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    Problems with low frequency humming sound

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    MatsP

    Posts : 4
    Join date : 2014-11-07

    Problems with low frequency humming sound

    Post by MatsP on Thu Mar 26, 2015 4:40 am

    Hi guys!

    Bought a Grandmeister 36 secondhand and although I really love the amp I´m experiencing some disturbing very high sounding low frequency humming sounds on all channels. They´re not as high as the guitarsignal but nearly...It´s the same problem wherever I play and with all my guitars and cabinets and cables playing straight into the amp. So the problem must be the amp must´n it? Should I try changing the tubes around-and in that case which one of them..
    Yes, I can get rid of the humming sound with the noisegate but I´d rather not -cuz it cuts out tails when I´m playing soft.
    Any ideas out there what could be the problem?
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    bordonbert

    Posts : 745
    Join date : 2015-01-28
    Age : 97
    Location : Southern England

    Re: Problems with low frequency humming sound

    Post by bordonbert on Thu Mar 26, 2015 9:25 am

    You've done a good job and ruled out cables, cabs and guitars.  Hope you've swapped out the mains cable too!

    Is the hum there only when you actually play notes, sort of overlayed, or is it when your guitar is plugged in but silent too?  Does it stop when no lead is plugged into the amp input?  Is it there on all settings of the power soak? You could do a check on the bias with your magic pick but I wouldn't bet on that giving you the answer.  I have assumed it's there on all channels too which would perhaps point towards something in the power amp/power supply areas, though with the GM's active switching circuits that isn't a given.  Please remember power supply and power amps run to VERY VERY HIGH VOLTAGES!  Don't be tempted to fiddle, it more than bites!  Evil or Very Mad

    My guess is there is really too much that could cause this to be able to get any useful blind advice here.  You could swap out the tubes but as I said, there is so much this could be and I can't see that being the issue.  I think you will be best advised to take it in to a tech and have a bit of proper diagnostic work done.  Sorry if that's not what you really wanted to hear but it will give you a solution.

    Maybe someone else can offer a blinding insight?
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    namklak

    Posts : 185
    Join date : 2015-01-30
    Location : Denver, CO

    Re: Problems with low frequency humming sound

    Post by namklak on Thu Mar 26, 2015 10:57 am

    The only thing I'd add is that if the noise gate cuts the hum, it's probably not in the output section.
    Are you using the effects loop?  Pedal board with active power supply?  I guess I'm driving towards ground loop.  I'm guessing a different tube amp with the exact same setup does not do this?

    BTW, if you get this working right, I think you will be satisfied with the GM36. I love this amp, probably the best amp I've owned for a number of reasons. I'm in a semi-pro Allman Brothers tribute band (covering tones from Duane, Dickie, and Warren), and I've had nothing but extremely positive feedback from band members and sound guys.
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    bordonbert

    Posts : 745
    Join date : 2015-01-28
    Age : 97
    Location : Southern England

    Re: Problems with low frequency humming sound

    Post by bordonbert on Thu Mar 26, 2015 11:25 am

    Good spot Namklak.  I come at this from a TM36 which has no noise gate of course and I missed it.  Don't mention pedal boards, they're another one of my pet gripes!  Collections of dozens of ultra expensive pedals, most of which get used once a month in the bedroom!  Laughing  ( Embarassed  Oops, there I go again!)  The power supply from a pedal board should really be floating not grounded itself and be immune to that sort of thing but you're right, it might be unusual or something might be out of whack.

    MatsP

    Posts : 4
    Join date : 2014-11-07

    Re: Problems with low frequency humming sound

    Post by MatsP on Mon Apr 13, 2015 5:48 am

    Thanks for you replies guys -I had´nt been hanging around the forum for a while..

    And "Bordonbert" -the hum is there and all the time my guitar is plugged straight in the amp, on all settings , no effects no power supply  no nothing in between the amp and guitar except for the cable .
    I really do think I have to get it to a tech... Sad

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