New RMX 1450 question (Bob Lee?)

Discussion in 'Amps and Cabs [BG]' started by GrooveMonkey, Sep 21, 2003.

  1. I just hooked up my new QSC RMX 1450 which replaced my RMX 850.

    I'm running it in bridged mono into a SWR Goliath III 4X10 cab rated for 700w.

    My Preamp is a SansAmp RBI.

    The 1450 clips with the level of the RBI just around 12 O'clock (which is really loud) but gets very non-musical quick. It's a very abrupt, sharp, popping sound that can't be good.

    • Channel 2 is turned down
    • The channel 1 clip limiter is on
    • 50Hz filter is on
    • I'm using the same speakon as before +1 +2 on amp side

    any thoughts?
  2. I also checked to make sure the inputs weren't set to paralell.

    I tried my P-Bass through it with better results but still got the POP when slapping and plucking hard.

    I disabled the clip limiter and still got the same pop!?

    I took my compressor out of the effects loop and still got the pop.

    I pushed the -20 pad on the preamp input and still got the pop but with the level set higher.

    I tried a different cable between the amp and cab with bananna plug to 1/4 in. jack and still got the pop.

    Could it be the cab's own (tweeter light bulb) limiter?

    All four speakers jump and pop at the very instant that the clip indicator blinks.
  3. I don't think this will solve your problem but I found out it is better to have your amp set on stereo even though parallel will work. Parallel in bridged mode is for sending the signal to another source. As far as the clipping, if you have an active bass check the battery first, then check the input signal your putting into the RMX, it could be to hot coming from your bass or your preamp. hope that will help some.
  4. Bob Lee (QSC)

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

    Jul 3, 2001
    Chester, Connecticut
    Former Technical Communications Developer, QSC Audio
    GM, where do you have the amp's gain control set?
  5. The 1450 was set to max gain. I've been getting better results by rolling off the gain to about 2 O'clock on the 1450 and setting the preamp out slightly above 12 O'clock.

    Is this the way to do it?

    I've allways been told that the power amp should be set to max sensitivity and volume controlled with pre-amp level....

    thanks for getting back to me.
  6. Bob Lee (QSC)

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

    Jul 3, 2001
    Chester, Connecticut
    Former Technical Communications Developer, QSC Audio
    Take what you've always been told with a few grains of salt. If a power amplifier were meant to be run at full gain all the time it wouldn't have gain knobs.

    If you get better results with one technique than another, it's clear what direction you should look in. Work with the settings that give you better results and experiment from there.
  7. The 1450 is rated at 900W into 8 Ohms in bridged mono. The Goliath III should be able to handle that assuming that it is in good condition. The caveat is that the RMX could produce peaks that are higher than 900W and you might be causing a problem. Keeping that baby on 10 is only going to make any transients on the input cause a bigger surge. If it were my cab I would be looking for a bad voice coil. It sounds like you could be sending one or more speakers into excessive excursion and that sound is the motor banging around. Without hearing it in person it is impossible to tell.

    I'd double-check the dip switch settings on the RMX, check the voice coil resistance and operation of each driver and inspect them for cone tears or other signs of damage, and verify that the amp has not been modified for the "high sensitivity" inputs a-la Lord Valve. The RBI has a hotter and more "normal" output via the XLR as compared to a device like the SansAmp BDDI.

    The RMX's that I have used exhibited a lot of headroom on the inputs so I'd be surprised if you were clipping the amp. Like any other problem it is best to take a stepwise approach to diagnosis. Strip items out of your signal chain, maybe to the point of just plugging your bass into the 1/4" input on the RMX, and see if one component makes the problem happen.
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