinational lead is required e.g.TLP07CF-6 or TLP07CF-MHR4It is recommended that the internal batteries be removed when the unit is externally powered. Alkaline and lithium batteries are the most suitable because of their long life and reliability. They have a long shelf life and can be relied on to yield their full rated capacity. A conventional 9V transistor radio battery is NOT recommended.Battery Life: 6 to 7 hours continuous minimum expecte

    The clicking noise disappears when the 2AOCPH-HR4 is disconnected. The clicking is there when the 2AOCPH-HR4 even if the Micron receivers are turned OFF. There is no clicking when the 302 and the Micron are connected together alone and the Red is powered off a seperate power source.

    I contacted Tanky at Micron for advice. He seems to be at a loss as why. He suggested :
    " It seems that there is an issue with the power connection to the camera. An internal clock oscillator from it is leaking out to the receiver audio input."

    I have checked my red power cables and they are all soldered to 4 pin XLR the same way and all have the same results.

    Obviously, having a single v-mount battery to power the whole is a very practical solution. I wanted to avoid having to consumer 9volt batteries.

    I naively assumed that the Red Epic had a line audio setting (as the Red One had it) but it does not. Therefore my setup is dubious from the start as I am having to juggle line and mic levels. I get the impression that the Red Epic sound card was designed to power a set ref mic and that you have to buy the I/O box to have proper audio input management.

    Thank you so much for your thoughts. I will see about ungrounding the Red audio input cables.
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  8. #8  
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    Let me know how it works out.
    It is standard practice in pro audio systems to float shields on outputs between any connected devices that share the same power ground reference. Normally this would be electronics connected to the same AC ground, but the same principle should apply to distributed battery powered devices too. If two devices are grounded together through their power source and through the audio path, that is the text book definition of a ground loop. It can act as an inductive/capacitive resonant circuit causing spurious oscillations. Shields should be grounded to common reference at one point only.
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  9. #9  
    Hello David
    I unsoldered the ground pin keeping pins 2 & 3 but sadly it had no effect on my issues. All the same it is excellent to know this troubleshooting technique. Many thanks
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  10. #10  
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    Quote Originally Posted by Christopher Lowden View Post
    Hello David
    I unsoldered the ground pin keeping pins 2 & 3 but sadly it had no effect on my issues. All the same it is excellent to know this troubleshooting technique. Many thanks
    What happens if you connect the mixpre to the camera without wireless receivers connected to the mixer?
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