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Suppose I buy a pro amp but my LFE voltage is to low

Discussion in 'Home Theater Projects' started by Darren_T, Sep 26, 2003.

  1. Darren_T

    Darren_T Second Unit

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    Ok, suppose I do buy a pro-amp but my AV receiver's LFE voltage is too low for the pro amp's input. What do I do to correct the situation?

    My AV receiver is an Onkyo TX-DS777. I couldn't find the LFE voltage in the specs.

    Thanks.

    Darren (pro-amp newbie)
     
  2. Lewis Besze

    Lewis Besze Producer

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    Most receivers put out 5v or more on the sub out,which should be ok.I would also get a BFD.
     
  3. Darren_T

    Darren_T Second Unit

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  4. Brian Bunge

    Brian Bunge Producer

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    Darren,

    I bought my BFD from Musician's Friend and I think it's about the best price you'll find.

    EQ won't help much will nulls as the null will still be there and you'll just be wasting amp headroom. You'd use it more for dealing with peaks in the response. Also, it's a good thing to have regardless of what sub you're using.

    A lot of people are using the box that SVS had Marchand design for them when they have pro amp issues. IIRC, it runs about $200 but has other features that make it useful as well.
     
  5. Darren_T

    Darren_T Second Unit

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    Thanks Brian,

    I'm all for another gadget [​IMG] I just don't want to spend another $200 bucks for the fix if a pro-amp has probs with my reciever but it doesn't sound like it will.
     
  6. Jeffrey Stanton

    Jeffrey Stanton Stunt Coordinator

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    I had problems with getting my pro amps to run off my Yamaha DSP-A1's LFE. Had to use a pre-amplifier (Pioneer C-60) and have it CRANKED (100% volume) to get my Mackie pro amp enough signal to run my subwoofer. I still think the LFE voltage could be slightly on the low side (& could be losing some headroom with my amp), so will add one of the SVS/Marchand black boxes to the mix like Brian said, eventually...
     
  7. Darren_T

    Darren_T Second Unit

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  8. Pete Mazz

    Pete Mazz Supporting Actor

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    Some pro amps require less input signal voltage than others. Some are as high as 1.5V and some as low as .75V. Some also are switchable. Look at the input signal spec on the amp.

    Pete
     
  9. Ronnie Ferrell

    Ronnie Ferrell Second Unit

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    Darren,

    Best Deal on a BFD along with the best guide there is!

    There is a link on this page that links to another forum. I did not want to post a direct link to that forum. (did not know if it was OK here)

    Anyway I got mine from Bob. Just email him and he will hook you up. He is VERY prompt with answering emails!(He works for a pro audio distributor I think.) His email address is listed on the other forum.

    The price is $100 plus shipping which mine was only $4. Tax charged only in Cali. I got it is about a week from Cali to TN.


    Ronnie
     
  10. Frank Carter

    Frank Carter Screenwriter

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    I had a problem with a Samson amp and Yamaha receiver before the SVS/Marchand box was being sold. Tom V. recommended this RCA mini amp to boost the signal and it worked well. It's cost me $60.
     
  11. Joseph Sabato

    Joseph Sabato Stunt Coordinator

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    I had the same concern so I wrote to QSC Tech Support about it ( have not bought the amp yet) and they do not believe I would have a problem with my Denon LFE since it has been able to drive both my SAE power amp ( 1V sensitivity ) and my Dynaco 416 power amp( 2V sensitivity ) to full output. These are not "pro" amps, and were designed for audio. I thought there may have been another factor like input impedance on the pro amps at issue, but they assured me that it was not... if the preamp can output 1.15V, it coud drive their amp to full outpuy. As a backup, I still have my Yamaha C2 preamp that I could put in line (it can put ot 10-11 Volts!), but I would rather avoid that. Good Luck.
     
  12. Richard Little

    Richard Little Stunt Coordinator

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    this is kind of the $200 dollar solution that you didn't want but... http://www.rane.com/bb22.html and http://www.dvwarehouse.com/product_i...oducts_id/6318 these products appear to be specifically made to deal with the problem of consumer gear to pro gear, but it defiantly adds to the total cost. I've been wrestling with this dilemma for a while. The current hope is that someone will post a "How To" on the QSC PLX2402 modification or at least simple "replace resistor A with a new resistor B"
     
  13. brucek

    brucek Second Unit

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    Darren,

    If you have checked that the specs indicate the output level of your receiver don't match the input level of the pro amp then simply add a line amp as suggested.

