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Thread: Amp Noise

  1. #1

    Amp Noise

    One of my amps has started making a soft crackling noise. The noise sounds like a combination of static and rustling leaves.

    The amp in question is a Weber 5F1 Champ clone that I built about 5 years ago. It is modified with a 5F2A tone stack replacing the low level input jack. Speaker is a Weber 8" alnico.

    Troubleshooting to date is as follows:

    1. Replaced the 12AX7, 6V6GT, and 5Y3 tubes with new ones. No real change in the noise but the original 6V6GT apparently was on the way out as the new tube (JJ 6V6S) sounds louder and better.

    2. Checked all mechanical and soldered grounds, all are good.

    3. Touched up a few suspicious looking solder joints and replaced the wire to ground from the 12AX7 cathode resistor and bypass cap.

    4. Tubes are not microphonic. Tapping on the solder joints between the input jack and the grid input of the 12AX7 with a wooden chop stick creates some noise but I think that is to be expected.

    5. Cleaned volume and tone pot with Deoxit.

    6. Noise seems to be in the 12AX7 stage as it goes away when the tube is pulled or volume turned down.

    7. Tube sockets all cleaned.

    8. Noise seems to increase as amp warms up.

    All this has resulted in a noticeable decrease in the noise but it is still present. It is not hiss.

    Any other suggestions or thoughts?
    Bill "The Piranah" Haegele

  2. #2
    Les Paul Forum Member
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    Re: Amp Noise

    That type of noise is typically caused by one of three things,

    1. A faulty / noisy valve (tube)
    2. Dirty valve pins / sockets
    3. Noisy plate load resistors

    You seem to have eliminated the first two so that tends to suggest it is likely to be the plate load resistors (the 100K resistors on pins 1 & 6 of the 12AX7). Carbon composite resistors are renowned for being noisy in that position so if yours are carbon comp that would make me even more suspicious that they are the cause but other types can become noisy as well.

  3. #3

    Re: Amp Noise

    Quote Originally Posted by PaulD View Post
    That type of noise is typically caused by one of three things,

    1. A faulty / noisy valve (tube)
    2. Dirty valve pins / sockets
    3. Noisy plate load resistors

    You seem to have eliminated the first two so that tends to suggest it is likely to be the plate load resistors (the 100K resistors on pins 1 & 6 of the 12AX7). Carbon composite resistors are renowned for being noisy in that position so if yours are carbon comp that would make me even more suspicious that they are the cause but other types can become noisy as well.
    Yes. Thank you. I intend to look at the 12AX7 plate resistors when I get a chance. They already are either carbon film or metal film. I forget which.
    Bill "The Piranah" Haegele

  4. #4
    Les Paul Forum Member
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    Re: Amp Noise

    Using higher wattage resistors can often help as well. If you currently have 1/2 watt or 1 watt resistors there replacing them with 2 watt resistors might help.

  5. #5

    Re: Amp Noise

    Quote Originally Posted by PaulD View Post
    Using higher wattage resistors can often help as well. If you currently have 1/2 watt or 1 watt resistors there replacing them with 2 watt resistors might help.
    Good to know. Thanks.
    Bill "The Piranah" Haegele

  6. #6
    Les Paul Forum Member LeonC's Avatar
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    Re: Amp Noise

    One other thing to check--typically more of a problem in older amps from the 50s/60s--is that the individual pin sockets in the tube sockets need retensioning so that they make better contact with the tube pins.
    Full Disclosure: I built Valclone Amps

  7. #7

    Re: Amp Noise

    Quote Originally Posted by LeonC View Post
    One other thing to check--typically more of a problem in older amps from the 50s/60s--is that the individual pin sockets in the tube sockets need retensioning so that they make better contact with the tube pins.
    Did that when I swapped tubes.
    Bill "The Piranah" Haegele

  8. #8
    Les Paul Forum Member corpse's Avatar
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    Re: Amp Noise

    This happened to me several times and it was oxidation in the speaker jack. Five sec with emery cloth and all better- both the plug and receptacle.

