Home › Forums › Help/Technical Questions › Hum from brand new 12ay7 mic pre

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  • February 12, 2009 at 11:28 pm #77732
    bigmahon
    Participant

    Hi everyone,

    Just bought a new 12ay7 mic pre, and it is humming quite loudly. Any ideas what this could be? Power supply? One of the tubes? I tested it with more than one microphone, and it hummed with all of them. I am using the 1/4″ out into a MOTU firewire interface.

    Thanks for your help.

    February 12, 2009 at 11:29 pm #93220
    The EH Man
    Moderator

    Pull the tubes, one at a time and see if it stops.

    February 12, 2009 at 11:45 pm #93224
    bigmahon
    Participant

    Thanks for the speedy reply. This may be a stupid question, but are you saying pull out and re-insert each tube one at a time?

    February 13, 2009 at 12:11 am #93227
    The EH Man
    Moderator
    Quote:
    Thanks for the speedy reply. This may be a stupid question, but are you saying pull out and re-insert each tube one at a time?

    Pull the 1st tube and let it warm up. See if there’s any hum. Then put the tube back in and pull the 2nd tube. It’s possible one of the 12AY7s is causing the hum. I found that in a friend’s preamp.

    February 13, 2009 at 7:49 am #93239
    bigmahon
    Participant

    Couple of things. I pulled both tubes one at a time, and the hum stopped each time. In other words, with only one tube in (regardless which one) there was no hum. I also noticed that you said “one of the 12ay7’s”. I have 1 12ay7 and 1 12au7. This shouldn’t matter though, right?

    Thanks again for your continued support

    February 13, 2009 at 11:25 am #93243
    The EH Man
    Moderator

    There’s a good possibility it’s the 12AY7. You can replace it with a 12AU7 to see if that takes care of the hum.

    February 14, 2009 at 4:32 pm #93304
    bigmahon
    Participant

    Hi again,

    The problem appears to be with the 1/4″ out jack. When I used the XLR out the unit did not hum.

    Do you recommend using the XLR out to 1/4″ in on the back of my MOTU interface?

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