Cabinets / impedance question (can I do this?)

Discussion in 'Amps and Cabs' started by Ben R, Apr 13, 2008.

  1. Ben R

    Ben R Member

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    Hi, guys.

    First off, I thank anyone with a clue in advance for their reply & advice on this. I'm not very knowledgeable with electricity :jo. All this impedance stuff with connecting things with certain ohms (and whether it needs to be over or under a certain number) seems to confuse me. One of my rigs at the moment is a Spider Valve 212 amp. I also have a number of cabinets. One of my external cabinets is a Mesa Road King 2x12. I want to be able to use the internal speakers in the 212 Combo (Vintage 30's), and also both speakers in the Mesa Road King Cabinet. I'm confused as to whether or not I can do this. I've attached a photo with a diagram of the back of the Spider Valve combo and also an image of the jack plate on the back of the Mesa Cabinet (see below).

    Basically, the Spider Valve says to either use output "A" (I can use both jacks available combined as 8 ohms, or only one of the jacks as a 4 ohm total); or just use output "B" (for an 8 ohm total). I want to connect it as I've shown below in the diagram. If I do it this way, I'd use output "A", but I'd be using the Mesa cabinet (the jack for 4 ohms) PLUS the Vintage 30's in the combo (8 ohms total). If this output from the power amp says using both jacks like this should be 8 ohms, will I blow something if I do this? I assume that I'm either perfectly safe or I'm gonna' blow something hardcore. can someone please answer this for me and also explain why? Again, thanks in advance. here's the diagram...

    [​IMG]
     
  2. Ben R

    Ben R Member

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    I should add that I realize that I can just go into the combo cabinet at 8 ohms, and one side of the Mesa cab at another 8 ohms & it would be fine. But, that Mesa cabinet has an open back side and also a closed back side, which each have different speakers. I want to use all of them (the 2 Vintage 30's in the combo and also the 2 on each side of the Mesa cabinet). Again, thanks in advance for the reply.
     
  3. KBN

    KBN Member

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    I would go ahead and follow the advice written on the amp and not do that.
     
  4. Austinrocks

    Austinrocks Member

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    a tube amp will run with a mismatched load at reduced power, you cutting your power by close to half out of the amp, and reducing the life of your tubes.

    Running more speakers does not make you louder, having more power makes you louder, so your really not doing your self any good mismatching the amp.

    You know the correct connection and can do it,
     
  5. walterw

    walterw Gold Supporting Member

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    actually, you've got that exactly backwards. the double jack (B) is for a 4 ohm total load, and the single (A) is for an 8 ohm load. the (B) jacks are parallel, so two 8 ohm loads into it will give you the 4 ohms it's supposed to.

    the short answer to your question is "no".
     
  6. Ben R

    Ben R Member

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    OOPS!!! I realize now that I typed it backwards. I meant to say it as you corrected me (in terms of repeating what the the loads are).

    In any case, thanks for the feedback. I'll avoid doing this. Thank God for those of you with a clue! :jo
     

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