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Output transformer buzz

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  • Output transformer buzz


    I recently assembled a AX84 SEL for Doberman amps.
    Everything looks good (to my virgin ampbuilder's eyes), but the output level seems very low. If the main volume knob is pushed over 3 o-clock, it seems as much sound comes out of the output transformer than the speaker.

    Any thoughts on this?

  • #2
    Originally posted by psykar View Post
    Any thoughts on this?
    Yep... If your OT is vibrating sympathetically then there are almost certainly WATTS being dissapated in it. It's not uncommon for an output transformer to vibrate sympathetically. It IS uncommon to be able to hear this effect when your not using a "dummy load". If you can't hear the amp loud enough in the speaker to entirely distract from these sympathetic transformer vibrations then something is hooked up incorrectly at the output transformer secondary OR your speaker is wired incorrectly, or toasted.
    Last edited by Chuck H; 12-07-2010, 06:56 PM.
    "Take two placebos, works twice as well." Enzo

    "Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas

    "Being born on third base and thinking that you must have hit a triple is pure delusion!" Steve A


    • #3
      The most common problem would be a short at the speaker connector, either the plug or the jack. The output transformer will measure close to a dead short. Measure the resistance across the speaker terminals with the speaker connected and you should see less than 1 ohm. Un-solder one of the wires from the output transformer and the reading at the speaker should go up to about 3/4 the nominal impedance. If you still measure less than 1 ohm, there is a short somewhere. Unplug the speaker, still see the short, it's in the plug.
      WARNING! Musical Instrument amplifiers contain lethal voltages and can retain them even when unplugged. Refer service to qualified personnel.
      REMEMBER: Everybody knows that smokin' ain't allowed in school !


      • #4
        Solved now!
        Wiring problem for sure. I guess I didn't understand how Cliff style jack where wired. I had the jack grounded to circuit but not to OT ground.
        Sounds good now except for little hiss, but thats another story...


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