Guitar amp / cab question
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Posted on Aug 09, 2008 10:01 am
Johnny Hero
Member Since: Apr 26, 2002
What I have is 2 heads (Marshall JCM900 and Mesa Dual Rec). I also have 2 Marshall cabs that can be run in stereo, and require an 8OHM input. What I want to do is run each head through 1 side of each cab.
On the Marshall, I have 2 output jacks, with a switch to change between (4)16 and 8. No worries, I set the switch to 8, run one output to each cab, I'm all set.
On the Mesa, I have 4 output jacks. One is labeled 16, one is labeled 8 and 2 are labeled 4. Obviously I can run the one 8 output into one of the cabs, but now I'm out of 8OHM outputs and still have 1 side of the second cab with no input.
Can I use one of the 4 or 16 OHM outputs on the Mesa? By doing so, would I damage anything?
Another alternative I thought of would be to use a Y cable (such as this one: www.zzounds.com...tem--HOSYPP111) on the 8OHM output of the Mesa. Would this work? Or would I want to use it on the 16OHM output since I'm splitting the signal in half, thus dividing it by 2?
I'm seriously lost when it comes to OHMs. Any input is greatly appreciated.
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olddogMember
Since: Jul 02, 2003
Aug 09, 2008 03:45 pm On a tube amp it is a bad idea to mis-match impedence levels either higher or lower. It can cause damage to the tubes and/or the transformer. If the amp expects an 8 ohm impedence/load then you should stick to that. With solid state amps running higher impedence than the amp expects is okay but results in reduced output, lower impedence than expected can damage the amp.
Dan
Aug 09, 2008 04:30 pm So would my Y cable idea work then? or no?
olddogMember
Since: Jul 02, 2003
Aug 09, 2008 06:22 pm I'm not sure. I would guess using a Y cable would be putting the speaker cab's in a parallel config, which if they are 8ohm cab's would yeild a 4ohm load, but it's been far 2 long since my electronics classes in high school to be sure, so wait for some one with more knowlege on the subject than me to chime in. ;)
Dan
Dematrixhttp://www.reverbnation.com/2ndgMember
Since: Nov 27, 2007
Aug 09, 2008 07:18 pm By running the mesa on 8 with a Y cable, to a side of each cab you are effectivley just doing what you'd do on any cab in stereo on 8, you'd think.
Just make sure its ok to run the mesa on 8 in stereo.
maybe with a splitter cable to an 8ohms cab, one has to run the mesa on 4.
Mmm not sure, sounds iffy to me.
im thinking there is going to be power issues with 2 heads in the one box via means of just a Y cable.
But hey i really for sure dont know on this one.
Dematrixhttp://www.reverbnation.com/2ndgMember
Since: Nov 27, 2007
Aug 09, 2008 07:34 pm oh yeah i just remembered, my guitarist is wanting to do a similar thing but, instead of using the boxes in stereo he is going to buy some contraption that blends the 2 heads together and then shoots out the signal to the boxes, just in mono though. im pretty sure thats what he said anyway.
i can find out the website if you want?
Apparently as long as one of your amps has a ground lift then its all good.
Noize2uCzar of MidiAdministrator
Since: Apr 04, 2002
Aug 09, 2008 09:06 pm Johnny, I would hold out until either Walt or Rob stop by. Rob knows more about how the cabs will load the amp head then I do so he might shed a better light on this.
I don't think the Y cable would do what you want as it will not actually turn the 2 8 ohm loads into a 16 ohm load. At least I don't think it will work that way.
Aug 09, 2008 11:02 pm The Zzzounds link doesn't work, but I'm going to assume that the adapter splits the output of the amp in two. If this is the case, use the 4 0hm output from the Mesa using the Y adapter.
Since your cabs can be run in stereo, they have separate (discrete) inputs. This will create two parallel 8 ohm loads, which according to Ohm's Law, results in a 4 ohm load.
Aug 10, 2008 12:37 am Hey Johnny Hero. Putting a Y cable on a guitar head is not the best thing that you can do to your guitar heads.
On your Marshall, the outputs on the back of the head, are parallel. And it will except a 4 ohm load. By setting the switch to 4.
But, for some reason,(I have a few thoughts on it, nothing confirmed) putting a y cable on the amp. Seems to make them run a little hotter. Which burns the EL34's or 5881's out very quickly.
By running the output from the parallel jack on the head, doesn't seem to cause this. At the shop that I work in, we own around 30 Marshall, and Mesa heads. And we have tried this several times. And now it is company policy not to y the cab's.
As far as running the cab's stereo. It might be an interesting stereo contrast to run the Marshall on one cab, and the Mesa on the other. Each head has a preamp out, so you can use either head as the so called master. You might want to use a stomp box for the effects. Ratter then the foot switch for each head. Or, use the Mesa effect loop to run the Marshall.
One other suggestion that I can make to you. Is to run a small fan on the output tubes of the Marshall when running two cab's. You can even use a battery operated to do this. Just the smallest amount of air movement going across the tubes. Will extend their life an incredible amount.
Aug 10, 2008 12:58 am Johnny, I think that if you use large gauge cables and adapters, you'll be fine with it. The Law of Ohm doesn't know the difference between a Marshall and a Mesa Boogie.
Unless their specs are lying to you.
Aug 13, 2008 02:59 pm Are the cabs 2x12s or 4x12s.My guess is that if its a 2x12 stereo marshall the speakers will be 2,75 watt 16Ohm speakers giving a total of 8Ohms in parallel when connected with one cable.
If you were using two amps with a speaker cable from each to two sockets on the one cab both amps should be set to 16Ohms.When you connect two cables from the Marshall head connected to the top and bottom cabs powering one side of each cab the amp should be set to 8Ohms.To obtain the correct output with the Messa you could get a Y splitter then connect the single jack to the 8Ohm socket and the other two ends to the top and bottom cabs.If the cabs are 4x12s you will have to find out what Ohmage each side of the cab is when run in stereo and whatever this value is when connecting two cabs you just halve that number to match the output value on the amps.The Marshall head outputs are in parallel.Some 4x12 cabs have 8Ohm speakers and are connected in pairs to obtain a versatile end resistance.Tricky or watt;)
