using pro-audio amps

Discussion in 'Home Theater Projects' started by drexel, May 29, 2003.

  1. drexel

    drexel Agent

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    how do you drive a subwoofer with a pro-audio amp using your receiver's standard RCA subwoofer output? Using something like the cheap Nady pro amp, which doesn't have an rca input, how would you get the subwoofer signal to the amp in the first place? Also, what type of problems have people encountered by driving subs with pro-audio amplifiers?
     
  2. Kyle Richardson

    Kyle Richardson Screenwriter

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    You can pick up some RCA to 1/4" plug adapters at most pro music shops or even Radio Shack. Pro amps work fine except for the voltage mismatch between consumer and pro products. You might find that you have to turn the sub output up on the receiver to add a bit more voltage being sent to the sub amp.
     
  3. Allen Ross

    Allen Ross Supporting Actor

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    yeah if you search ebay they got some old Crown DC 300s that i think are exclent buys, i just snagged my DC 300A II (check sig) for 215 shiped, i still don't know what i am going to use it, possibly on some new Pi speakers or possibly on a sub. who knows.
     
  4. Doug_M_Fraser

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    I have Crown K2 Pro Sound Amp driving a Stryke HE15.2.

    The problem that I was running into was that I could not drive the Crown hard enough to realize its full power output. I had the subwoofer output of my Integra 9.1 processor turned up to +9 dB to compensate for the input sensitivity differences of the pro sound amp. The bass was OK but didn't have the sound I was expecting. To address the problem I got a Balance Buddy from Rane see this link:

    http://www.rane.com/bb22.html

    Wow what a difference ! I now have the subwoofer output set at -3 dB. The bass has real punch and just rocks the house. The difference is that the dynamic range is significantly larger. I suspect that with the subwoofer output of the Integra 9.1 turned up, the larger volume level dynamic signals were being clipped. While I didn't hear any distortion the "slam" was just not there.

    Here is good paper on unbalanced to balanced connections

    http://www.jensen-transformers.com/an/an003.pdf

    --------------------

    Here is an excerpt from the Rane BB 22 Manual for those technically inclined:

    "The Rane BB 22 Balance Buddy is a handy professionalized tool used to provide isolation for and convert unbalanced -10 dBV consumer level RCA outputs up to balanced +4 dBu professional XLR inputs. The BB 22 converts one pair from -10 dBV to +4 dBu.

    Conversion Ratio

    The casual observer would think to convert -10 dBV to +4 dBu, you would need 14 dB of gain. The casual observer would be wrong. You only need 12 dB of gain. The reason is not only do you change levels, you also change reference levels—from dBV to dBu. The first (dBV) references everything to 1.0 volt, while the second (dBu) references everything to 0.775 volts (this comes from the old power reference of 0 dBm, which equaled 1mW into 600 ohms, which equaled .775 volts).

    Driving Impedances

    Some people wrongly feel you cannot use a transformer to convert between -10 dBV and +4 dBu because of low impedances. This is not a problem as long as you use them to interconnect equipment with at least 15k ohms input impedance.

    Since most professional products have input impedances of 20k ohms or greater (50k and 100k ohms are not uncommon), this should never be difficult. A 15k ohm load winds up looking like 1k ohm to the equipment with the -10 dBV output (due to transformer action). This may seem excessively low, but is not in practice. The maximum transformer output level of +24 dBu occurs with an input level of +10 dBV, which equals 3.16 volts. And 3.16 volts driving 1k ohms only requires 3.16 milliamps, which is a very modest requirement for any -10 dBV equipment to deliver."

    --------------------------

    The Rane BB 22 is simply a passive step up transformer. A criticism against the passive transformer approach is the frequency response rolls off at low frequencies (
     
  5. Pete Mazz

    Pete Mazz Supporting Actor

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    Quite a few pro amps now have switchable input levels to compensate for what Doug talks about. My Carver has one and it makes a big difference.

    Pete
     
  6. Allen Ross

    Allen Ross Supporting Actor

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    yeah i just read that my crown DC 300A II has a jumper that i can solder to change from 1.7v to .775v, I def plan on doing that, as soon as my Weller iron comes in. [​IMG]
     
  7. Seth_L

    Seth_L Screenwriter

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    If you use a BFD you can set the input levels to either -10 or +4. Also if your amp has a gain knob you can just turn it up. [​IMG]

    My DA5ES has no problems driving my QSC PLX2402 at 0dB on the reciever's control. The amp's gain is set to 24dB.
     
  8. Ryan Hawke

    Ryan Hawke Agent

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    I've been using a Crest VS900 in my system for a while and it works great. I'm driving it with an Outlaw 1050 and it has plenty of power for the AV15 (maybe too much...). I really like the build quality and reliability of pro equipment and would recommend trying a pro amp. I wouldn't suggest the Nady because I've heard that they are really cheap (although I'll confess that I'm just passing on heresay), but you should look at used amps in pro audio classifieds and on eBay. Good luck!
    --Ryan
     
  9. Allen Ross

    Allen Ross Supporting Actor

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    Ryan one word


    CROWN

    [​IMG] [​IMG] [​IMG] [​IMG] [​IMG] [​IMG]
     

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