Stereo power amp... Using 1 side only VS. bridge

Discussion in 'Amps [BG]' started by K2000, Jul 25, 2011.


  1. K2000

    K2000

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    Nov 16, 2005
    Location:
    Brooklyn
    I have a 4 ohm Bill Fitzmaurice cab, which I am powering with a Carvin HD1800 amp, with just one channel. The other channel is inactive. Seems fine but the fan is coming on and the amp seems to run a little hot. I'm not really pushing the amp too hard (volume is at noon) so I'm wondering... Would it be easier on the amp to run it bridged into the cab?

    At 4 ohms stereo, one side of the Carvin's 600 watts is a perfect match for the BFM cab (Omni 212, rated 600 watts with two 300 watt speakers).

    At 4 ohms bridged, the Carvin puts out 1800 watts :eek:

    I guess I'm mainly trying to avoid fan noise if possible, and not run the amp any harder than I need to. (And not blow any speakers ;) )

    Comments?
     
  2. 3506string

    3506string

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    I'd say leave well enough alone. IIRC bridging an amp into a 4 ohm load effectively places a 2 ohm load across each side of the amplifier. The fan doesn't mean the amp is running too hard. If the amp is clipping and going into protect mode then it is running to hard. The extra voltage is only going to make it more likely for you to toast your drivers
     
  3. staindbass

    staindbass Gold Supporting Member

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    Jun 9, 2008
    if you bridge for 1800 watts, and only use 600, it should be easier on the amp. if it has the capability to be bridged it should handle it as it was made to do that. try the bridged setup and see if the amp runs cooler. that will tip you off as to how hard it is working. i have a few thousand watts, crown microtechs ,enough to easily toast my speakers, but i never have. i like the headroom. i think a 1600 watt amp running at 600w sounds more solid than a 600w amp running at 600w.
     
  4. Andy_D

    Andy_D

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    I'm looking at the same question.... Crown XLS1000 powering 600 watts of speaker cab. Bridged mono it's 1100 watts at 4 ohms. Running just 1 channel would be 535 watts at 4 ohms. I too am concerned about overpowering speakers. I know that under powering speakers can be as bad or worse than overpowering due to distortion. I would think that power matching as closely as possible is the best solution. Not so much power that you blow your speakers if not careful, but also not under powering to the point of distortion.

    To the experts out there... correct me if I'm wrong on this as I'm attempting to apply some logic here. I'd like to know the correct answer to this. I'm not a power or volume freak but rather am just seeking some good clean tone.
     
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  6. Zooberwerx

    Zooberwerx Gold Supporting Member

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    IIRC, bridged mono works best when dealing with the wide voltage swings of an 8 ohm load. Example: I use a QSC RMX 1450 bridged to power an 8 ohm Acme B-4. OTOH, I also use a larger RMX 2450 bridged to power two 8 ohm subwoofers (4 ohm load) and have had no thermal problems.

    Riis
     
  7. CharlieC

    CharlieC Supporting Member

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    I run my Crown XLS1000 bridged-mono and on loud gigs I rarely use half of its rated power. At end of the day, the amp's fan is quiet as a mouse and the amp has not even broken a sweat. When running the same rig at reasonable volume levels, whether 4 or 8 ohm loads, the fan is dead quiet and the amp weighs less than my bass guitar. I paid for 2 channels and I like using them, especially when this Class-D amp does not seem to mind.

    Cheers!
     
  8. billfitzmaurice

    billfitzmaurice

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    If you're not an electronics expert don't mess with bridging. It's not about watts. Watts mean nothing, it's all about voltage swing. If you don't need the doubled voltage swing that bridging gives all you stand to gain is doubling the chances of blowing your speakers. If you don't know whether you need to double your voltage swing you aren't an electronics expert. If you're not an electronics expert don't mess with bridging.
     
  9. Bob Lee (QSC)

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

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    Forget "knowing" that because it isn't true. ;)

    To the OP: if you get the volume you want with the single amp channel and it isn't clipping much, just leave it that way.
     
  10. jnewmark

    jnewmark Supporting Member

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    Sort of an offshoot question. When adding a single 12 cab at 8 ohms to a 212 cab at 4 ohms, would it be better to daisy chain the cabs for a close to 2 ohm load on one side of a power amp, giving, say, 750 watts, or run the amp in stereo, giving a 4 ohm load to the 212 for 450 watts, and an 8 ohm load for the 112, givving it 300 watts ? Any pros or cons for each way ?
     
  11. Bob Lee (QSC)

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

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    You've got two cabs and two channels. Might as well put one on each.
     
  12. jnewmark

    jnewmark Supporting Member

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    Would I then need to use a Y cable to get the preamp signal to both channels ?
     
  13. Bob Lee (QSC)

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

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    That, or if there are switches to parallel the inputs, you can use them. Either way.
     
  14. Marko5657

    Marko5657 Supporting Member

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    I bet those who make money re-coning speakers just looove the advice you guys give, haha…

    (not including Mr. Lee or Mr. Fitsmourice)

    :)

    And those of you speaking of doubling/tripling the handling rating of a cab to a guy who thinks his power amp has a “volume” knob…


    Shame on you.
     
  15. robb.

    robb.

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    did you know that class AB amps are least efficient (i.e. they generate the most heat) at 1/3 power?

    robb.
     
  16. Bob Lee (QSC)

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

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    An amp operating at 1/3 of full power is being driven extremely hard, with massive clipping.

    A class AB amp will tend to generate the most heat at 1/3 of full, but the least efficient operating point is actually at idle.
     
  17. robb.

    robb.

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    har, har.

    yes, in terms of RMS of dynamic music, we agree. i had to laugh a little, though, that the intuitive advice wasn't necessarily good advice.

    robb.
     
  18. BassmanPaul

    BassmanPaul Gold Supporting Member

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    One on each channel will give the ability to balance the volume from each cabinet with the amps faders.
     
  19. K2000

    K2000

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    Oops, I should have called it a level knob (which adjusts volume).

    "3. CHANNEL LEVEL CONTROL
    A precision input LEVEL attenuator is used to adjust the volume levels. To deliver the amps maximum power without reducing the headroom of the signal source, the level controls should be turned full on."

    :rolleyes:
     
  20. Bob Lee (QSC)

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

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    It's a gain control.

    And those instructions aren't very good. ;)
     
  21. Growly Lytes

    Growly Lytes

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    Hi Bob,
    or anyone that knows about this....
    I use a class H poweramp,
    For jamming at home i usaully have the level control of the poweramp at no more than 1/4 of full.Does this mean the amp is running hard ? Would setting the control to 1/2 be better, i get the volume & sensitivity thats needed for home practice ?
    I always thought s.s amps work harder & heat up more when they are pushed harder than usual, i always thought that using less power means less heat & stress on an amp, but i bet im wrong ?
     

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