Ohms question

Discussion in 'Amps and Cabs' started by Prerequisite, Jan 25, 2012.

  1. Prerequisite

    Prerequisite Member

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    One of the speakers in my Twin is pretty much gone (almost produces a fuzz tone). I have 2 places to play at this weekend, but if I order a speaker now it won't arrive until next week..

    How bad is it to unsolder one of the speakers and play using just 1 x 12? I know there is an impedance mismatch (8 ohm amp with a 4 ohm speaker) but what are the consequences of this? (I don't know much about this stuff, so bear with me please).
     
  2. Frank Speak

    Frank Speak Member

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    Supposedly, Fenders can take a total impedance mismatch. You might want to check with a tech before trying it, however. ;)
     
  3. Tele Wacker

    Tele Wacker Member

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    You could do it but! Actually, a Twin is a 4 ohm output instead of 8 ohm. I had an old twin and had a speaker solder joint go bad during a gig. I didn't realize it was the bad solder joint until the next morning. I was puzzled what was wrong at the time.
    See if you can borrow a 12" 8 ohm speaker from someone. I'd sure loan you one if I was close to you.
     
  4. Prerequisite

    Prerequisite Member

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    Ok. And I'll do that.. I'm also thinking about pulling two of the power tubes and then disconnecting the bad speaker to run at half power.
     
  5. Moddjobbs

    Moddjobbs Member

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    Yeah, Typically, a fender amp can handle an impedance mismatch of 100% +or-. Another possible option that comes to mind for your situation is to remove the two inner output tubes, and run only one speaker. You'll be pushing about 60 watts at an 8 ohm load, which will leave your output transformer quite happy. You might find the sound suits you even better than the stock output.
    Read all about it here:
    http://fenderguru.com/amps/twin-reverb
    EDIT: Just saw your response above. It might work out great for you!
     
  6. Prerequisite

    Prerequisite Member

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    Silverface Twins? I've always thought they were 8 ohms. My tech told me to get a 4 ohm speaker when I replaced the other one (the one that is working fine right now). :omg

    I'm pretty confused right now, haha. Thanks for the offer, it's the thought that counts!
     
  7. Prerequisite

    Prerequisite Member

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    The problem is that it has now occurred to me that I may have purchased the wrong speaker in terms of ohms - the one that is running ok is a 4ohm 100 watt speaker. Will it be ok to push an 8 ohm load into a 4 ohm speaker?

    Actually, even though I'm running all 4 6L6s, will it be ok to run just one 4ohm speaker?
     
  8. Moddjobbs

    Moddjobbs Member

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    The plot thickens! To get you through your gig, I would recommend just leaving the single 4 ohm 100watt speaker, and running it at a matched 4 ohm output impedance with all 4 Tubes. At least until you can get a replacement pair of 8 ohm speakers!
     
    Last edited: Jan 26, 2012
  9. KWCabs

    KWCabs Member

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    Not sure what year or what model speakers you have, but I'll say that 4 ohm speakers are not particularly popular. Usually you would wire 2 16 ohm speakers in parallel to get an 8 ohm load not two 4 ohm speakers in series. So I would definitely check if I were you before replacing anything. That said, Fenders are notorious for being able to handle mismatched loads, but that's not a guarantee.
     
  10. TimSt.L

    TimSt.L Member

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    I've always been told it's better to have the ohms higher on the cab than the head. I don't know how true it is. But when I run into an ohms mismatch issue, I always referred to that rule and it's never failed me yet.
    And yes, I've heard fenders are fine with this situation too.
    Apparently mesas are as well, they actually have it in they're manuals that it's not a big deal with theyre amps!
     
  11. EADGBE

    EADGBE Member

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    The ohms should match. Otherwise you run the risk of damaging your amp.
     
  12. Prerequisite

    Prerequisite Member

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    Ok I figured it at all out. I was supposed to have 2 8ohms speakers in my amp. One of them went bad a couple of weeks ago so I bought a new Jensen - that was a 4ohm (my mistake). Now the other 8 ohm has gone bad (I haven't actually played this amp yet with the 4 ohm and 8 ohm at the same time except to test it after I had the new one put in).

    So it's ok to run all 4 tubes at 4 ohms with just the one 4 ohm speaker? Am I at risk for blowing the speaker? I don't really crank the Twin (windows would break if I did) so I don't think I'd run it at a full 100watts.
     
  13. Moddjobbs

    Moddjobbs Member

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    No problem running it as you state above With 4 tubes at 4 ohms with one 4 ohm speaker. The amp will be happy, and I wouldn't worry at all about blowing a hundred watt speaker. No way you're giving it even close to that much power! It'll match up just fine. Glad you got the impedance issue figured out! Enjoy :)
     
  14. Rockledge

    Rockledge Member

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    I would say if it is a vintage twin, don't do it. Simply because when components get old they change value and in changing impedence you run the risk of heating up already changed components stressing them more.
    If you have had it gone over by a tech in the past few years and had things like bloody caps replaced then I wouldn't worry about it as much.
    Either way, I wouldn't push it very hard. You also don't want to cook the remaining speaker by exceeding it's wattage capacity.
    I would suggest not running it over 3, at 5 you are likely pushing more than 80% of the amps wattage.
    Unless of course you know the speakers capacity and know that it will handle anything the amp can put out.
     
  15. ChorusCrackpot

    ChorusCrackpot Member

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    4 ohm-> 4 ohm = Good.
    4 ohm-> 8 ohm = Okay.
    8 ohm-> 4 ohm = BAD- you'll blow the amp up!
     
  16. ChorusCrackpot

    ChorusCrackpot Member

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    4 ohm-> 4 ohm = Good.
    4 ohm-> 8 ohm = Okay.
    8 ohm-> 4 ohm = BAD- you'll blow the amp up!
     

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