16 ohm head into a 8ohm cab ?

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by skyeking69, Sep 4, 2005.


  1. skyeking69

    skyeking69 Member

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    I just got a JTM45 clone that has a 16ohm output
    but the two speaker cab I have are both 8ohm..I don't think it's a good idea to run this head with my cabs...
    Any suggestions how to fix this ??:confused:

    Thanks
     
  2. John Phillips

    John Phillips Member

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    Do you want to run both cabs at once?

    If so, there are two simple solutions - either make a special series-connection cable or splitter box, or rewire both cabinets for 32 ohms (speakers in series) and run them in parallel, which will give 16 ohm either way.

    If you're intending to only run one at once, it isn't that easy, and you may be best replacing the speakers with 8-ohm ones so you can wire them in series for 16 ohms.

    This is assuming the amp is as fragile/valuable as an original JTM45 though. In the other thread I assumed it was an original, but if it's a modern clone the transformer is probably sturdier. Given that the OT ratio in a JTM45 is a bit on the high side, you're probably safe to simply run a mismatch at 8 ohms anyway (although not with both cabs at once).
     
  3. skyeking69

    skyeking69 Member

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    Thanks John

    Yes it is a Clone. with Mercury Mag. and Radiospares OT. I don't plan to run both cabs. One is a
    Boogie hardwood 1x12 with a V30 8ohm. And the one I plan on using
    is a new Avatar 2X12 with a V30 16ohm and G12H 70 anniversary
    If I used a Dr. Z airbrake would this resolve my problem as well ??
    Thanks again
     
  4. John Phillips

    John Phillips Member

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    It probably won't make any difference, because the Airbrake is closer to an 8-ohm load than a 16 anyway.

    I wouldn't particularly worry about it either way with a modern amp - although aren't MM one of those companies that won't warranty their transformers if you use an attenuator? (I could be wrong on that.)

    If you're getting a new cab, why not just get a 16-ohm one? I know that means wiring two dis-similar speakers in series, but I think the minor tone problems that can occasionally cause would be outweighed by running the amp at the right impedance.
     
  5. skyeking69

    skyeking69 Member

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    I already have the Avatar cab....yes I wish it was a 16ohm cab
    But I have to live with the 8ohm version.
    How do I re-wire my cab to run a 16ohms ?

    Thanks again
     
  6. John Phillips

    John Phillips Member

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    You can't... you'd need two 8-ohm speakers. You can only get 8 ohms or 32 ohms with two 16-ohm speakers.

    Actually you only need one new speaker - if you swap the 16-ohm V30 into the Mesa cab (which obviously makes it a 16-ohm cab), put the 8-ohm one in the 2x12", you then only need an 8-ohm H30 to make the 2x12" a 16-ohm cab.

    You could even possibly get away with running the 8-ohm V30 and the 16-ohm H30 together in series - that would make a 24-ohm cab (which is safe enough from a 16-ohm amp), but the disadvantage would be that 2/3 of the power would go to the H30, so the total cab rating would be only 45W not 60, and the V30 wouldn't be driven quite as hard. It might sound good though.

    Hope this isn't starting to get confusing... :)
     
  7. skyeking69

    skyeking69 Member

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    Well my brain is alittle on overload...but I understand
    I will swap the V30 speakers...and try the 24ohm cab
    to hear it first. If I like it, it stays...If not
    I'll look for an 8ohm H30.....
    Thanks for the help John!!
     
  8. sundaypunch

    sundaypunch Member

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    I just had the same issue. I have a 4-ohm Bassman cabinet that sounds great and I have always been afraid of running my 8-ohm amps into it. I ended up buying a Weber Z-Matcher after seeing it mentioned in another thread here. It is $80 for the 50-watt version and $100 for the 100 watt version. I just figured it was a one time investment and now I can run any of my heads with any of my cabinets.
     

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