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400RB min impeadeance??

Discussion in 'Amps and Cabs [BG]' started by plastica, Aug 7, 2004.

  1. plastica


    Dec 21, 2003
    watertown wi usa
    ok I have an OLD 400rb (says 4-87 under the ser#) I know it is rated 200 watts @4ohm. but i have had other amps rated at 4 and then they say in the manual that they are safe down to 2ohms. I did not get a manual with it, and the new ones are obviously not the same as the power has been upped from what i have read. so downloading a manual would not answer my question.. I would like to plug my 8 ohm single 18 in parrelel with my 4 ohm 2-15 cab as i am crankin this thing up at times and the 15s are getting tired so i nead to either add the 18 on this amp or bi amp
  2. winston


    May 2, 2000
    Berkeley, CA
    I just used my '87 400RB on a gig last night into a 4 ohm Euphonic Audio Wizzy 1x12 cab. The input volume, boost, and master were all above 1/2 way. I was playing in a small pub with drumset, percussion, 2 guitars, 3 horns, keys, and violin. I could feel/hear myself well but the amp was extremely hot to the touch. I've never had the amp overheat on me but I suspect that could happen if you cranked it up into a load lower than 4 ohms.

    You might consider wiring the cabs in series--I think that would give you a 5.3 ohm impedance--low enough to get decent power, and you'd have the 18's extra surface area working for you. There's only so much volume you can expect from a 200 watt amp.
  3. plastica


    Dec 21, 2003
    watertown wi usa
    ok , i took an electronic corse covering series and paralell resistance (among many other things) . if memory served me 4 ohm and 8ohm in series is 12. even at an 8ohm load you are not making the full 200 wats (im told about 1/2) so at 12 ohm your getting like 75wats if my math is even close. that just will not do. i guess another option would be to run another 4ohm cab in series (8ohm), and parralel to the 18' . this would put me back at 4ohms. i guess another option here is to just disconect one of the 15s making that an 8 ohm cab also.
    I have noticed that the gk runs hot. but everyone i know that has one says its normal. when you make 200watts in a 17lb? amp its got to get warm. thats why it has that big heatsink. I am hoping one of the GK gurus has the book or knows for a fact if it was designed to handle 2 ohms. I know alot of companys try to make amps that would go that low just for the fact that so few people understand impediance (i understand it but not so sure i can spell it lol). alot of times people just keep pluging stuff in not knowing it matters.