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DC at output of GK 700RB II amp

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  • DC at output of GK 700RB II amp

    I have a GK 700RB II that has a slight thump/pop at output as the mute relay turns on. At amp power on there is -0.082VDC at output and after the mute relay kicks over the output goes to +0.064VDC. It's not a terrible thump, just a slight DC sound, not close to damaging drivers. Does this sound normal? It just seems strange to me that the circuit utilizes a mute relay and there is still a little DC sound once the relay kicks over.

    Second question - bias pot, what would be an appropriate place to measure bias in this circuit? It is R28 in the schematic.
    EDIT - I now see there is a two pin header labeled BIAS. I have 10mV across that, does that seem normal? I have the service manual for the original 700RB and that says to set the bias pot to read 5mV across the header.

    gallien-krueger_700rb-ii_sch.pdf
    Last edited by disorder; 09-28-2014, 12:04 AM.

  • #2
    A slight dc offset on the output is fairly common, and yrs you can measure the bias across those pins .
    It usually says what to set it at on the schematic but 2 to 5 millivolts sounds about right.

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    • #3
      I'm reading 10mV now. When power amp circuits start to get this complicated I no longer can follow what even the bias pot is doing. Can someone tell me if 10mV is normal on these amps?

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      • #4
        The schematic you posted for the 700RB II says 10mV between the 2 pins of J5 (bottom right of schematic). So your 10mV is normal.
        Originally posted by Enzo
        I have a sign in my shop that says, "Never think up reasons not to check something."


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        • #5
          Can't believe I missed that. Thanks.

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