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Thread: General question on SS amps with failed outputs

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    Master Destroyer nosaj's Avatar
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    General question on SS amps with failed outputs

    Just have a general question on SS amps

    I've got a Marshall DX250 with a failed output putting about 4vdc on the output. They said it would squeel of and on and now it just squeels.
    My question is how do you guys vet the speaker for problems?
    nosaj

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    Run another known good amp into the speaker.

    Then run the amp (if it's working properly) into a known good speaker.

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    Senior Member nevetslab's Avatar
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    Quote Originally Posted by nosaj View Post
    Just have a general question on SS amps

    I've got a Marshall DX250 with a failed output putting about 4vdc on the output. They said it would squeel of and on and now it just squeels.
    My question is how do you guys vet the speaker for problems?
    nosaj
    On mounted speakers, you don't have front access to push evenly on the cone to test for mechanical damage. I'll of course check for nominal DC coil resistance, which will usually be around 60%-70% of the rated impedance (5.6 ohms for an 8 ohm spkr typ). Then, I'll sweep the speaker, first disconnecting the amp from it. I have a generator that can drive speakers directly, but in lieu of that, a separate working amp will suffice, and sweep it from 10Hz thru 200Hz or higher. If it's blown, you'll hear a kazoo sound to it. 4VDC on the speaker cone will force the cone in one direction from nominal resting position, though usually won't cause it to open (less than 3W on an 8 ohm spkr).

    On multiple spkrs, I do the same thing. I'll usually park the oscillator frequency around 40-50Hz, and put my finger thru the spkr frame opening to feel if each of the speakers are vibrating. Sympathetic resonance normally will NOT feel as strong as a working speaker when multiples are in the cabinet.

    Cone tears are another story....but can usually be heard when sweeping the cabinet/spkrs.

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    Master Destroyer nosaj's Avatar
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    Quote Originally Posted by nevetslab View Post
    On mounted speakers, you don't have front access to push evenly on the cone to test for mechanical damage. I'll of course check for nominal DC coil resistance, which will usually be around 60%-70% of the rated impedance (5.6 ohms for an 8 ohm spkr typ). Then, I'll sweep the speaker, first disconnecting the amp from it. I have a generator that can drive speakers directly, but in lieu of that, a separate working amp will suffice, and sweep it from 10Hz thru 200Hz or higher. If it's blown, you'll hear a kazoo sound to it. 4VDC on the speaker cone will force the cone in one direction from nominal resting position, though usually won't cause it to open (less than 3W on an 8 ohm spkr).

    On multiple spkrs, I do the same thing. I'll usually park the oscillator frequency around 40-50Hz, and put my finger thru the spkr frame opening to feel if each of the speakers are vibrating. Sympathetic resonance normally will NOT feel as strong as a working speaker when multiples are in the cabinet.

    Cone tears are another story....but can usually be heard when sweeping the cabinet/spkrs.
    I've got a hp200cd I can manually sweep the freq range on it, which I'm guessing is similar to what your describing.

    I just don't want to quote an amp repair with out including the speakers.
    nosaj

    nosaj

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    Master Destroyer nosaj's Avatar
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    Quote Originally Posted by nosaj View Post
    I've got a hp200cd I can manually sweep the freq range on it, which I'm guessing is similar to what your describing.

    I just don't want to quote an amp repair with out including the speakers.
    nosaj

    nosaj
    Sounded allright sweeping through audible frequencies no rattle or buzzing ot with speaker. DCR right about 6.1 each speaker.
    Just wanted to make sure.

    Thanks,
    nosaj

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