Some Silly Marshall Questions

Hey Everyone,

Just had some stupid questions, your help is appreciated. I owna Marshall JCM900 Dual Reverb head, and plug it into a 1960A cab. Now I have never really bothered to check out the way to set it up properly, and would like to know about the ohm selectors on the back, which input I should be plugging it into on the cab, any sort of info about that would be cool.

Secondly, I am toying with the idea of buying a 2nd head, and wondered if it is possible to run 2 heads through one quad box, or is that just gonna blow the **** out of my celestians?

I know, they're stupid questions, but I just plug in and play at the moment, and want to know a little more about the tech side of my setup.

Well what does your cab run at?8ohm's?I would wager it runs a 8ohm's.Best to have your head set to that.

Usually guitar cabs run at 8ohm's...put two together to have a full stack and then you might want to switch to 4ohm's.

I have no idea about running two heads into one cab at the same time,but I think you can have an amp selector set up so you can kick in whatever amp you want.I think "voodoo labs" make an amp selector.Just be carful with tube heads,since turning them on without a load(connected to speakers)can damage the amp.

hope that helps.

Mate, to be honest, I don't know what ohm's my amp runs at, but I also don't recall having an 8 ohm option on the back of my amp. I remember a selector for 4 or 16. I will check it today when I get home. Like I said, I don't really have a clue about the tech side of it, so I wanna learn some more. Your info on the head helps, wouldn't want to go damaging my head man! Cheers

[font=trebuchet ms]Ach, that's a sad, sad, thing. A guitarist who doesn't have intimate knowledge of his gear is like a painter who doesn't know which end of the pencil to sketch with!

As I recall (please understand that 'the Marshall sound' holds no allure for me, so I have not spent much time using their gear), the 1960 cabs have a Stereo/Mono switch on the back, and two jacks. In Mono mode, all four of the 16 Ohm speakers are connected together. One jack gives all-parallel connection for a total cab impedance of 4 Ohms. The other jack gives Parallel-Series connection for a net impedance of 16 Ohms. Either jack will work happily with your amp, provided that you select the matching output setting.

In Stereo mode, the four speakers are split up into two pairs of parallel-connected speakers, with each pair presenting an 8 Ohm load. This setting would allow two separate amps to each drive two of the four speakers in the cab, again provided that their outputs are matched to the load (8 Ohms, in this case).[/font]

Well, forgive me Lord, for I have sinned. I don't know my gear inside out, like I said, I just plug in and play, BUT, I am here and trying to learn about this stuff, so your info is greatly appreciated. To continue with the silly questions, if I was running 2 heads, I would obviously have my cab set to stereo, but what would the setting on the back of my amp need to be, considering I have only 4 ohm and 16 ohm choices?

[font=trebuchet ms]If you must run a mismatch, it's best to set the amp for a lower impedance than the actual load. In this case, set the amp for 4 Ohms to drive an 8 Ohm load.[/font]

OK, more info, now I have had a chance to check out the back of the amp. There is a 16 ohm and an 8 ohm output. The 16 ohm output is actually labelled 16 (4), which is where I was getting confused with what options were available. This is the output that I have used from day one, and have had the cabinet in mono mode.

If I switch to 8 ohm, for instance if I am using an 8 ohm heil talk box, I would switch to 8 ohm, does this still get split amongst the speakers, so each speaker handles 2 ohms?

[font=trebuchet ms]Some background reading.[/font]