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scratchy GK 700 RB II

Discussion in 'Amps and Cabs [BG]' started by craig3x, Jul 28, 2012.


  1. craig3x

    craig3x

    Apr 5, 2012
    just what the title reads. It's scratchy only through the horns on my cabs. changed cables, cleaned the POTs, etc. (none of the POTs are scratchy when adjusting them). If I turn the treble all the way down, it almost goes away completely. But obviously that isn't a fix. Any ideas what it could be?
     
  2. WingKL

    WingKL

    May 12, 2007
  3. gjbassist

    gjbassist Supporting Member

    Sep 7, 2005
    Kansas City, MO
    Do you have another head you can try with your cabs? That way you can be sure it's a head problem and not an issue with your cabs.
     
  4. craig3x

    craig3x

    Apr 5, 2012
    its the head....not my cabs
     
  5. +1.

    How do you know and what cabinets are you using?
     
  6. Have you cleaned the effects return jack or tried looping a instrument cable from send to return?
     
  7. craig3x

    craig3x

    Apr 5, 2012
    looping from send to return? can you explain that?
    I'm using a GK 115 and an Eden 210 cabs. sounded fine before this started happening
     
  8. craig3x

    craig3x

    Apr 5, 2012
    i know its the head and not the cabs cuz it happens to both of the cabs
     
  9. Use an instrument cable to connect the effects send and effects return jack (looping). Un-used the effects return internal contacts can get dodgy. Looping the effects jacks bypasses the internal connection in the return jack.
     
  10. will33

    will33

    May 22, 2006
    austin,tx
    Common occurence, especially with folks who never use the effects loop ( like me ). It's a switching jack that when it gets dirty, can cut off the signal from preamp section to power section, or at least cause a fizzy connection. General maintenance/cleaning is all it takes to fix.
     
  11. craig3x

    craig3x

    Apr 5, 2012

    but if was the jacks, wouldn't all the speakers in the cabinets sound scratchy? It's only coming from the horns...on both cabs
     
  12. will33

    will33

    May 22, 2006
    austin,tx
    Are you using the GK biamp/separate tweeter amp function?

    It could be an indication of a problem in the high amp, or it could just be bad tweeters in both cabs if you use a lot of topend boost.

    Try to isolate the problem some more, through running fullrange vs. biamping, etc.

    It could also be that the tweeter is just picking up signals of a problem. They don't make noise of their own, they just reproduce what they're given.

    Any sort of shoddy cable, many amp problems, or other sort of electrical oddities are better picked up by tweeters/higher frequency stuff.

    I know....I burned up my 800rb because I didn't listen to it when it was telling me it was getting sick. Even went so far as to think I had a bad high speaker when it was the amp telling me to take it to the doctor.:p
     
  13. Have you tried it yet? Or is it too much trouble :cool:
    The poor connection could be affecting the higher frequencies more, for now. It can and will get worse and the list of troubles is very long it can cause.
     
  14. JohnPativens

    JohnPativens

    Sep 20, 2005
    Italy
    Hi everyone,

    Upping this thread rather than opening a new one since my GK 700rbII has become pretty noisy lately.
    I'd open it and clean its pots, but I'm afraid there might be some DC leakage also causing the crackles.
    Contour, Boost and Woofer are the noisiest
    Sometimes I get a distorted sound and volume drops at moderately high gain/master settings when note sustain is decaying. As if the dirty pots were giving electrical interferences.
    Could it be just dirty pots causing all of it?

    I also tried the send/return trick suggested by B-string, but it doesn't solve the problem for Boost pot.
     
    Last edited: Apr 29, 2015
  15. DC leakage is pretty rare on an operational amp with G-Ks. If the distortion on note decay is constant even with the loop cable in the effects jacks the power amp bias needs to be re-adjusted.
     
  16. JohnPativens

    JohnPativens

    Sep 20, 2005
    Italy
    Hi,
    nope, it is not constant. It behaves that way after long time of no use, closed in it's rack ( I've been using the gk class D heads a lot on the last two years).
    At first all pots were noisy, and it had that occasional distortion on decay at 12 o'clock of gain/woofer, plus volume drops.
    I've been using it the last four days, now volume drops and distortion are gone. Eq pots are still noisy though (wind-like noise) while Contour, Boost and Woofer give the worst crackles, especially when bass signal is passing through.
     
  17. Oddly, sitting unused is pretty hard on an amp. Try rotating all controls fully clockwise and counter clockwise several times, if that doesn't clear it up the pots need some treatment. Getting the proper cleaner/lube into them will require removal of the preamp board from the amp.
     
  18. JohnPativens

    JohnPativens

    Sep 20, 2005
    Italy
    Did that. All pots but Contour and Boost get quiet at first, they're a little noisy again the day after.
    Those two keep crackling no matter what I do instead.

    What's the best kind of cleaner for pots? I know you use Caig Deoxit and Faderlube in US. Not easy to find those in Europe.
    I read it has to be a Dry Contact Cleaner; I tried that to clean the volume pot on one of my basses and it washed away its lubrification, it was loose and two days after it was stuck! :banghead: ..And I had to replace it.
     
  19. See if Tech spray's "RidOx" is available?

    Sounds like the cleaner got into the bushing for the shaft of you bass's pots. That is the reason the preamp board must be removed. Don't just remove knobs and spray down the shaft.
     
  20. JohnPativens

    JohnPativens

    Sep 20, 2005
    Italy
    I removed the volume pot and sprayed the dry contact cleaner inside the small cavity next to the three pins. It became very loose at first, completely lost that smooth greasy friction. Then it got stuck.
    I guess it should be better a lubricant contact cleaner instead.

    Never heard of that RidOx. I'll check it up.
    Here we have these:

    KOC WebSite: Maintenance and Repair products

    DUE-CI Electronic

    DUE-CI Electronic
     

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