  9. #9

    Re: Amp Noise

    Quote Originally Posted by corpse View Post
    This happened to me several times and it was oxidation in the speaker jack. Five sec with emery cloth and all better- both the plug and receptacle.
    Both input and speaker jack are clean.
    Bill "The Piranah" Haegele

  10. #10

    Re: Amp Noise

    I decided to replace both plate resistors and the cathode resistor/bypass cap on the 12AX7.That seems to have done the trick. After a total of about an hour playing and just sitting idling there is just a barely audible hiss. I'm satisfied.
    Bill "The Piranah" Haegele

  11. #11
    Les Paul Forum Member ourmaninthenorth's Avatar
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    Re: Amp Noise

    Got exactly the same problem at the moment.

    Really useful thread @bluesky...thanks Pal.

    Shakespeare walks into a pub, the Landlord says "get out, you're Bard"

  12. #12

    Re: Amp Noise

    Quote Originally Posted by ourmaninthenorth View Post
    Got exactly the same problem at the moment.

    Really useful thread @bluesky...thanks Pal.

    Thank PaulD for the probable fix.
    Bill "The Piranah" Haegele

  13. #13
    Les Paul Forum Member ourmaninthenorth's Avatar
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    Re: Amp Noise

    Quote Originally Posted by bluesky636 View Post
    Thank PaulD for the probable fix.
    Couldn't agree more, lots of extremely knowledgeable and helpful people here.

    I've spoken to the builder of my amp, another exemplary brain on this type of dodge, he stands four square behind his work and will put it right. It's only local lockdown restrictions and other life stuff getting in the way that's stopping the fix going in.

    But at least I'll have something to contribute in the diagnostics, by repeating some of the findings here, at the same time as taking an intake of breath through my teeth and having a sage like expression on my face.

    Saves standing there wondering if the amp guy is indeed speaking in English.

    I once listened to a couple of geezers at Matamp for 3 hours non stop, I swear I only understood two words and they were "tea" and "sugar"


    Shakespeare walks into a pub, the Landlord says "get out, you're Bard"

  14. #14
    Les Paul Forum Member
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    Re: Amp Noise

    You're welcome. After 35 years of fixing and building the things there are many faults that you pretty much know instantly what the problem will be. Of course you still get the ones that keep you baffled for days trying to find the fault - still learning after all these years!!

  15. #15

    Re: Amp Noise

    Unfortunately, the noise seems to have returned.

    I swapped out the only tube I hadn't swapped previously, the 5Y3 rectifier, and it made no difference.

    Given that the noise goes away when the volume control is turned down (the tone control has no effect other than to cut the highs out of the noise), the only component that hasn't been examined or swapped is the 0.022 mfd coupling cap between the V1A plate and the volume control. I'll take a look at that in the next few days.
    Bill "The Piranah" Haegele

  16. #16
    Les Paul Forum Member el84ster's Avatar
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    Re: Amp Noise

    If noises like that persist after trying the usual fixes, things can sometimes get weird, meaning more strange unlikely sorts of things.
    Keep in mind that the 5 year point seems to be when metal contacts tend to corrode enough to start causing noise- tube sockets, jacks, certain types of grounds.

    I had an amp on my bench once for several days with noise that none of the usual cures would help. I was pulling my hair out until someone else found it: little corrosion on the input jack grounding switch! Now that’s one of the first things I check.

  17. #17

    Re: Amp Noise

    Quote Originally Posted by el84ster View Post
    If noises like that persist after trying the usual fixes, things can sometimes get weird, meaning more strange unlikely sorts of things.
    Keep in mind that the 5 year point seems to be when metal contacts tend to corrode enough to start causing noise- tube sockets, jacks, certain types of grounds.

    I had an amp on my bench once for several days with noise that none of the usual cures would help. I was pulling my hair out until someone else found it: little corrosion on the input jack grounding switch! Now that’s one of the first things I check.
    All those items were checked/cleaned.
    Bill "The Piranah" Haegele

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