2204 volume drop

Discussion in 'The Workbench' started by JM5010, Jun 29, 2020.

  1. JM5010

    JM5010 Active Member

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    Amp was working perfectly. Brought it outside to play it above bedroom volume, and as I turn the treble knob up, the volume starts dropping.

    Now the amp is stuck in this “low volume” fit. The master halfway up sounds like bedroom volume, which is not normal at all.

    I feel like the power outlet messed something up in the amp.

    Anyone ever have this issue?
     
  2. Matthews Guitars

    Matthews Guitars Well-Known Member

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    I'm guessing a coupling capacitor has shorted out. If it's not a preamp tube, that is. Try swapping out your preamp tubes first.

    If it's not that, it's probably time for your amp to have a doctor's visit.
     
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  3. JM5010

    JM5010 Active Member

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    Just looked over the amp- No burned parts or anything.
     
  4. JM5010

    JM5010 Active Member

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    Swapped preamp tubes already. I hope it’s just a coupling cap.
     
  5. Matthews Guitars

    Matthews Guitars Well-Known Member

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    Check the voltages too. It's not completely impossible that your amp might actually need some new filter caps. It's old enough that it could happen. But to lose so much volume, you'd probably have other apparent sound problems if it was a bad filter cap.
     
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  6. JM5010

    JM5010 Active Member

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    What coupling caps could be the culprit? Just in the preamp section?

    Also, can a bad filter cap cause clean sounds to have a slight distorted character?
     
  7. Matthews Guitars

    Matthews Guitars Well-Known Member

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    All coupling caps are in the preamp. ANY capacitor in the audio path could be at fault.

    Yes, a bad filter cap can cause distortion or ghost notes. And humming and crackling and popping, and sometimes, fireworks.

    Those original capacitors are now 40 something years old. They may still be good. But they may have failed by now, too.

    They weren't intended to last 40 years plus. Many of them do because they're high quality parts and the usage pattern of the amp has a lot to do with capacitor service life.

    Using the amp more often extends capacitor life. Letting it sit for years in storage is bad for capacitor service life.
     
  8. JM5010

    JM5010 Active Member

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    Fixed! It was the coupling cap in the first stage.

    Might replace them all at this point.
     
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  9. Matthews Guitars

    Matthews Guitars Well-Known Member

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    Probably not necessary to replace them all. Just ones that go bad. The type of cap used is a tonal determining factor. Leave them if they're good.

    I have some favorite film cap types depending on the amplifier they're going into. For example, I love the shiny dark blue Paktrons in Fenders. In a Fender they're good tone.
     
  10. jgab

    jgab Active Member

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    I had this exact same problem and it was a coupling cap in the phase inverter.

    Glad you fixed the amp. How did you go about finding out which one it was?

    Do you have a picture of the guts? Interested to see which brand of coupling caps you have in there.
     
  11. Seanxk

    Seanxk Well-Known Member

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    I presume they are ''lego caps'', these don't normally go bad, but if they are close to the board, which they usually are, they can't take a push from the side, because of leverage the side hits the board first and levers out the wire from the body, it may still work too but it's not going to perform well.
     
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  12. neikeel

    neikeel Well-Known Member

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    Glad you found the cause. I was going to suggest dodgy treble pot (based on your symptoms) as all the preamp signal goes via the treble pot wiper to the MV pot.
    - shows what I know!
     
  13. JM5010

    JM5010 Active Member

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    I tapped on the coupling cap with a chopstick and it was not making ear pleasing sounds. I decided to just go ahead and replace it and everything was okay again. Glad it was just one cap.
     

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