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Intermitent Problem with Super Champ x2

Discussion in 'Amp Tech Center' started by Geezer15, Feb 28, 2021.

  1. Feb 28, 2021 #1
    Geezer15

    Geezer15 TDPRI Member

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    Buxton
    The issue is this. When plucking a string, hard, there is no sound from the amplifier at first but then as the string vibration reduces the amp produces the sound. It is like a delay, pluck the string, nothing, then sound. It is similar to a compression, I guess, like the sound is limited at first. This occurs on both channels, with any of the effects on or off. It is not the guitar or the lead. These have been changed and tested elsewhere. As I say it doesn't occur all the time but once it starts then it carries on for the rest of the session. Switching on and off again doesn't help. It also doesn't seen to matter if the amp has been on for a while before it starts to happen. ie sometimes it happens straight away and sometimes after its been on a while. Does any one have any suggestions, It doesn't sound like it needs new valves from the symptoms I have read.?
     
  2. Feb 28, 2021 #2
    dpang2836

    dpang2836 Tele-Meister

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    Only 3 Tubes in there? I would switch them out. But then I think you have some Solid State stuff inside that could be the Issue?
     
  3. Feb 28, 2021 #3
    drew1d

    drew1d Tele-Meister Silver Supporter

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    Westchester NY
    Does it happen at louder volumes? I would check for a blown voice coil on the speaker. It’s pretty easy, disconnect the leads, and measure the resistance (Ohms) on a multimeter. If it’s an 8 ohm speaker it will probably show up more than 6, but if the voice coil is blown, it will much less.
     
  4. Feb 28, 2021 #4
    archetype

    archetype Fiend of Leo's

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    Williamsville NY
    1. Reset the amp's defaults. This is the baseline you'll troubleshoot from and reduces the likelyhood that what's loaded into non-volatile working memory is corrupt. This will lose all the customization you've done to voices, etc. Do this:

    FACTORY PRESET RESTORE — To restore all presets to their factory
    settings: Press and hold the TAP button for 4 seconds until the TAP LED
    lights up. Release the TAP button; the TAP LED will stay lit during the
    restore process (about 5 seconds). When the TAP LED goes out, restore
    is complete. You can backup valued presets before the restore function
    is performed using Fender FUSE software.

    2. The speaker is working and makes sound, so the voice coil isn't open. Either the VC has continuity or it doesn't. I suppose it could melt and short itself to a different resistance, but if it's stock it's a 40 Watt speaker in a 15 Watt amp, and unlikely to be damaged by anything an SCX2 does. BTW, 15 Watts is just wishful thinking for an SCX2.

    3. Try a different speaker. If a different speaker sounds right, it's possible that your original speaker's VC is rubbing the bore or the plug. In that case, it make take some moments before the VC engine can get the coil moving and make sound. If so, replace the speaker. It's 10", 8 Ohms, and there are many possibilities.

    Don't take this the rong way, but did you, uh... push on the cone 'to see if it moves properly?' The SCX2 stock speaker probably doesn't have a close VC gap, but pushing on the cone can misalign the coil in the gap and introduce rubbing.

    4. Substitute known good tubes. Start with the 12AX7. You can substitute any 12A**, 7025, or 5761 to check functionality.

    Report back here. Good luck!
     
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  5. Mar 1, 2021 #5
    Geezer15

    Geezer15 TDPRI Member

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    Buxton
    Thanks guys, This occurs at all volumes. The voice coil is reading 6.9 ohms. I changed the 12AX7 but that didn't solve the issue. I don't have any power tubes to hand to swap. I may be able to hook up a spare speaker, just need to dig it out and check its rating. I haven't pushed on the cone, certainly not deliberately. To be honest, I was thinking of a component failure rather than the speaker until 2 of you have suggested it could be the problem. I have now done the factory reset.
     
  6. Mar 1, 2021 #6
    Geezer15

    Geezer15 TDPRI Member

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    I have the spare speaker on stand by but of course, the amp hasn't played up since. There is a chance the reset might have sorted it, of course. I haven't done anything else to it since it last played up. It has been a bit noisy this evening, a hiss and crackle that comes and goes which it wasn't doing before. I shall keep it on for a good while and see if it goes back to the fault.
     
  7. Mar 5, 2021 #7
    Geezer15

    Geezer15 TDPRI Member

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    Buxton
    So just to update the fault seems to be sorted. It must have been the factory reset that worked, even though it has never been tweaked using the software.
     
  8. Apr 1, 2021 #8
    Gpa23

    Gpa23 NEW MEMBER!

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    I have the opposite issue. When I strum or pick the volume drops after about 1 second, until I do it again then drops again. Any ideas?
     
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