Mesa 400+ Ohmage/Homage

Discussion in 'Amps and Cabs [BG]' started by Naggon, Apr 12, 2014.

  1. Naggon


    Nov 8, 2006
    Vancouver, BC
    I know there are a ton of threads about understanding ohms and I've been surfing them for a while trying to figure this out, but they seem pretty case-by-case and I can't get a good handle on how it all works, so I'm gonna ask anyhow.

    I have a Mesa 400+, and I'm playing through a 4x12 cab with two separate inputs, each input corresponding to two of the speakers. When I bought this cab, I was told that it was wired at 4 ohms, but it has no labeling.

    Because I'm using two of the outputs on my mesa and my single cabinet with two inputs is essentially acting as two separate cabinets, I'm trying to figure out which ohm setting I should be using.

    btw, the label above the two inputs right in front of the second tube from the left on the image below says "SPEAKERS: 2 OHM LOAD (eg. two 4 ohm cabinets)"


    Attached Files:

  2. catgut


    Jan 15, 2014
    Seattle, WA
    Consult with the speaker manufacturer. Generally speaking. 4x12 would not be wired for 2x 4Ω loads to make it a 2Ω load. 2Ω loads are generally larger cabinets or more drivers. More likely your cab is 2x 8Ω loads making it 4Ω. So use the 4Ω taps. But you need to get the cabinet info or all you'll get is general info. Can you look on the drivers? Do they say 16Ω on each? That would give you the 4Ω load.
  3. Naggon


    Nov 8, 2006
    Vancouver, BC
    That makes sense. The speakers are EVM 12L's, which are 8Ω. So, does this mean that each input should be at 4Ω, because there are two 8Ω speakers?
  4. Seems strange that it'd be wired that way.

    Have you checked how the cabinet is wired inside? It's much more common to see two input jacks which are in parallel (so you could daisy chain another cabinet) instead of each going to a separate pair of speakers.

    If it is going to separate pairs of speakers, as you say, it should be 4 ohm a piece - assuming the 8 ohm speakers are in parallel.

    You could also rewire the cab so that the speakers are running series-parralel, this would give you an 8 ohm speaker cab, which you could also run off your 400+ and it'd also let you add another 8 ohm cab at a later date.
  5. BassmanPaul

    BassmanPaul Inactive

    We could be of more help if we actually were told the make and the model of your speaker cabinet.
  6. Bassmec


    May 9, 2008
    Ipswich UK
    Proprietor Springvale Studios
  7. beans-on-toast

    beans-on-toast Supporting Member

    Aug 7, 2008
    Connecting cabinets can get confusing.

    It sounds like you have a modified 412 cab with four 8Ω speakers. Pairs are connected together in parallel giving you two 4Ω inputs.

    If this is the case, use two speaker cables running from the cab to the 2Ω jacks on the Mesa.

    Now for an explanation. The 400+ has pairs of 2, 4, and 8Ω jacks. Each pair of jacks is wired in parallel. If you had only one 2Ω cab it would be plugged into a 2Ω jack on the Mesa. In your case, you have essentially two 4Ω cabs. You want to run them in parallel. So plugging each into the 2Ω jacks will connect 4Ω parallel to 4Ω which gives you a total of 2Ω.

    You could rewire your 412 cab so that all the speakers are in parallel. Then you would use a single cable running from the cab to the 2Ω jack on the Mesa.
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