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Interesting Markbass LMII issue

Discussion in 'Amps and Cabs [BG]' started by flyman, Mar 14, 2008.


  1. flyman

    flyman Whoa!!

    Aug 2, 2005
    cincinnati, ohio
    A few months ago, I purchased an LMII. I've been using it with 2 Dr. Bass 1x12 cabs with no problems. I've been using 1/4" cables, since that's what my other head used. I recently purchased an 8 ohm Schroeder mini12+L. It also works fine with the LMII. However ...... Last night I hooked up the Schroeder & one of the Dr. Bass cabs. It worked for a while, then I turned it off for a few minutes while I did something else. When I turned it back on, it powered up, but the minute I played even one note quietly, the note started to be heard & then the amp went dead. It's was still on, but absolutely no sound. Turning it off & back on several times produced the same results. The amp still plays fine with either cab, but not both. I haven't tried both Dr. Bass cabs again, but unless something has gone wrong with the LMII, I don't expect a problem. I'm going to try that tonight.

    Thoughts?

    Regards,
    flyman
     
  2. Sounds like it could be an impedance issue. From what I understand the LMII doesn't like going under 4 ohms, so maybe the Schroeder is a bit under 8 or something? I'm not an expert, it is just a possiblity.

    joel
     
  3. tombowlus

    tombowlus If it sounds good, it is good Gold Supporting Member

    Apr 3, 2003
    North central Ohio
    Editor-in-Chief, Bass Gear Magazine
    What are the impedances of both cabs? Are you running less than a 4 ohm load? You may be experiencing thermal shutdown.

    Tom.
     

  4. +1 I know that Jorg does a 4ohm version of the mini112, which would give you a 2.67 impedance with the DR. Bass 8ohm cab... not good for many heads, including the LMII.
     
  5. flyman

    flyman Whoa!!

    Aug 2, 2005
    cincinnati, ohio
    Yeah, an impedence problem was my 1st thought, but the Dr. Bass cabs are both 8 ohms & when I ordered the mini12 from Jorg, I told him I wanted 8 ohms, but I suppose it's possible he made a mistake. I will try the 2 Dr. Bass cabs again tonight to see if possibly something has happened in the LMII, but I doubt it. :confused:

    flyman
     
  6. ::::BASSIST::::

    ::::BASSIST:::: Progress Not Perfection.

    Sep 2, 2004
    Vancouver, BC Canada
    You might want to take the back panel off the Mini 12L and look directly on the driver for the impedence. Sounds to me like you have a 4 ohm Mini 12.
     
  7. tombowlus

    tombowlus If it sounds good, it is good Gold Supporting Member

    Apr 3, 2003
    North central Ohio
    Editor-in-Chief, Bass Gear Magazine
    You can also test the impedance with a simple multi-meter from Radio Shack, or Lowe's, or wherever.
     
  8. flyman

    flyman Whoa!!

    Aug 2, 2005
    cincinnati, ohio
    I think I might have one of those around somewhere. How would I do that?

    flyman
     
  9. joelb79

    joelb79

    Mar 22, 2006
    Lansing, Michigan
    Use a 1/4" speaker cable and put the positive on the tip and the negative on the ring portion, then turn the meter dial to 100's of ohms.
     
  10. Jazzman

    Jazzman

    Nov 26, 2002
    Raleigh, NC
    You will be measuring DC resistance, which will be approximately 2/3 to 3/4 of the nominal resistance. ...but it is close enough to determine if it is a 4 or 8 ohm impedance driver.
     
  11. Keep in mind that impeadance varies with frequency. I had my LM2 shut down using 2 EAcxl112 when I was using my octave pedal. Wasn't playing that loud and the amp was not hot. The cxl112s are a little less than the stated 8 ohms. This caused my LM2 to shut down. I know of others who have had the same problem.
     
  12. Tony G

    Tony G

    Jan 20, 2006
    NY
    This is a little messed up. I've never heard of this happening with any other amp before. If your amp goes down to 4 ohms, you should be able to use two 8 ohm labeled cabs, or one 4 ohm labeled cab. I understand in this case the cabs need to have their specs measured just to make sure everything is cool, but this is the 3rd time in the last two weeks somebody has posted about a very similar situation to this with either the LMII or F1. I've never encountered anything like this before in person, and never even read anything like this before here. Has anyone encountered this seemingly harmless situation forcing their head to cut out with any other amp?
     
