Metallic Fizz Sound (with Video): What To Do?

Discussion in 'The Workbench' started by mAx___, Nov 7, 2018.

  1. mAx___

    mAx___ Active Member

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    Hi, I have a 2xKT88 Marshall Major build with an extra gain stage that creates a fizzy resonance that to the best of my hearing it seems to be coming out directly from inside the OT. It's a 100w Merren ultra linear transformer. I thought it was the spring retainers of the power tubes but I removed them and the fizz was still there. It happens when I turn up both volumes past 3 o'clock, just when the amp sounds the best.
    I have it connected to a Rivera Rockcrusher at -8dB.

    I tried replacing all of the tubes but the problem was still there. I also chop-sticked the board to see if I could find the source of the fizz but found nothing wrong.

    When the extra gain stage is disengaged (it's on a switch), the resonating OT doesn't happen but the amp has no gain, of course.

    Any ideas on how to fix this? Thanks a lot.

     
  2. ampmadscientist

    ampmadscientist Well-Known Member

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    Did you try reversing the primary wires of the OT?
    It "is" wired in ultra linear mode? Pin 4 of each output tube is wired to the 40% taps of the OT?
    You are sure that the pin 4 taps and pin 3 taps of the OT are not mixed up?
     
  3. FourT6and2

    FourT6and2 Active Member

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    video doesn't work
     
  4. mAx___

    mAx___ Active Member

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    Yes, pin 4 of each tube is wired to the UL taps of the OT. I’ll double check if anything is mixed up but I’m pretty sure the wiring is correct.
    I haven’t tried reversing the primaries. Wouldn’t that blow a fuse or a component? It happened to me once...

    BTW, the chassis is not bolted on the cab (for easy access), could that be a cause?

    If not, and assuming that the OT wiring is correct, what part of the circuit should I look at and modify?

    Thanks so much.
     
  5. mAx___

    mAx___ Active Member

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    Can you see the video now?
     
  6. FourT6and2

    FourT6and2 Active Member

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    No. It says video unavailable. What country are you in? Post a direct link.
     
  7. mAx___

    mAx___ Active Member

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    Let's try again. I'm in the US...

     
  8. FourT6and2

    FourT6and2 Active Member

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    Post the actual direct link to the video. Stop trying to embed it because it's not working. Maybe you have it set to private or something.
     
  9. mAx___

    mAx___ Active Member

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    Yes, it was set to private, I’m sorry.
    Now it should work
     
  10. Chris-in-LA

    Chris-in-LA Active Member

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    Can you hear it on the video? All I hear is faint guitar riffs.
     
  11. FourT6and2

    FourT6and2 Active Member

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    Ok video works now.

    Are you saying that faint guitar riff is coming from the transformer and not the speaker?
     
  12. mAx___

    mAx___ Active Member

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    Correct. The sound is not coming from the speaker and it has that fizzy resonance on top...
     
  13. FourT6and2

    FourT6and2 Active Member

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    That's weird. I'd say it's a bad transformer then. If it is actually coming from the transformer...

    I assume you put the speaker cab in another room or something to record that video? You say you're running some sort of attenuator? Are you sure the sound isn't coming from the attenuator?
     
  14. ampmadscientist

    ampmadscientist Well-Known Member

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    Well the winding of the OT could be loose and vibrating.
    It is normal to get "some" resonance from the winding, but it's usually not very loud. The plates of the output tubes can rattle also which is normal.
    So it could be a loose winding in the OT. I have heard this happen before in some amps.
     
  15. mAx___

    mAx___ Active Member

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    Yes, the cab is all the way back in the garage inside an isolation box. The attenuator is right here where the amp head is so i'm sure the sound is coming out from inside the amp. Which I wouldn't mind as much if it didn't have those fizzy overtones...
     
  16. mAx___

    mAx___ Active Member

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    Arrrghhh...it sounds like it's something that cannot be repaired... :(
     
  17. FourT6and2

    FourT6and2 Active Member

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    Are you sure it isn't the attenuator? Have you tried removing it from the signal chain and then seeing what happens?
     
    mAx___ and Chris-in-LA like this.
  18. mAx___

    mAx___ Active Member

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    I thought of it. But because the problem only happens when I crank both volumes to past 3 o'clock, I was afraid to blow out the speakers on my 4x12. The amp has an extra gain stage and two KT88. OT is 100w.

    What do you guys think, could I go direct at almost full volume without the attenuator into 4 30w speakers?
     
  19. ampmadscientist

    ampmadscientist Well-Known Member

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    There is probably nothing to worry about. I hear the OT winding vibrating all the time when I work on amps.
    If it bothers you that much, you can put another OT in...but it's actually normal.

    It makes sense that the speaker is isolated....If all I hear is the output vibrating.
    I use a resistor, but same idea as attenuator basically.

    I don't think there is anything really wrong, but normal vibration.
     
    Last edited: Nov 14, 2018
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  20. FourT6and2

    FourT6and2 Active Member

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    I disagree. The OT should not be audibly producing what your guitar is doing. A little hum from the PT is normal. But the OT should be dead quiet. This guy's OT isn't merely vibrating a little. It's actually producing sound, like a broken speaker. That's not normal.
     

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