Another Airbrake and /13 FTR37 Question...

Discussion in 'Amps and Cabs' started by ronw, Jan 28, 2008.

  1. ronw

    ronw Member

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    I ordered an airbrake to control some of the noise my FTR puts out. I understand how an attenuator works. However, I'm not sure how to hook it up if I use the amp in half power mode. You know, the amp's got different ohm outputs. Normally, in half power mode with 16 ohm speakers wired in parallel, the 4 ohm option is to be used. Do I still use the 4 ohm option going to the attenuator? Or, use the 8 ohm option? The only reason I'd be using the half power mode is because there is less hum and hiss emitting from the amp.

    I know there was a thread that talked about this, and explained how to hook up the airbrake. But, I can't find it. So, I would appreciate it if someone would explain, one more time, how to do it.

    Thanks!
     
  2. gtrfinder

    gtrfinder Supporting Member

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    Sorry this does not answer your question, but...
    If you are going to use an attenuator why not leave the amp in full power mode. I'd be willing to bet that you'll get approximately the same results, with little tradeoff in tone.
     
  3. ronw

    ronw Member

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    True, I am just trying to get the noise down. There's ample more hum in full power mode than half power mode.
     
  4. ronw

    ronw Member

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    I know there was quite a bit written about this a little while ago here, but seems to have been deleted. Any FTR/airbrake users in the house???
     
  5. myles111

    myles111 Member

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    You need to do nothing in regard to the Z Airbrake. Unlike the THD Hotplate the Airbrake has no specific impedance and works from 4-16 ohms just fine.

    So ... it is no concern in full power or half power mode or whether the cab impedance is set to matching value to the cab or 1/2 the value in an amp where somebody pulls half the output set to reduce power.
     
  6. jcground

    jcground Member

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    The Airbrake is optimized to work with amps that expect an 8-ohm load. It will work with 4-ohms or 16-ohms, but if you can wire it up to an output where your amp expects 8-ohms nominal, that'd be my recommendation.

    I've heard of some users with 4-ohm amps having trouble with the Airbrake (do a search here). You also shouldn't use an Airbrake with an amp that expects 2-ohm loads or 2.7-ohm loads. There is no such thing as an attenuator that will match any impedance.
     
  7. ronw

    ronw Member

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    Thanks for the replies and help. Perhaps my brain doesn't work fast enough, but the half power option on a /13 doesn't click for me...and I don't mean the click channel. :)

    I'm sure all this is common knowledge to most of you all, but there is a little tag dangling down on the back of my cab that says if I'm in full power mode, then hook up the cab to the 8 ohm option. There are two 16 ohm speakers in the cab that are wired separately. This makes sense to connect each speaker to the 8 ohm option...a parallel connection.

    What I don't understand in the context of the airbrake is what option to connect the attenuator to when in half power mode. The little tag says to connect to the 4 ohm option when in half power mode. What's going on here? By cutting the power in half, does the amp think it's being hooked up to a 4 ohm load? If so, then should the airbrake be hooked up to the 4 ohm load? Or, since the airbrake naturally wants to see an 8 ohm load, should I hook it up the 8 ohm option even when in half power mode.

    Or, does any of this really matter when using the airbrake. I just don't want to blow up the amp. know what I mean? Please forgive my lack of understanding here. Thanks!
     

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