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Ampeg B500DR

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  • #1

    Ampeg B500DR

    Hi, new here.

    This amp came across my bench with no apparent faults...............also with no output! No signal at the preamp out and unit is dead with a signal going into the preamp in. Everything looks good, no DC at the output jacks and everything lights up as it should. Voltages are where they should be as far as I can tell. Should I hear an audible click when powering up from the protection relay?

    Thanks to all!
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  • #2
    Not sure what a preamp in jack does.

    There is a speaker relay, look at your schematic. Look for DC on the amp side of the relay. TP11 is a handy place.

    But if even the preamp out signal is dead, find out why. It will probably solve the relay issue. The relay runs on +15v, so do all the op amps. If it is missing...
    Education is what you're left with after you have forgotten what you have learned.

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    • #3
      While my B-500DR documentation doesn't seem to have the Preamp schematic, the block diagram in the owner's manual does at least give you patch points to see where you do and don't have signal. The Balance Line out has a pre-post setting, so you may be able to see if you have signal from the input stage in Pre there. Then, you have Effects Send which is post-EQ section, and from the Effects Return level, you get to the Master Volume to the Preamp Output jack.

      On the power amp side, you have a Power Amp input jack that defeats the feed from the Preamp, and TP11 as Enzo stated can tell you what you have at the output stage before the relay on the Output A side. I don't see a TP on the output for the B-side ahead of the relay, but you do have the inductors on both outputs L101 and L201. The power amps in this unit are virtually the same as all of their MosFET power amps in the SVT Pro series and a few other models.

      Do you have the schematics?
      Logic is an organized way of going wrong with confidence

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      • #4
        The TP is just a spot in the schematic. I think they only put them on the one channel so as to leave the drawing uncluttered. Just assume the two channels would use similar test points.

        My factory B-500DR file also lacks preamp. It is possibly in my paper files, but those are buried in storage.
        Education is what you're left with after you have forgotten what you have learned.

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