# ohm question



## GuyB (May 2, 2008)

I'm a complete ignorant about these things so, here's the question.
I just bought a Mesa Transatlantic and the Mesa cab that goes with it. I never had a cab/head before, always combo. There are 2 outputs on the amp that go to the cab : 8 ohm and 4 ohm; there is one input of 8 ohm in the cab (and a 8 ohm output that should go, I guess, to another speaker if needed). Up to now, I only used the 8 ohm output of the head and what I'd like to know is if I can use the 4 ohm output to the 8 ohm input of the speaker without problems. If I can, I will try it but can you give me an idea of what could be expectated with the tone or anything regarding the general functionning of the amp. Thanks in advance.


----------



## WCGill (Mar 27, 2009)

100% percent mismatch isn't a problem, go for it. It shouldn't hurt the amp, the tone might change and the power output probably won't be full, depending on what the OPT ratio is.


----------



## GuyB (May 2, 2008)

Thanks WCGill. I'll try that today.
Just by curiosity, what do you mean by : "100% percent mismatch" ? And what is the "OPT ratio" ?


----------



## WCGill (Mar 27, 2009)

Running an 8 ohm speaker from a 4 ohm tap is a mismatch of 4 ohms, 100% more of a load than the tap is designed for. The output transformer has a turns ratio to match different loads to different tubes. The primary load on the tube side is different for 6L6's versus, say, EL34's. The secondary may be wound for one load, say 8 ohms, or have 4 and 16 ohm taps on the winding. The number of wraps of wire on the primary (tube) side compared to the secondary (load) side is the turns ratio. The primary can also vary for the same tube, which was the point I was trying to make.


----------



## GuyB (May 2, 2008)

Thanks again, I appreciate.


----------



## jb welder (Sep 14, 2010)

Not sure what you are trying to achieve here. Why not use the 8 ohm jack to your 8 ohm cab. The 4 ohm jack is for running a 4 ohm cab (or two 8 ohm cabs).
Are you looking to get less power out of the amp? Is it under warranty? If so, make sure to check the owners manual about mismatching head and speakers (some manufacturers will not warranty such scenarios).


----------



## GuyB (May 2, 2008)

I was just curious and if it was something I could do, just curious to experiment with the tone that it would give. The owner's manual says that using the 4 ohm output from the amp to the 8 ohm of the cab is a "safe mismatch". I asked here to get more info on this and be more secure.


----------

