Crackling on Reverb Knob?

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by kfowler11, Dec 22, 2005.

  1. kfowler11

    kfowler11 Guest

    Hey guys! I have a Peavey Classic 30 amp that i'm having a little trouble with. When I turn the Reverb knob, I get a crackling noise. It stops as soon as I stop turning. Anyone know what the problem is and how to fix it? Is it just dirty?

    Thanks!

    Kevin
     
  2. Wakarusa

    Wakarusa Member

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  3. kfowler11

    kfowler11 Guest

    What's the best way to clean it?
     
  4. Wakarusa

    Wakarusa Member

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    The best way to clean it is a combination of two products: Caig DeOxit D5 (the red stuff) and Caig MCL (the blue stuff).

    You need to get some of the D5 inside the pot, rotate the pot full scale 5 or 10 times, wait a few minutes, get some of the MCL inside the pot and repeat. The D5 cleans and deoxidizes, the MCL restores the lubrication.

    Why is inside in italics?

    The bad news is that you need to pull the chassis out of the cabinet to access the back side of the pots (might as well do 'em all while you're in there). Electrical safety rules apply. You need to squirt the stuff in the opening in the back of the pot. Anywhere on the face of the pot (including trying to sneak it along the shaft) is ineffective.

    The worse news is that, if I recall correctly, a Classic 30 uses mini pots soldered upside down to the PCB so access is difficult. If you (or your tech) get the Caig goo in the spray cans, they come with a small tube to help you reach tight spots.


    And, finally, the disclaimer... the problem is more than likely dirt. A scratchy pot can also be an indication of a failed capacitor allowing DC voltage onto the pot. But clean 'em first.
     
  5. kfowler11

    kfowler11 Guest

    Thanks for the info! I took the knobs off and cleaned the outside of the pots with a dust cloth. I also roated the reverb knob back and forth about 10 times. For now, it seems to have cleared the problem. We'll see how long it lasts. I love these amps but they're so cheap it's hard to justify putting in a shop for service.

    Thanks again!
     
  6. bob-i

    bob-i Member

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    Actually getting the cleaner insode is not as hard as Todd says. Get the cleaner, or just go to Radio Shaft and get the tuner cleaner they sell, and get piece of rubber hose that'll fit over the threads on the pot. Take the knob off, fit the hose on and spray into the hose. The cleaner will seep in slowly. After about 5 minutes work the control back and forth.

    The problem with the surface cleaning you did is the problem will come back soon. Do it right, the pot will last longer.
     
  7. Wakarusa

    Wakarusa Member

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    Gotta disagree with you Bob (besides, he did ask for the best way :) ). Anything that goes in around the shaft won't uniformly cover the carbon track (the bit that needs cleaned) and will have to make its way through the friction grease (the part the definitely doesn't need cleaned).

    I agree that mechanical action (rotate back and forth a bunch of times) is only a temporary fix.
     
  8. StompBoxBlues

    StompBoxBlues Member

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    Sounds like the guys were on the mark. But just to let you know...

    I have had "knobs crackling" also on a few amps where it was not the potentiometer at all, but the tube. This is common...it has to do with the tube (very non-technical) "settling in" when you change the pot setting it changes the way the tube is working and the tube then settles in at a new setting when you stop.

    Main point, it VERY much seemed to me to be the pot going, but changing the tube was what fixed it.

    It's also an easy, quick thing to check, just change out the tube that is responsible for the reverb section...no rebias needed since it is a preamp tube. If it doesn't fix it, then I'd look at the pot. But in this case, it sure could have been what everyone suggested, the pot.
     
  9. kfowler11

    kfowler11 Guest

    Great info. Todd's right in that Peavey didn't make it very user friendly to get to the pots. For now, I'm going to let is be and see how long it lasts before it returns. I've got a new speaker on the way and may try to do some "cleaning" then.

    I'll check the FAQ section but is there a good safety check list or procedure listed somewhere? Besides the obvious of unplugging it from the wall. I know the amp still carries a significant charge.
     
  10. RL in Fla

    RL in Fla Member

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  11. bob-i

    bob-i Member

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    Well... I took his "best way" to mean "how can I... a non-tech... do this". I've had great success with the tube method, but yes, it's not the prefered way of doing this. I'm usually concerned about non-technical folks opening up amps. I've seen quite a few not be able to get things back together correctly.
     

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