#1
I accidentally came across the fact my cab was only 8ohm the other day, as when i bought it i was assured that it was 16ohm.

So what damage has this caused?

Thanks
#2
EDIT: disregard this first part. I was wrong.
If it is a tube amp, the possible result is fire and brimstone... well, I am kidding about the brimstone. But you are at risk for drawing too much current through the amp and suffering a meltdown.


But first, Why do you now think that the cab is an 8Ω cab? Because if it has multiple speakers, each speaker could be 8Ω individually, but the total impedance is not necessarily 8Ω. How many speakers are in the cab, and what is the impedance listed on the individual speakers?
For example: http://jensentone.com/wiredia.php
Last edited by cedricsmods at Aug 21, 2009,
#3
If it's still working, there's probably no damage, but it's being really rough on your output transformer. (I'm assuming you have a tube amp) running a tube amp with low/no load ranges from at best blowing all your tubes to frying your output transformer as well to at worst frying EVERYTHING.
#4
yeah its a DSL50 (tube amp) well stupidly i didnt think to even check the back of the cab, which i now know says "8 0hm" but i looked at the speakers and each speaker is 8 ohm...

its a marshall AVT412 cab with celestion g12avt speakers i think.

but i mean i've had it a few months now and its been running fine, sounding alright, just the high gain is REALLY muddy... but i dont use it anyway
#6
Running a speaker of lower impedance on tube amp is actually SAFER than running with a higher impedance than rated, or no load at all. You'll get less than maximum power transfer, but expect no damage if the load is half the rated impedance.


Running a speaker of lower impedance on solid state amp is MORE DANGEROUS than running with a higher impedance or no load at all. You'll get less than maximum power transfer, and will generate excessive heat in your output transistors. This can cause them to fail. IF this happens, your amp will stop working completely. Major repairs will be necessary.
Meadows
Quote by Jackal58
I release my inner liberal every morning when I take a shit.
Quote by SK8RDUDE411
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Last edited by SomeoneYouKnew at Aug 21, 2009,
#8
Quote by Torbjorn 66
if that's true you have made me very happy indeed
What do you mean IF? I said it, didn't I? Take that to the bank.
Meadows
Quote by Jackal58
I release my inner liberal every morning when I take a shit.
Quote by SK8RDUDE411
I wont be like those jerks who dedicate their beliefs to logic and reaosn.
#9
hahaha sorry i ever doubted you sir, you are a gentleman and a scholar.

but i was just sayin, can't trust everything you hear.
#10
Quote by Torbjorn 66
hahaha sorry i ever doubted you sir, you are a gentleman and a scholar.

but i was just sayin, can't trust everything you hear.
Fair enough, bro.
Meadows
Quote by Jackal58
I release my inner liberal every morning when I take a shit.
Quote by SK8RDUDE411
I wont be like those jerks who dedicate their beliefs to logic and reaosn.
#11
Quote by SomeoneYouKnew
Running a speaker of lower impedance on tube amp is actually SAFER than running with a higher impedance than rated, or no load at all. You'll get less than maximum power transfer, but expect no damage if the load is half the rated impedance.



Are you sure you're not stating that backwards?

I'd feel safe connecting an 8 ohm cabinet to a 4 ohm output, but not the other way around.
#12
SomeonYouKnew, I think you've got that backwards dude. No load is zero Ohms, not infinite. Also, you get less than maximum power from using a cab with too much impedance, but it's still safe.

You know I've heard that some old marshalls had deliberately mismatched speakers (mismatched too low). Added to the character, but they had to be built to take the punishment.
#13
My Mesa Boogie manual actually recommends connecting your cabinet to a lower rated output jack on the amp to get a smoother sound. I routinely run my 16 ohm cab off the 8 ohm output.
#14
Less for tube amps is correct. If you use a higher load, then you cause the tubes to see a higher primary impedance. With the way that a tube works, this may cause the tube to go above its maximum dissipation and burn out or can be much worse and destroy the output transformer.
#15
ok so you're not directly answering my question:

what damage will have been caused by me running the AMP at 16ohm through an 8ohm cab? Bearing in mind the amp still works with no noticeable change from when I first got it...
#16
Quote by Torbjorn 66
ok so you're not directly answering my question:

what damage will have been caused by me running the AMP at 16ohm through an 8ohm cab? Bearing in mind the amp still works with no noticeable change from when I first got it...


