Different Speaker Outputs On Marshall DSL 40C

[sohosteve]

Maybe this is a stupid question but I want to attach an extension speaker cab to my combo and I'm fearful of causing it damage so thought it best to ask some advice.

The amp has three outputs 16, 8 and 8 ohms.
The 16 ohm output is attached to the internal speaker.

Does that mean that I could safely attach one or two additional 8 ohm speaker cabinets to the remaining output sockets without unplugging the internal speaker?
Or would this cause some kind of uneven draw on the output transformer?

As I say, I'm sorry if this is a stupid question.

[g1]

The 8ohm outs are non-functional when the 16ohm out is in use.
See page 3 of user manual.

[sohosteve]

Aha!
Thanks.
So it was a silly question after all :-)

So if I wanted to run an extension cab I'd need swap the internal speaker to 8 ohm and have an extension cab with an 8 ohm?

I love that you're using my quote as a tagline by the way! :-)

The 8ohm outs are non-functional when the 16ohm out is in use.
See page 3 of user manual.

[Enzo]

No, you'd keep the internal 16 ohm and wire an external 16 ohm in parallel for an 8 ohm total.

[sohosteve]

Ah.
I do actually have a spare 16 Ohm Celestion speaker but it's in a Marshall 1 x 12 cabinet which has an input jack in and another output jack socket.
I'm not sure how I'd go about utilising this cab in conjunction with the internal speaker.
Is there not some way that I could just plug some cables in rather than having to change wiring.
Sorry if I'm being dumb but I'm not an electronic engineer and don't understand the workings or ohms, watts etc...
Beyond it not being wise to use a smaller wattage speaker with a larger wattage amp...

No, you'd keep the internal 16 ohm and wire an external 16 ohm in parallel for an 8 ohm total.

[Steve A.]

No, you'd keep the internal 16 ohm and wire an external 16 ohm in parallel for an 8 ohm total.

So would you plug the 16 ohm internal speaker into one of the 8 ohm jacks and the 16 ohm external speaker into the other 8 ohm jack? Or would you need to wire up the internal and external 16 ohm speakers in parallel and plug them into one of the 8 ohm jacks?

I'll check the schematic when I get to my computer....

Steve A.

[The Dude]

So would you plug the 16 ohm internal speaker into one of the 8 ohm jacks and the 16 ohm external speaker into the other 8 ohm jack?......

Correct. It's detailed on page 3 of the user manual.

[Steve A.]

Correct. It's detailed on page 3 of the user manual.

With sohosteve buying the amp used he might not have the manual which I was unable to find on the Marshall site (perhaps you have better luck!) When you click on support they will help you find a "Stockist" (a dealer who sells Marshall products) and a useless FAQ but that was about it.

https://marshallamps.com/products/am...series/dsl40c/

I did find a PDF of the manual and attached it here:

DSL40C manual.pdf

BTW looking at the schematic I did not find any switching circuitry to disconnect the 8 ohm jacks when the 16 ohm jack is being used, or vice versa so I guess that Marshall is just hoping that people won't do it because they said so. Here is the schematic of the OT and speaker jacks:





Steve Ahola

P.S. BTW the "tone shift" switch is very bizarre! The first two poles make sense although I would change the values a bit but the 3rd is just plain nuts!
SW4A 470pf -> 235pF treble cap
SW4B 33k -> 99k slope resistor
SW4C .022uF -> .011uF mid cap???

It looks like there is an unused pole in which case it would be possible to toggle between a Marshall tone stack and a Super Reverb AB763 tone stack... now THAT would be a mod worth doing, at least for me.





P.P.S. You could turn the 1M bass pot into a 250k pot by adding a 330k tapering resistor across the active terminals. It would change the taper but going from 1 to 10 you should be able to hit all of the Fender values...

[sohosteve]

Hi Steve
Thanks for the PDF of the manual - very interesting and as you say it explains everything I needed to know.

Regarding the Tone Shift/Tone Stack
Now that is very interesting!
Pardon my ignorance if I ask any dumb questions but as already stated, I'm not an electronics guy, just a meddler on a tone quest with a soldering iron and bad attitude ;-)

In what way would you 'change the values a bit' and what would the outcome be?
Also what would you do with the one thats' 'just plain nuts!'?

Or are those considerations negated by your final suggestion in your P.P.S? eg 'You could turn the 1M bass pot into a 250k pot by adding a 330k tapering resistor across the active terminals.'

Steve Ahola

P.S. BTW the "tone shift" switch is very bizarre! The first two poles make sense although I would change the values a bit but the 3rd is just plain nuts!
SW4A 470pf -> 235pF treble cap
SW4B 33k -> 99k slope resistor
SW4C .022uF -> .011uF mid cap???

It looks like there is an unused pole in which case it would be possible to toggle between a Marshall tone stack and a Super Reverb AB763 tone stack... now THAT would be a mod worth doing, at least for me.





P.P.S. You could turn the 1M bass pot into a 250k pot by adding a 330k tapering resistor across the active terminals. It would change the taper but going from 1 to 10 you should be able to hit all of the Fender values...[/QUOTE]

[Enzo]

By nuts, are you referring to the unused section of the four section switch? They show it on the schematic just as reference. it was not needed and has no function.

[Steve A.]

By nuts, are you referring to the unused section of the four section switch? They show it on the schematic just as reference. it was not needed and has no function.

No, I was referring to reducing the value of the mid cap from .022uF to .011uF. Maybe that mode works for some types of music but it sure doesn't work for me! I have the DSL15C and will see what is involved in revising the tone stack. If that 4th pole is readily available- not a given- I will use it for something or other...

Steve A.

P.S. So what would happen if both the 16 and 8 ohm taps on an OT were used simultaneously? I doubt that it would work very well...