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Thread: Behringer Ultrabass BX4500H schematic

  1. #1
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    Behringer Ultrabass BX4500H schematic

    I am in the process of repairing 2 of these bass-heads. I do not have the schematic, as You all might know, Behringer will not release their schematics.
    Still, I have managed to get something from Captain Hook! - and I have been comparing a lot, handdrawing a lot, and looked a lot through a microscope.
    Has other done similar, and shall we swap informations?
    It seems, that 2 typical faults in this output board, is a bad through-hold connection on the 2 main e-caps, and the output transistors is not pressed enough to the heat-zink, by the 3 mm screws. I can still see, the stribes from the paintbrush, used for applying the heat-zink-compound.
    In one of the 2 units, the transformer primary is 0 - 120 - 230 Volt ac.
    There is opel loop between 0 and 120 Volt, but ok between 120 and 230 Volt.
    I can start the powersupply by applying 120 Volt between 120 and 230 Volt wire.
    That output amp is the Grounded Emittter type of amp, like Peavey also has made some of their amps.
    Regards to all from Soeren Poulsen Denmark

  2. #2
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    Behringer Schematics


  3. #3
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    Behringer Ultrabass BX4500H schenatic / repair

    Thank You so very mouch.
    I have spend some hours, tracing schematics on the Internet, and now I have some 15 different schematics. Well, pressuer creates counterpressure!
    I have taken a lot of photos of these amplifier boards, and it is writen P3000 on the board. It has 2 times 3 output transistors, 2SA1943 and 2SC5200, with MJE15032/33 as drivers. On the schematics I have found, the emitters of the drivers is connected to Gnd by each a 6,8 Ohm resistor, but this amp has an extra 6,8 Ohm resistor from the connectingpoint of the 2 emitter resistors of the drivers, and to Gnd.
    Prior to this amp, I has been working on a Fender small pa amp, with the same type of output circuit. It took me hell of a time to get the schematic, and it turned out to be a Sunn amp, that Fender had sold under their brand. I do not have a homepage, to put it on, but if any is interested in the Fender SR6300P schematic, let me know, then I will send it to whoom want's it.
    Regards Soeren Poulsen Denmark
    Attached Files Attached Files

  4. #4
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    Hello Soeren,
    I am very interested in the BX4500H schematics that you have spent so much time creating, but when I try to open your attached file I only get a black screen. My BX4500H works fine, but I would like to modify it slightly by inserting a very steep 25Hz high pass filter (as recommended by Eminence) in the preamp stage to keep my Eminence Lab 12C driver from destroying itself in the 4.5 cubic foot vented enclosure I am building for it. Are those schematic files still linked to your post? If not, would it be possible to email them to me at jrerbes@att.net? Thank you so much. John Erbes

  5. #5
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    Hello John Erbes.
    Well I do not have the schematic of the output amplifier in the Ultrabass BX4500. Someone attatched the pre-amp schematic, and it looks great, but the amplifier is the type, called "The tail wagging the dog", as my friend in Australia wrote.
    Enzo has told us, that the output amp looks a great deal like the QSC 700 schematic, and I agree. If anyone want them, I have taken a lot of pictures of the Ultrabass BX4500 output module, so just ask for it, and I will mail them.dscn4587.jpgdscn4588.jpgdscn4589.jpg I have attatched 3 for Your reference.
    All best wishes to You all Soeren Poulsen Denmark

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