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8ohm amp into 4ohm cab?

Discussion in 'Amps and Cabs' started by Miles, May 21, 2011.

  1. Miles

    Miles Member

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    I have an old 4ohm Musicman 212RH cab I'd like to leave at our practice space.

    My amp is a '71 Traynor Bassmaster (8ohms)

    Is this a safe mismatch?

    I've done tons of searches, but the varying opinions have tied my Saturday Morning head into knots.

    Help!
     
  2. Rockyrollercat

    Rockyrollercat Member

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    No, the amp needs an 8 ohm load. If the speakers are wired in parallel just wire them in series.

    RRC
     
  3. 8len8

    8len8 Member

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    Don't mean to disagree, but I've used several 4-8 ohm amp heads with a 32 ohm attanuator and have had no problems in several years. I think a few amps here and there might be sensitive to speaker impedance, but most are not and just result in less efficiency...
     
  4. freaksho

    freaksho Member

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    i've tried a number of times to get a consensus on impedance mismatching so i could get away with using what i have. trust me: you won't. techs and amps makers will only go on record saying you shouldn't, while many users will say they do it all the time with no problems. and others will say it's fine as long as the speaker impedance is the higher one. bottom line is you will have to decide whether you are willing to take the risk. (fwiw i decided to play it safe and not mismatch.)
     
  5. solitaire

    solitaire Senior Member

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    These topics keep coming up all the time. 1:2 missmatch is OK but wouldn't run dimed. More than so is not OK. Preferably impedances should match though.
     
  6. Miles

    Miles Member

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    Thank you for the replies so far. I am usually using my 1965B Marshall cabinet that is 8ohms for a match.

    While the Traynor is tough as nails and I could probably get away with it, I may just play it safe and not use that Music Man cab for now. Plus, the music man is a great deal brighter when using dirt pedals. It sounds killer and I would love to use it, though.

    Any other thoughts?
     
  7. 8len8

    8len8 Member

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    A friend of mine has a similar situation. He takes an 8 ohm load (either a commercial load or a high wattage resistor) and places it in parallel with the 8 ohm cab so they both add up to 4 ohms. This probably impacts the tone a little, but not too much.
     
  8. JeffHaddad

    JeffHaddad Supporting Member

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    Common wisdom is that it is okay to mismatch by double or half - i.e. 8 ohm into either a 4 ohm or 16 ohm cab. If you were to run two speaker cabs with the Traynor of 8 ohms each you would be running a 4 ohm load, so that scenario seems to have been anticipated by Traynor. Plus, they're known for being built like tanks.

    Rockyrollercat - if a cab is 4 ohms when wired in parallel, then wiring those same two (presumably 8 ohms each) speakers in series would make a 16 ohm load, not 8.
     
  9. papersoul

    papersoul Member

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    4 into 8 is OK.....not perfect but can get away with it. 8 into 4, not so good....
     
  10. wademp

    wademp Supporting Member

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    I run my 8ohm vintage 30 into my 4ohm blackface bandmaster and have never had a problem. I always heard that running a speaker of double ohms is okay but not to run a lower ohm into a higher ohm amp.
    Everytime I read a thread on this; there are always conflicting answers. All I can tell you is what has worked for me...
     
  11. RCM78

    RCM78 Member

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    I wouldn't use a load that's less then the amp wants to see. More is usually OK so rewire the cab for 16ohm's provided you have two 8 ohm speakers wired parallel...
     
  12. Braciola

    Braciola Silver Supporting Member

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    You got that backwards.

    OP, to answer your question, yes, 8ohm out of the amp into 4ohm cab is fine.
     
  13. GroovyTubes

    GroovyTubes Member

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    http://www.legendarytones.com/ohms.html

    According to this (which is what i've based off of for a while) it really isn't safe. A higher cab is OK, but not higher head. Towards the bottom of the page.
     
  14. nickyjoe

    nickyjoe Member

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    Mesa lists a"safe mismatch" one being an "8 ohm cabinet" at 4ohms. I've heard one holy grail amp maker...used 8 to 4ohms mismatch.
     
  15. jlagrassa

    jlagrassa Supporting Member

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  16. QRSS

    QRSS brutalist

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    this one almost slipped by without arguments. lol who revived this?

    i find both arguments convincing and remain confused so i always match.
     
  17. EADGBE

    EADGBE Member

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    Aspen Pittman among others says not to do it. Make sure the impedance matches.
     
  18. riffmeister

    riffmeister Gold Supporting Member

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    I would not worry too much about a 1:2 mismatch:

    8 Ohm tap into 4 or 16 Ohm cab

    Maybe not a good idea chronically, but for a short while (few rehearsals and/or gigs) I wouldn't be too concerned.

    I would worry about a 1:4 mismatch:

    16 Ohm tap inot a 4 Ohm cab
    4 Ohm tap into a 16 Ohm cab

    Although I would certainly make every attempt to get it right.
     
  19. VaughnC

    VaughnC Supporting Member

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    The main concern with mismatch in a tube amp is flyback voltage. And flyback only occurs when the speaker impedance is higher than the amp impedance. However, while a speaker impedance that's 2X higher than the amp impedance is usually safe with most amps, you can never be 100% sure how much flyback voltage your particular output transformer will tolerate. So, I'd never go beyond 2X speaker impedance.

    Going in the other direction, a speaker impedance that's less than the amps impedance will stress the output tubes, but this scenario is unlikely to damage an output transformer due to the fact that: 1)there's no flyback voltage is produced under these conditions, and, 2)the tubes themselves are self current limited so they can't deliver enough current to damage an output transformers winding. As a matter of fact, tube amps typically have shorting type speaker jacks in them that puts a dead short on the output transformer if you forget to plug in a speaker cable...and this is what protects the transformer from flyback from a too high impedance (or open circuit) load.

    So, given a choice, I'd rather have a too low impedance load on a tube amp than too high, but 2X is probably safe for most amps. Beyond 2X, and not knowing how much your output transformers insulation will tolerate from flyback...hold your breath as output transformers and replacement costs aren't inexpensive these days.
     
    Last edited: Jul 4, 2011

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