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Thread: output ground reference

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    Don't forget the joker g1's Avatar
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    output ground reference

    I'm assuming the sleeve of the phones jack is grounded, though I guess it is a schematic error that omits it?
    It can't just float like this?
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    Member Jon Snell's Avatar
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    JK7 is not floating at all. The schematic shows it grounded on the sleeve. T goes to Ch1 and R goes to Ch2.
    There is a switch built in that disconnects the loudspeaker common to mute the speakers it when the headphones are used however.

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    Lifetime Member Enzo's Avatar
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    That assumes several things. The drawing does not show a ground connection on the jack. Just that it is wired to the PA common. There is no common connection to a "ground" shown. Note in the power supply, there are symbols for chassis ground - earth - and for power supply ground. Note upper right C12, goes from V+ to PAGND Though that PA common is not so labelled I would assume that is what PAGND means. C14 is the V- equivalent. There is one ground connection shown, the power supply ground is wired to pin 3 of CON1.

    One infers JK7 sleeve must have a ground connection, but it is not shown. And I never assume, having been burnt before. Some Hartke's for example require the input connector ground pin to be connected to PA ground or the input stages will float, causing DC out.

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    Member Jon Snell's Avatar
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    It is a Chinesium drawing and I suspect the lone dot on the ground link has not been included in the drawing.
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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    Quote Originally Posted by Jon Snell View Post
    It is a Chinesium drawing and I suspect the lone dot on the ground link has not been included in the drawing.
    That dot should be here -
    Click image for larger version. 

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    Don't forget the joker g1's Avatar
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    Quote Originally Posted by Dave H View Post
    That dot should be here -
    Click image for larger version. 

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    That makes sense. I've sourced schematic for the mono versions of this power amp and it shows a ground symbol for the sleeve of the phones jack. The speaker jack sleeves get disconnected when phones are in use, as Jon mentioned above.

    Seems the muting circuit is active in the unit I'm working on (Q4 etc). I wanted to make sure the phones jack wasn't tied into it in any way, and came across the drawing error.

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