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Quad 405 amp - output protection ?

Discussion in 'Electronic Repair' started by N Cook, Jun 24, 2004.

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  1. N Cook

    N Cook Guest

    Straight across the output of each channel of this 1985 amp
    is a diac and triac, what and how do they protect anything ?

    electronic hints and repair briefs , schematics/manuals list on
    http://homepages.tcp.co.uk/~diverse
     
  2. Mike Diack

    Mike Diack Guest

    You forgot to mention the resistor and capacitor.
    The R and C form a low pass filter - any DC that appears on the output
    (either polarity) passes through the LPF, and if above the trigger
    voltage of the"diac" (SBS actually) (around +/- 8 volts IIRC) triggers
    the triac and crowbars the output, at which point (hopefully) the rail
    fuses expire and your wooffer voice coil is saved from becoming toast.
    Clever circuit - saved my bacon on more than one occasion.
    M
     
  3. N Cook

    N Cook Guest

    It makes sense now - i wasn't thinking about speaker protection.
    In internal failure as passing high level DC already we can assume that at
    least
    one output tranny has failed or seriously biased-on so crowbarring
    more to fail a fuse or 2 makes sense
     
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