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DOD SR 231 QX - Power Transformer

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  • #16
    thanks a lot for the guidance!
    i have learned a couple of things


    • #17
      hi! quick question

      after I installed the transformer and checked the unit's functions everything seemed OK. Put some signal in and had some scope readings.
      The only thing I do not like is a HUM coming out of the newly installed transformer. I do not see it going into the audio signal but I can hear it even coming through the housing with the cover closed.
      is that something "normal" or i could raise a claim to MOUSER?


      • #18
        This is acoustical hum from the newly installed transformer. That's one of the specs transformer mfgr's don't publish. Surprised you're finding that on such a small xfmr. You could try unmounting the xfmr, and temporarily sit it in some foam insulation, so it can be safely powered back up to then listen to it unmounted. That would be your 'baseline' for audible acoustic radiation. Is the chassis Aluminum or Steel? The magnetic field will couple to steel. You could try installing a neoprene rubber pad between the mounting tabs of the xfmr...1/16" thick would be sufficient. I assume the form factor of the xfmr is an EI core, open frame, with mounting tabs at each end. You'd cut the isolation pad and add mtg holes to align with the mtg holes in the chassis, and see if that helps quiet it down.

        I've had to deal with this sort of thing in product development years ago when I was a product development engineer at BGW Systems (pro audio power amp mfgr), and have rejected many prototypes, as well as worked with the xfmr vendors to revise their design for lowering the radiated stray field and mechanical mounted resonance. I'm equipped with accelerometers and their mating preamps, as well as measurement microphones to quantify the acoustical noise.

        Does the xfmr feel hot? In general, the closer you run the xfmr to it's rated VA rating, the higher the radiated stray field and acoustical noise. But, this is also where you get into selecting one mfgr's design over another, when you have that luxury during product development. Here, we've selected a 'best-fit' replacement for the product, and now finding an undesireable artifact. Tougher task, though might be able to minimize it. Now, fabricating an acoustical enclosure to fit over it is a lot more difficult. Easier to find a different suitable xfmr, which, of course, takes it out of the realm of being affordable in the first place, as I know you were looking for the least expensive solution in order to justify keeping the unit.

        See what you can find out.....good hunting.
        Logic is an organized way of going wrong with confidence


        • #19
          you're the man! that's a lot of info... let me analyze


          • #20
            Might even take cobbling small soft rubber grommets into the mounting tabs of the xfmr to 'shock-mount' the xfmr to the chassis. At first, I was thinking neoprene rubber sheet under the xfmr and mtg tabs, though the mtg hardware would be clamping it back down, so not as good of a vibration-isolation system. All depends on how different the mechanical noise is unmounted from the mounted noise.
            Logic is an organized way of going wrong with confidence


            • #21
              thanks, I might try that.
              in the meantime i have contacted mouser and asked them if the noise is normal
              i am comparing it to a previously bought for another application and much bigger 370EX transformer... which is far quieter


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