Sudden signal loss when using effects loop

Discussion in 'Amp Input - Normal or Bright' started by Miotch, Jul 21, 2021.

  1. Miotch

    Miotch Senior Stratmaster

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    Budda SD-18, about 18 months old.

    Been running volume pedal in effects loop ever since I got it.

    Worked great until two days ago when I noticed significant signal loss. Unplugged "return" jack on back of amp and everything is fine. When I plug back into the return, problem is back. Tried two different volume pedals and the same thing.

    Pulled chassis and everything look well put together, no noticeable bad joints.

    Out of curiosity, ran patch in the effects loop and there is no signal loss.

    Tried different cords and same problem.

    Set the volume pedal aside and ran my board through the effects loop (I normally use board in front of amp and only use volume pedal in effects loop) and there is a signal loss.

    So, in a nutshell, when I use the effects loop, I have a signal loss and when it is open or patched there is no signal loss. I would have thought that running a patch would create the same symptoms of running a board or pedal in the loop, but it doesn't.

    Can't think this would be a tube problem and the jack itself seems to click OK, be soldered OK and works when I run a patch between send and return.
     
  2. stormsedge

    stormsedge Senior Stratmaster Gold Supporting Member

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    Looks like you've covered what I would try...except--what happens if you run your pedal board into the front of the amp? I'm suspicious of something on the board...maybe a bad pedal (had more than a couple), bad patch cord, or DUNDUNDUNNNN--my favorite---a patch cord not fully plugged in:oops:--happens to me about every other time I mess with my board. Happy Hunting!
     
  3. Miotch

    Miotch Senior Stratmaster

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    Board and/or volume pedal in front of the board works normally. I've just had to put it all in front until I sort this out. I also just tried replacing the pre-amp tubes and didn't make a difference. I did double check all the patch cords.
     
  4. Miotch

    Miotch Senior Stratmaster

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    Well I'm a dumbass. Somehow got confused when I was trying to run different cables earlier. Tried it again with different cables and works perfectly. Tried old cables and it didn't work. New cables and it did. Repeatable and verifiable results.

    Hence, my final answer is "cables."
     
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  5. rocknrollrich

    rocknrollrich Most Honored Senior Member

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    Glad you got it figured out. Just a bit of info for edification purposes...
    A patch cable straight through may not always tell you what you want to know.
    It depends on a few things regarding effects loops.
    Is the loop:
    Series or parallel
    Is it buffered or non
    Are the jacks shorting or non shorting types.

    The answer to these questions would make a difference when trouble shooting via a patch cable.
     
  6. Miotch

    Miotch Senior Stratmaster

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    Thanks. I wondered about it a bit (not that I understand squat about how it works, I just replace stuff, always starting with the easiest and cheapest).

    Couldn't find schematics, but on another forum, someone quoted Jeff Bober, the amp designer, as saying:

    "It’s closer to line level (+4), but it is post Master, so it varies with the Master Volume level. The effects loop in the amp is a very basic post-Master series loop. ... "

    Whatever the heck that means !!! At least it gave me a chance to look closely inside and determine changing jacks would be a piece of cake, if I had the proper ones to put back in. And, it's pretty inside, so I got some amp eye candy.
     
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  7. The Ballzz

    The Ballzz Senior Stratmaster

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    And what? No pics? You know the rules!
    Amp Porn Must Be Freely Shared! :p
    Gene
     
    Last edited: Jul 22, 2021
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  8. Miotch

    Miotch Senior Stratmaster

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    I'm bad. Bad, I tell ya. I was on a mission and didn't think about grabbing my phone for a photo until after I put it back together. I will though. Sure as it rains in the Sahara.