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To Bridge or Not to Bridge?

Discussion in 'Amps and Cabs [BG]' started by Laklandfan, May 15, 2019.


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  1. Laklandfan

    Laklandfan Supporting Member

    Oct 15, 2010
    New Orleans, LA
    Hello,
    Was looking through the forums and couldn't quite find the answer. I've been using stereo power amps for a long time, but I've only ever used them as split channels. I'm curious about bridging, because I read a lot postings that people seem to be running in bridged mode. I was wondering if there is any downside to running bridged? I never do anything at 2ohm, so only consideration for 4 or 8 ohm. Does bridging shorten the lifespan of the amp? Higher heat or other stress on the components? Thanks.
     
  2. BasturdBlaster

    BasturdBlaster

    Feb 19, 2012
    Crandon WI
    Should have no problems but I can't say it's "better" to use bridge mode unless you have issues with not enough power in stereo mode and you feel comfortable that your cabs can withstand the extra power.

    Can I ask what your amp and cabs are? I'm just curious, hehe

    In my experience, the amp does get warmer with a 4 ohm bridge load vs a stereo 8 ohm load.

    For my xls1002, power goes from 215 watts to 550 watts for each of two 8 ohm cabs. Although my cabs can likely handle the extra power, I still prefer to use stereo mode since it's enough for my needs:)
     
    Last edited: May 15, 2019
    Laklandfan likes this.
  3. lz4005

    lz4005

    Oct 22, 2013
    If the amp is designed to operate bridged and you're within the rated ohms it won't wear any more than using it in stereo mode.
     
    Aqualung60, five7, 40Hz and 2 others like this.
  4. Essentially one power amp channel drives the plus side of the speaker cabinet and the other channel drives the minus side. The two channels are driven by identical signals 180 degrees apart. This releases a huge amount of power, most likely way more than the cabinet can safely handle. DO NOT USE 1/4” plugs in bridge. It’s dangerous for the amp and to you personally. The barrel of the plug is live with respect to ground. SpeakOn plugs only.

    I have been using power amps of one sort or another since the Sixties. I have never felt the need to bridge any of them. The best way to get louder is to add speaker cabinets not power. I use a pair of 4Ω 2x10s one on each channel in parallel mono. It gets as loud as I need.
     
    Last edited: May 16, 2019
  5. Laklandfan

    Laklandfan Supporting Member

    Oct 15, 2010
    New Orleans, LA
    I use greenboy cabs and they seem pretty power hungry, needing lots of watts but then they give great tone and loud volume. The issue is not the amount of power that I currently have, because I like the tone I'm getting from it. I've tried amps that produce less wattage and the tone isn't there to my ears. Band members have noted my tone gets better as wattage (is this headroom?) increases. I'm wondering if I could find a lighter and shallower amp than my plx3602, but giving about the same wattage. If bridging is the way for a new amp to do that, then I could do that. I was just wondering if bridging was a safe way to go in the long term.
     
    BasturdBlaster likes this.
  6. I used to run my old heavy (Class AB) Carvin DCM amps in my PA rig in bridged mode and never had any issues. When I downsized my PA and went shallower and lighter with Class D Behringer iNuke amps several years ago, I noticed a very audible "pumping" when I tried them in bridged mode. I know some will argue the difference in quality levels, but I have heard similar stories about other Class D amps exhibiting the same sort of pumping. And for the record, that's the only issue I ever had with the iNuke amps. I did over two years' worth of bar-band weekend warrior stuff with them without a failure.
     
    Laklandfan likes this.
  7. BasturdBlaster

    BasturdBlaster

    Feb 19, 2012
    Crandon WI
    Plx3602?!

    Holy Moly!
    775 per side at 8 ohms, 28 lbs.
    With GreenBoy cabs.
    You're good, nothing will compare IMO. :thumbsup:
     
    Gary Warner and Laklandfan like this.
  8. Laklandfan

    Laklandfan Supporting Member

    Oct 15, 2010
    New Orleans, LA
    No problem with sound at all. Honestly, it doesn't suck. :). But I hear the siren song of the 10-15lb range. Luring me to my doom? If only QSC would chop the 3602 in half and put a single channel in a shallow 04 series chassis. :drool:
     
    BasturdBlaster likes this.
  9. Laklandfan

    Laklandfan Supporting Member

    Oct 15, 2010
    New Orleans, LA
    If I had roadies I'd just get a CA9 or even a CA12 :hyper:. Amps age in dog pounds, every year I get older my amp gets 7lbs heavier.
     
