Psst... Ready to join TalkBass and start posting, make new friends, sell your gear, and more?  Register your free account in 30 seconds.

Sansamp & QSC PLX users help

Discussion in 'Amps and Cabs [BG]' started by seansbrew, Aug 29, 2005.


  1. seansbrew

    seansbrew Supporting Member

    Oct 23, 2000
    Mesa AZ.
    Hey fellas I have decided to start experimenting with a pre-power setup. Here is the story: I have a schroeder 1210 and a 1212 cab that I want to power with a QSC PLX 1602 that has been sitting in my closet for a couple of years. I just recieved a mint conditon Sansamp RBI from a fellow TBer. I love the sansamp as an effect but figured I would try it out as a pre amp with my QSC to see if I will have enough power to push the Schroeder cabs ( 500 watts stereo @4 ohms, 4 ohm cabs)
    But first I have some questions: Does anyone here use the filters on the QSC power amp or do you run it full range. I play mostly 5 string bass and dont know whether to engage the 30hz roll off filter or not. Also how much pre amp signal do I send to the power amp ? And how much power do I send to the speakers. I have no way of knowing how much input from the Sansamp I need ( I am used to having a pre amp clip light). I have meters for the power output of the amp, so I guess I am ok there. I ultimately plan on getting an Eden Navigator as a pre amp but figured I would try the Sansamp first.
     
  2. BruceWane

    BruceWane

    Oct 31, 2002
    Houston, TX
    Low-cut filters - They're simple to switch in and out, so try 'em and see if you like 'em. It depends on your bass, your preamp, and the room you're playing in, so nobody is going to be able to give you any kind of "rule" regarding their use. I can tell you that they can be very good for tightening up excessively "flabby" lows, and for enabling your rig to crank out seriously high volume levels if necessary.

    Setting levels - technically, it's best to turn the level on the power amp all the way up, then turn up the output of the preamp until the power amp clips on the absolute peaks (for example, slapping an open e) then back off a hair on the preamp output. You then use the power amp level to set your actual playing level. This gives you the best signal-to-noise ratio. Basically, you want to be able to drive the power amp to full output with as little gain in the preamp stage as possible. HOWEVER......depending on the preamp, there may be various reasons to turn the output higher, and keep the power amp attenuators lower. Technically you'll get more noise the more you turn up the preamp, but it's doubtful you could hear it, especially in a live setting.
     
  3. Jeff O'Connor

    Jeff O'Connor Supporting Member

    Feb 16, 2004
    Stratford, CT
    I have a RBI also love it! The RBI sends out a great strong signal. be weary! you're gonna be pumpin'! good luck! :bassist:
     
  4. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Gold Supporting Member Commercial User

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    That depends mostly on what your loudspeaker cabinet can handle. Fortunately, with an instrument like the bass (unlike with some recorded or mixed live music), we can be sure that there's not usually going to be significant energy below the low B's fundamental. So if you don't set the filter, you're no worse off than if you use an amp that doesn't have such filters (that is, most power amps). So don't agonize over it. Try the amp with the filter on and with it off.

    The best approach is to have the preamp levels high, just below clipping when you're playing your hardest, and then turn up the amp only as much as you need to.

    You'll get the best signal-to-noise ratio with the preamp fairly hot and the power amp turned up only as needed. It's not all that critical, though.
     
  5. seansbrew

    seansbrew Supporting Member

    Oct 23, 2000
    Mesa AZ.
    Thanks for that replies; this will give me a starting point.

    Bob, the frequency response for each cab is 40hz to 18 khz
     
  6. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Gold Supporting Member Commercial User

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    The 30 Hz filter might be a good idea to protect your loudspeakers from overexcursion, then.