JCM 800 and cabinet ohms

  • Thread starter Thread starter DevL
  • Start date Start date
D

DevL

New member
So I've always ran through one or two Marshall cabs, but recenetly I decided to switch to something a bit heavier and deeper, I wanted V30s so i just wanted to get a Mesa to balance out the 800's sound!

Would it be better to run one cable from the head into the 4ohm imput or two cables from the head into each of the 8ohm imputs?

or is the stereo used for two amps?

Thanks for any tips
 
Let me see if I'm understanding you.....you have one JCM 800 head and you want to run it into two cabs? Are the two cabs the same ohm rating?
 
I'm just gonna guess you have two cabs.....

If you have two cabs, and both are 8 ohm mono cabs, set the amp to 4 ohms, and run a cable to each cab. One head, two cables, two cabs.

Then cover your ears. :)

Some Marshall 4x12 cabs are stereo cabs though and many of them are 16 ohm mono with just one single jack on the back. You gotta make sure of what you actually have. Many Mesa cabs are 8 ohm. The two don't jive for a simple hookup. If that's the case you're gonna have to rewire one of them. Generally speaking of course.....
 
What's an "imput" ?
facepalm.jpg
 
I don't think he's going to be able to find his way back here.
 
My first day of computer school - "What's the difference between imput and input?" The teacher kindly told me that imput is not a word.
 
Since no one has given a serious answer, I'll bite. I will have to first assume you have a newer cabinet that has four speakers, and you can either run two speakers in stereo, or all four as a mono load. This is almost always 16Ω speakers in parallel, so you either have two 8Ω 'loads' to run a stereo signal from whatever power amp(s), or they continue to get put in parallel for a total of 4Ω.
Now, if you're asking if it is better to run two cables from the same JCM800 head set to 4Ω, and put into a 'Left-Right' jack (each at 8Ω), or just one cable from the head set to 4Ω and the mono input of the cabinet, my answer is you end up identical, but I'd use one cable. I mean, a dollar is a dollar whether you have four 25¢ pieces or two 50¢ pieces, if that makes any sense. So either way works just fine, but I usually go with the least amount of cable. Less 'stuff' to go wrong. But some egghead may come up with formulas for branch inductance or cable capacitance, and say they sound different. F*ck 'em. It's the same, so go with whatever you want, and enjoy.
 
This is really delayed, but I finally got the new cab! I found my way back! hah

The new cab is actually a 2x12 and 1x15 cab and has 8ohm imput. My JCM 800 has the option of 4/16, so i'm assuming the 4 output on my amp is the best option for running just this one cab?

If I were to get another cab the same, I would have to switch the head to 16?


Thanks to everyone who replied btw!
 
No, if the cab is 8 Ohms and the choice is just 4 or 16 come out of the 16R tap.

Running a valve amp at a lower Z than specifed will run the valves harder (but only if you drive the bllx off it all the time!)
Running a valve amp into a HIGHER load than specc'ed runs the risk of overvoltage and flashover. In the limit, no load at all, O/C equals almost certain destruction of valves, valve holders and possibly output traffs.

The opposite obtains for transistor amps but NEVER run lower than 8R unless the book says you can. No load is STILL not a good idea even for sstate amps.
Dave.
 
How do you have the only JCM800 in the world that doesn't have an 8 ohm output? Every one that I have seen in the last 30 years either has a selector switch for 4, 8 and 16 ohms or it has a bunch of jacks on the back, on of which is an 8 ohm jack.

if the cabinet is 8 ohms, set the amp for 8 ohms. If you have two 8 ohm cabinets, set the amp for 4 ohms.
 
You must log in or register to reply here.
Back
Top