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Question for you QSC users....

Discussion in 'Amps and Cabs [BG]' started by MascisMan, Feb 16, 2004.


  1. MascisMan

    MascisMan

    Nov 21, 2003
    Dallas, Tx
    I currently purchased a RMX 1850HD and practiced with it for the first time tonight. Before I was using an Ampeg B2R into an Ampeg SVT-410HLN. Now I am using the B2R as a preamp (until I get another one) and using one side of the QSC to power the 410 cab.

    Here are my questions. On the QSC where do you guys have your gain knobs at? Are they on full and then you adjust the master volume to taste? Or is there a happy medium between the preamp and the power amp?

    I went through the rehearsal and noticed clipping here and there on the especially hard played parts. I had the QSC gain almost all the way up and the B2R master volume around 10-11 o'clock or about 4 (on a 1-10). The cab sounded good but I want to make sure I am not going to damage anything with the clipping here and there.

    Will this change when I get my preamp? Im looking into an Ampeg SVP-Pro or BBE BMax. As far as my wiring goes I am using instrument cable from the preamp to the power amp and a Speakon from the power amp to the cab.
     
  2. Schwinn

    Schwinn

    Dec 4, 2002
    Sarasota, FL
    You were clipping because you were only using one side of the amp. If you use bridged mode, you won't have that problem. Also, I turn the gain of the power amp all the way up (channel one only in bridged mode) and use preamp controls to adjust volume, but other players do it the opposite way. Power amp clipping now and then won't hurt anything, but it's better to run in bridged mode nonetheless.
     
  3. MascisMan

    MascisMan

    Nov 21, 2003
    Dallas, Tx
    Hmmm. my cab is rated at 500 watts RMS @ 4 ohms. Would running 1800 watts be ok? Thats over 3x times the posted limit. I thought the rule of thumb was dont go over 2x the limit.

    Is there anyway I can keep the current volume and adjust out the clipping?
     
  4. Jon Burnet

    Jon Burnet

    Jan 21, 2001
    Memphis, TN
    the way it was explained to me... its like doing 80 in a 4 cylinder and a 6 cylinder. sure you can do 80 in both, but the 6 cylinder is working less hard to get there.
     
  5. Eric Moesle

    Eric Moesle Supporting Member

    Sep 21, 2001
    Columbus OH
    Remember, just because your amp is CAPABLE of that wattage, doesn't mean that is what your cab is seeing. You'd have to crank the amp up all the way, peak the preamp, and slam notes as hard as you can to get anywhere near the max power output rating. For normal playing, cabs rarely see even one-half of the amps max wattage.
     
  6. MascisMan

    MascisMan

    Nov 21, 2003
    Dallas, Tx
    wow thats interesting, I will try that tonight at practice Eric and see how it goes. The back of the cab has the horn attenuator, should I adjust that in anyway to compensate or is that more to taste?
     
  7. Bridging it will definately stop the clip light from coming on. I've never been able to justifly using 1/2 of the amp and letting the other side idle. I turn the pre-amp up and adjust the volume with the power-amp volume control. This gives me quieter operation and a bit of protection from a dead short or transient pops that could cause the power amp to output its full power and fry the speakers.
     
  8. MascisMan

    MascisMan

    Nov 21, 2003
    Dallas, Tx
    Grey~
    yeah I think that is what Bob Lee recommends also. I will try both and see what happens. Im running the 30hz filter right now and am thinking also that if I bump it up to the 50hz filter it my restore a little headroom as well. The cab plays down to 48 hz.
     
  9. Schwinn

    Schwinn

    Dec 4, 2002
    Sarasota, FL

    You won't use all 1800 watts. You can play at the same volume in bridged mode, but have more "headroom" to avoid clipping. Frying your speaker isn't an issue if you play at sensible volume and listen for distortion.
     
  10. MascisMan

    MascisMan

    Nov 21, 2003
    Dallas, Tx
    I see. So what do you guys think of me changing the filter to 50hz as opposed to the 30hz setting. The cab plays down to 48hz, so technically I would only be missing out on 2hz. Not sure if that would even be a difference or not. I know the manual says that on the 50hz setting there is a slight bump at 100hz for added fullness.
     
  11. Eric Moesle

    Eric Moesle Supporting Member

    Sep 21, 2001
    Columbus OH
    No no no, you're cab is likely rated FLAT to 48hz, where it begins to slope off, but you are still getting some fequency range output below that. 30hz cutoff is generally fine, which is where I keep mine. You can try it, but you will lose a tiny tad of booty . . . :hyper:
     
  12. GRoberts

    GRoberts Supporting Member

    Jan 7, 2003
    Tucson, AZ USA
    I would love to hear from someone like Bob lee regarding whether to dial up the power on the amp and use the input gain on the preamp for volume or the opposite.

    I co-host a jam. A very good local player came in and asked if he could tweak my amp. He adjusted the input gain control using the VU meter to establish the maximum peak, and the used the Master power to set the volume. That is counter intuitive to me. It looks like overdriving the output power with input gain.

    What is the best approach in order to get the most clean power and best sound?