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brick pad?

Discussion in 'Preamps / Channel Strips' started by larrye, Jan 6, 2006.

  1. larrye

    larrye Active Member

    I just got my GT brick today and I think I really like it. BUT it seems to have a little too much gain. Is there an adjustable inline pad I can put in the line between the brick and my soundcard to lower the gain without destroying all the good stuff from the brick?

    Thanks a bunch for any ideas you may have!!

  2. therecordingart

    therecordingart Well-Known Member

    I actually built some "padded" mic cables with a -20db attenuation. You can't even tell them apart from a regular cable so I had to label them. If you have about a dollar for resistors, a spare mic cable, and know how to solder....I suggest you do the same.

    Anyone want the link on how to do it?
  3. moonbaby

    moonbaby Mmmmmm Well-Known Member

    Do you have a "table-of-values" to build an "H-pad" at various attenuation amounts? I have been looking for one lately. I want to pad the outputs of my Brick...Thanks!
  4. Sebatron

    Sebatron Well-Known Member

    If you replace the 12AX7 to a 12AT7 ,,
    that should reduce the gain a bit....

  5. Pre Amp

    Pre Amp Guest

    Whow! Totally cool. I will def remember that.
  6. larrye

    larrye Active Member

    The only trouble with replacing the tube is I need ALL the gain the brick has for my ribbon mic.

    I have seen several attenuators on line, but I don't know which to buy or if I should insert it before the bricks input or after the output, before it goes into my soundcards breakout box.

  7. moonbaby

    moonbaby Mmmmmm Well-Known Member

    First off, I did try replacing the 12AX7 with a 12AT7 (tried a 12AU7,too). This did lower the gain, but it had (2) undesireable side-effects: a) it made the signal sound more "hi-fi" with an extended frequency response, removing the "attitude" the Brick imparted (not always a bad thing), and (b) resulted in less-than-needed gain for my favorite Beyer M160 ribbon mic.
    As for the attenuator, you definitely need to place it at the OUTPUT of the Brick. You can get a factory-built attenuator from Shure or Audio-Technica. I use the Shures, they are very handy on all sorts of balanced sources. I was hoping that Recordingart would be posting some tech data on the in-cable pads, as I sometimes need more than the -15dB value that the Shures provide. The A-T's have a 3-way switch, so maybe I'll get that next time.
    One warning: If you are using the Brick into an unbalanced device like a soundcard, you may not be able to use an attenuator like what's been discussed. This is because you will terminating its output in a way that it might "see" as a short circuit. The tech support dept at Groove Tubes will be able to advise you on that. If that IS the case, your best bet will be to insert a gain control device (I use an FMR RNLA) between the Brick and the soundcard. Now THAT's attitude!
  8. Sebatron

    Sebatron Well-Known Member

    Yes , that is completely true , the 12AT7 has a much wider bandwidth and frequency response than the 12AX7 and has superior noise floor characteristics.
    Some would interpret that as a very ' desirable effect ' or improvement.

    Another mod you could try ,, rather than messing 'round with attenuators ,, would be to locate the 'stopper resistor' connected to the one side of the potentiometer.
    As this unit doesn't allow the user to attain zero level ( or mute ) from turning the potentiometer fully anti-clockwise to zero ,, this means that one side of the potentiometer ( or the ' gain control ' ) is not completely shunted to earth.
    It most likely runs through a resistor.
    This resistor would be located connected to the rightmost pin of the potentiometer ( when looking directly at the pot with shaft facing you and pins pointing upwards).
    You could reduce the value of this resistor to set the minimum gain to a lower level. .... so it would not distort so easily .
    Increasing the value of the potentiometer will also preserve ( or even increase ) the gain so maybe you should also change that.
    Doing both could actually increase the whole gain range from a little lower to a little higher.
    This would have the undesirable effect of also setting the instrument gain to a lower level ...... then again this may be a desired effect for keyboards or really hot line level signals as they would not appear as hot or distorted because of the limited dynamic range and capabilities of the circuit.
    I'm sure with a few mods ( some of them with side-effects ,, desirable and un-desirable) the Brick could become a very useable preamp.

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