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Quick QSC Query

Discussion in 'Amps and Cabs [BG]' started by nicoli, Nov 26, 2003.


  1. So I was reading my owner's manual for my RMX 850 last night, and I came across one section that has me a little confused.

    I have parallel inputs selected, but more often than not I'm running this with only one cab (home practices and most rehearsals).

    According to the diagram for connections, it seems like only having one cab connected in this manner (parallel inputs, out of channel 1 speakon jack) means I'm sending the same amount of power as I would in bridged mono, is this correct (don't think it is, but figured I'd double check)?

    Just curious as to exactly how much punishment my speakers are enduring :D
     
  2. BillyB_from_LZ

    BillyB_from_LZ Supporting Member

    Sep 7, 2000
    Chicago
    Parallel input is not the same as bridging.

    Using a parallel input connection is like having a hidden Y cord that allows you to send a mono signal (like from a bass preamp) to both inputs of a stereo amp.

    I presume that you have the speaker connections going to 1+ and 1- of the speakon. If you don't know the answer, most likely you are. To use the bridge mode, the output connector needs to be rewired to 1+ and 2+.

    Using parallel inputs, you won't damage the amp if you only connect a speaker to one channel. Just keep the level control for the other channel turned all the way down.

    BTW, it wouldn't hurt the speakers to run them in the bridge mode, as long as you don't go crazy and push them too hard.
     
  3. 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
    The connection diagrams don't mention anything about power. Where do you see that?

    Running in parallel mono is just the same as running in stereo but with a Y-cable to bring the input signal into both channels. Thus, you would have the same power available on each channel as in stereo.
     
  4. Bob Lee, I realize it doesn't say anything about power... I'm looking at the diagram on page 16 of the manual.

    It shows one speakon output in parallel mode, then has two arrows from it labelled 'To Channel 1 speaker' and 'To Channel 2 speaker'.

    The diagram above this has 2 speakon outputs, the first saying to Channel 1 speaker and the second saying to channel 2 speaker.

    Like I said, I didn't think this meant I was sending twice as much power but I figured I'd double check as the diagram left me a bit unsettled. Thanks for the clarification.

    One more quick question... when running two cabs (parallel inputs), if I turn up the volume for Channel 1 it only gives the cab plugged into channel 2 juice. The Channel 2 gain control gives both cabs power when I have Channel 1 turned all the way down... shouldn't I have independant volume controls in this mode? :confused:
     
  5. todd 4ta

    todd 4ta

    Apr 3, 2003
    Indiana
    What that diagram is showing is that the top speakon connector has the channel 1 and channel 2 outputs available, but you have to wire your speakon connector as shown (esentially you would have two speaker cables wired into one speakon connector, one cable would be +1,-1 and the other would be +2,-2).

    If you're using a normal cable with just a single cable (wired +1,-1), you just using the channel 1 output from the top connector.
     
  6. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    Nope. For independant volume control, use "Stereo" mode.
     
  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
    Yes, you should. Make sure the amp is not in bridged mono (switches 6 and 7), and that the Speakon plugs on your cables are wired to terminals 1+ and 1-.
     
  8. Bridged Mono is definitely set to off, not sure about the wiring on the speakon plugs though...

    I bought this used and the guy gave me the speakon he was using with it. I think he was running an 8x10, probably in bridged mono... So based on BillyB's earlier post I guess there's a chance the wiring has been changed. I haven't modified the one I bought since buying it though so it should be normal (in theory at least).

    I'll try to check it out after the gig tonight.
     
  9. patrickj

    patrickj

    Aug 13, 2001
    Baltimore, MD
    Could you (or anyone) show an example wiring scheme of a speak-on connector on the cab side? 1+ and 1- correspond to the traditional +/- leads, what do the 2s connect to?
     
  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
    It depends on the speaker. Some manufacturers, for example, use them in bi-amp cabinets with 1+ and 1- for the LF driver and 2+ and 2- for the HF.
     
  11. This is pretty conventional. I use Pair #2 for the highs in my bi-amp rig. All drivers are phased inside the cab for (+)Red = Forward cone movement. Many older JBL models are reverse from this.
     
  12. I think the wiring must be different on one of my plugs... running the rig in stereo at the gig last night and during setup one of the channels wasn't putting out any juice... switched the cables with each other and no problems after that.

    I suppose I'll get another regular cable for when I'm using two cabs together (and as a backup, since I've been meaning to get one) and keep the other one setup for when I want bridged mono.

    Thanks for the input guys, not sure that I'd have figured this one out on my own. I'm fairly new to speakon plugs and didn't realize the engineering behind how they were wired.
     
  13. 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 idea. Be sure to label them so you use the right one! (Although, if you get stuck, they're very easy to change in the field--it only takes a minute or two, and you don't even need a soldering iron, just either a Phillips screwdriver or 1.5 mm Allen wrench, depending on when the plug was manufactured, and maybe a 3/4" or 19 mm open end wrench if the bushing is screwed on really tight.)
     
  14. amos

    amos

    Oct 23, 2003
    SE Portland Oregon
    Okay I found a thread that has actually answered some of my questions

    I think I've deciphered that running my two 1x12 cabs in parallel mode would be the most efficient. this would allow me to use speakon cables exclusively (the cabs only have one speakon connection).

    My only question is: the impedence of the cabs (8ohm) would not change, correct?

    And standard speakon cables would work fine correct? (I know to run speakon cables bridged requires modification of the cable)

    My cabs are coming in wednesday and I'm picking up my QSC PLX 1602 before then and I want to be able to get everything set up as quickly as possible.

    Thanks so much
    David
     
  15. The impedance of the cab itself and it's handling capacity will not change regardless of the total load on the amp.