# Ran my head @ 16 ohms into an 8 ohms cab - any harm done?



## Peter (Mar 25, 2008)

Hey guys,

Was doing some head/cab swapping with a friend's gear at a jam last night and was plugged into a 16ohm cab for a bit. I forgot to switch my head back to 8ohm when switching back to my cab, and ran it at about 3/4 volume for ~3-4 hours with my head @ 16ohms and my cab is 8ohms.

Head seems to work fine this morning after - I'm wondering if I should have it serviced by a tech before I play again, or if some of the stuff I've read online like "one step out isn't too bad" rings true. Anything I can check on/with the amp myself to see if I've damaged something?

Any advice you can give is much appreciated! Classic rookie mistake huh!


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## keto (May 23, 2006)

It should be fine if it's still working. I always try and remember a safe mismatch as "head goes into cab" and if the math comes out as a whole number 1 (1 being a direct match, 8->8) or smaller it's ****GENERALLY**** safe. So, you were on the wrong side of the equation ( 16/8 = 2, larger than 1). What a lousy explanation lol, I just know it works in my head.

Mesa in their manuals ENCOURAGE you to mismatch saying something to the effect of 'you might find something that sounds good'. I think it depends on the size/power handling of the tranformer(s), somebody actually educated in the matter is likely to be along shortly.


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## greco (Jul 15, 2007)

There was a long and detailed thread about on this topic just recently.

http://www.guitarscanada.com/amp-tech-section/33872-stupid-question.html

Cheers

Dave


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## dwagar (Mar 6, 2006)

yeah, it should be okay. 
Depends on what kind of amp somewhat, but they generally take one step just fine. Always try for a match when you can though.


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## Peter (Mar 25, 2008)

Thanks for the info guys I will sleep a bit better now!

The amp is an Egnater Tweaker 15w so I'm thinking the output transformers probably aren't that big compared to larger amps. Hopefully it works next time I plug it in!


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## Peter (Mar 25, 2008)

Well I turned it on to play for the first time since last night, and after playing at mid volume levels for ~5 minutes it started to sputter and crackle and the volume dropped out. Everytime I strummed it would crackle and sputter like that.

Left it on standby for a few minutes to go get another guitar just to make sure it wasn't the guitar, and when I got back it wasn't making the noises with either guitar - it worked fine from then on in.

I'm hoping it's just a dusty pot, but is there a chance if I hurt something when I ran it at the wrong impedance that it would display this behaviour?


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## parkhead (Aug 14, 2009)

congratulations you've just proved that the internet is full of half truths and BS 

the harm to your Output transformer happens when you mismatch upwards 

or run it with no load at all 

in that case the transformer charges up but has no Outlet (speaker) 

the charge then jumps windings in the transformer to dissipate and burns a pathway accross the windings 

shorting your transformer...


when you mismatch downwards you are running the amp hard into the primary 

since the secondary is mismatched the transformer wants to pass more current (it has an easier load) 

more current overheats the primary like a fuse wire and if the transformer is underdesigned will burn open just like 

a fuse wire ...


if the amp still runs and sounds the same you did not burn the output transformer 

some OT designs are grossly under spec so you should be careful... 

on the other hand I frequently mismatch just to hear a differnt tone an have yet to cook a transformer 

p


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