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Noisy Carvin

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  • #1

    Noisy Carvin

    Carvin X100B version 2 (1993) . This one has some crazy noise/oscillation from the fx loop wiring . I found that moving the "wire loom" from the main pcb to the fx level switch makes a hug difference. Or just touching it . The loom is 7 wires zip tied together with no shield.

    Other things that greatly affect the squealing/noise = if the fx level is on 0 or +4 , if the Presence and Treble is on 8 to 10 ...also if i push the 3k graphic slider up all the way. It depends on how you have all that stuff set . The higher i go it really acts up .
    Its not a tube .

    Theres not really a lot of play to move that "loom" anywhere. The noise is only on the Lead channel and does it with the gain level and master volume on 0 !

    Im wondering if a multi conductor cable with shield might cure this? But somethings not right as its a factory design and surely it didnt go out the door like this ?

    attaching a video and scem =

    s24104N_X100B_schematic.pdf


    x.mp4








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  • #2
    Exactly. Fix it, don't re-engineer it.

    Perhaps start by looking over the grounding circuit in th FX returns.
    Education is what you're left with after you have forgotten what you have learned.

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    • #3
      Clean and run a plug in and out of the effects return jack a few times. I've seen switching jacks cause this problem. The connection is just poor enough that the jack acts like an antenna.
      "I took a photo of my ohm meter... It didn't help." Enzo 8/20/22

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      • #4
        You might also just un bundle the loom. It's probable that moving one or two specific leads away from the problem area AND the other leads in the bundle would fix it.
        "Take two placebos, works twice as well." Enzo

        "Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas

        "If you're not interested in opinions and the experience of others, why even start a thread?
        You can't just expect consent." Helmholtz
        • Likes 1

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        • #5
          Referring to clip, it seems that the noise is introduced by your hand and goes away when you withdraw.
          That's not unusual with sensitive high impedance circuits and long unshielded cables.

          Noise doesn't sound like oscillation to me - more like mains harmonics.
          Last edited by Helmholtz; 10-27-2021, 03:34 PM.
          - Own Opinions Only -

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          • #6
            Ok , I fixed it. The jack and grounds were fine , so I separated the 7 wires and experimented with lead dress..

            I found that if i ran 1 of the wires on its own at a way different route , and tucked away a shorter wire under the return jack .........no noise . Amp is great now .

            Thanks boys
            • Likes 4

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