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Why is my Fender --> RBI --> PLX --> Avatar sooo quite?

Discussion in 'Amps and Cabs [BG]' started by orskard, Mar 9, 2005.

  1. orskard


    Mar 17, 2004
    Hey guys, i play a fender p bass special, i would call it a hot passive bass. Into a rbi and qsc plx 1202 then to a 2x10 8 ohm avatar.

    I want to run it bridged at 4 so i get 600 watts into 700 watt cab. It sounds really really quite and i cant turn it up past Noon with out the red clip limiter on. I have all the switches on the PLX to the right. im using a speakon that is wired for bridged workings. Is it my RBI's settings? Should i keep the level down on that and use the PLX channel one volume. Right now i have my settings like this.

    Drive, less than noon
    Pres. about 11 o'clock
    Blend about 10 o'clock
    Bass at 11 o'clock
    Mid at 11 o'clock
    Treble probally around 1 or 2 o'clock
    and my level less than 3/4ths, so around 2 o'clock.

    Why is my bass cliping so early? My old peavey head was going louder than this is, whats my problem?

  2. Bob Rogers

    Bob Rogers Left is Right

    Feb 26, 2005
    Blacksburg, Virginia
    My guess is that you are sending too hot a signal from the RBI to the PLX. Turn the RBI all the way down. Turn the PLX up to say 3/4 or a bit higher. Then gradually increase the level on the RBI. Just a guess without knowing these units.
  3. Muzique Fann

    Muzique Fann Howzit brah

    Dec 8, 2003
    Kauai, HI
    I tried an RBI for a bit and found it about half as loud as a BBE preamp - they just don't have enough ooomph IMO.
  4. orskard


    Mar 17, 2004
    I am probally wrong but, doesnt the preamp just add more pregain? So really if i got a louder preamp it wouldnt only make the gain higher and clip sooner?

    Or am i totally wrong?
  5. Ralphdaddy

    Ralphdaddy Supporting Member

    Nov 6, 2003
    Chicago, Illinois
    I don't own a preamp but I'll give this a whirl. The preamp is the tone shaping section of a pre/power setup and also controls the initial volume. Your best bet is to crank the poweramp up and then use the preamp's volume control to control your overall volume as turning down the volume on the pre will decrease its workload and put more of the work where it should be getting done, the power amp. So crank the QSC, turn down the RBI and you should be golden. Let us know what happens.
  6. Joe P

    Joe P

    Jul 15, 2004
    Milwaukee, WI
    Was your Peavey louder with the same cab? If it's really-really quiet, then maybe the two drivers are wired out of phase - that'd be pretty darn quiet!

    Of course you can check this by putting a 9V battery across the unplugged amp-end of the speaker cable, and making sure that both speaker cones go the same way.

  7. TheChariot


    Jul 6, 2004
    Boston, MA
    Or your speakon might be doofy.
  8. orskard


    Mar 17, 2004
    i tried making the PLX up and using the level as volume, and it worked, i didnt use it much and im not going to try it now, its getting kinda late. will do more on it tomorrow.

  9. Glenn D.

    Glenn D.

    Aug 20, 2002
    Fort Collins, CO
    The PLX, like a lot of PA power amps, is used to seeing a hotter signal than the RBI puts out. You can have the PLX modified to accept a lower signal. I've got the same rig and I have no problems with volume. You can search this forum for PLX modification and you should find the answer. If not, search for "Bob Lee" and email him.

    Glenn D.
  10. PB+J


    Mar 9, 2000
    arlington va
    I think glenn is right--I had a similar rig: passive jbass--into RBI--into plx 1202--into 600 watt 4 ohm cab. I generally bridged the two channels and kept the qsc's level knobs at about 1 o'clock, and in a loud gig the rbi's vol knob would get up to about 2 o'clock(drive at 11), and I'd start to see the little red light coming on.

    Then I switched to an avalon u5 for a preamp, and suddenly the QSC was WAY louder--even wiith the avalon's level set to the lowest point, I don't need more than 10 oclock on the lvel knob of the qsc. like night and day. I don't completley understand this, but there it is

    Bottom line is the RBI always worked fine for me. But it made the qsc work a lot harder. Never had a problem, but completly different setting foro the two preamps
  11. Glenn D.

    Glenn D.

    Aug 20, 2002
    Fort Collins, CO
    The Sansamp RBI output is right around dB; the Avalon is more like +4 dB. Power amps like +4 dB better. The PLX mod is to increase the sensititivity to let the RBI drive it better. And if it's done by an authorized repairer, you still have the warranty.

    Glenn D.
  12. 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 PLX 1202 puts out up to 1200 watts in bridged mono into a 4-ohm load, not 600.

    Put switches 4, 5, and 6 to "stereo," like the manual shows.
    If the amp clip LEDs flash a little while you, don't worry too much about it. If the clipping gets significant, then you should do something about it.

    Ideally you would run the power amp at less than full gain and put a hot signal into it from the preamp, but you can do whatever works.
  13. orskard


    Mar 17, 2004
    maybe i didnt say this, but my avatar is 8 ohms, not 4 ohms. So its 600 watts.
  14. 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
    Sorry, I took "bridged at 4" to mean you wanted to run the amp bridged into a 4-ohm load.
  15. kasbrey


    Aug 23, 2002
    Northampton UK
    I have an RBI -QSC RMX850 - EDEN 410XLT rig and can assure you that the RBI puts out +10db, more than enough to drive the QSC.
    I specifically bought the RBI because I couldn't get enough output from my Bass Pod Pro (max +4db).
    Are you using the 1/4" jack? I had no problem using this output but prefer using the balanced Sansamp XLR connection as this seems to sound better when I have to set the gains a little lower (the output pad switch to its loudest setting).