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help! have i destroyed my amp?

Discussion in 'Amps and Cabs [BG]' started by Mr. voodoobass, Sep 24, 2005.

  1. well today i was loading in my amps in a new rackcase and did something stupid by mistake.
    when i conected all the cables at the back i...

    ... :scowl:

    went from preamp out
    speaker out on the poweramp.
    and conected my cabs to poweramp input.

    when i didn´t get any sound, i disconected one of the speakercables and put it into the "preamp" (into speakerout on my SWR220, i use it as a pre only).
    i heard a screetching noice and turned it off.
    then i noticed what i had done.
    after i had put everything back the right way i started everything up again.

    well, i get sound out of it but at a really low volume(with master at max).
    the thing is that it´s the same with the SWR as with the poweramp.
    all the fuses are ok so i wonder what has really happened.
    my bandmate did something similar some weeks ago with his keyboardrig, but there was no problem after that.

    does someone has the ability to tell me if i´ve really fried something?
  2. protoz


    Nov 30, 2000
    A local tech would be able to tell you if you blew your gear up.

    It would be hard on here to say anything without pictures of the inside of your amp/pre
  3. Munjibunga

    Munjibunga Total Hyper-Elite Member Gold Supporting Member

    May 6, 2000
    San Diego (when not at Groom Lake)
    Independent Contractor to Bass San Diego
    Hmmm ... this is a tough one. Did you try your amps with another cab? If it's doing the same thing with both amps, I'd suspect you cooked the speakers. Does the combo work OK by itself now?
  4. Surprising as it sounds, i woudn't think anything would be damaged from the first part.

    First time, you had seperate power amp input going to spkrs. That means the power amp input has essentially zero signal to amplify. That means the power amp output has effectively zero output, so connecting seperate power amp output to the preamp output of your combo wouldn't have any effect, the preamp output would see a very low impedance load, but they don't put out much signal, so a shorted output shouldn't blow anything on the preamp. The power amp output would see the preamp output as a higher than normal load, so it shouldn't be damaged. You're connecting two voltages sources in parallel, true, but both are approx 0 volts at idle, so while normally disasterous with either /both are really producing signal, in this case, not necessarily deadly.

    The second part is troublesome. Its not completely clear what you did, but if you got screeching out of the speakers, its sounds like you connected output of an amp to its input, causing feedback, just like mikes feeding back, only through direct electrical connection between inputs/outputs, not acoustical. That could result in ugly ultrasonics and high outputs, if speakers were connected to power amp outputs at that point, speakers or amps could be toast.

    See if combo works on its own, and try different speakers, connect various combinations until you find out what works and what doesn't.

  5. thanx, stevesux.
    one speaker was conected to the poweramp-input
    the other speaker to the SWR.
    preamp-out to the speaker-out of the poweramp.
    the preamp section seems fine as the clip and limiter lights flashes when they usualy do.
    i didn´t try the cabs with another amp.
    i did try a different amp´s line out to my poweramp with no sound at all.
    i´ll look into it more tomorrow.

    oh, and i will get it to a tech later. just wanted to know what could have happened.
  6. yeah, and do check if there were any dogs in the area with bleeding ears, or maybe some bats fell out of the sky

    anyway, hope nothing serious happened to any expensive gear!
  7. tadawson


    Aug 24, 2005
    Lewisville, TX
    If I had to guess, I would bet that the poweramp took out the output stage of the preamp that you had it errantly patched to. Since everything else seems fine, it is probably not too expen$ive to fix . . .

    - Tim
  8. yeah, i do hope it won´t be...
    in any case, i´ve learned to look TWICE before conecting.
    :mad: at myself right now.
  9. tadawson


    Aug 24, 2005
    Lewisville, TX
    Yet another reason to have/use speakon cables for amp outputs. Mighty hard to plug one into a 1/4" jack!!!! :D :D :D :D

    - Tim
  10. ok, i´ve done some simple troubleshooting this morning.
    using my ampeg V4 with the cabs. -works fine( :hyper: )
    using it with the poweramp.- works just fine.
    using it with the poweramp in on the SWR. -works fine!

    started to feel better and went on to go from preamp-out from the SWR to poweramp-in on the ampeg(something i´ve tried before with quite nice results).
    the result?
    a very weak signal, and it didn´t mather to turn up the gain, just started clipping and distort and not getting any louder.

    so, i´ve narroved it down to the preamp section of the SWR sort of.
    sounds a little cheaper(yeah, yeah we´ll see about that) to fix than i thought yesterday!
  11. tadawson


    Aug 24, 2005
    Lewisville, TX
    Woohoo! I win! That is what I suspected would die! With any luck, just a transistor or op-amp chip. I would guess that the parts will be less than $10, but how much to do the work will depend on how that preamp is built . . . . and how hard it is to get to/change parts . . . .

    - Tim
  12. i will try to get it to a tech this week.
    it shall be intresting to see where it all lands.
    the funny thing in this story is that i got this rackcase to finally, start protecting my gear alittle :rolleyes:
  13. FireBug


    Sep 18, 2005
    i've seen the inside of a 350x. its very neat and pretty with a minimal amount of parts. makes me wonder why they're so expensive...

    i don't think the labor will cost that much.
  14. went to a tech today and he thought just a transistor or maybe even some resistors has blown. fairly simple work, around an hour.
    said he had fixed another SWR with the same "problem" last week, strange huh?
  15. tadawson


    Aug 24, 2005
    Lewisville, TX
    The problem sounds about right, but to have seen the same problem twice, yeah, that is odd. I would have thought that the scenario that you had inadvertently created would have been one in a million . . . or higher . . . .

    Or perhaps this is just a favorite "failure mode" of that preamp, and you triggered it in a pretty creative way. A lot of gear does have "typical" failure modes, and once a tech has seen it once or twice, it gets a LOT faster to fix. I used to work on older Tapco CP500 power amps back in the 80s, and it got to the point that I could order the parts with about 95% accuracy by just hearing the problem description over the phone and not having seen the amp . . . . sometimes things are that predictable. (Or in the Tapco case, the design just had that big of a weak spot . . . )

    - Tim