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Power amp clipping too easily

Discussion in 'Amps and Cabs [BG]' started by GrooveMonkey, Nov 22, 2002.


  1. I'm using a QSC RMX850 with a SansAmp RBI trough an Ampeg BSE410HLF cabinet.
    Look at the attached picture of my settings.

    The power amp is bridged for 830w at 4 ohms

    The cab is a 4 ohm cab.

    If I turn the power amp up (left knob on power amp) any more than shown in the photo it clips.

    If I turn the level or Drive on the SansAmp any more than shown in the photo it clips.

    ***!!!!??????

    I've disconnected the BBE and Craptacular Alesys compressor to rule them out.

    Could it be the cabinet?
     
  2. I'll try my best. Let's see. I have some questions first:

    - Do you have the impression the amp is supplying its max power? If so, no wonder it's clipping. Try to ease down on the bass knob setting.
    - Could there be another reason why the clip light acts up (protection of some sort)
    - Do you have the cab hooked up correctly for bridge mode?
    - Is something else clipping and setting off the clip detector in the power amp?

    Regards,
    Joris.
     
  3. - Do you have the impression the amp is supplying its max power? If so, no wonder it's clipping. Try to ease down on the bass knob setting.

    No, I'm not even using half power.


    - Could there be another reason why the clip light acts up (protection of some sort)

    I do have clip limiting enabled on the amp

    - Do you have the cab hooked up correctly for bridge mode?

    Nope, it's using the correct out from the power amp.


    - Is something else clipping and setting off the clip detector in the power amp?

    I've taken everything out of the loop but the preamp.
     
  4. BruceWane

    BruceWane

    Oct 31, 2002
    Houston, TX
    Some of the built in limiters on power amps are pretty low quality. They do work, but they're pretty drastic and severely limit power. Try turning it off.

    I'll betcha this is the culprit. You either have to use a speakon connector specifically wired to bridge or a banana connector plugged so that it "straddles" channels 1 & 2. Otherwise, you're only getting half your wattage. Check your manual for schematics on how to properly hook up in bridged mono.
     
  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
    ?????????

    Good. Keep the clip limiter turned on.

    What outputs are you using on the amp? If you're using Speakon connectors, use only the upper Speakon output, and make sure the Speakon plug on the speaker cable is wired to pins 1+ and 2+ at the amp end and whatever your cabinet requires at the other.
     
  6. I'll look into the bannana plug tomorrow. Thanks for the advice!

    The Speakon that I'm using now is a prefab and I'm not sure how it's wired.
     
  7. Just one other thought.

    The little (or big) control knobs on power amps, ARE NOT volume knobs. Generally, they adjust the sensitivity of the power amp to the input signal.

    On some power amps, you can have the knobs on 1 or 2, and still achieve full power output dependant upon the preamps output. Sometimes, it is a delicate balace between the preamp out, and the power amp level to acheive full power w/o clipping.
     
  8. My two cents worth: to really tell, the amp should be hooked up to a dummy resistive load in parallel with an oscilloscope, and a signal generator should input a pure sine wave into your setup. Then by looking at the scope, it can easily be determined when your amp is going into clipping and how much power is being generated. Like previous posts have said, knob position can be unimportant.
     
  9. Wow, also really good to know. Thanks. I've been trying the balancing act between power amp and pre amp for a while but not thinking of the amps sensitivity, only volume.
     
  10. I answered this in the "other" forum, but you can't use a prefab speakon on a bridged QSC - or probably any other amp.

    Look at the manual - It tells how the speakon has to be wired for bridged operation. You use the 1+ and 2+ terminals on the speakon connector. Storebought speaker cables aren't wired that way.

    If you don't have a manual you can download one from http://www.qscaudio.com

    You can rewire the Speakon you have or use the red terminals on the back of the amp.

    hth -
     
  11. Allan, Thanks. I took my speakon connector apart and it's wired +1 -1. I'll be rewiring it and getting back to all of you later.

    Also the cable i'm using is 6 feet long and 12 guage.
     
  12. Good deal, GM. Let us know how it works :)
     
  13. Yep yep the pinouts on the Speakon was it! Much more headroom now. I'll know even more after practice tomorrow. I feel like a bonehead tho, the pinouts are right on the back of the power amp. Thanks everyone for the great help. I'll be having another cable made with the bannana plugs on it so I can compare them and so I can have a spare.