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Power Amp advice

Discussion in 'Amps and Cabs [BG]' started by KIRKSFANGS, Jan 21, 2003.


  1. Greetings --- I am currently running an Alembic
    FX-1 with the power supplied by a Crown CE1000 power amp. I am having alot of clipping problems when slapping or going into the sub registers. I have researched the problem and have gotten it narrowed down to one of two factors...
    One theory is that the amp isn't getting enough power from the wall -- this could be it cause I've noticed that the problem increases when more load is put onto the circuit I'm running on ( PA , guitar amps , etc). The other school of thought is that since the CE1000 works on a "switching" internal power supply , that there is a lag time between when the power is needed to when the amp actually delivers it -- thus again , the amp is
    "starved" for current.
    I would appreciate any suggestions that would get me the clean full - range power I am looking for. As you can imagine , alot of the fun is taken out of playing when you have to constantl moniter a problem like this.....
    Thanks a Bunch !! ---- Kirk
     
  2. 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
    I doubt that it's a problem with getting enough juice from the AC line, but you could meter it to see if the voltage is low. There's no lag like you describe in a power supply; it has a reservoir to handle big short-term peaks.

    If you have it available, look at the envelope of an uncompressed slap bass track in ProTools or some other digital recording software. The attack of each slap often runs a good 8 to 15 dB hotter than the rest of the signal. That's 6 to 31 times the average power in the signal. If you're averaging 30 watts from the amp, then, the peaks would need anywhere from 180 to 900 watts to be reproduced cleanly.

    Your amp is the lowest powered model in the CE range, so you might just need more power. If you're not running in bridged mono, try it.

    You could also try adding a limiter to bring the peaks down somewhat.
     
  3. man, Bob! I've never seen an engineer that was able to apply the techno-speak to this specific application as deftly as you do. I just wanted to take a sec and thank you for your contributions, I've learned soo much from your posts.
     
  4. Bob --- Thaks for the input --- I am running bridged mono into 4ohms -- this should give me 1100 watts RMS --- You really think I might need more ? If that's the case , why will a 450 watt amp not have this problem ? Not questioning your expertise at all , just trying to learn . Thanks again
     
  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
    For what you're doing, you might need more power. Slapping has a high crest factor (ratio of peak power to average), so it's really easy to clip even a moderately-powered amp.

    Can you hear distortion when the amp clips? If not, you can try just living with it. A lot of instrument power amps don't have clip LEDs, so you don't know if they're clipping until the distortion becomes audible. So there's a precedent. ;)

    I don't know about the 450-watt amp. Tell me more about it and what it does when you use it.
     
  6. hands5

    hands5

    Jan 15, 2003
    good 'ol USA/Tampa fla.
    none
    So Bob, which Crown or QSC power amp would you recomend using with the Alembic F-1X preamp or SWR Grand prix IOD.Basically I want real tight/full lows and low mids/ real clear but not zingy"highs.I understand that the instrument that you play also may have something to do with the type of sound that a player may want,
     
  7. 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
    Well, how much power do you want, how much weight do you want, how much do you want to spend, what features do you want ... ?

    A well-designed power amp will be accurate and sound only as good or as bad as what you put into it; if you want clear highs or crisp mids or whatever, they have to be in the signal going into the amp. I can tell you that the PLX amps are extremely accurate in that regard, and the RMX amps only slightly less so. I don't know about the Crown amps, but I'm sure they have comparable design goals.

    Ask around, try some out, and see what you like.
     
  8. Bob --- Yes , there is audible distortion when the amp clips. So are you saying that the switching power supply in the Crown is not a factor ?? Just trying to narrow down possible remedies ...
     
  9. 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
    I don't think it's likely to be a significant factor, but then I've never put a CE1000 through the paces either on the bench or in actual use. But even a soft, saggy power supply can do peaks well if its voltages are high enough for the situation.

    Slapping requires either lots of headroom, good limiting, or gentle clipping (like in a tube amp). You don't seem to have any of these, so go ahead and think about how you want to approach the problem. As is often the case in audio, there's more than one way to get to where you want to go.
     
  10. Fuzzbass

    Fuzzbass P5 with overdrive Supporting Member

    You're certain that the distortion is coming from the power amp and not the preamp?
     
  11. Yes --- tried several different preamps with the same result -- thanks for the input , though !!
    Kirk