#1
ok so i basically have a "math problem" for all you tech wizards. the amp is a 2x12 tube combo. the amp has 3 loudspeaker jacks in the back. the first 2 jacks are labeled together as 1x8ohm and 2x16omh. my friend is selling a 4x12 halfstack cab for $200 which seems like a really good deal. so my question is, can you connect my amp to a 4x12 cab and just use it as a head??? if so, how exactly would you do it and would it be as loud as a regular halfstack?

your help is greatly appreciated...

heres a link to the manual if that helps http://www.marshallamps.com/downloads/files/ma-handbook.pdf
Last edited by WastedWill at Nov 10, 2013,
#2
22. Speaker Output Jack Sockets x 2
These two jacks are tapped from the 8Ω winding of the
output transformer and are wired in parallel. The required
total load impedance of 8Ω will be realised with either of
the following configurations;
One 8Ω cabinet plugged into one of the 8Ω outputs.
Two 16Ω cabinets plugged into each of the 8Ω outputs.*
Note: The cable from the internal speakers of the
MA100C combo should be plugged into either one of
these sockets. If using an extension cab, then the internal
speakers must be disconnected, otherwise the total
impedance will be too low for the amp!
* 16Ω and 16Ω in parallel gives a total impedance of 8Ω.


23. Speaker Output Jack Socket
This jack is tapped from the 16Ω winding on the output
transformer. When using a single 16Ω cabinet it should be
plugged into this socket.
Note: The cable from the internal speaker of the MA50C
combo should be plugged into this socket. If you want to
use the internal speakers and an extension cab then the
internal speaker lead must be transferred to one of the
8 Ohm outputs and the extension cab itself must be
16 Ohms and plugged into the other 8 Ohm output. If the
internal speakers are not required then simply ensure the
impedance of the extension cab is matched to the amp.


By disconnecting the cable from the internal speakers of the combo, you will effectively using your combo as a head. Just plug the cab into the 16ohm single jack. This is assuming that the cab is 16ohms

Yes it would be as loud as a regular halfstack. The theory is that every time you double your sound source (in this case the speakers), you gain 3dBs of sound level.

So this means really you're not going to be that much louder (only 3dBs), but you will find that your sound will be fuller, and thicker. Thats been my experience anyways.
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Last edited by red.guitar at Nov 10, 2013,
#3
Ok, let me tell you how I go about it. I often run a 2x12 combo on top of a 4x12. All the speakers involved are 16 ohm. So the combo is normally 8 ohm and there's a 16 ohm input on the 4x12. If you just hook them both up as is you are looking at 5,3 ohm. That's doable if you can run the amp at 4 ohm (which I can) but there's a small problem. The top speakers (ie the combo) is receiving more power which is spread across half as many speakers so it will drown out the 4x12.
So this is how I fix that. Rewire the 2x12 in series for a total of 32 ohm. Now with the 4x12 hooked up as well you have a total of 10.3 ohm (so run the amp at 8 ohm). Now every speaker receives exactly the same power.
The downside of this is that the combo can't really be run by itself without rewiring back the way it was. However, as a 6x12 you're now cooking with gas.
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