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technical question about power amp outputs...

Discussion in 'Amps and Cabs [BG]' started by Grahams Groove, Oct 6, 2004.


  1. If i am running 2 cabs (each 8 ohms) using a mackie 1400i, is it possible to bridge that and use both outputs, or do I have to run it in stereo?

    Also, I assume that it's possible to bridge it (but figured it'd be good to ask anyway), but is there a way to bridge the power so I'm getting a 4 ohm load, and biamp it still? (I'm using a ADA MB-1 which has 1/4" outputs on the back...1 for full range, and then 2 seperate ones for low and high for bi-amping)

    Thanks
     
  2. you can't bridge it and biamp it without adding a second amp. when you're bridging, the amp is acting as one channel, and biamping is defined as using two amp channels (or two amps, whatever).

    the mackie website has your answer for bridging.:

    1400 watts @ 4 ohms bridged

    in general, if both channels are rated to 2 Ohms in stereo mode, an amp can handle a 4 Ohm load when bridged. it is not a hard and fast rule, though, so always verify this first.

    robb.
     
  3. IvanMike

    IvanMike Player Characters fear me... Staff Member Supporting Member

    Nov 10, 2002
    Middletown CT, USA
  4. I've read hours worth of stuff, but nothing fully answered this question/concern that I have...

    If I am running the mackie 1400i into 2 seperate, 8 ohm cabs (making a 4 ohm load), is it possible to bridge the power so I can get all 1400 watts and still use the 1/4" outputs on the mackie to goto each cab? (I cannot daisy chain the cabs because they each only contain a single 1/4" input jack)

    If thats not possible, what od I need to do to get all the juice from this amplifier, keeping in mind that each cab has a single 1/4" input jack...

    Thanks,
    Graham
     
  5. IvanMike

    IvanMike Player Characters fear me... Staff Member Supporting Member

    Nov 10, 2002
    Middletown CT, USA
    if the mackie can run at 2 ohms per side than it should be able to be bridged at 4 ohms
    more than likley it has bannana jacks on the back one for channel a/1 and one for channel b/2 right next to each other
    there should be a switch on the back to select bridge mode - you should engage this while the amp is off
    you will need two speaker cables that have 1/4" plugs on one side and bannana plugs on the other.
    you should be able to connect a one bannana plug between the 2 red terminals of the 2 channels - usually channel 1/a will be positive in bridge mode, there will be a tab that says ground on one side of the bannana plug - this should be in channel 2/b's red terminal
    you can then plug the 2nd bannana plug into the back of the 1st bannana plug, making sure that the ground side of the 2nd plug is plugged into the ground side of the 1st one
    plug the 1/4" plugs into the 2 cabinets
    generally with most power amps, you use channel 1/a's input and input sensitivity knob to control the whole thing, so you should plug your preamp into channel 1 and use that channels gain knob
    plug the amp in, stand back, and insert earplugs
     
  6. As far as I understand it you would need to daisy chain two 8 ohm cabs to run a single bridged 4 ohm load from the poweramp.When the amp is bridged all the power is directed into one channel ( usually channel A ). I have a Crest LT1000 and when using it bridged with an Avalon U5 and my pair of Aguilar GS112 8 ohm cabs I had to daisy chain them, I couldnt see any other way around it because the second channel output is effectively dead. I hope this is correct info....
     
  7. ah! the actual question!

    and the actual answer is, "no." like ivanmike said, you will have to buy a new speaker cable with a dual banana plug on one end and a .250" plug on the other end. unless there is a 1/4" jack on the back panel that is clearly labelled "BRIDGE" (which, incidentally, there isn't), you won't be able to bridge using a .250" plug.

    robb.
     
  8. I hate to sound like an idiot (perhaps for a second time..) btu would someone please direct me to where dual ended banana plug with a 1/4" tip on the other end can be purchased?

