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Should the center tap output of a 3 output amplifier transformer be tied to the AC ground?

Discussion in 'Radio and Communications' started by Triode, Sep 30, 2016.

  1. Triode

    Triode Member

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    I have a digital headphone amplifier board that I've added all the connections and a transformer to. From the enclosures I had I picked an aluminum box because it was about the right size.

    This requires that I use a 3 prong cord and attach the ground to the case for safety, and that I use jacks that have an insulated connection so I don't get interference off the shell. So my question is, is there any benefit to a metal enclosure, or should I just go to wood or plastic?

    Actually maybe I'm asking the wrong question here. I do get buzzing when I let the ground of the jacks touch the shell, which is tied to ground, but should I? Should the center tap of my transformers output also be tied to the ground? It's a 15-0-15 transformer, and if my basic knowledge of transformers is correct, tying one output to ground shouldn't create a circuit or anything, just put the other two outputs relative to ground, and (I'm really not sure, just explaining my best guess) should get rid of noise from the shell/ground since everything would be referenced to the same ground. But I don't want to explode my amplifier or transformer, so I'd like a second opinion on this.

    Thanks!
     
  2. MikeMl

    MikeMl Well-Known Member Most Helpful Member

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    Are you using any line-filtering on the AC line?

    The reason you get hum into the audio is because of the common-mode noise that exists between Neutral (White wire in the AC cord) and Ground (Green wire in the AC cord). The reason for the common-mode noise is that the White wire has current in it, while the Green wire (is supposed) not to have any current flow along it. These two wires are tied to each other in the AC distribution panel, but you can have tens to hundreds of mV between the two by the time you get to your box...

    Connect the Green wire to your metal box. Dont connect anything on the transformer secondary side (either in the power supply itself, or the headphone amplifier PCB) to the box (means floating the Jacks).
     
  3. Triode

    Triode Member

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    Sounds good (no pun intended) I was considering just putting a boot around the jacks by taking a plastic panel plug and mounting them in it. But I wasn't sure if this was a band-aid solution if touching the shell/ground should not cause a hum.

    Thanks for the reply!
     
  4. dave

    Dave New Member

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  5. MikeMl

    MikeMl Well-Known Member Most Helpful Member

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    I use the plastic "shoulder washers" on the barrel connection of input/output jacks. Look at who is selling these. Any relation?
     

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