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Amp Buzz, Need tech's opinion PLZ.

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by disappear_85, Dec 1, 2017.

  1. disappear_85

    disappear_85 Member

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    Hello, First i will apologize in advance if my English and grammar skills are bad.

    I Have a brand new amp, Krank SST, Its a hybrid amp ( tube preamp with solid state power section )

    I can't remember if the buzz was there when i opened it from the box as i was busy struggling to dial in a tone, But now i can hear a buzz coming from the amp, its not loud but it is there, it is not affected by volume or any preamp setting or channel changes, even if you set everything to zero including the master volume the buzz is still there.

    I've swapped the tubes, tried the amp on a different wall socket (same room) with a different cab and a different speaker cable, with and without power conditioner and the result is still the same.

    I unplugged the guitar and tried the guitar in the FX return (bypass the preamp) nothing has changed.

    what could it be? a bad filter cap? the amp is brand new from the box, although it might have been an old stock from years back.

    I pocked inside the amp to see if there is anything loose, but i think everything is intact.

    The only thing i remember doing to the amp is cleaning the pots, jacks and tube sockets with a WD40 Contact cleaner, but i cant for the life of me remember if the buzz was there before i did those things.

    Any Help would be appreciated, Thank you
     
    Last edited: Dec 1, 2017
  2. Avatar Tech

    Avatar Tech Member

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    The first logical thing to do is talk to whoever you acquired the amp from. If it was purchased at a retail store, see if you can return it, exchange it, etc.

    As for trying out a different outlet, the only way it would change anything is if you used an outlet that is on a completely separate circuit. Usually (though not always) all the outlets in a given room are on the same circuit.

    When the amp is making the noise, try unplugging the cable from the input jack and note whether the noise continues after the cable has been removed. If the noise goes away, it's quite possibly something that's getting introduced into the amp via the guitar or instrument cable.

    Similarly, you could try removing the preamp tubes an running the amp. If it still makes the same noise under this condition, then it's probably something in the power section.

    Whatever the results, still, I'd recommend initiating a conversation with the person/store who sold you the amp.
     
  3. disappear_85

    disappear_85 Member

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    Thank you for your response, Unfortunately returning the amp or exchange is note an option, as i'm from the middle east and had the amp brought to me by my friend from the U.S

    I tried the amp with no cable at all and still the same result

    Could i run the amp without preamp tubes at all? i thought that might damage it, and i already tried the amp at zero on every single knob, including the master and still there is a buzz.

    My other solid state amp don't produce such buzz ( peavey Supreme XL )

    Could it be that it is a noisy amp by nature? or a bad filter cap?

    Would a bad filter cap buzz even at zero volume?

    Thanks for taking the time to response.
     
  4. jthomas666

    jthomas666 Member

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    Downeast Maine
    You might record the amp's buzz and post it here or on YouTube with a link here. Start with no guitar plugged in and then plug a guitar in and let folks hear it. Make sure that the video is sufficiently long (maybe 2 1/2 to 3 minutes). That may suggest the next logical step.

    I have no idea about the wall current in your country (Heck, I don't even know where you are located. Ain't the interwebs great?) but are you sure that the amp is designed to work with your voltage and the AC frequency?
     
  5. Avatar Tech

    Avatar Tech Member

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    Yes it could be a bad filter cap, but it could be any number of other things too. And in a brand new piece of gear with a high gain preamp I'd suspect something other than a filter cap. I can't find a schematic for this amp. Maybe someone will chime in who has more direct experience with the Krank brand. Ultimately, you have to figure out where the noise is getting introduced into the circuit if you're going to attempt to remedy it. Another clue would be to note which specific controls affect the noise. Does it change when you adjust the treble knob for example? Do any of the controls affect the noise at all? This information is all helpful. The video suggestion above is a good one too.
     
  6. disappear_85

    disappear_85 Member

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    Here is a video i made with no guitar plugged in, all knobs at zero.

    our current is 230v i think, we usually run anything from 220v to 240v with no problem, Th amp has a switch on the back 120/240v , i switched to 240v and changed the fused for the recommended rating.

     
  7. disappear_85

    disappear_85 Member

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    A schematic is no where to be found, i already sent an email to Krank asking if i can get it from them, still waiting for a reply.
    Here is a video, i hope you can help

     
    Avatar Tech likes this.
  8. jthomas666

    jthomas666 Member

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    I'm just a hobbyist, so hopefully someone with more knowledge will jump in soon, but here is my first thought:

    1. I doubt that the buzz is normal for this amp. I found the manual online and this is an amp with high gain, but it should not hum like was shown in your video.