    Also, I'm still unclear as to how I would run both cabs on this...if someone wouldn't mind explaining the ocnnection process and how this should be setup in detail.

    I appreciate all the help once again...

    Graham
     
  9. Passinwind

    Passinwind I Know Nothing Supporting Member

    You want two banana to 1/4" cables, or one that goes from one banana to two 1/4" females. These are available many places, try Markertek if you want to purchase online. The nice thing about banana plugs is that they stack easily. You plug the banana end into the two hot terminals (1+, 2+) of your power amp, unless it has a separate dedicated bridge output. Stack the second banana into the first one, plug in two 1/4" speaker cables, run those to your cabs, you're done. Make sense?
     
  10. Now I think I understand, my sub-questions form this are...

    a)Is one way of doing it better than the other?

    b)I'm not sure I understand the reason for stacking...

    added* c) Is there a technical name for banana cables, or is that what they are actually called?
     
  11. For example...

    say I go with this cable...
    1/4" to banana

    Will I need two of those? If so, how do I wire/connect it all so that I end up with a 1/4" tip for each of my two cabs?
     
  12. Passinwind

    Passinwind I Know Nothing Supporting Member

    a) I prefer two single-ended cables, because it's hard to fit heavy gauge cable ends into most common banana plugs. I like female 1/4" ends, because I have lots of different length 1/4" male/male speaker cables that I might want to use. For a dedicated bass rig, less extraneous connectors might be better.

    b) You have two cabinets, and only one set of terminals on the amp to plug into. Stacking banana plugs is one simple way to do what you need to do, which is to parallel two cabs across one set of amp output terminals.The banana plugs have a male side and a female side, which is how you stack them. There are a bunch of ways to do it with "wye" cords too, or you could install another connector into one of your cabs.

    c) Banana is the common, scary technical term. :cool:

    say I go with this cable...
    1/4" to banana
    (link deleted)

    Get two of those, and you're done. 10' might be longer than you need though. Plug the front of one banana plug into the back of the other one. Plug that whole deal into the amp's mono outputs, and the two 1/4" ends into your cabs. IvanMike already told you exactly what you need to do, but sometimes reading it from another source helps, no?:cool:

    Edit: If you're still having trouble grokking this, I could send you a picture of the exact configuration I use. I don't have any Mackie amps around, but you'd get the idea, I'm sure.
     
  13. (b) the way dual banana (DB) plugs are made, you can plug one into the back of another. so if you plug one DB plug into the amp, you can plug another into the back of the first. (c) they're called dual banana plugs because there's two prongs which look vaguely like bananas.

    another option would be to get a DB to .250" cable and "daisy-chain" -- plug the DB plug into the amp's red terminals and the .250" plug into one cabinet. then use a .250" to .250" cable to connect the other jack on the cabinet and the other cabinet. that is how most people do it. (a) there is really no difference between that and the way passinwind suggests, except that DB plugs are not technically locking, so if you get heavy cables, there is a slightly higher risk that they might spontaneously unplug. the longer you have them, the more likely it becomes, as their spring contacts lose their spring force.

    robb.
     
  14. Passinwind

    Passinwind I Know Nothing Supporting Member

    I think Graham mentioned that he only has one 1/4" input on each cab, hence he wants to do something at the amp end.

    Robb's right about banana plugs going limp. I use 14 gauge usually at the plug, and make a really short adaptor cable to female 1/4", then I use some sort of strain relief, like a zip tie, or something similar to keep everything less stressed. I keep extra banana plugs in my kit, and switch out when they get loose.

    The actual designator for the banana plugs in question is MDB, for male double banana.
     
  15. IvanMike

    IvanMike Player Characters fear me... Staff Member Supporting Member

    Nov 10, 2002
    Middletown CT, USA
    now that's a porn star name if i ever heard one.............
    :p
     
  16. 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
    Radio Shack, Sam Ash, GC, and many other places sell dual banana plugs. IIRC, the ones at RS are about $3 each.