reason837

Hey guys,
I'm sure tons of people ask questions like this, but I just want to make sure I'm going to do the right thing before something gets damaged.

I have a 50 watt JCM 800 2205, a 1960A 4x12, and a Mesa rectifier 2x12. The mesa cab is 8ohm, but has a "paralleled out" jack as well.
The 1960, as I'm sure you already know, is either 8 or 16 ohms.

What would i go about doing (as far as the 1960 and the head switch) to make sure this can be hooked up safely? Can it even be done?

Any help is much appreciated. Thanks!

American Viking

A 4x12 cab cannot be wired both 8ohm and 16ohm no matter what.

The 1960 cab should have a 4ohm and/or 16ohm Mono and 8ohm Stereo inputs. The 8ohm Stereo means you would only be running one half of the cabinet, whichever side you're plugging into.

You can run the amp set to 4ohms and plug into the 16ohm Mono side of the 4x12 and the 8ohm input of the 2x12. This isn't truely matched impedance though. I myself wouldn't do it but some will argue and say it's fine. It will make sound for a while but it is not good for it.

Look at the speakers inside each cab and let me know what the ohms are on each speaker. You may be able to rewire it with little effort and get everything matched the way it should be.

__________________
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Ken

If I'm reading correctly, the 2x12 8 OHM cabinet in a "parallel out" mode implies the regular wiring is series: two 4 ohm speakers giving 8 Ohms. In parallel that would be 2 ohms which seems unlikely! But, perhaps the Mesa cabinet has two 8 Ohm speakers which will give either 16 ohms out or 4 ohms out? How do you know the cabinet as is rates 8 ohms? Something here doesn't make sense.

Tell us exactly what you have with the Mesa; I have a hunch it can be jacked for 16 ohms, which would make a nice match for your 4x12 at 16 ohms. Run both speaker cabinets with the amp set at 8 ohms. But make sure you know exactly what you have first!

Ken

reason837

I'm looking at the back of the mesa right now, there are two jacks, one is "8 ohms in" and the other is "paralleled out."
The speakers are vintage 30s.

is it possible to just switch the 1960 to run at 8 ohms instead of 16, thus having two 8 ohm cabs?

Ken

You can't wire four 16 ohm speakers to have an 8 ohm output.

Since your jacks are labeled "in" and "out" on the Mesa, I would think that means you use the 8 ohm jack if you have only one input, and while you are using that input you can add a second cable to run directly to another cabinet that will run in parallel with the Mesa. so if the Mesa is 8 Ohms and you have an 8 ohm cabinet (you don't) you plug it into that "parallel out" jack and run the amp at 4 ohms. You would have to use the stereo output on the Marshall and thus have just 2 of the 4 speakers in the circuit. You COULD run the Marshall cabinet (at 16 Ohms) in that output, yeilding a 5.3333 ohm load. If you set your amp at 4 ohms, you will be fine.

Ken

American Viking

The paralleled out is if you were going to run one cable from the amp to the cab and another cable from that cab to another cab. You shouldn't worry about this.

Like I said before, if you flip the switch on that 1960 cab to stereo and run one side at 8ohms, you're only running one half of the cabinet. The stereo switch divides the cab into two 8ohm halves, the mono switch runs all four speakers at 16ohms on the right input and 4ohms on the left.

You cannot change the 1960 cab whatsoever, all the options are already provided for you on that back panel so the only other thing we can do is maybe rewire that 2x12. This is really easy you just have to take the back panel off and tell us what ohms the speakers are, you don't need any tools to rewire the thing it's just pull a clipped wire off of one spot and clip it somewhere else.

__________________
-I'd rather be a good liver than have one...