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Quick ohm question...

Discussion in 'Amps and Cabs [BG]' started by JJd2sc, Dec 30, 2003.


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  1. JJd2sc

    JJd2sc

    Jul 31, 2003
    Marietta, Georgia
    If i was to run an ampeg svt-410 (4 ohm) and an svt-115 (8 ohm) what would the ohmage be? I was wondering if it would be safe to run into a 4 ohm jack in my mesa 400.
     
  2. E.O.M.

    E.O.M.

    Dec 7, 2001
    Grand Rapids, MI
    It would drop the total impedence somewhere between 2 and 4 ohms, but closer to 2 (I don't know the exact number). This is not a safe impedence to run your amp at unless it's designed to go that low. If it says not to run it lower than 4 ohms, then this would not work unless you want to fry your amp.
     
  3. JJd2sc

    JJd2sc

    Jul 31, 2003
    Marietta, Georgia
    Is there any way of me adding a 15 to my setup with this amp?

    Edit : I dont have the manual to the amp, and all they have online is a maunual for the 400+. Does anyone know the safe impedence to run this at?
     
  4. jive1

    jive1 Moderator Staff Member Supporting Member Commercial User

    Jan 16, 2003
    Alexandria,VA
    Owner/Retailer: Jive Sound
    Three ways to do this

    1) Run the cabs in series, not parallel. You'll need a special cable to do this. Do a search and you'll find how to do this. That will bring your ohms to 12, but you will be getting less power from your amp. 400 at 4 ohms would be around 200 at 8 ohms, so my guess is around 100-150 watts at 12 ohms. BTW ohmage is not a word, the proper term is impedance. Lower impedance means there is less to impede the power from the amp.
    2) Get a power amp that runs at 2 ohms.
    3) Replace your 4 ohm cab with an 8 ohm cab.
     
  5. Just FYI, I didn't see it already, but this setup will give you a 2.66.... Ohm load. You can figure it out from I = I1I2/(I1+I2). Just plug in the two impedences and you can figure it out for any parallel wired cabs.

    Geoff
     
  6. JJd2sc

    JJd2sc

    Jul 31, 2003
    Marietta, Georgia
    Might be a retarded question, but is there a way to rewire a cab into an impedence that would work? I don't think so because of the 410 already being at 4 ohms, but would it be possible to make a cab 16 ohms or something? Im calling mesa tomorrow and asking if its safe to run the cab at a lower impedence with the fan higher. Im sorry for the stupidity in the post, but I really dont know too much about heads/cabs, but im learning!
     
  7. Don't worry, you CAN run both cabs of the 4 ohm tap. You'll lose some power, probably 50-75 watts. Forget all that rewiring nonsense. The problems you'll encounter between two series wired cabs will kill more of your volume than the power you'll lose to presenting your amp with an incorrect secondary impedance.
     
  8. jive1

    jive1 Moderator Staff Member Supporting Member Commercial User

    Jan 16, 2003
    Alexandria,VA
    Owner/Retailer: Jive Sound
    If you don't mind the possibility of frying your amp and/or voiding your warranty, then you can try this. Some amps can tolerate a lower impedance than it is rated better than others, but I personally wouldn't chance it. Best to call Mesa and make sure.
     
  9. Eric Cioe

    Eric Cioe

    Jun 4, 2001
    Missoula, MT
    I thought the 400+ could handle a 2 ohm load? :confused:
     
  10. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    The Mesa 400+ is an all tube amp. The rules are different for tubes..... Psycho's right on this one.
     
  11. Do your homework and repair amps, both ss and tube, for over a decade like I have, and then MAYBE you'll have cause to make a post like that, but you won't because all the knowledge and experience you'll pick up along the way will show you that you don't know everything you think you do and that I'm right, but you're obviously not there yet.

    Also, it's better to use the FOUR ohm tap for a 2.66 ohm load than the two ohm tap. Tube amps don't like HIGHER impedances.
     
  12. jive1

    jive1 Moderator Staff Member Supporting Member Commercial User

    Jan 16, 2003
    Alexandria,VA
    Owner/Retailer: Jive Sound
    Since I don't have much experience with tube power sections other than guitar amp combos, what are the rules for tube amps in respect to impedance?
     
  13. jive1

    jive1 Moderator Staff Member Supporting Member Commercial User

    Jan 16, 2003
    Alexandria,VA
    Owner/Retailer: Jive Sound
    I stated clearly in my post that some amps tolerate a lower impedance better than others. Obviously I'm not an expert in all amps, but I'm not stupid either. No need to get nasty.
     
  14. Don't project yourself as an expert and make comments like "voiding your warranty" unless you're absolutely certain what you're talking about. I'm not being nasty, nor have I called you stupid. This forum has a lot of misinformation, epsecially among younger and newer posters who believe every word they read here. I posted the facts. You decided to be cute about it, so replied in a manner that made things clear.
     
  15. jive1

    jive1 Moderator Staff Member Supporting Member Commercial User

    Jan 16, 2003
    Alexandria,VA
    Owner/Retailer: Jive Sound
    Sorry if I came across as an expert. That's why I said, I'd call Mesa to be sure.

    I lost the cute battle 30 years ago.
     
  16. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    PGB posted a long and detailed answer to a similar question in another thread. The short answer is that guitar amps are different. They're not running the tubes as hard because they're not as concerned about max clean power as us bass players. So if you run a higher a higher impedance on a bass amp, the tubes are forced to work outside the parameters they were designed for........ something like that. How am I doing PBG?
     
  17. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    PGB posted a long and detailed answer to a similar question in another thread. The short answer is that guitar amps are different. They're not running the tubes as hard because they're not as concerned about max clean power as us bass players. So if you run a higher a higher impedance on a bass amp, the tubes are forced to work outside the parameters they were designed for.
     
  18. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    PGB posted a long and detailed answer to a similar question in another thread. The short answer is that guitar amps are different. They're not running the tubes as hard because they're not as concerned about max clean power as us bass players. So if you run a higher a higher impedance on a bass amp, the tubes are forced to work outside the parameters they were designed for.
     
  19. That's the quick and dirty, but as a rule, higher impedances than rated with ANY kind of tube amp is bad. Just like you can get away with running some s/s amps at lower than their rating, so too can some tube amps handle higher loads than rated, but bass amps generally are already at max output because of the higher current demands of bass. If anyone needs more detail, I've covered this extensively in other threads on this forum.
     
  20. And just how was he supposed to know that you are the only living person/legend qualified to advise other people on the the subject of tube amplifiers?

    That's definitely a big NO. You made an obviously personal attack.

    You yourself don't have a solid basis in amplifier theory, or any theory for that matter, so you most definitely are no expert yourself. You're an experienced person, there's no doubt about that IMO. But no expert. No way.

    There's lots of misinfo circling this forum, but generally we don't jump people for spreading it. Instead, see it as a chance to give someone's knowledge a little touch up, while backing up your own story.
     



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