tube head and cabinet connections

Discussion in 'Amps and Cabs [BG]' started by jambassist, Sep 23, 2002.

  1. jambassist


    Sep 1, 2002
    Easton, PA
    i know this i gonna sound like i'm dumb, but when it comes to this stuff, i admit that i am. i have a mesa/boogie 400+ head and a bag end 210 cab. the cab is 4 ohms and there's a 4 ohm output on the head. i'm thinking of adding a 15" cab to this setup. the 15" cabs from bag end are 8 ohms. there's 8 ohm outputs on the head. so i plug the 4 ohm cab into the 4 ohm jack and the 8 ohm cab into the 8 ohm jack. is that correct. i know things can get weird with tube heads and impedance, that's why i'm asking.

    thanks in advance, and again sorry if it's a really stupid question.
  2. Actually, it's a very interesting question. Here's the official lowdown from the 400+ manual...

    Two 8-ohm, two 4-ohm and 2-ohm speaker jacks are provided on the Bass 400 Plus. The
    amp will produce its full power at all of these impedances, provided that the total
    impedance of your speaker cabinets is matched to the output(s) used. (Slight mismatches
    are not a major problem, but they will cause slightly lower output and may shorten tube
    life.) When using more than one speaker cabinet, remember that the total load impedance
    goes down as more cabinets are connected. For example, if you use one 8-ohm speaker
    cabinet, use one of the 8-ohm jacks. But if you use two 8-ohm cabinets, they will be
    operating in parallel and the total load will be 4 ohms. Therefore, plug each cabinet into a
    4-ohm jack. If you want to use two 2x15 cabinets where each cabinet is rated at 4 ohms
    (which is how Boogie 2X15’s are wired), connect both cabinets to the 2-ohm Jacks

    A 4ohm load combined with an 8ohm load = 2.67ohms. If I read the manual correctly, you should select the speaker outs that most closely match your total speaker impedance, in this case, you'd plug both cabs into the 2ohm jacks.
  3. On further thought, the different impedances of the cabs may give you problems regarding balancing the cabs. The 8ohm cab is only going to get half the amount of power as the 4ohm cab. It might be wise to get a 15" cab rated at 4ohms, maybe something like the EBS-15H, or 15F.