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  1. #1
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    Default OT: TRS to XLR Concerns

    Hello,

    I have had some recent issues with one of the two DigiMax FS units with loss of phantom power to four of the inputs.

    I had an acquaintance come by to help me to determine what the possible cause was and he made mention of the following article.

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    Source: Patchbays

    Also, the following are his comments, "But most of all, I know from my embarrassing experiences taking a synthesizer mic preamp to Backline and being asked if I used the phantom power through a TRS
    patchbay or the time I built custom gear for someone heading out on tour and plugging in their TRS footswitch immediately blew the supply because I didn't put rectifier diodes to protect from the reverse voltage (short). Remember, using TRS - XLR cables is fine. It's just having phantom power on while patching the TRS creates the issue."

    As to my current concern, I use an internal mic'ing system that uses phantom power via a TRS endpin jack which then goes to a male XLR plug for connection to the interface.

    As to my question then: "Would inserting a TRS plug into a TRS endpin jack while connected to a socket with phantom power enabled, cause such a short?"

    Anyone care to comment on this?

  2. #2

    Default Re: OT: TRS to XLR Concerns

    Quote Originally Posted by mr_es335 View Post
    Hello,

    I have had some recent issues with one of the two DigiMax FS units with loss of phantom power to four of the inputs.

    I had an acquaintance come by to help me to determine what the possible cause was ...


    As to my question then: "Would inserting a TRS plug into a TRS endpin jack while connected to a socket with phantom power enabled, cause such a short?"

    Anyone care to comment on this?
    Phantom power was designed for use only with XLR connectors. It was not intended to be patched through TRS patchbays, and live patching a mic line with phantom power through such a patch bay can indeed cause a short, and even damage in some cases. Decades ago I worked at a studio with a Neve 8048 console. The patch bay that was included with this console included patching at the mic inputs. However, phantom power did NOT appear on the jacks (it was somehow isolated from them). So, connecting a mic that wanted phantom into the patch bay through an adapted cable would not work, because there was no phantom power there. There was also never a short or damage from patching phantom power. If I had a mic level TRS patch point, I would always make sure that phantom was OFF for that circuit (allowing enough time for any residual voltage to "bleed down") before doing any patching. A friend of mine had a console that had mic level patch points with phantom power, but there was also a switch panel directly above that patch row allowing phantom to be turned OFF while patching.

    I use Digimax FS units both in my studio and in remote recording situations. I have never seen any reason to connect the mic inputs to patch bay, since they have inputs on the front panel. If you must have a TRS adapted cable in between, make sure that the connection of the XLR to the front panel is made LAST, after plugging in the TRS part, and only then turn on the phantom power to the input. (paranoid belt and suspenders style caution).
    Cary B. Cornett
    aka "Puzzler"
    www.chinesepuzzlerecording.com

  3. #3
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    Default Re: OT: TRS to XLR Concerns

    Cary,

    Thank you for your very information response. Much appreciated!

    My current setup is:

    Guitar with internal condenser mics --> TRS Female socket --> TRS Male Plug ------ XLS Male Plug --> DigiMax FS with phantom power enabled.

    Here is the mic:
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    Not aware that what I was doing was potentially "wrong", I would power-up my rig, connect the TRS plug - which was connected to the DigiMax FS XLR socket with phantom power enabled, set the levels via RME's TotalMix, then launch SAC.

    I gather that from what I have read and what you have stated, that plugging in the TRS jack with phantom power enabled could have caused the dead input channels on the FS? Would this be correct? If so, I will have to get my prescription for my ID-10-T pills updated - as it looks like I really need them - again!

    Thanks, again, Cary!

    PS: I hope that are able t resolve your BC2000 issues?

  4. #4

    Default Re: OT: TRS to XLR Concerns

    With the added details you gave, yes, damage could have happened that way. With that setup in your guitar, you would FIRST plug the cable into the jack on the guitar, and THEN plug the XLR end into the mic input. This should be safe. When done, unplug the XLR end FIRST before pulling the cable from the guitar.

    I haven't solved my BCF problem yet, about to look at the other forum to see if an answer is available...
    Cary B. Cornett
    aka "Puzzler"
    www.chinesepuzzlerecording.com

  5. #5
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    Default Re: OT: TRS to XLR Concerns

    Cary,
    With the added details you gave, yes, damage could have happened that way.
    ...If any here are at all acquainted with Fawlty Towers and the episode called "The Builders"...this is how I feel at present.

    Here is the clip: The Builders - "You're naughty boy, Fawlty"

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