250 watt #300-794

Discussion in 'Archived Threads 2001-2004' started by James Slade, Feb 11, 2002.

  1. James Slade

    James Slade Second Unit

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    Does or doesn't this amp from PE come with bass boost at 30Hz enabled. I have hear yes and no stories. And if it does can a guy like me who has soldered once in his life easily remove it?

    Also is it really that terrible of a thing for a Adire Alignment Shiva for H.T. use?

    I am going to buy this amp no matter what (unless someone knows a Canadian supplier), I would just like to know what I am in for!

    Thanks
     
  2. Mark Krawiec

    Mark Krawiec Agent

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    there's another post somewhere here where someone said PE will actually do the mod to get rid of the boost before they send it to you. it's an easy modification-but if they'll do it for you, all the better. i'd try a gentle email to see if they'll do this.
     
  3. Brian J Dupuis

    Brian J Dupuis Second Unit

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  4. Jeffrey Noel

    Jeffrey Noel Screenwriter

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    James, it's a great amp. I have the remote version of the amp, and it pushes my PE 12" DVC great. I bought mine in October and it came with the boost disabled. I'm sure that they are shipping them all disabled now.
     
  5. Kyle Richardson

    Kyle Richardson Screenwriter

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    Brian is correct. This amplifier is no longer shipping with the bass boost enabled!
    Kyle Richardson
    Acoustic Visions
     
  6. Wes Nance

    Wes Nance Stunt Coordinator

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    Just remember that with boost disabled, the rumble filter is disabled also. To enable the rumble filter, you could (I'll probably do this with mine) enable bass boost of 1db at the lowest hz (20-24).

    I'm making a PR sub, so I think I'd like to have the rumble filter enabled.

    Wes Nance
     
  7. Jeffrey Noel

    Jeffrey Noel Screenwriter

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    Wes, what exactly does the rumble filter do?
     
  8. Patrick Sun

    Patrick Sun Studio Mogul

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    A rumble filter is basically a high pass filter that starts under 20Hz, and it's designed to cut out frequencies under 20Hz to provide protection for the subwoofer driver (but some rumble filter are designed to cut out frequencies under 18Hz), it all depends on application.
     
  9. Michael R Price

    Michael R Price Screenwriter

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    Wait a minute. If you put in 56k and 120k resistors like it says the defaults are ('no boost'), then you still have a Q=.707 rumble filter with -3db at 20Hz. I think you need to remove the resistors entirely to remove the boost. I put the component values into LspCAD to mess with it. It's a 2nd order highpass equal component Sallen Key (what's that?) filter, I think. The larger the resistors, the lower the filter frequency. The higher the ratio between the two resistors, the higher the Q of the filter, and the more boost you get.

    My friend with his down-to-10Hz Shiva sub might be having a problem with this. So I'm looking into it.
     
  10. Wes Nance

    Wes Nance Stunt Coordinator

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    Michael,

    That's very interesting! My previous statement was simply based on a question I asked to Paul at Parts Express, who posts a lot in the tech forum:

    ____________________

    > the ad says it has 6db

    > of boost at 30hz, and the sheet that came

    > with the amp gives all the boost resistor

    > values, and says the default is no boost.

    Originally these had 6dB of boost at 30 Hz. The newer units do not. Yours does

    not have any boost.

    > Also, if boost is disabled, is the rumble

    > filter active?

    No. The response is critically flat down to 10 Hz. For a mild boost and rumble

    filter protection you could opt for the 1dB boost at

    20-24 Hz. If you don't

    notice any problems however, I'd leave it as is.

    -Paul

    ___________________

    What do you think?

    Wes
     
  11. Michael R Price

    Michael R Price Screenwriter

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    Wes, I'm confused now. If they've got those 56k and 120k resistors in there like the PDF says, then I'm pretty sure the 20Hz rumble filter is still there. However, that completely contradicts what Paul says.

    So either:

    a) Paul is wrong and the rumble filter is there, or

    b) they removed the resistors to eliminate the filter entirely, or

    c) I'm seriously missing something.

    I wonder if Paul or someone from PE could clarify this...
     
  12. I have modeled the KG series amps (use a very similar Xo section) and you can tweek the Q and frequency of the SSfilter by changing capacitor and resistor values. High Q values will give you steep roll offs, but also a boost at (ie. the 6db at 30hz). you can set the SSfilter to have no boost and a shallower roll off. The only way to dissable BOTH the SSfilter and boost is to effectively bypass this circuitry by shorting across the resistors...NOT by changing the resistors to different values
     
  13. James Slade

    James Slade Second Unit

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    This is great info. Keep it coming, I think a lot of people on the forum are learning from this thread not just me. The amp is on the way, hopefully by the time it gets here we will all agree on what to do about the boost!!!!
     
  14. Michael R Price

    Michael R Price Screenwriter

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    I think, James, that the amp will come with 56k and 120k which gives you no boost and a Q=.707 rolloff with -3dB at 20Hz. A 'bass boost' will give you a steeper rolloff (increasing the ratio of the second resistor to the first). The larger the resistors, the lower the filter's corner frequency is. To remove the filter entirely I think you need to remove the resistors entirely, not short them out. Removing them makes the resistance infinite, which should cause the filter's cutoff to be lowered... infinitely, I guess. You can mess with this in LspCAD (free Adire demo).
     

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