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Behringer B300 transformer specs

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  • Behringer B300 transformer specs

    Hi All.
    I have a Behringer B300 powered speaker with a blown power transformer.
    i would like to have a new one wound locally.
    Does anyone have the specs: voltages and current ratings for the windings?
    Thank you in advance!

  • #2
    Can't the rewinder get that from the old transformer?

    The Behringer schematics do not include transformer information.
    Education is what you're left with after you have forgotten what you have learned.


    • #3
      The company I normally use aren’t willing to strip the old one. They only wat to do new winds. Its unfortunate.


      • #4
        .You can make an estimate. The maximum operating supply for an lm3886 is 84V. That translates to a primary voltage of about 62Vrms. Now that is at idle so you need to allow for the drop at the specified load current, say 10% and then another 5% for margin. That gets you to 53V. The nearest off the shelf will probably be 25-0-25. Get the biggest that fits in the space available. Check the specs to calculate the worst case DC supply is not over 94V at idle.

        We shoud also look at this from the poit of view of rated output and speaker impedance. as that might give us a lower number. What is the speaker impedance?
        Last edited by nickb; 11-24-2020, 11:12 PM.
        Experience is something you get, just after you really needed it.


        • #5
          Those are absolute maximum values, not to be even approached.

          Datasheet suggests +/-35V for 50W@8 ohm and +/- 28V for 60W @ 4 ohm so knowing speaker impedance you have your answer as far as voltage.

          EI core area gives you transformer VA, so knowing the V you easily calculate the A

          IF transformer winding "company" canīt do that simple Math, then they are absolutely incompetent for the job, thatīs transformer winderīs 1-2-3

          Path 2: you have probably exposed winding ends where they join the cables leading to the power supply.
          So measure wire diameter, both primary and secondary.

          Knowing core section and voltages they can calculate turns.

          If not, tell them to close shop and sell burgers instead.

          Post a transformer picture, it might also have a low voltage secondary to get +/-15V rails.

          Plan But transformer inside a can or tupper , liberally brush it with acetone or car paint thinner.
          Cover, let reast a couple hours, repeat.

          After a few hours impregnation varnish should be softened.

          Pull laminations, Iīs first, first ones are harder, then it becomes easier.

          When bobbin is free, start cutting paper and unwinding wire, keep notes.

          Messy (thatīs why they donīt want to do it) but you will have the perfect blueprint to copy it.
          Juan Manuel Fahey


          • #6
            Pretty sure the transformer is a toroid, like the one here:
            Education is what you're left with after you have forgotten what you have learned.


            • #7
              I feel I shoud point out that my estimate is more conservative at 33V ( = 1.4 *(25-1.4)) than Juan's of 35V despite the criticism of starting with the max datasheet values. I did also state that we need to know the speaker impedance as that could lower it.
              Experience is something you get, just after you really needed it.


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