Mo' Bass issue and power questions

Discussion in 'Amps and Cabs [BG]' started by whipps, Jan 31, 2005.

  1. whipps


    Jan 31, 2005
    I am currently running the Mo' Bass in bridged mono (900watts at 4ohms) daisy-chained into 2 Ashdown MAG 410T cabinets (350watts at 8ohms each). This should give me a little headroom in the amp as the cabs are taking a total of 700watts at 4ohms. These cabs are new but not so different power-wise from my old cabs(410 taking 400watts at 8ohms and a 15 taking 350watts at 8ohms). When I switched to the new cabs I also took the amp out of the rack case as I noticed the amp becoming pretty warm. I played thru the new cabs for about 40 minutes and the amp shut down. Before shutting down the external temp of the amp seemed cooler than it had been before. After about 20 minutes I was able to turn it back on.
    Any thoughts on:
    -Power amp to speaker good power match?
    -Amp shutting down?
    Thanks a ton!
  2. IvanMike

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

    Nov 10, 2002
    Middletown CT, USA
    run it in stereo mode with the cabs one on each side. not sure what that amp puts out into 8 ohms per side.

    just realize when using the swr in bridge mono mode into 4 ohms that translates into each side of the amp "seeing" a load of 2 ohms. i'm not sure if that swr is rated for 2 ohms per side.

    anyhow, you may notice that running stereo into those cabs gives you enough volume.
  3. Cantstandsya


    Jul 27, 2001
    Fontana, CA
    SWR(Stereo) amps are notorious for getting hot and shutting down when ran at 4 ohms Bridged.IME the Mo' Bass is seriously lacking in volume/headroom for it's power rating.If you really want SWR you'd be better off with a 750X or an SM900.
  4. whipps


    Jan 31, 2005
    In stereo in only puts out 260watts per side at 8ohms. I think my best option may be getting external power. I love my mo' bass as you can't touch the SWR sound, all those juicy tube pre-amps. I wish that the power would behave at what the amp is rated.
  5. Ian Perge

    Ian Perge Supporting Member

    May 11, 2001
    Evansville, Indiana
    I'd agree that adding additional power would be the best way to keep your sound and running at 8 ohms while gaining additional power/volume. Bassist Bryan Beller, who as well as using the Mo' Bass professionally in the studio and live was the co-designer and a major proponent for it at SWR does the same thing for additional headroom and explains in great detail here and might help (third paragraph.)

    If you still have problems but want to keep that trademark SWR + studio-level effects sound in your rig, you might want to consider switching to the preamp-only Mini Mo', which gives you the flexibility of running whatever power amp and configuration you like, as well as improving on some of the Mo' Bass "issues" such the power rating, construction, and unity gain. The added flexibility is what made me personally decide between the Mo' Bass and Mini Mo'.
  6. OK, perhaps it's too late for me to be thinking through this correctly, but wouldn't that mean the amp is actually seeing a load of 16 ohms, not 4?
  7. IvanMike

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

    Nov 10, 2002
    Middletown CT, USA
    unluss you modify your cabs or amp or use special cables. using parallel input jacks on the amp or cab, stacking bananna jacks, daisy chaining cabs, etc will always result in a parallel connection of the cabs. 8+8 in parallel = 4 ohms.

    ok, there are a few exceptions, but they are marked as such and i've never seen one.
  8. Alright, well don't I feel silly now. Thanks for clearing that up.
  9. Is the fan on the amp running? If you have a fan defeat switch make sure that the fan is turned on.

    Your assumption that the amp is putting out 700 watts into 2 350 watt cabs is incorrect. The 350 watt designation is what the cab is rated to handle. The amp will put out its full 900 watts into any 4 ohm load.

    The 4 ohm rating on the cabs is a nominal rating. The impedance of the cab varies with frequency. It's very possible that the impedance is dropping significantly below 4 ohms often enough to cause the power amp to overheat. I could never get my 2 4 ohm Acme cabs to behave with my SWR 350.

    Rick B.