LH 1000 Hartke bass amp fizzles out after a few minutes use

Discussion in 'Amps and Cabs [BG]' started by Wayne451, Jun 23, 2021.


  1. Wayne451

    Wayne451

    Jun 22, 2021
    Bought this amp years ago second hand. I never used it much. Kicked out a couple of time, no sound, replaced the preamp tube once and that didn't really help. Now it will work fine for a few minutes before beginning to make a fizzing sound on each note then going quiet. I have built a few tube amp projects so I'm familiar with some of the components internally. There are some markings inside the amp that indicate the right output transistor board was "new" at some point. I cleaned the pots which seemed to help a little but the problem came back. I'm using a TOA PA wedge with a 15 inch speaker, a horn, and two small tweeters. I use the speakon out with bridge switch engaged. The speaker works well with my ancient Traynor 100 watt amp that requires a 4 ohm load. The resistance of the cable to the speaker measures 7.5 ohms. I know this probably not ideal but should be ok if it's higher rather than lower. I was hoping someone might have experienced some of the same issues and could point me in the right direction. I don't have a lot of money to spend on this but I'm handy with a soldering iron and have a VOM meter, etc. I'm thinking the fizzled sound might point to the preamp section of the amp. Any ideas? Any help would be really appreciated. I know people often say to call Larry Hartke but, really? I think he must be retired by now and tired of hearing peoples problems with this amp, lol.
     
  2. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
    Have you tried each power amp channel in dual (not bridge) mode? If it works fine on one channel but not on the other channel, it points to a failure in one of the power amps.

    Try bypassing the effects loop with a short shielded cable between the effects send and return.

    Try running your bass into the effects return (the volume will be lower but that's fine for testing purposes). If the problem remains, it points to the problem likely being within one of the power amp channels.

    Unless you are familiar with electronics, have a scope (to be able to view where there is and is not signal throughout the signal path) and understanding how the circuitry works (especially direct coupled multistage amplifiers with global feedback, a particularly tricky type of circuit to troubleshoot because each stage is interrelated with each other by the feedback), it's QUALIFIED service tech time.
     
    DrMole, dbase, SirMjac28 and 6 others like this.
  3. Wayne451

    Wayne451

    Jun 22, 2021
     
  4. Wayne451

    Wayne451

    Jun 22, 2021
    Hi Agedhorse,
    Thanks for you quick response. Had previously tryed A outlet and had the same issue. BUT, didn't try the B outlet until just now as per your advice. It seems to work fine for about the 15 minutes I tried it at different volume levels and didn't experience any problems that surely would have shown up by now. So, until repaired, I suspect I have what would be equal to a LH500. I could probably get by with the 500 watts since I just use it to terrorize the neighbours anyway. I do own a digital occiloscope so I may delve in it at a later date. I've found a couple of different schematics on line which should be helpful. It's good to know that the preamp section appears to work as it should. Not sure the effects loop trick will tell me anything more than I've discovered at this point. If you still think so, please advise. Otherwise, I'm much oblidged for your assistance. Have a great day!
     
    EatS1stBassist and mikewalker like this.
  5. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
    If output B works, the problem is isolated to power amp A.

    Before you delve into this, learn how direct coupled multi-stage (w/ global feedback) power amps work, it's a little like a cat chasing it's own tail. Everything affects everything else throughout the amp, they are notoriously tricky. Also, be sure whatever scope you are using can handle the voltages, some PC based scope interfaces can not handle either the voltage of fault current in the event that you connect the ground to something other than ground. That's a quick way to destroy either the interface or even the laptop.
     
  6. Wayne451

    Wayne451

    Jun 22, 2021
    Good advice, agedhorse. I'll probably leave this for the meantime and do a little reading before I tackle this.
     
