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Few smps and/or amplifier questions

  1. Mar 10, 2016 #1
    signal ground questionb.png signal ground questionb.png Hi folks , maybe you can help me out , so i've built a powerful smps with two separate transformers and secondaries being driven by one common two IGBT half bridge topology.
    I have also put 4x500w rms amplifier channels into the box , they are not kit's they are basically discrete component made boards after a well known schematic.

    heres the problem , i have launched two of the channels already from one of the two smps transformers and they work.But now I need to wire up the other two channels to the second smps transformer and it's corresponding output , but in the input stage there is signal ground which is tied to each channel and it's then tied to each channels PSU ground via 10ohm resistor and a capacitor in parallel.

    Now since i have two separate transformers measuring with a multimeter from one secondary ground across the other i get about 80v DC which is normal because the transformers are not perfectly identical ,
    The question then is what should I do with the input signal grounds ? If I simply connect the signal ground to all 4 channels and on each channel a 10ohm resistor to the actual ground then I will get huge currents running from the first two channels to the second two channel grounds and that will be definitely bad.
    Should I simply take away the resistors and leave the input grounds connected to the psu ground only via a capacitor?

    P.S. I originally put the 10ohm resistor to stop any ground currents in the signal ground because using only a capacitor resulted in some HUM.
    I have also done this in one other amplifier I have built before but that ahd only two channels yet each channel had a separate mains transformer psu yet I too lifted the signal ground to the psu ground via the 10ohm resistor , never measured voltages but it works just fine.

    Oh and one other question , when I assembled my smps for the second time I used a choke in the input for high frequency noise supression back into the mains.I have taken that pasrt from another big commercial smps , but when I load tested my smps i went above 1KW , probably 1.5kw and the inductor got hot and the varnish burned off , I have some thick copper enamel wire I could wrap my own heavy duty choke but i don't know how much turns of wire I need to make it effective ? I assume it doesnt have to be that specific but some overall value that I could use maybe?
  2. jcsd
  3. Mar 11, 2016 #2
    as one of the members on PF wrote to me in PM , he would like to know the schematics of the smps itself to say more , so I will post the schematics and our discussion here just in case.


    Attached Files:

  4. Mar 12, 2016 #3


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    Looking at the schematic, I can't see how there can be a potential between the different grounds. I think they should all be connected to the same conductor.
    If they are all separate local grounds, then I can't see how any DC current can flow between them. If you are getting 60mA DC flowing between two "grounds" then I suspect there must be some connection that is not shown on the schematic.

    Since you are not getting any help here, I suggest you try Electronics Point.
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