Mesa Strangeness

Discussion in 'Amps and Cabs [BG]' started by Matt Dean, Jan 29, 2009.


  1. Matt Dean

    Matt Dean Supporting Member

    Jan 2, 2007
    SF (North) Bay Area
    A strange thing happened tonight at rehearsal... my m-pulse 600 started to make a crackly static kind of noise, then when quiet... as in dead. Lights all still on. There was another bass rig in the room, so I plugged in to try to isolate the problem. The bass and cord worked fine, so thought it must be the amp. I turned the amp off and on... still dead.... then suddenly the sound came back on.

    :rolleyes:

    The amp work fine for about 40 minutes, then crackled and went out again... and then came back on in about 5 minutes. We decided to quite then.

    Any m-pulse user had this experience? Anyone have any ideas?

    Thanks in advance... Matt
     
  2. ReBass

    ReBass Supporting Member

    Aug 11, 2007
    Orange County, CA
    I'd start with the preamp tube.
     
  3. Along with the tubes, this symptom (although typically not that extreme) can also be caused by a problem with the effects loop jacks. Try plugging and unplugging a cable in the send and return jacks a few times to see if that has any impact on the problem. I can't remember exactly why this is, but it has something to do with 'jumper's getting stuck open on occasion in the effects loop if you haven't used it (i.e., inserted a cable) for a while. If you have an older model with the separate active/passive inputs, they can also cause a similar problem (the newer models have a single input and an active/passive switch). If you have the dual input model, again, try plugging and unplugging a cable from the jack you don't typically use.
     
  4. Hi.

    +1 for the dirty/oxidized jack switch contacts.

    A dirty tube socket or malfunctioning tube isn't that far fetched either.

    When It started working again, did You rotate all the knobs (sliders ?) too? Old SWRs have a bit cheap potentiometers that behave just like that.

    Regards
    Sam
     
  5. Matt Dean

    Matt Dean Supporting Member

    Jan 2, 2007
    SF (North) Bay Area
    Thanks for the ideas guys! It's an '06, so it's got the rocker active/passive switch. I don't use effects, so the effects loop jack has bee unused for some time... I'll try inserting a jack. The head did get bumped the other day in transit, so maybe the pre tube is loose.

    Thanks again for your help.
     
  6. Vic

    Vic There's more music in the nuance than the notes. Gold Supporting Member

    Oct 14, 2002
    Central Illinois
    Staff, Bass Gear Magazine
    Kudos to Ken for bringing this up... I've also had this happen before... especially on an EBS head.

    IF that is the problem...

    However, you'll need to put a cord in there that connects the send to the return. I don't think plugging anything into one jack will do it. Depending on how the jack is made, you might be able to buy time by plugging and removing a plug several times, but sometimes that contact is not part of what touches the plug, so a longer term solution would require taking the cover off the amp and literally cleaning those contacts with some emery cloth and then using electronic cleaner/protector/lube to inhibit future fine surface corruption like that.

    Works like a champ, but it's a bit of a PIA for a non-tech. The solution that always works no matter what, however, is to just put a shunt cable between the send and return. George L stuff works great for that since you can make it to the exact length you need. You can literally make a little jumper cable you can leave in there all the time that even looks halfway decent.
     
  7. Matt Dean

    Matt Dean Supporting Member

    Jan 2, 2007
    SF (North) Bay Area
    Thanks Vic... I agree that Ken has a wealth of knowledge about all things bass. I'm probably in the non-tech camp, but have been known to dive in anyway, so I'll probably open up my m-pulse and take a look. I want to check my tubes... any advice on what to look for?

    Matt
     
  8. Vic

    Vic There's more music in the nuance than the notes. Gold Supporting Member

    Oct 14, 2002
    Central Illinois
    Staff, Bass Gear Magazine
    For the part I'm talking about, it depends on the location and design of the jack. If they're inaccessible or completely enclosed, there probably isn't much you can do other than the plug/pull many times and/or the jumper cable. Otherwise, it'd be about finding the contact points on the jack that break the circuit to the rest of the amp when you put effects in the chain. It may not be obvious. Sounds like maybe the external solutions will be most likely for you.

    Otherwise, again, IF this is the problem, which can be verified if the amp "comes back" as soon as you plug the jumper cable in (a good test for you to perform next time, btw), then at some point, you could probably also just have the jacks replaced at Mesa or a qualified service center. Either way.
     
  9. Matt Dean

    Matt Dean Supporting Member

    Jan 2, 2007
    SF (North) Bay Area
    Thanks Vic... I think I'll open my head up this weekend. I'll let ya'll know what I find.
     
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    Primary TB Assistant

    Here are some related products that TB members are talking about. Clicking on a product will take you to TB’s partner, Primary, where you can find links to TB discussions about these products.

     
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