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SansAmp / QSC RMX1450 Clipping

Discussion in 'Amps and Cabs [BG]' started by GrooveMonkey, Dec 6, 2003.

  1. My SansAmp / QSC RMX1450 setup is Clipping again. I've posted about this before and have checked all the dip switches on the power amp. The switches are set to bridge mono just like the diagram on the back of the amp, with the exception of the inputs being set to parallel (I think, I don't have the amp here to look at it). Changing the input dip switches dosen't seem to have a noticable affect on the clipping problem. The clip limiter is enabled and the filter is on and set to 30Hz. I'm using an 8ohm SWR Goliath III cab.

    My SansAmp levels are as such:

    Drive: 10:00
    Blend: 3:00
    Bass: 1:00
    Treble: 11:30
    Level: between 9:00 and 10:00 <<====

    With these settings and a compressor (Alesis 3630)set to 6:1, threshold 0dB, attack/release at min, using my P-Bass I can clip the amp if I play moderately hard. By this I mean fingerstyle with some heavy handedness. Yes the compressor is switched to the on position.

    What bothers me is that the very instance that the clip indicator lights up I'm blessed with the loudest, non-musical, Ka-PoP! similar to unplugging your bass from the amp while it's turned on and cranked as loud as it'll go. Could this be the clip "limiter"? If it is, I think I'd rather let it clip...

  2. I got this from the QSC website:

    Input Impedance 10 k ohms unbalanced, 20 k ohms balanced

    Input Clipping 10 Vrms (+22 dB)

    I'm using the unbalanced input on the QSC. Would switching to the balanced input be better? Or would it simply pad the input signal to 2X the unbalanced impedence?
  3. amos


    Oct 23, 2003
    SE Portland Oregon
    I'm not sure how to solve your problem but it does make me slightly worried since I just purchased a SansAmp RBI and am Getting a QSC PLX 1602 shortly. the only other thing i was planning on running was a Power conditioner, equalizer, and my digitech bnx3 processor
  4. I wouldn't worry about the SansAmp. I'm sure this is an issue with the levels and inputs that I'm using. I'm going to try thr balanced input on the QSC, it has a higher resistance. The QSC website says:

    We recommend that the gain controls be set between half-way and fully up. The input sensitivity of QSC amplifiers is at about 0dBV or (1Vrms). Amplifier gain controls set at a lower position require input signals to be set to a higher level to obtain suitable power levels. There are other noise and gain alignment considerations. Particularly with unbalanced input lines, the hotter your signal is at the input of an amplifier, the more noise propogation you will have into your amplifiers. Also, the gain structure of your system may become such that you will reach the maximum gain travel of a fader, at your source device, before obtaining expected power within your amplifiers.
  5. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Commercial User

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    GM, some questions:

    Is the amp clipping prematurely, or is your complaint that you are overdriving the amp, and it is otherwise behaving normally?
  6. Bob,

    I'm most likely overdriving the amp. I did some tests using different levels while having no load on the output (I can do that right?).

    With the Bass, Mid, Treble, set flat and the Level on the RBI set to 4 it's fine. If I boost the bass to +2, or move the level above 4, it will clip under heavy playing (slapping). I'm using a passive P-Bass.

    I played around with the gain knob on channel 1 of the RMX. With it backed off to 26 it's less likely to clip but noticably quieter.

    My main question is, why does it make that godawfull KAPOP!!! when the clip indicators just start to glow? My other RMX does the same thing. My ampeg combo simply distorts a bit and will allow the occasional flicker of the clip indicators.

    Thanks for your help everyone.
  7. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Commercial User

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    You're running in bridged mono. Therefore, make sure channel 2's gain control is turned all the way down. Set switches 4 and 5 to STEREO INPUTS. Use channel 1's gain control only. Make sure channel 1's clip limiter is turned on.

    Make sure your amp output is connected correctly.
  8. hi GM
    tech 21 tell me that the XLR ouput on the sansamp has a pad which gives -4db...this seems to be the one to feed the XLR on your amp?
    the jack connections are 0db...now thats what they say...dont ask me to explain too much except they give advice on how to remove the pad if your XLR is not hot enough...and that seems to be the reverse with your situation
  9. What's the difference between stereo and parallel inputs?
    I'm pretty sure it's set to stereo (I'm at work and can't check now). I'm already doing the rest of what you suggested.


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