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Thread: HK Audio Actor active bass speaker

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    HK Audio Actor active bass speaker

    Hi, Does anyone have any experience with these amps mainly the setting of TR3 (a trimpot) which appeares to be concerned with the I/P limiting of one of the bridged power amps. The service instuctions dont mention this adjustment only concerning themselves with setting up the quiecsent current.
    Any advice would be gratefully received. John.

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    "Thermionic Apocalypse" -JT nickb's Avatar
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    Need a schematic at least. The Service Documents on the web are of little technical value.

    The big question is why do you think you need to adjust it?

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    Experience is something you get, just after you really needed it.

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    Supporting Member Jazz P Bass's Avatar
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    If the amp is anything like some of the QSC amps (as concerning the I/P limiting circuit) this should be a once and done adjustment.
    QSC has you drive the amp to full power into a dummy load (we are talking a serious dummy load on high power amps) and then adjust it.

    I would try contacting the manufacture and ask.

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    The TR3 resistor is designed to equalize the gain in the shoulders of the bridge amplifier.
    If the amplifier was repaired, you need to connect the dummy load instead of the woofer
    and adjust this trimpot to the minimum distortions.

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    This amplifier senses over-current by measuring the voltage across the emitter resistors which then turns on the opto-LDR across the input. I don't see TR3 or any trimpot for this in the schematic.
    Sometimes the LDR can go bad. Maybe temporarily remove it and see how the amp runs.


    https://music-electronics-forum.com/...1&d=1560019308
    Attached Files Attached Files

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    "Thermionic Apocalypse" -JT nickb's Avatar
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    Quote Originally Posted by dmeek View Post
    This amplifier senses over-current by measuring the voltage across the emitter resistors which then turns on the opto-LDR across the input. I don't see TR3 or any trimpot for this in the schematic.
    Sometimes the LDR can go bad. Maybe temporarily remove it and see how the amp runs.


    https://music-electronics-forum.com/...1&d=1560019308
    Thx for schemo. TR3 is on sheet 13 top right.

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    Last edited by nickb; 06-08-2019 at 11:33 PM.
    Experience is something you get, just after you really needed it.

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    Ahhh I was looking at page 29 - different version.
    Looks like the trimmer adjusts the bias on the FET. I would connect a load resistor of the rated minimum load and maximum wattage.
    Feed tone or music in, turn up until clipping on oscilloscope then adjust trimmer to reduce gain slightly.

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