#1
I've got a Marshall JCM2000 DSL401. It's a 40w 1x12 combo that I've installed a 50w Eminence GB128 in. I absolutely LOVE the sound I'm getting out of it, but 10w is NOT enough headroom, so I'm planning on getting an empty 1x12 cab and sticking another GB128 in that.

The DSL401 has two outputs, one dedicated 16ohm, the other an 8/16 switchable. Since the GB128 is an 8ohm speaker, I have no choice but to wire the two speakers in parallel with each other to get a 16ohm load. Basically, I want to be able to:
-Use the combo as is with the speaker wired normally, plugged into the 8ohm out
-Use the extension cab as an 8ohm cab that can be used alone with other amps
-Use the extension cab and the speaker in the combo together to get a total load of 16ohms(duh)

Currently, the speaker in the JCM is just wired straight to a 1/4" plug which connects to the 8 ohm output. When using the extension cab, that 1/4" would be plugged into one of the jacks on the cab, and a speaker cable would go from the other jack to the 16ohm out on the JCM(so actually pretty backwards)

Here's the crappy schematic I drew up, might be a little confusing with the lack of jacks and whatnot, but I'm sure it's vaguely understandable. Please, let me know if this would work for what I'm trying to accomplish, or if there's any more direct ways to wire it up..Feel free to call me an absolute imbecile if my attempt at making a schematic makes no sense
Thanks



Well....apologies for the MASSIVE picture...
Last edited by guitar42697 at Feb 16, 2016,
#2
As long as they are wired in series you will get a 16ohm load which is fine.
2002 PRS CE22
2013 G&L ASAT Deluxe
2009 Epiphone G-400 (SH-4)
Marshall JCM2000 DSL100
Krank 1980 Jr 20watt
Krank Rev 4x12 (eminence V12)
GFS Greenie/Digitech Bad Monkey
Morley Bad Horsie 2
MXR Smart Gate
#3
Quote by guitar42697
I've got a Marshall JCM2000 DSL401. It's a 40w 1x12 combo that I've installed a 50w Eminence GB128 in. I absolutely LOVE the sound I'm getting out of it, but 10w is NOT enough headroom, so I'm planning on getting an empty 1x12 cab and sticking another GB128 in that.


I think you're a bit confused.

"Headroom" has nothing to do with the wattage rating of the speaker compared to the wattage rating of the amp. Adding a second GB128 will do nothing to increase what the rest of us know as "headroom." It won't increase volume significantly, either.

Running two 8 ohm speakers in parallel will produce a 4 ohm impedance, not 16. Running two 8 ohm speakers in series will produce a 16 ohm impedance (and that appears to be what you're planning). But with most amplifiers, increasing the impedance (what you're doing by changing it from 8 ohms to 16 ohms) actually decreases the power output of the amp.

Here's something else. The speaker in the combo (according to the manual) is supposed to have been a 16 ohm speaker. It's plugged into one of the two outlets. The outlets are already wired in parallel, so if you plugged a second 16 ohm speaker into the second outlet and then threw the switch to 8 ohms, you'd be fine (remember that two 16 ohm speakers in parallel produces an 8 ohm load). That's what Marshall suggests.

From the manual:

The DSL401 is fitted with two parallel wired
loudspeaker jack sockets and a selector to switch
between the normal 16 ohms (to suit the internal
speaker) or 8 ohms. This makes the choice of
extension cabinets even wider. For instance, not
only could you use a Marshall 1960 4x12" cab,
with or without the internal speaker (set amp to
8 ohms if using both, keep on 16 ohms if using
without internal speaker), but you could also
make the choice of various Marshall 1x12" or
2x12" extension cabs. But always make sure
that the output selector is set correctly !
i.e.
1 x 16 ohm speaker = 16 ohm output
2 x 16 ohm speaker = 8 ohm output
1 x 8 ohm speaker = 8 ohm output
#4
Quote by dspellman
I think you're a bit confused.

"Headroom" has nothing to do with the wattage rating of the speaker compared to the wattage rating of the amp. Adding a second GB128 will do nothing to increase what the rest of us know as "headroom." It won't increase volume significantly, either.

Running two 8 ohm speakers in parallel will produce a 4 ohm impedance, not 16. Running two 8 ohm speakers in series will produce a 16 ohm impedance (and that appears to be what you're planning). But with most amplifiers, increasing the impedance (what you're doing by changing it from 8 ohms to 16 ohms) actually decreases the power output of the amp.

Here's something else. The speaker in the combo (according to the manual) is supposed to have been a 16 ohm speaker. It's plugged into one of the two outlets. The outlets are already wired in parallel, so if you plugged a second 16 ohm speaker into the second outlet and then threw the switch to 8 ohms, you'd be fine (remember that two 16 ohm speakers in parallel produces an 8 ohm load). That's what Marshall suggests.


Whoops, I messed up there LOL

I was typing this up at 5am, mixed series and parallel up.

I'm not trying to get more volume out of the amp, and what I meant by headroom was not the headroom used when describing how much the speaker can take before breaking up, but rather, for instance, say you have a desktop computer with components that draw a total of 450w at peak, and a 500w power supply. 50w would be the headroom.

Yep. I know the original speaker was a 16ohm. I'd probably have gone with a gb1216, if they weren't so damn hard to find.
#5
Quote by guitar42697


I'm not trying to get more volume out of the amp, and what I meant by headroom was not the headroom used when describing how much the speaker can take before breaking up, but rather, for instance, say you have a desktop computer with components that draw a total of 450w at peak, and a 500w power supply. 50w would be the headroom. .


Both amp manufacturers and speaker manufacturers lie. Particularly when it comes to wattage ratings. The amp folks overstate wattage output, the speaker folks understate capacity. In short, if you put the two together (a 40W amp and a 40W speaker), you're generally in good shape. A wattage rating in a speaker is a measure of the ability of the voice coil to shed heat (most of an amp's power -- something like 85% -- is actually wasted as heat). In an open-back combo, you won't have as much of an issue with that as you might have in a closed-back cabinet.
#6
Quote by dspellman
In an open-back combo, you won't have as much of an issue with that as you might have in a closed-back cabinet.


Not so sure in this case - not with the tubes dangling about an inch from the speaker cone, not to mention, this is one of the pre 2003 ones, with overheating issues (which I remedied with a 12v pc fan hooked up to a manually variable power supply)
#7
Quote by guitar42697
Not so sure in this case - not with the tubes dangling about an inch from the speaker cone, not to mention, this is one of the pre 2003 ones, with overheating issues (which I remedied with a 12v pc fan hooked up to a manually variable power supply)

there is a component in the power section that causes the over heating, fix it with one of the correct value and it will not have issues. The heads also had this issue and mine is now fixed
2002 PRS CE22
2013 G&L ASAT Deluxe
2009 Epiphone G-400 (SH-4)
Marshall JCM2000 DSL100
Krank 1980 Jr 20watt
Krank Rev 4x12 (eminence V12)
GFS Greenie/Digitech Bad Monkey
Morley Bad Horsie 2
MXR Smart Gate