    2. Have you eliminated all possible sources of radio frequency interference in the surrounding environment (e.g., florescent lights, computers, maybe the breaker/fuse box for your home). To my ear the buzz sounds like something coming in from the environment, even without a guitar plugged in.

    and

    3:

    Your hum sounds closer to 60 Hz that 120 Hz to my ear. That could be due to a lot of things wrong, including a bad tube (as in the Uncle Doug video), a bad filter cap, or bad lead dress. Can you please check and provide information regarding the AC frequency of your wall power as that could change things.
     
    Avatar Tech likes this.
  9. EADGBE

    EADGBE Member

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    Don't use WD40 on an amp. Caig faderlube or Caig deoxit D5 would be better.
     
  10. disappear_85

    disappear_85 Member

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    its the WD40 contact cleaner, designed for circuit boards and such, im lucky that i found this where i live, lol
     
  11. Avatar Tech

    Avatar Tech Member

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    I wish I could tell you exactly what's wrong by listening to the sound but I can't :)
    A handful of decent quality pics of the guts might go a long way in getting some suggestions, but unless someone spots a specific problem it's all gonna be guess work I'm afraid :-(
     
    pdf64 likes this.
  12. disappear_85

    disappear_85 Member

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    Thanks for taking the time to response, Krank amps said they dont have the old build files, so no schematic, but he guessed its a loose ground connection.

    if you are interested in some gut pictues i'll take some tomorrow and post them, just let me know
     
    Avatar Tech likes this.
  13. Avatar Tech

    Avatar Tech Member

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    Post them if you have time. Someone might notice something...
     
  14. pdf64

    pdf64 Member

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    What technical competence and resources do you have available? eg have you got a test meter, if so what type of measurements do you have experience with?
     
  15. disappear_85

    disappear_85 Member

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    I'm not technical guy, but i do own a meter to test for shorts when i solder a cable, simple stuff.
    Here are some test i did today from the ground ( chassis ) to all jacks on the amp, i think i found a short, tell me what you think, maybe its nothing.

    on a 200 ohms setting :

    Footswitch jack
    sleeve : 1.6 ohms
    Ring : 127.5
    Tip : 127.5

    Is this a short? shouldn't the ring and tip reads "OL" on the meter? i disconnected the foot switch internal cable which goes to relay, but still there is a buzz with no changes.

    all other jacks tested fine ( send & returne, Speaker, input )
    Ground to sleeve : 1.4 ohms
    Ground to Tip & Ring : OL

    On the continuity Setting :

    Footswitch jack
    sleeve : beep
    Ring : 127
    Tip : 127

    Send & return jacks :
    sleeve : beep
    Ring : OL
    Tip : 766 with no beep

    Speaker and input jacks tested fine.

    Here are some gut pics, i don't know if they are useful or not, but every thing looks fine to me, i sported 1 shady solder point but the resistor is firmly in place and poking it does nothing.

    Thank you all for taking the time to help

    [​IMG]
    [​IMG]
    [​IMG]
    [​IMG]
    [​IMG]
    [​IMG]
    [​IMG]
    [​IMG]
     
  16. Avatar Tech

    Avatar Tech Member

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    On the TRS footswitch jack, the tip and ring might have pull up our pull down resistors in their circuits so without knowing more about the switching circuit I'd assume that entire circuit is ok. If there were a problem, your foot switch wouldn't be working correctly.

    If it was assembled in 2010, and then not used for 7 years, I suppose it's possible that the electrolytic caps might be drying out and not up to snuff.
     
  17. HaroldBrooks

    HaroldBrooks Member

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    Not sure if this was already mentioned, but make sure you aren't using any dimmer switches in your home. They make a lot of electric intefearance picked up by high gain circuits.
     
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  18. disappear_85

    disappear_85 Member

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    I guess you're right, I'll have to take to some random electrician to check those caps , i cant figure out how to drain them with their contacts underneath the PCB.

    There is no dimmer in my room, and there is no dimmer connected to my breaker box.

    I give up, second amp to give me troubles with barley any usage. fist my Peavey XXX, and now this one.
     
  19. pdf64

    pdf64 Member

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    A regular electrician isn't going to be able to do any useful checks on the caps.
    Bad HT caps would more likely have a pile of hum along with the buzz.

    With ac heaters, buzz can indicate that the heater circuit has lost its reference to the amp's chassis / 0V.
    I'd expect that amp to have dc heaters though.
    You could take a tube out and check whether it's 6V dc or ac between socket contacts 4/5 and 9, and then between the chassis 0V and those points.
     
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  20. HaroldBrooks

    HaroldBrooks Member

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    I'm assuming you already tried different guitars, cables.

    I recently fixed a buzz in a vintage amp I owned, that appeared when I started using a compressor up front. A capacitor had a high voltage wire running directly over it, and this was adding to the existing hum. Take a look if you can to make sure nothing is out of place.
     
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