  13. Of the very few issue posted like this, most involve the EA cabs, which are NOT 8ohm nominal impedance, and my guess is, this thread is an impedance issue also.

    I run my LMII and F1 HARD into 4ohms day after day after day, as many others do, with no problem at all.

    Given the hundreds of these that have been sold, this seems like a non-issue, and is more of a mark against the strange impedance issues of some EA cabs than the LMII or F1. IMO.

    I always run these heads HARD at 4ohms...never an issue. I have had other brands amps shut down in the past due to heat, but very, very rarely. I also assume that there are some instances where you can run an LMII or F1 (or any small amp) hard enough to result in a temporarly thermal shut-down... especially if you are turning the amp up very loud to overcompensate for small inefficient cabs at high volume... but this is and should be very rare.
     
  14. Tony G

    Tony G

    Jan 20, 2006
    NY
    I frequently run my LMII into my 4 ohm UL410 as you know, and have had no problems (and don't expect one). I also used to run my LMII with two UL112's (8 ohms), and never had a problem (and didn't expect one). My point is that I've never heard of something like this happening no matter what head it is. If your head runs safely at 4 ohms, two 8 ohm labeled cabs should be no problem. It is very confusing to read reports like this. I'm sure it is more of a cab being not quite it's labeled impedance, but to me that is messed up. I would never have expected to hear anything like this, regardless of the gear brand.
     
  15. Your description of '8ohm labeled' makes no sense. If an 8ohm labeled cab is not 8ohms, then the label incorrectly stating that it is 8ohms is not going to make it safe for a 4ohm minimum head:smug: Thank goodness the EA stuff seems to be the only cab line where the label doesn't seem to match up with the actual impedance.

    That being said, is the MB stuff more sensitive to slightly lower than 4ohm nominal impedance?.... I'm not sure, since the vast majority of EA cab users seem to power their cabs with EA heads, which are 'safe' for 2ohm operation.

    It seems that if you have two 8ohm cabs that are ACTUALLY 8ohms:smug:, there should be no problem except is you really overpush the amp, which is why the temporary shut down circuitry is there.
     
  16. Tony G

    Tony G

    Jan 20, 2006
    NY

    What I mean to say is that I read you guys saying that no cab is exactly 4 ohms, or 8 ohms. If I see a cab that is labeled 8 ohms, but has an actual rating of 7.3 ohms or something, well to me that doesn't seem right. To me that cab is "mislabeled". But say you didn't know that your 8 ohm cab was actually more like 7.3 ohms. Then you put two of those together thinking that those two "8 ohm labeled" cabs should be just fine with a head that runs safely down to 4 ohms. Then your head fails and it seems it might be due to a sensitive impedance issue. Something seems screwy to me.

    I don't know, maybe I'm misudernstanding the whole thing. Please just carry on with this conversation without me. :atoz:
     
  17. Correct. It seems the only cabs that are labeled 8ohms that are 'meaningfully' below an 8ohm nominal impedance (i.e., that might cause a 4ohm minimum safe head problems when two are used together) are a number of the EA cabinet models. I don't know how else to say it.:)
     
  18. Tony G

    Tony G

    Jan 20, 2006
    NY
    Corrent???



    I think I see what you are saying. You've never encountered this outside of EA cabs?
     

  19. One of my famous typo's:)

    Yes... I've never heard of this issue outside of the EA cabs, and it's not really an issue with the EA cabs when you use them as designed with the 2ohm safe iAmps (the NL-210 seems to be the primary culprit).

    That being said, emjazz has had his LMII briefly shut down with his two Berg 12's (HT112/EX112). IMO, that might be an issue of pushing two small, relatively low SPL cabs too hard in a situation where you need a lot of volume. A low SPL cab or cabs can eat up 500 watts when you are playing loud and hard pretty easily. Again, the thermal shutdown safety feature is a good one, and as long as the vast majority of owners have never experienced this, and that the few that have are explainable, it seems a non issue to me.

    Interestingly, I wonder if this is why EA was so resistant to come out with a 4ohm version of the NM410:eek::cool:
     
  20. Tony G

    Tony G

    Jan 20, 2006
    NY

    Ok, I think I've finally got it. :D
     

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