Re-wiring A Jcm 800 Cab... Issues!

Discussion in 'Cabinets & Speakers' started by dumper, Jan 21, 2019.

  1. dumper

    dumper New Member

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    I've just rewired my 4x12 cab to become two 2x12s to accommodate for a Montgomery-Ward head. One pair of speakers is playing loud and clear, the other side sounds extremely underpowered. One speaker at maybe 60%, the other at maybe 25% of the expected volume (and compared to the other pair).

    I've tried this amp through a peavey cab with two 8 ohm inputs and she works fine.

    The amp has two 8 ohm outputs, so I'm going from each into my "new" 2x12s (all the same speakers, celestion 16ohm wired in parallel for 8ohms). The "good" pair of speakers is wired to a regular mono phone jack. The "bad" pair is wired to a two-lead Cliff jack that was original to the cab.

    The contacts on the "bad" jack all seem to be tight, nothing visibly wrong. I've re-done the wiring once, cleaned up all the connections and triple-checked which wires go where... my only thinking is that maybe I have the poles wrong on my "bad" jack, since I can't find a schematic telling me which lead is which, I'm just going off of the pictures I took before I re-did the wiring (and maybe I've had the poles wrong for years and didn't know it).

    Could having my pos/negative incorrectly connected on my Cliff jack cause this problem? Or would I not be getting any sound at all?

    Thanks!
     
  2. charveldan

    charveldan Well-Known Member

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    Montgomery Ward amps aren't very powerful.
    BTW my first guitar & amp was from MW in the 70's.
     
  3. Jon C

    Jon C Well-Known Member

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    2 8ohm jacks as in a Total Combined resistance of 8ohm ( as in Marshall or Orange standard ) ? ……just curious because way too many guys get that wrong and end up dropping combined resistance to 4ohm in turn damaging amp
     
  4. dumper

    dumper New Member

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    2 pairs of 2 16ohm speakers wired in parallel for 8 ohms... effectively two 8ohm 2x12s in one cabinet
     
    Jon C likes this.
  5. Jon C

    Jon C Well-Known Member

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    Ok so total resistance of 8ohm then ……
    It's been a source of confusion for some
    Not here in this crowd so much
    There is someone, daily it seems, on another Forum ( I'm sure you can guess which one ) that sees the two 8ohm jacks and thinks 'an 8ohm cab plugs in here and another 8ohm cab there' …… That is a 4ohm total resistance should both be plugged in …… happens all the time
     
    Last edited: Jan 21, 2019
  6. dumper

    dumper New Member

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    There are no markings on the amp indicating the impedance, but my friend who "tweaked" it told me it needed to be plugged into two 8ohm separate circuits. It worked great using a different cab I borrowed, which had two 8ohm stereo ins.
     
  7. ampmadscientist

    ampmadscientist Well-Known Member

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    You take the speaker out, and check them 1 at a time.
    The speaker must move in/out like a piston. Move the cone in/ out by hand. Make sure that the cone is free to move in/ out by hand.
    If the cone makes a scraping noise or is frozen (will not move in/ out) the speaker is blown.

    I suspect you have at least 1 frozen speaker (blown speaker). Or at least one speaker is blown.

    Test each speaker by touching a 9V battery to the terminals. The speaker should POP.
    Check each speaker with an ohm meter, make sure they all read the same.

    When you hook a 9V battery to the speaker cable, all the speakers should move in the same direction at the same time.

    I do these tests EVERY time, on every speaker cabinet.
    WHY do I do this?
    Because I really give a shit. I live in a world where no body gives a shit.

    AND: I find problems with about 50% of the speaker cabinets / speaker cables / speaker jacks I test.
    And all these problems are fixed, the right way.
    Either it's right or I won't do it.
     
    Last edited: Jan 21, 2019
  8. GIBSON67

    GIBSON67 Well-Known Member

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    Show us pics of the good wiring and the bad wiring...give us your impedance readings, too.
    Do the 9 volt test on each speaker then on each pair to make sure they all move in the same direction.
     

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