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SVT4 PRO sound cuts but comes back when playing hard

Discussion in 'Amps [BG]' started by ph0ngwh0ng, Nov 12, 2012.

  1. ph0ngwh0ng

    ph0ngwh0ng

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    Mar 3, 2012
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    Hi!

    I am an unhappy owner of an Ampeg SVT4 pro head. So far, I had to change the whole board inside because the temp circuit would fail for no reason.

    Now, I got a new problem. When I play, the sound will cut out, but if I strike my bass strings hard, sound will come back instantly (and the problem is the amp because it happens even if I'm plugged directly in the amp and my bass plays perfectly fine in another amp I own) Like if when a peak signal is received, the amp comes back to life? I dunno..

    Anyone has run into the same problem?
  2. Jerrold Tiers

    Jerrold Tiers

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    Point #1.....

    Whoever replaced the whole board for a temp circuit problem was too lazy to fix it, and "has done took you", in my opinion. There are only a few parts in that circuit, and any tech worth a hoot could deal with it in short order. Replacing the board is the most expensive possible solution for you, and coincidentally the least trouble for the tech.

    That's water under the bridge now, so I am just tellin' you...........

    Point #2...

    What you have is probably a bad connection somewhere, with some oxidation that needs a bit of extra voltage to break it down and make contact. After a while vibration breaks it loose again, and there you are.

    Might be as simple as a little used loop jack, so it may be time to try contact cleaner on the jacks, plugging into each one maybe 10 times or so to knock off any corrosion.

    If that doesn't do it, may be a solder connection that needs to be touched up..
  3. Tuned

    Tuned

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    Dec 6, 2007
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    That's bound to be a cold solder joint or something similar. The sudden surge overcomes the issue and it will last until it gets rattled open again. A repair tech should ne able to find it.
  4. hodgy

    hodgy

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    Disclosures:
    Tech Support- Ampeg/ Mackie
    +1000 what Jerrold said, plus another 1000 for Point #1.
  5. Foz

    Foz

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    Jul 26, 2008
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    ask for the old board - repair it and have a spare?
  6. arai

    arai

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    Cold solder joint was my first thought too
  7. BassmanPaul

    BassmanPaul Gold Supporting Member

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    Fully agree with Jerrold's post. I am not familiar with the amp in question but effects loop jacks are notorious for causing problems like this. If your amp has one, link the Send to the Return with a signal cable and see if that helps.
  8. ph0ngwh0ng

    ph0ngwh0ng

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    Thanks a lot for the replies. I will try to see if the effects loop is the problem. From the schematic though, hitting the "effect bypass" button should solve the problem if the effects loop is indeed the problem, no?
  9. BassmanPaul

    BassmanPaul Gold Supporting Member

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    That's a block diagram not a schematic. From that I would agree with your assessment. However it would not be the first switch contact that I have seen cause trouble.

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