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Feed backish hum!?

Discussion in 'Pro Audio Equipment' started by lawless, Jul 4, 2007.

  1. lawless

    lawless Guest


    Recently I purchased a used Grace 101 mic pre and it is acting strange.

    Basically, when I power it on (nothing plugged into it line or mic) the LED

    slowly changes from green to red. When I plugged it into my mixer the

    signal was red lined on the mixer! Is it possible that I was supplied the

    wrong wall wort with it? Or what? I am seriously frustrated....Please

    advise :(
  2. lawless

    lawless Guest

    Note: The wall wort specs read 6VDC 1000mA

    The Grace 101 reads 6VDC 800mA

    Could this be the cause? Also, I tries plugging the 101 into

    different power outlets and got the same result: a steady rise in signal

    until redline...which is strange because nothing is plugged in to the pre.

    I know it is actual screaming noise because at one point I plugged the pre

    into a mixer (balanced out into balanced in) and heard the menacing

    screech through some headphones laying a few feet away. F#$k!!
  3. AudioGaff

    AudioGaff Distinguished Member

    Feb 23, 2001
    Silicon Valley
    Assuming that you know what your doing and how to interface the gear you have, (and that can be a very big assumption) It would appear that you have a defective unit. Contact the maker for warranty repair or your favorite repair shop.
  4. lawless

    lawless Guest

    Yes, I am a noob...but I think with only the supplied ac adapter plugged in to the pre, that the Grace's LED should not be slammed in the red. I thought perhaps that it was the wrong ac adapter for the pre???

    Well...lesson learned the hard way...no more ebay gear. The buyer had 100% positive on 70+ items over 5 years so I thought I was safe.
  5. Boswell

    Boswell Distinguished Moderator Resource Member

    Apr 19, 2006
    Home Page:
    The power supply rating is fine, as long as it's a regulated unit. It may be too late, but make sure the connector is wired correctly such that the + and - outputs of the power supply go to the + and - power input pins of the 101.

    The problem sounds like high frequency oscillation inside the pre-amp. This may possibly be due to poor output filtering in the power supply, but, as AudioGaff says, it's more likely to be a fault in the pre-amp, which will require a service.

    I've had lots of good bargains from Ebay, but you get what you pay for, wall warts and all.
  6. Space

    Space Distinguished Member

    Jun 26, 2007
    You have the gain knob all the way to the left, the trim knob all the way to the right and 48V(phantom power) OFF...right?
  7. lawless

    lawless Guest

    Yes, That is how I first turned the unit on. I then connected a cond. mic and turned phantom power on and about that time I noticed the red light.
    Since then, I tested to see if the pre would red line w/out anything plugged into it...and to my dismay it did.

    On the plus side, I contacted the seller and he is willing to take the pre back and expressed regret that the unit arrived broken.
  8. hueseph

    hueseph Distinguished Member

    Oct 31, 2005
    Vancouver, BC, Canada
    Pleas say you didn't buy it on ebay. There's been a few scams going on.

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