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How do you bridge an amp?

Discussion in 'Amps and Cabs [BG]' started by Resko One, Mar 25, 2009.


  1. Resko One

    Resko One

    Mar 12, 2009
    Wisconsin
    I've got a SWR 350 and an Ampeg PR-410H Cabinet. The cab is 8 ohms. Is the any way I can get my amp to run at 4 ohms with just this one cabinet?
     
  2. No
     
  3. smogg

    smogg

    Mar 27, 2007
    NPR, Florida
    I'm not crazy, I'm just a little unwell
    Amps are reactive to the load. In order to get an amp to see a 4ohm load it must be present. You either need two 8ohm cabs or one 4ohm cab for an amp to run @ 4ohms.
    "Ya canna change the laws a physics captain."
     
  4. You can only bridge an amp with stereo output amplifiers. Depending on the topology of the amplifier sometimes not even then.

    Paul
     
  5. Bassgrinder77

    Bassgrinder77 Banned

    Jan 23, 2009
    The amp's got to be a bridgeable stereo amp.
     

  6. Actually, what he is talking about is bridging an integrated amp head or power amp with two separate power amps (i.e., loosely called a 'stereo' amp... even though that's not quite accurate). Examples are the SWR900, the Eden WT800, and the Puma1000.

    If the case of bridging the two separate amps of a 'stereo' amp into an 8ohm cab, each individual power amp will 'see' a 4ohm impedance, resulting in the amp running at 4ohms per side into a single 8ohm cab.

    Of course, the monoblock SWR350 does not allow for this bridging.
     
  7. No it doesn't. All that is required is two identical power output sections. If you have two identical MONO power amps they can be bridged too. All you have to provide is two identical signals 180 degrees apart in phase. Yes it's easier if the amp has the required circuitry built in but it is possible.

    Paul
     
  8. Resko One

    Resko One

    Mar 12, 2009
    Wisconsin
    What if I rewired my 8 ohm Ampeg PR-410H To a 4 ohm load. Is this possible? That would create a 4ohm draw from the amp correct? Where's Jerrold Teirs when you need him!
     
  9. Sorry no way to do that. You either have four 4Ω drivers in series/parallel or four 16Ω drivers in parallel.

    Paul
     
  10. Resko One

    Resko One

    Mar 12, 2009
    Wisconsin
    If there 16 ohm then I can run them in a series and achieve a 2 ohm load correct? My 350's manual Says it's stable at 2 omhs and would actually be a little better matched for the 600w Ampeg cab.
     
  11. Resko One

    Resko One

    Mar 12, 2009
    Wisconsin
    It appears that their 4- 32 ohm drivers ran in a series. How can I get this to 4 or 2 ohms?
     
  12. silky smoove

    silky smoove Supporting Member

    May 19, 2004
    Seattle, WA
    I think with that configuration you'll be tied to 8 ohms for the cabinet without getting new drivers.
     
  13. RickenBoogie

    RickenBoogie

    Jul 22, 2007
    Dallas, TX
    Time to re-think your method here. Either get another 8 ohm cab, or, sell what you have and start over. Of course, you still have option 3, run what you have at 8 ohms.
     
  14. Resko One

    Resko One

    Mar 12, 2009
    Wisconsin
    Nevermind. Scratch that. Their ran parallel. Theirs no way to get a lower ohm load out of this cabinet. Looks like I need an amp with more power.
     
  15. Resko One

    Resko One

    Mar 12, 2009
    Wisconsin
    I got the cab for $200 which was a steal in the first place. I could just run it at 8 ohms but then it's horribly underpowered. My amp is quoted at 240@ 8 ohms. the cab says 600 rms. I got the amp for a steal too. $180 for a SWR 350! Perfect condition. I got a guy willing to sell me a SWR 750 for $500 or I could pick up a Eden D115XLT for $200. Which is the better choice though?
     
  16. smogg

    smogg

    Mar 27, 2007
    NPR, Florida
    I'm not crazy, I'm just a little unwell
    mmmmmmmmmm......not quite, bridging a stereo or dual mono amp will still only output to the load presented. Example: My Crown CE1000 puts out 275w @ 8ohms, 450w @ 4ohms, & 560w @ 2ohms per side. In the bridged mono configuration it puts out 900w @ 8ohms and 1,100w @ 4ohms. Again the amp is reactive to the load present. With an 8ohm cab it can only put out what load will draw, it takes a 4ohm load to draw the 4ohm rated output of the amp. The only way the amp can "see" a 4ohm load is only if a 4ohm load is actually present.
    Regardless of mono or dual mono or dual mono bridged, the amp(s) will/can only output at the load presented.
    hope this helps, smogg
     
  17. babebambi

    babebambi

    Jan 7, 2008
    YTZ
    you see, what KJung described is is exactly what smogg's amp is doing. They are just saying it differently.

    when bridging two power amp to run a 8ohm load, each power amp is running half of the total load, which is 4ohm.

    to illustrate by repeating the power rating of smogg's amp

    450w @ 4 ohm x 2 channel
    900w @ 8 ohm x 1 bridged

    560w @ 2 ohm x 2 channel
    1100w @ 4 ohm x 1 bridged

    see the correlation?

    another way to understand it is to look at
    the speaker load as a stone to be lift off the ground.
    the amp as ppl lifting the stone
    think of the weight of the stone in (ohm)
    and how many time the stone can be lifted in (watt)
    so as the number of ppl lifting the stone increase,
    the weight seems lower to each person
     
  18. Underpowerd where? Live gig, practice? 240 watts outa a 4-10 should be pretty loud. Add a 2-10 8 ohm cab or a single 15, 8ohm to get 4ohms. So add the Eden cab..
     
  19. smogg

    smogg

    Mar 27, 2007
    NPR, Florida
    I'm not crazy, I'm just a little unwell
    Wow, what a great way to tie it all together. My apologies to KJung for not grasping his phrasing properly. Good job BB.
    TB rocks :bassist:
    Resko One: hope all this helps you some.
     
  20. My apologies for using overgeneralized, layman's non-precise language:)
     

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