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paulevans253

Speaker ohm setting

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I have a vetta 2 mk2 head and 2  marshall cabs a 1960a and b i run amp in stereo and would like some help on the ohm settings when running 1 or both cabs. Ive looked in manual and it dosent help me

marshall-1960a-jcm900-338008.jpg

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The bottom line at the very least is make sure the speaker cab ohm setting is MORE than the amp's ohm setting. That's the critical thing.

 

So now that your cab is in mono you have two ohm choices. If you're Vetta is set to 4 ohms you want to plug into the 4 ohm input. And if you accidentally plug into any other input, since the cab's ohms will be larger you will be safe. That's what I would do. Keep you're Vetta at 4 ohms so even if you accidentally plug into the wrong thing, you'll be OK. If you're Vetta is set to 8 ohms, you now have one input on the cab that could potetentially harm the Vetta. That would be the 4 ohm input. I'm not sure but I believe the 8 ohm speaker cab inputs are disconnected if you go to mono. If you choose to set the Vetta to 16 ohms there is a lot more potential for harm. Bottom line, keep your Vetta ohms at 4 in your situation and plug into the 4 ohm input on each of the cabs. By keeping the Vetta at 4 ohms you're protected from any mistakes. What matching the ohms exactly between the amp and cab does is maximize the amount of power the cab will use.  You can use either ONE of the two left outputs or two right outputs to do this BUT, it seems to me there was an issue with running either of the two same outputs together with the other ouputs not in use. Using either only the left or only the right outputs at the same time is bad as I recall.

 

WARNING:  I can't remember exactly the situation but I seem to recall that you DO NOT want to use ONLY both the left or right outputs at the same time. It changes the output ohmage I think. I can't remember exactly what has been said and I could even be wrong about this. It has been awhile but I would not do that and research it to confirm what I remember.

 

If you're going stereo into ONE cab set the speaker cab switch to stereo (I have a 1960A cab so this is all confirmed). This makes two of the 1/4" inputs 8 ohms. That means you need to set your Vetta's ohm output to 8 ohms. as well. BUT if you accidentally have 4 ohms selected you'll still be good. If you accidentally have the Vetta on 16 ohms and do this,  you run a great risk of burning out your amp.

 

Hope this helps

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