  10. Wasnex

    Wasnex

    Dec 25, 2011

    Additionally the two amps are tied together at ground, so one side of the output goes positive while the other side goes negative. This is why you shouldn't use a speaker level DI with an amp running in bridge mode...because it grounds out one side of the differential output.

    FYI, Many Class D amps always operate in bridge mode, and we don't realize it.
     
    Last edited: May 16, 2019
  11. I second all of the above regarding the use of 1/4" plugs with a caveat. There are many older amps (the classic SWR SM-400 among them, as well as lots of old PA amps) that aren't equipped with SpeakOn outputs that specify using their banana jacks when in bridged mode. I would STRONGLY recommend using a high quality banana plug and inserting it into the jacks as designed instead of using bare wire through the sides of the posts, and using a SpeakOn on the other end, installing a SpeakOn jack on the speaker cab if not already equipped. And above all, DO NOT TURN THE AMP ON UNTIL ALL CONNECTIONS ARE SECURE AND ALL SWITCHES ARE SET PROPERLY! That should already be "standard operating procedure", but it is doubly important when you're running an amp in bridge mode.
     
    BassmanPaul and Laklandfan like this.
  12. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    If you have an accident and short the output, something as simple as a 1/4" connector coming loose (which is one reason why 1/4" connectors should not be used in bridge mode), the results can become expensive in a hurry. Usually the damage is worse when this happens in bridge mode because the protection circuits are not as effective and can fight each other.
     
  13. Arthur U. Poon

    Arthur U. Poon

    Jan 30, 2004
    SLC, Utah -USA-
    Endorsing Artist: Mike Lull Custom Basses
    I agree with you 100%, Paul.

    I briefly tried my Crest CA9 in bridge-mono once, into my 8ohm Bergantino HT210/HT115 cabinets. This was in a big hall that was empty, before any of my bandmates showed up for the gig. I tried it out of sheer curiosity, and I honestly didn't notice any difference in volume, either. I instantly switched my CA9 back to stereo mode.

    And I also agree, if one is looking for additional volume, add more speaker cabinets, within your amplifier's rated ohm capability.
     
    Last edited: May 15, 2019
    Laklandfan likes this.
  14. Just curious, as an aside, what is the actual physical contact area of a banana plug/jack versus that of a Speakon versus a 1/4"? Is the contact area substantially greater than a 1/4" plug/jack and therefore electronically superior, or is the big advantage just the lesser chance of a short and a more secure, less prone to inadvertent physical disconnection type of thing?
     
    BasturdBlaster likes this.
  15. sawzalot

    sawzalot Supporting Member

    Oct 18, 2007
    I've never had trouble running a power amp in bridged mode provided it was driving a load it was rated for. I've never used 1/4" connectors ever, so I can't comment there.
     
    BasturdBlaster likes this.
  16. stick with your PLX amp, anything else won't be as awesome.
     
  17. Laklandfan

    Laklandfan Supporting Member

    Oct 15, 2010
    New Orleans, LA
    I've used QSC since the beginning started with the PLX series then moved to the current PLX II. Played many many gigs all over, and power was not always the best, but the QSC never had a problem. I'd never say anything bad about QSC. If QSC was lighter/smaller that would be nice. Maybe Bob Lee will hear my heart's prayers. :)
     
  18. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    Banana and SpeakOn are similar in contact area, 1/4" is substantially less. The bigger advantage is that SpeakOn's are impossible to short, shock-proof (important for bridged applications), and more mechanically secure.
     
  19. dab12ax7ef

    dab12ax7ef Supporting Member

    Sep 25, 2011
    Pittsburgh
    Sorry for the sidetrack, but for class D amp such as a D800+, is it ill advised, or even dangerous to run the Speakon cable to a Speakon to 1/4” adapter to a speaker cab? Or should I get an adapter to the banana plugs on the older Eden cab?

    Edit: upon reading the manual, it looks like this amp is a “bridge tied load, ...so touch proof connectors are and added layer of safety”. Ie: it is not a good idea to use 1/4 adapter with it?
     
    Last edited: May 16, 2019
  20. ctmullins

    ctmullins fueled by beer and coconut Gold Supporting Member

    Apr 18, 2008
    MS Gulf Coast
    I'm highly opinionated and extremely self-assured
    Bridging is a great way to generate enough voltage swing to exceed Xmax and trash drivers. <insert analogy about trust fund kid wrapping his Lamborghini around a tree>

    If you’re looking for more volume, then more drivers is usually the better approach.
     
    agedhorse likes this.

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