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DSL40C & Extension Cab Question

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  • DSL40C & Extension Cab Question

    I am demoing an extension cab that I may purchase to go with my Marshall Combo, but I want to ask a question before I fire it all up. On the back of my combo, I have 3 plugs for speaker outs. 8ohm with a lightning bolt, 16 ohm with lightning bolt on the opposite side and 8 ohm in the middle, no lightning bolt. The amp came stock with an 8ohm 70/80 Celestion speaker, though that wasn’t what was in the amp when I bought it. It came with a 65w Creamback, 16ohm, plugged into the 16ohm out with the lightning bolt. Later, I bought an 8 ohm 75w Creamback and installed that, plugged into the 8ohm out with the lightning bolt, just because the other speaker used the out with the lightning bolt.

    Right now, I still have the 75w, 8ohm Creamback in the amp. The extension cab is 16ohm mono, with a “link” input for daisy chaining cabs. My question is:

    Can I just plug the cab into the 16ohm out and play away? Or do I need to disconnect the internal 8ohm speaker first? I just don’t want to blow anything.


  • #2
    Do not unplug the internal speaker. I suggest you read the manual. From what I can see you want to plug the 16-ohm cab into the last speaker output (1x16).

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    • #3
      I don’t have the manual. Thanks for the link.


      • #4
        Ok, so that manual was for the DSL40, not the DSL40C. When I downloaded the DSL40C manual, it stated specifically that when the 16ohm output is in use, the other two 8ohm outputs are not operational.

        Problem solved. Thanks again.


        • #5
          That is how we get things done around here, brother

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          • #6
            Well, plugging into the 16ohm output certainly did not disable the other 8ohm outputs. My 8ohm internal speaker still works with the 16ohm external cab as well. The manual says it should disable the other speakers, but no. I actually prefer this, as I like the sound of the 75w Creamback with the V30 clones in the extension cab. If I end up buying the extension cab, I think I will take out one of the V30 clones and put my 65w Creamback in the extension cab.


            • #7
              If the manual says not to use the 8 ohm and the 16 ohm at the same time . Then don't

              When it says

              Not Operational

              It means run one eight with lightning bolt
              Run one sixteen with a lightning bolt
              Or both eights

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              • #8
                The lightning bolts aren't pointing at those jacks per se. They're simply cute little icons on either side of the "Loudspeaker" label. They just appear to be pointing at those jacks. They just indicate that those jacks are a higher voltage than the other line-level jacks.

                Starting left-to-right, you can do one 4-ohm speaker into either of the left most jacks, or two 8-ohm speakers. Or, you can do one 8-ohm speaker into either of the middle two jacks, or two 16-ohm speakers. Lastly, you can do one 16-ohm speaker into the right-most jack.

                Click image for larger version

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                • #9
                  Yep, what Artie said, DO NOT mix different impedance speakers, even says so in the manual. You can unplug the internal speaker and use the ext cab into the 16 ohm out, or use the internal speaker into the 8 ohm out with no ext speaker. If you want to use both, you need to get speakers with matching impedances and use the appropriate jacks. Plugging into the differently "grouped" jacks is using multiple taps on the output transformer and they are not made for that.

                  Read the warning from the manual:

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                  • #10
                    Thank you guys for the advice. However, the manual you are all looking at is the wrong one. I have the DSL40C. The manual posted is for the DSL40CR, big difference. My amp does not have a 4ohm out at all. This is what the manual says for mine:

                    LOUDSPEAKER OUTPUTS ––––––––––––––––––––––––
                    IMPORTANT OPERATIONAL NOTE: With all-valve amplifiers it is imperative that the amp is connected to a load whilst in operation and that the impedance output(s) on the amp matches the total impedance of the speaker cabinet(s) being used.
                    Failure to comply with these points will result in damage to the amplifier.

                    The DSL40C features three outputs, a dedicated 16Ω output and two 8Ω outputs.
                    The DSL40C must not be run into an impedance less than 8Ω.

                    7. 16Ω SPEAKER OUTPUT
                    For the connection of a 16Ω speaker cabinet. It should be noted that when this Speaker Output is in use the remaining Speaker Outputs (8 & 9) are not operational.

                    8. & 9. 8Ω SPEAKER OUTPUTS
                    For use when the total impedance of the speaker cabinet(s) being used is 8Ω. That is, when using either 1 x 8Ω cab or 2 x 16Ω cabs

                    Here is a pic of what mine looks like.

                    Click image for larger version

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                    So when I plug the extension cab into the 16ohm port, according to the manual, the other two SHOULD BE NON OPETATIONAL, but they are not. It also says I can plug 2 16 ohm cabs into the 8ohm ports at the same time.

                    Just to confirm, should I still unplug the internal 8ohm speaker when I am running the 16ohm extension cab, even if that port is supposed to be non operational?

                    Thank you all.


                    • #11
                      Your description reads like the switching element of the 16 ohm speaker output jack (7) is broken.

                      If it were my amp, until that jack is repaired, I would use only the 16 ohm jack OR only the 8 ohm jack(s).

                      Edit: I should've written the reason why earlier. Most likely the 16 ohm jack is connected to the 16 ohm tap on the output transformer and the two 8 ohm jacks are wired in parallel and connected via the switching element to the 8 ohm tap on the output transformer. Only one output transformer tap should be in use.
                      Last edited by JamesPaul; 01-20-2021, 08:21 PM.
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                      • #12
                        Yes,,,,,, do unplug the built-in speaker when using your extension. You will be giving the amp not enough resistance if running both at the same time.
                        That lets the amp run too hot iirc. I'm not an amp tech btw.(!)

                        I think what will happen is this;
                        The 16ohm output will no longer see a 16ohm load because the other speaker/s will drag it's perceived value down,,,,,,and at the same time the amp's 8ohm output will be "seeing" less than that for the same reason. So both outputs are going to push and pull too hard (the transformer), and then that will create more heat. It's the proper resistance of our speakers that keep our amps safe, but also functioning within optimal push/pull for tone and dynamics.

                        Some amps are fine if you run more resistance than "optimal", which basically forces it to run cooler. Cooler running is darker tone with softer dynamics.

                        Last edited by dave74; 01-21-2021, 02:07 AM.


                        • #13
                          Perfect. Thank you all for your advice and input, as always.


                          • #14
                            Yes, again, no matter what model, you don't want to run off of multiple taps on the output transformer.