    Why the hesitation to add the line amp?

    brucek
     
  14. Darren_T

    Darren_T Second Unit

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  15. brucek

    brucek Second Unit

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  16. Greg_R

    Greg_R Screenwriter

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    Why don't you purchase a pro amp with selectable input sensitivity? (ala Crown, etc.)
     
  17. Richard Little

    Richard Little Stunt Coordinator

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  18. Jon Carlson

    Jon Carlson Extra

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    I'm confused about BFD features. Can a BFD be used to boost the sub-out signal from my Yamaha receiver if I feed a pro amp? Or is the BFD simply the best parametric equalizer for subwoofers at its price point, but not necessarily useful for boosting the sub-out signal from a consumer(Yamaha) receiver to a pro amp?

    The long story: I recently purchased a JBL MPC200 pro amp for a diy sub using the stryke AV12 driver, but need the Yamaha and the JBL set to max to get any appreciable bass output and I'm not a bass nut. Even at the max setting, its just loud enough compared to the other 5 speakers. The problem is almost surely a mis-match between Yamaha's consumer level(RX-V2095 receiver) and JBL's pro input/output levels, and may be Yamaha-specific. I get plenty of bass output using bass test tones if I crank the receiver's volume (which takes the other speakers out of the equation), so the issue isn't the JBL amp itself. And I get plenty of output when I feed the sub with an older plate amp set at the half-way point, so the problem is not with my receiver. Again, I think the problem is the consumer/Yamaha-to-JBLpro-level mismatch.

    I'm considering an rca-to-xlr (consumer to pro) converter options like the 'ART cleanbox' which has the option to boost the signal, but at $50.00 its half the cost of a BFD. If the BFD would fix my input dilemma, I'd buy one. I might purchase one for its equalization functions anyway, but that's not the issue I'm addressing here.

    Thanks for your wisdom.
    Jon

    Edit: found my answer, no boost on BDF. Sorry for the errant post.
     
  19. Jeffrey Stanton

    Jeffrey Stanton Stunt Coordinator

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    Jon:

    I have been having the EXACT same problems with my Yamaha LFE being mis-matched with several different pro amps.

    I am going to call Yamaha again. The first time they said that the LFE output should be plenty to drive a pro amp. Well, it isn't. I've had to use pre-amps to get the LFE up to operating level, but I suspect it is STILL to low as I have to crank the Pre-amp all the way to get barely acceptable woofage out of my Mackie (pro-amp)-Tumult combo.

    I've asked the question as to what's going on here at least a dozen times since last October, and nobody seems to know a real answer to this question...just gets me a lot of "maybe"s and not much more. Even the people at Mackie were no much help, or Yamaha. People at Mackie said it sounded like I needed to get the LFE voltage up (said it was a pro vs. home electonics input mismatch) and recommended I buy a $100 mixing board to get the LFE up to where it should be. And Yamaha said the voltage was fine. I think they're wrong and will call them again...

    Jeff S.
     
  20. Jeffrey Stanton

    Jeffrey Stanton Stunt Coordinator

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    I talked to Yamaha tech support about the apparent voltage mis-match and they said:


    "There are no adjustments that will allow for the signal to increase. The receiver outputs a line level signal and that signal should be fed into a power amp. I can not support the Mackie for I do not know the product and its requirement. Please contact Mackie and see if the unit will
    accept a line level signal."

    Okay so I contacted Mackie. First I got the specs for the LFE and the Mackie in front of me:

    Yamaha: SUBWOOFER (1.2 v/1.2 kilohms)
    Mackie : INPUT SENSITIVITY - 1.23 V (+4DbU FOR RATED POWER INTO 4 OHMS)

    They said the mismatch looked like it was with the impedance. The 1.2 kilohms impedance of the Yamaha sounded like it was on the low side to them and recommended either a mixing board (which comes with a low impedance input, like for microphones) OR get an impedance matching transformer otherwise known as a bridging transformer. They suggested checking with Shure.

    Shure sells one but is only made for use of up to 300 ohms.

    Swell.

    Anyone know anything about bridging transformers or who to get one from? Am I going to have to convert everything to XLR connectors instead of RCA to get this "bridging transformer" hooked up? Could this possibly get any more complicated?

    No wonder I've been asking questions related to this for a year now on various forums and nobody's had a clue thus far.
     

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