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Thread: Bugera 333 212 combo, very low output

  1. #71
    Senior Member Enzo's Avatar
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    There is a thread around here for a BX1200 Behringer amp..\ Look it up. Jazz P Bass posted your schematic over there, I assume by mistake. Go get it.
    Education is what you're left with after you have forgotten what you have learned.

  2. #72
    Senior Member Enzo's Avatar
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    OK< if there is no DC on those resistors, check the JFET for problems by resistance to ground while running.
    Education is what you're left with after you have forgotten what you have learned.

  3. #73
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    I did check resistance to ground at the point where the diodes are connected to the resistors and got .437k . Thanks for the link to that schematic that is very helpful. I have been looking for that for a long time.

  4. #74
    Senior Member Enzo's Avatar
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    .437k is 437 ohms, which seems really low.

    Look at the gate pin of that JFET, is ther voltage present? Or simply remove the transistor and see if your sound comes back.
    Education is what you're left with after you have forgotten what you have learned.

  5. #75
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    that is the pin on the right looking at the flat side of the transistor correct? It has .477 volts there.

  6. #76
    Supporting Member Jazz P Bass's Avatar
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    Quote Originally Posted by Enzo View Post
    There is a thread around here for a BX1200 Behringer amp..\ Look it up. Jazz P Bass posted your schematic over there, I assume by mistake. Go get it.
    http://music-electronics-forum.com/a...242224-333.zip

  7. #77
    Senior Member Enzo's Avatar
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    I never know which pin is which on JFETs, there is no standard. One is ground, another goes to the two resistors, and the remaining one is the gate. An ohm meter will sort those out.

    If you got half a volt there, and no DC voltage on the other two, then that was the gate, and I suspect that part. Try removing that transistor and see if the amp wakes up.
    Education is what you're left with after you have forgotten what you have learned.

  8. #78
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    Rechecked the voltages on the 3 pins, had basically none on the other 2 , so I removed the transistor and now have full volume. It definitely doesn't sound 100 percent correct, has some popping and volume inconsistencies, kind of fades off a little bit after hitting a note, but has full power. Going to order a new part tonight, any brand that you might reccomend over others? The effects loop doesn't make a loud popping noise either, it does give it quite a bit of a boost when kicked in.

  9. #79
    Senior Member Enzo's Avatar
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    The sole purpose of that part is to mute the amp briefly when changing channels. If you do not get loud noises as you channel switch, then you could leave it out.

    Brand? It is just a transistor. get it from a real parts house, not ebay.
    Education is what you're left with after you have forgotten what you have learned.

  10. #80
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    I hooked my other amp's line out up again to the effects return again, and the issue with the volume cutting out is present when using the preamp from the other amp, but fine when the effects send is ran into the front of the other amp, so sounds like likely something in the power section causing that. Going to have the power tubes tested on Monday, maybe go thru and check the grounding spots. It has a little corrosion on the poles that the boards mount to. My plan when I get it running properly was to take the boards out, clean up all the mounting posts, clean all the dust and debris out and clean the pots.

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