  7. SteveFromBerlin

    SteveFromBerlin

    Jan 3, 2008
    Berlin
    I've had this problem with one power amp side of a LH1000 when attempting to buy one used. The owner took it back and had it repaired. If I remember correctly it was just something minor and done within 20 mins by a professional. Could have been the signal lead going from the preamp to the power amp, but I'm not sure.

    Excellent amps, except for the pre-EQ XLR output. Good luck!
     
    Wayne451 likes this.
  8. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
    What’s wrong with the DI out being pre eq? If not switchable, pre is the better option from a sound guy’s perspective.
     
    Bass4Brkfast and Ggaa like this.
  9. IBJammin

    IBJammin

    Apr 16, 2015


    I have a LH500 in my closet with similar symptoms. This video and his comments may help, if you know how to find and test the components he replaces before engaging in actual replacement.
     
    SteveFromBerlin likes this.
  10. IBJammin

    IBJammin

    Apr 16, 2015
  11. Steve, I also prefer the option of pre/post DI. My Hiwatt came from the factory post only. I stay away from boosting the bass control when going post DI.
     
    SteveFromBerlin and agedhorse like this.
  12. SteveFromBerlin

    SteveFromBerlin

    Jan 3, 2008
    Berlin
    If I buy an amp that has a sweet tube driven good old Fender-ish Tone Stack, I prefer to be able to hear that through the XLR. Maybe that‘s just me.
     
  13. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
    With heavily voiced amps and speakers, this can become a (big) issue for some sound guys working difficult rooms.
     
  14. SteveFromBerlin

    SteveFromBerlin

    Jan 3, 2008
    Berlin
    Sure. The thing is, you are talking about bass amps and cabs in general and I am specifically speaking about the LH 500 and LH 1000. In my opinion they are dialed in perfect and can‘t really be made to sound too extreme. I‘d love to hear this sound through it‘s XLR as I think it even helps to find you a good place in the mix.
     
  15. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
    I was specifically answering your comment about “the sweet Fender-ish tone stack thing” which by definition is heavily voiced.
     
  16. FunkHead

    FunkHead Supporting Member

    Mar 10, 2007
    I don’t know much about the Fender Tone Stack but on the LH1000, 2-10-2 is supposed to be “Flat” . I see people often comparing the LH1000 to Fender Tone Stack but I have never used it.
     
  17. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
    The native Fender tone stack is quite voiced. You can get into “flatter” territory but you can also get into very heavily voiced territory.

    Sound guys often struggle with signals that are heavily voiced, and though they may sound good on stage through the bass rig, may not be representative of what a larger PA is capable of not the environment that the FOH is being mixed for in the context of a band mix.
     
    Wayne451 and keith rosier like this.
  18. For sure, players have to be very careful EQ'ing from the amp perspective and sending it post DI. I know what my basses need to speak clearly in a given room. I usually give my post signal a slight rise in the upper mids around 700hz and lower treble 2-3k. I never boost bass on my stage rig or to post DI because you're asking for trouble when you boost bass. The kick handles most of the low end on stage, and is usually booming on stage just from house bleed. I add clarity just to have an articulate tone that works with the mostly "heavy kick" mixes of 99% of venues I work. If I don't give the house a little rise in the mids and treble I end up with a tone that is anemic and sounding flat compared to the mic'd rigs and hyped drums. Most house engineers spend very little time, if any, on the bass and will just turn you down if your tone is boomy and lacking.
     
  19. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
    Good house FOH engineers spend as much or as little time as necessary to make each instrument sound good and appropriate to fit into the mix. If the bass tone needs a little top end in the house, that's the FOH guy's job because you are not in the same listening environment as they are.
     
    jbrew73 and FunkHead like this.
  20. You would think (or hope) that's the case, but sadly it isn't for a lot of jobs. Flying around as I do...I can tell you some stories.
     
    SteveFromBerlin likes this.
  21. Primary

    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.

     
    Jul 29, 2021

Share This Page

  1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
    By continuing to use this site, you are consenting to our use of cookies.