1. Please take 30 seconds to register your free account to remove most ads, post topics, make friends, earn reward points at our store, and more!  
    TalkBass.com has been uniting the low end since 1998.  Join us! :)

No amp should be run at 4 ohm bridged???

Discussion in 'Amps and Cabs [BG]' started by cb56, Dec 13, 2004.

  1. cb56


    Jul 2, 2000
    Central Illinois
    I recently had to put mt Ampeg B4r in the shop for a minor problem (wouldn't power up) It was under warrany and has since been fixed.
    While it was in the shop I thought I would go ahead and buy a power amp to use with my SVPCL preamp. After shopping around I decide on a Yamaha P2500s. The sales brochure said it would do 1300 watts at 4 ohms bridged. Perfect, since I had been using the Ampeg B4r bridged at 1000 watts into my Ampeg 410he and svt15e cabinets.
    When I got the Yamaha amp home, I read the owner's manual and it said the minimum load in bridge mode was 8 ohms. emailed Yamaha and here is the response....

    "Thank you for the email. The amp can be run at 4 ohms bridged but we do not recommend it. The 4 ohm and 2 ohm bridge specs in the brochure are primarily for comparison purposes. Many amp manufacturers will state that their amp is a very high rating but fail to mention that this is a 2 ohm bridged rating. Unfortunately, in order to compete we need
    to list these ratings also.
    Running any power amp at 4 ohms in bridged mode is very hard on the ampand I would question any manufacturer that gives the ok for this unless it is a commercial grade power amp or bass amp designed for this."
    So my question is, have I been wrong to run my Ampeg at 4 ohm bridged? Or is it a "commercial grade amp" where the Yamaha isn't?
  2. Well, Ampeg states that it is perfectly safe for the B4R to be run at 4ohms bridged. I'm sure that Ampeg Insider will back me up on this. That being said, I used to have a SVT-4Pro that fried a power amp when running with a 4 ohm bridged load. I'd be nervous about doing it...
  3. Transverz

    Transverz believer of the Low End Theory

    May 3, 2004
    Los Angeles, CA
    I believe your Ampeg fell under the "bass amp designed for this" caveat by Yamaha. Though a lot of their comments are quite puzzling.


    *edit* Oh, and I ran my former SVT-4Pro at 4 ohms bridged with no problems at all...
  4. metron

    metron Supporting Member

    Sep 12, 2003
    Im confused about their response. They say that they list 2 ohm bridge ratings because others do but do not recommend 4 ohm bridge operation. First Ive never seen any other manufacturer list 2 ohm bridge ratings. Second which are they suggesting you dont do? I dont think there is an amp out there that can run 2 ohms bridge because thats a 1 ohm load on each side of the amp and it would probably make the amp very unstable. I think 4 ohm bridge operation is common.

    I dont know. Personally I would not use the Yamaha in 4 ohm bridge mode if the manufacturer suggests against it. I think its stupid for them to list a spec but also to tell you you shouldnt use the amp that way though. Ampeg lists a 4 ohm bridge rating for the amp. Maybe PM Ampeg Insider to make sure its ok.
  5. IvanMike

    IvanMike Player Characters fear me... Supporting Member

    Nov 10, 2002
    Middletown CT, USA
    this sounds like false advertising on the part of yamaha. i have never heard of a reputable amp manufacturer giving a power rating for an impedance load that the amp couldn't handle. do they give a power rating for 2 ohms stereo as well???
    until recently, not many amps were designed to run at 2 ohms per side/4 ohms bridged. However, today quite a few are. But i have to state again, if yamaha listed a power rating at an impedance that their amp couldn't handle, that's just atrocious. QSC and Crown, (to name a couple) make a variety of amplifiers, some of which are only stable to 4 ohms stereo/8 ohms bridged, and some of which are stable to 2 ohms per side/4 ohms bridged. For any given amp they only state power ratings for the impedances that the amp is usable at. It sounds like yamaha is giving you the major runaround and a line of BS.
  6. Stinsok

    Stinsok Supporting Member

    Dec 16, 2002
    Central Alabama
    I ran my Carvin amp bridged at 4ohms into a 2.67 ohm load. Smoked it in about 10 minutes.
  7. xyllion

    xyllion Commercial User

    Jan 14, 2003
    San Jose, CA, USA
    Owner, Looperlative Audio Products
    Ummmmm, it is not bridged at 4 ohms if your load is 2.67 ohms. You had it bridged running a 2.67 ohm load which is lower than the rated specification.

    As for Yamaha, shame on them. Amps can be built to bridge into super low impedances if the manufacturer chooses to do so. It is more expensive to build amps that go into lower impedances. So, the manufacturer has to decide on a trade off between price and load capabilities.
  8. Arthur U. Poon

    Arthur U. Poon

    Jan 30, 2004
    SLC, Utah -USA-
    Endorsing Artist: Mike Lull Custom Basses
    Wow, I'm surprised at Yamaha's response. I agree that they shouldn't publish a spec-sheet contrary to their operating recommendations. Very strange. I'd also be hesitant to run it bridged into a 4 Ohm load if Yamaha has informed you not to.

    When I had an SVT-4 Pro I ran it bridged into 4 Ohms, it seemed to run a little hotter when compared to stereo mode. It never had a problem, but I only had it for a couple of months. If you don't receive any response from Ampeg Insider, I'd contact Tommy Wilson at SLM/Ampeg's repair dept/tech support department in regards to the B4R and it's recommended operating mode(s).

