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QSC Power Amp Help

Discussion in 'Amps and Cabs [BG]' started by huskies90, Jul 2, 2005.


  1. huskies90

    huskies90

    May 17, 2004
    I switched from an swr 350x to an interstellar overdrive and QSC rmx 1450. I did this because typically I would run out of headroom with the 350. Well, I just got back from a gig and I am still having the same problem as I had to crank up both the power amp and the preamp and the clip light was occasionally coming on when I needed to push it. Now this is just a basic classic rock band. No heavy metal or anything and nobody else is playing with big amps. What am I doing wrong??? Any suggestions??? I am thinking it is just the wrong cab combo. I have two 8 ohm Eden cabs – a 210 and 115 at 350 and 400 watts rms respectively and I ran them in stereo. I am afraid to run them bridged at 4 ohms because of both over powering the speakers and running the power amp too hot.

    Anyway, I thought going from 350 watts to 560 would be enough. I have another gig tomorrow and I may try running it bridged and cross my fingers…

    Any ideas?????
     
  2. lowphatbass

    lowphatbass ****

    Feb 25, 2005
    west coast
    Can you give us an idea of where the levels were on both pieces of your equipment?
     
  3. Even going from 350 W to 700W would only give you 3dB of extra headroom. Barely noticeable if you weren't loud enough before. And the 560W is less than that.

    You've got a 350W and 400W speaker. They split power evenly, so pretend both are 350W for a minute..... that's 700W RMS for the speakers. Unless the amp puts out more than 1400W RMS bridged you shouldn't be too concerned as long as you can hear it good, cut back if you hear distortion. Compress the signal a bit for slapping, which has lots of peaks, and you'll be good to go. Hard to actually average anywhere near 700W even with a 1400W amp playing live music.

    Randy
     
  4. huskies90

    huskies90

    May 17, 2004
    For levels, the power amp was pretty much all the way but I backed off when the clip light came on. The preamp was at about 1PM. The rmx 1450 is 1400 watts bridged at 4 ohms.

    The IOD is a bass distortion unit so it is going to be hard to tell if I am getting distortion.

    So, then, at what point or even how do I get a noticeable increase in volume????
     
  5. 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
    How much clipping do you get? If you mean just a quick flash now and then, it's nothing to worry about.

    Try running the amp in bridged mono if you need more power.
     
  6. huskies90

    huskies90

    May 17, 2004
    Hi Bob!! It was hard to tell how much the light came on because for the most part I was not facing it while playing although the guitar player in my band kept joking I had my back to the audience all night.

    I have an outdoor gig with another band on Saturday. These guys play loud (a drummer with his own PA - pretty scary) so I am going to set it up in bridged mode and let it fly.

    Can you or somebody please answer my other question:

    at what point do you get a "NOTICEABLE" difference in volume and if there is no difference between 350 and 550 watts, why the heck would anyone buy a 550 watt amp over a 350 what amp (assuming same brand of course)??????

    I would love to hear an explanation...

    :confused:
     
  7. Tash

    Tash

    Feb 13, 2005
    Bel Air Maryland
    Assuming all other factors remain the same (speaker area, sensitivity, etc.) doubling your wattage will give you roughly 3db of increase in SPL (loudness). This is a noticeable amount, but barely (under normal circumstances humans can hear a difference of roughly 3db but not any less).

    The reason you would buy a 550 watt amp over a 350 watt one is that the first amp will have a much easier time reaching the same volume level that the second one begins to clip at. This is called headroom.
     
  8. huskies90

    huskies90

    May 17, 2004
    Yes that piece I know from research here. But tell me what is the ADVANTAGE of that?? Both amps will clip once you get to the level humans can hear but one amp will clip sooner than later? Who cares??? Where do you go from there?? They are both equally as loud either way.

    Now, if I could just find an amp amp that goes to 11...
     
  9. Juniorkimbrough

    Juniorkimbrough

    Mar 22, 2005
    Mississippi / Memphis, TN
    Endorsing Artist: Lakland Basses
    I just recently got a RMX850 power amp. I'm running it in bridged mode(600 watts) into a 410 cab. I gigged with it for the first time last weekend and for the first time I could actually drown the guitar players out.

