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Ground?

Discussion in 'Electrical Engineering' started by DaveC, Mar 14, 2013.

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  1. DaveC

    DaveC Guest

    This is a segment of a schematic of a Yamaha receiver:

    http://www.tinyuploads.com/images/8LzeOF.jpg

    My question is about the 4 diodes in mid screen, 2 pairs, each pair
    back-to-back.

    What purpose do these diodes serve?

    The conductor common to all diodes runs to the left and connects to the
    shield on all low-level RCA output connectors.

    The conductor running to the right of the upper pair of diodes serves as
    ground for some circuitry, as you can see, and is also connected to ground at
    the bottom edge of the board, center.

    Here's where the ground conductor originates (seen at bottom of previous
    schematic):

    http://www.tinyuploads.com/images/8O0dYH.jpg

    The conductor running to the right of the lower pair of diodes runs to the
    right and connects to a terminal labeled "Earth" (top left corner in the
    following schematic):

    http://www.tinyuploads.com/images/zTnLl1.jpg

    These all serve as ground and/or earth and are connected together though
    these diodes: 3 conductors (analog ground, earth, output connector shield.

    Why the separation via diodes? What purpose do these diodes serve and how?

    Thanks,
    Dave
     
  2. Amplifier stages may have a separated ground to prevent ground
    loops in external cabling from inducing hum. The diodes serve to
    clamp the separated grounds at no more than the diode forward voltage
    drop (typically 0.6V). There's probably an interesting coupling between
    the separate grounded stages, possibly using op-amps to cancel out any
    differential signal between the two grounds.

    Difficult to be sure without seeing more of the schematic.
     
  3. DaveC

    DaveC Guest

  4. Guest

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