    QSC's PLX-series amps work fine bridged into a 4 Ohm load, but I'm not sure on their RMX series. PM Bob Lee @ QSC about this. I've ran my old PLX2402 in mono-bridge into a 4 Ohm load many, many times without a problem.

    If the Yamaha isn't going to work out for you, IMO you should return it for another brand of power amp that will.

    My 2 cents, -Art
  9. Brian Barrett

    Brian Barrett

    Nov 25, 2001
    Murfreesboro, TN (Nashville)
    Dealer LowEndBassShop.com, Builder LowEndBasses.com
    Return it. Thats is really poor to give you a response like that. Go get a good amp like a Crest!!! That way you know you have quality, you bass and cab is only as good as your amp and visa versa!

    Best of luck,
  10. Domt mean to hijack, but i have a question. If i run 2-8ohm cabs (daisy chained) into one channel to use bridged mode, is that an 8 or 4 ohm bridged load? :confused:
  11. Brian Barrett

    Brian Barrett

    Nov 25, 2001
    Murfreesboro, TN (Nashville)
    Dealer LowEndBassShop.com, Builder LowEndBasses.com
    4 ohm

    two 8's make a 4 ohm load.
  12. MJ5150

    MJ5150 Terrific Twister

    Apr 12, 2001
    Olympia, WA
    Hehehe....it's time for those Yamaha guys to give up making amps, and focus on those crappy dirt bikes they make. :)

  13. mikeyvr6

    mikeyvr6 Supporting Member

    Feb 19, 2002
    Plymouth, Wisconsin
    The RMX series is capable of 4 ohm bridged operation. I've been running my RMX1450 bridged into my 8x10 (pretty hard sometimes) for about 8 months now with no issues.
  14. BillyB_from_LZ

    BillyB_from_LZ Supporting Member

    Sep 7, 2000
    Not the FET900 I hope!!??? :confused:
  15. Bongolation


    Nov 9, 2001
    No Bogus Endorsements
    Yamaha's response reminds me very much of the SWR docs talking about using their amps in 2 Ohm mode.

    Though their published specs are for 4 and 2 Ohm usage, the docs seem to say that you shouldn't use 2 Ohm loads.

    Very confusing.

    I've been meaning to ask about this in regard to SWRs for some time and peoples' experiences with this.

    In any case, yeah, it's pretty bogus to use these fake specs if they don't translate into real-world use.
  16. IvanMike

    IvanMike Player Characters fear me... Supporting Member

    Nov 10, 2002
    Middletown CT, USA
    IIRC, the only thing SWR ever said about using their amps in the 2 ohm mode was that the clip lights would not be accurate, and that clipping would occur before the clip light engaged. Otherwise as far as i know, any amp they rated for a 2 ohm load was fine when doing so.
  17. IvanMike

    IvanMike Player Characters fear me... Supporting Member

    Nov 10, 2002
    Middletown CT, USA
    Crown has some neat-o amps that can put out something like 10K watts into 1/2 of an ohm. Of course you need three gorillas to lift them and they cost as much as a lexus, but hey, that's still cool. :cool:
  18. Bongolation


    Nov 9, 2001
    No Bogus Endorsements
    Check the section on impedance ratings on page 12 in this manual. It's not a yes or no at all, as I read it, more like "you can, but it'll burn up your amp sooner." Weird. If it's bad for the amp to run it at two Ohms, then why represent it as a two Ohm amp in the first place? :confused:

    Sorry I can't cut & paste the salient passage, but it's a .PDF file.
  19. Brad Johnson

    Brad Johnson Supporting Member

    Mar 8, 2000
    Gaithersburg, Md
    You can cut and paste from a .pdf file. Just use the "select text" feature.

    "You may be thinking that you’ve found the solution to the universe—just use speaker cabinets with really low impedances and you can
    get skull-crushing power out of your amplifier, right? Wrong. There’s a catch. Power amps have limits as to how low an impedance
    they can drive safely. This is what’s known as an amplifier’s “Minimum Impedance Rating.” If you try and operate a power amp below
    its minimum impedance rating, it will give you lots and lots of power for about five minutes…and then overheat, short out and fail completely.
    Here’s what this means to the power amp in the Black Beauty. Like most combos, the Black Beauty contains a mono...".

  20. cb56


    Jul 2, 2000
    Central Illinois
    Thanks for the responses. I don't want to give the impression that this amp is a pos or anything, just that I'm dissapointed because I looked at the specs sheet (little of which I understand) in the store and was lead to believe it could handle a 4 ohm bridge application.
    It's probably too late for me to return it because I've owned it for two weeks and have rack mounted it. I've been using it with 2 4ohm 210 cabs in stereo mode and it worked great.
    I suppose I'll be fine running into my 2 8 ohm Ampeg cabs because they will get 275 watts each at 8 ohms stereo which is still more power than an SVT3pro.
    I guess I can always go back to running my SVTCL into my B4r's power amps (1000watts bridged 4 ohms) and use the Yamaha as a back up.

    Looking back I guess I shouldn't have run out and bought something in a hurry just to get through some gigs while my B4r was in the shop. I could have bought a QSC rmx850 that would have given me 1000 watts Bridged 4ohms and for $100 less. I just would have had to buy it mail order and wait a couple weeks to get it.