    You might want to double check all your configuration switches to make sure you have everything set correct, I had a problem with mine clipping and this is what it ended up being.
     
  10. 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
    There is a difference between 350 and 550 watts, but it isn't really big. It just amounts to about 2 dB.
     
  11. huskies90

    huskies90

    May 17, 2004

    OK, so it there is no big difference and basically no point in owning a 550 watt amp over a 350 watt amp.

    So, then at what point DOES it make a difference?
     
  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
    When you have enough amp power and loudspeaker to do what you want to do. It may be a 2 dB step up. It might be a 5 or 10-dB increase.
     
  13. huskies90

    huskies90

    May 17, 2004
    I played a gig this weekend with the rmx 1450 in bridged mode. No problems and I was definitely loud enough. I am still paranoid about blowing a speaker but I got through the gig with everything in one piece and with no smoke or fire... :bassist:
     
  14. Dr. PhunkyPants

    Dr. PhunkyPants Guest

    Aug 11, 2002
    USA
    Hey all. I use an SWR IOD and just thought I'd mention that its output is rated at .775v. Last time I checked, that's a fair bit below the QSC.

    Bob or someone else at QSC can do a quick mod on the power amp that will improve the input sensitivity considerably. No brainer for your current situation.
     
  15. Dr. PhunkyPants

    Dr. PhunkyPants Guest

    Aug 11, 2002
    USA
    Most people don't realize that it's not too much power that damages speakers, it's too little. Clipping and excessive excursion can really wreck your cabs. Anyone who's killed a cab with an SWR 350 knows what I'm talking about.

    The rule of thumb in pro audio is to feed a speaker correctly, you run twice the rated wattage. We don't use the "double it" rule for bass, but considering the massive power consumption of bass frequencies, it's not a bad idea.

    In short, you are in little/no danger as long as your speakers don't sound like they are possessed by some distortion demon.
     
  16. Munjibunga

    Munjibunga Total Hyper-Elite Member Gold Supporting Member

    May 6, 2000
    San Diego (when not at Groom Lake)
    Independent Contractor to Bass San Diego
    Actually, a 1450 watt amp into 750 watts of speakers is just about perfect. Of course, you don't want to crank it to 11, but the extra power gives you the headroom you need to avoid clipping the amp when the speakers hit a transient that kicks the wattage up for a millisecond or two.

    I run a bridged PLX 2402 into each of my PA subs (EAW SB-220s), which are rated at 1400 watts continuous. This is just about right for them ... EAW likes 1.5 to 2 times the rated power of the speakers for the amps. Those subs can probably handle over 3,000 watts peak (each). Likewise, your speakers are probably good for at least 2,000 watts peak (combined). So if you're running, say, a 700-watt amp into them, then pop a string resulting in an 800-watt excursion, your amp will clip. You need the headroom.

    Bottom line, bridge the amp and go to town.
     
  17. 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
    If 0.775 volt is the nominal output of the preamp (you can figure the peaks are going to hit about 10 to 20 dB higher), then it's probably a good match.
     
  18. 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
    You can't kill a loudspeaker with too little power. If that were true, our speakers would be self-destructing while we're passing the time on TalkBass.

    What kills loudspeakers are two things: excessive power and overexcursion (too much power at too low a frequency). The potential danger in clipping is that the power the amp is putting out exceeds its power rating. A 500-watt amp driven into heavy clipping might actually be putting out 700 or 800 watts, and maybe more. On top of that, the dynamic range becomes very compressed, and the average power is much higher than usual. The driver's voice coil doesn't have as much space between notes and other relatively quiet time to dissipate its heat. And in full-range cabinets, the additional harmonics generated by clipping can burn out high-frequency drivers.

    If the loudspeaker's power rating vastly exceeds the amp's, you can drive the system into really heavy clipping all day long and not damage the loudspeaker. But it'll still sound like crap. ;)