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Thread: External Speaker for Marshall DSL15c

  1. #1
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    External Speaker for Marshall DSL15c

    I'm thinking about adding an 8 ohm 10" speaker (a cab I just happened to have laying around) to one of the spare 8ohm outputs in the amp and leaving the 16ohm internal speaker connected. This gives me a combined ohm value of 5.33 ohms. Marshal says not to exceed or use less than 8 ohms. What could possibly happen? premature tube life? Fried transformer?

    Any thoughts? is it worth the risk to my amp to try this?

    Thanks for any assistance ya'll can share.

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    If you use the 16ohm output and one of the 8 ohm output jacks (hate the way they labelled these, makes it looks like you can hook up two 8 ohm cabinets) the total impedance won't be 5.33. You aren't truly putting them in parallel, since they are on two separate secondary taps of the output transformer. It would be 5.33 if you put the internal speaker and the external cabinet to the two 8 ohm jacks. If you keep the internal on the 16 ohm jack and add the cab to the 8 ohm jack I think the tubes are essentially seeing a 4 ohm load. I could be wrong though.

    I personally wouldn't do it, not just if it is a random speaker you just happen to have. You get less total power output (since you will have mismatch impedance) and potentially damaging your amp.

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    Thanks for the feedback, I have a Marshall Ministack cab with an 8 ohm Eminence Rajin Cajin in it. Anyway I slice it, I get less impedance than is recommended so I won't mess with it. It just would have looked sweet to put the cab on top of the amp and run both. Instead I replaced the stock speaker with an 8 ohm Jensen CK12 that I took out of my Fender DRRI, it's much tighter and not fizzy when in the high gain channel. Much better than the stock for dirty tones.

  4. #4
    Old Timer olddawg's Avatar
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    Depends on how loud you are wanting to be. You can put an 8 ohm/ 5 watt ceramic resistor in series with your 8 ohm cab on the positive terminal and connect that 16 ohm load in parallel to the 16 ohm internal speaker. You will get more cone movement and dispersion. I doubt you would lose much perceptible volume. Wouldn't hurt to try.

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    Thanks olddawg, I may give that a try.

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    Quote Originally Posted by olddawg View Post
    Depends on how loud you are wanting to be. You can put an 8 ohm/ 5 watt ceramic resistor in series with your 8 ohm cab on the positive terminal and connect that 16 ohm load in parallel to the 16 ohm internal speaker. You will get more cone movement and dispersion. I doubt you would lose much perceptible volume. Wouldn't hurt to try.
    If you do this, you have to plug them into the 8 ohm jacks. When the 16ohm jack is used, the other jacks are not operational. (according to the handbook)
    The two 8 ohm jacks are for a single 8 ohm cab or two 16ohm cabs.
    Certified Dotard

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    Old Timer J M Fahey's Avatar
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    Please somebody post a schematic showing output transformer wiring, specifically because Marshall labelling is poor (maybe the user manual explains it better) and leads to confusion.

    Only after that an answer can be given with any certainty.
    Juan Manuel Fahey

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    Supporting Member The Dude's Avatar
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    Quote Originally Posted by g1 View Post
    If you do this, you have to plug them into the 8 ohm jacks. When the 16ohm jack is used, the other jacks are not operational. (according to the handbook)
    The two 8 ohm jacks are for a single 8 ohm cab or two 16ohm cabs.
    I can confirm that the 8 ohm outputs still work, even with the internal speaker plugged into the 16 ohm jack.
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  10. #10
    g1
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    So then you have to consider what glebert mentioned in post #2. You do not want to run off 2 taps at the same time.
    Use two 16ohm speakers plugged into the 8 ohm jacks.
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  11. #11
    Old Timer J M Fahey's Avatar
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    Quote Originally Posted by LesterPTelestrat View Post
    I can confirm that the 8 ohm outputs still work, even with the internal speaker plugged into the 16 ohm jack.
    Cool, but in practice that does mean much, since only very very few use switching jacks to automatically select the proper tap (Ampeg SVT, Music Man, a couple Fender)

    Most others either used a single or parallel pair jacks and a manual impedance selector switch or currently different jacks for different taps, NOT meant to be used at the same time but to let you choose proper impedance when plugging in.
    No switching involved so none cuts out when others are used, which is what you found.

    You *might* plug a 16 ohm speaker in the 8 ohm tap *and* an 8 ohm one in the 4 ohm one, but since you do NOT have any 4 ohm taps, forget it.

    What Marshall expects is you to get another 16 ohm speaker and use it with the current one, both plugged into the poorly labelled 8 ohm output.

    FWIW what I write on my amps is:
    * 1 x 16 ohms (single 16 ohm jack)
    * 1 x 8 or 2 x 16 ohm speakers (parallel 8 ohm jacks)
    * 1 x 4 or 2 x 8 ohm speakers (parallel 4 ohm jacks)
    for a grand total of 5 jacks, which is far more reliable and intuitive than 2 parallel jacks and a rotary swich (not to mention cheaper )
    Many do the same, as in Mesa Boogie.
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    Juan Manuel Fahey

  12. #12
    Better Tone thru Mathematics bob p's Avatar
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    so what happens when a dufus plugs an 8-ohm cabinet into one of the jacks that says "1 x 8 or 2 x 16 ohm" and plugs a 4-ohm cabinet into one of the jacks that says "1 x 4 or 2 x 8 ohm"?

    we all know that somebody will do it.
    "Stand back, I'm holding a calculator." - chinrest

  13. #13
    Old Timer J M Fahey's Avatar
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    so what happens when a dufus plugs an 8-ohm cabinet into one of the jacks that says "1 x 8 or 2 x 16 ohm" and plugs a 4-ohm cabinet into one of the jacks that says "1 x 4 or 2 x 8 ohm"?

    we all know that somebody will do it.
    They lose warranty coverage
    That´s specifically advised against.
    Juan Manuel Fahey

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