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Why does my GT Brick suck??!!!

Discussion in 'Preamps / Channel Strips' started by JLiRD808, Jan 19, 2011.

  1. JLiRD808

    JLiRD808 Active Member

    Ive had so many problems with this thing I dont remember how long its been since I could depend on it. These are pertaining to the Mic Input...Instr Input seems to work fine.

    I just replaced all tubes except the "pencil tube" and the problems persist....they are:

    Prolonged (3-5 sec) static noise when I turn on/off
    Very low gain...have to have it cranked up ALL THE WAY to get any decent signal (again just for mic)
    Sometimes distorted sounding...if I unplug/replug certain cables in the signal chain it "cleans up" for awhile

    My interface is an Emu 0404 PCI card with UNBALANCED input...the Brick has a Balanced output....could this be causing the loss of gain? Ive read in some forums that this is possible but it got very technical and I couldnt follow :mad:

    I basically consider it unusable for vocals which is sad to me cause Ive read so many great things about it...anyways any help u provide would be great...Im hoping its the "pencil tube" (even though we couldnt track a replacement down anywhere) or something simple in my signal chain.


    oh yeah Fender/Groove Tube customer service has been ignoring my emails for months....a**holes
  2. bouldersound

    bouldersound Real guitars are for old people. Well-Known Member

    [Edit] See Boswell's post. I didn't look to see if the Brick has transformer balanced output. The Rane Note is still good to know. [/Edit]

    I think the balanced/unbalanced connection could be a problem. The cold leg of the balanced signal is likely shorting to ground in the 0404's input jack. Do you have anything with balanced input you could connect it to for a test? Check out Rane Note 110 for ideas about how to connect balanced to unbalanced.
  3. Boswell

    Boswell Moderator Distinguished Member

    The Groove Tubes "Brick" has a fully-floating transformer-coupled output. It's OK to connect this to an unbalanced input, and there will be no loss of signal amplitude.

    The Brick DI input by-passes the first stage, so if the DI input works and does not show the problems you detail, it points to the fault being in the first stage.

    By the way, the Brick schematic can be found on a Gearslutz (Dead Link Removed)
  4. BobRogers

    BobRogers Well-Known Member

    Note that at +55dB it's not a very high gain preamp. But with that said I have not had the troubles with mine that you have had with yours. The fact that it is a pretty standard tube circuit may be a big help in finding a local tech.
  5. Big K

    Big K Well-Known Member

    Yes, the circuitry is surprisingly simple, which says nothing about its audio quality, though.
    Any technician should be able to fix that, quickly an cheap.
    Can be a capacitor and the Pentode, or a combination of both.
    The ECC83/12AX7A valves should be fine for the reasons Boswell already mentioned.
  6. Boswell

    Boswell Moderator Distinguished Member

    The first stage of the Brick is anything but standard using a FET input to feed a grounded-grid pentode. The noise during the settling time on switch-on indicates that the d.c. conditions are not right, so it would be worth looking for reasons why it might be giving trouble: the pentode has gone soft; a resistor has drifted high or a capacitor has gone leaky sending the d.c. feedback loop out of spec; the wiper contact on the bias-setting pot is high resistance or open-circuit.

    I don't know whether you can find old-fashioned valve technicians in Honolulu, but it's worth asking around.
  7. BobRogers

    BobRogers Well-Known Member

    It's always simple if someone else does the hard work.
  8. JLiRD808

    JLiRD808 Active Member

    Thanks guys!

    Would the first stage imply that "pencil tube" that the tech described? I guess it's one of the three tubes in the Brick and neither one of us had much if any luck finding a replacement for it.

    I'm calling my tech today to let him know Im not happy with the results...I dont know why he gave it back to me in this condition (and at the rate he charges!). I thought perhaps it was cause he had a balanced input in his signal chain following the Brick and I didnt. I'm glad I can rule that out...

    Thanks again...I'll keep everyone posted!

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