Most likely nothing has been damaged by this. I use an 8 ohm speaker with a 16ohm amp and have never had any problems.
#17
goooood

but from what other people are saying i find it hard to believe that nothing has happened. im a bit paranoid now haha
#18
Quote by Metalhead_28
Are you sure you're not stating that backwards?

I'd feel safe connecting an 8 ohm cabinet to a 4 ohm output, but not the other way around.
Quote by Metalhead_28
My Mesa Boogie manual actually recommends connecting your cabinet to a lower rated output jack on the amp to get a smoother sound. I routinely run my 16 ohm cab off the 8 ohm output.
Randall Smith makes some very nice amps indeed. He's also an idiot when it comes to technical issues.
Feel free to run your Mesa at higher impedances on his recommendation, then sue him for the repairs if the insulation in the primary windings of the output transformer punches through.

But definitely DO NOT recommend this to others.


Quote by Blaster Bob
SomeonYouKnew, I think you've got that backwards dude. No load is zero Ohms, not infinite. Also, you get less than maximum power from using a cab with too much impedance, but it's still safe.

You know I've heard that some old marshalls had deliberately mismatched speakers (mismatched too low). Added to the character, but they had to be built to take the punishment.
It is absolutely NOT SAFE.

Look at the schematic for any Fender tube amp that has its speakers connected via a plug. You'll see a shorting jack. When no speaker is connect to the output, the transformer secondary is shorted DIRECTLY TO GROUND.

Yes folks, that's right.
A DEAD SHORT is safer for the output of a tube amp than open circuit.

I'm not making this shit up, people.
This is real.
Meadows
Quote by Jackal58
I release my inner liberal every morning when I take a shit.
Quote by SK8RDUDE411
I wont be like those jerks who dedicate their beliefs to logic and reaosn.
#19
hahaha fair enough...

thanks SomeoneYouKnew


... so just to clarify, i'm good right? nothing should be harmed?
#20
Should be just fine, man.
Meadows
Quote by Jackal58
I release my inner liberal every morning when I take a shit.
Quote by SK8RDUDE411
I wont be like those jerks who dedicate their beliefs to logic and reaosn.
#21
Quote by Blaster Bob
SomeonYouKnew, I think you've got that backwards dude. No load is zero Ohms, not infinite. Also, you get less than maximum power from using a cab with too much impedance, but it's still safe.

Wouldn't a short to ground be zero resistance? An open circuit (one with no connection to ground) would have infinite resistance. You have it backwards Bob.
After this discussion I realize that I was incorrect in my first post. Going to edit a disclaimer in there.
#22
Quote by SomeoneYouKnew
Randall Smith makes some very nice amps indeed. He's also an idiot when it comes to technical issues.
Feel free to run your Mesa at higher impedances on his recommendation, then sue him for the repairs if the insulation in the primary windings of the output transformer punches through.

But definitely DO NOT recommend this to others.



Okay, you've inspired me to a little reading and I have to apologize. You're right.

I think the recommendation in the Boogie manual is perhaps safe for that particular amp, but certainly not a universal recommendation to make.
#23
Quote by SomeoneYouKnew
Randall Smith makes some very nice amps indeed. He's also an idiot when it comes to technical issues.
Feel free to run your Mesa at higher impedances on his recommendation, then sue him for the repairs if the insulation in the primary windings of the output transformer punches through.

But definitely DO NOT recommend this to others.


It is absolutely NOT SAFE.

Look at the schematic for any Fender tube amp that has its speakers connected via a plug. You'll see a shorting jack. When no speaker is connect to the output, the transformer secondary is shorted DIRECTLY TO GROUND.

Yes folks, that's right.
A DEAD SHORT is safer for the output of a tube amp than open circuit.

I'm not making this shit up, people.
This is real.

Allright, I believe you, but I specifically remember reading my backwards rule in on one of the stickies on UG, which I now can't find. Anyone know where that would be? Because it needs to be fixed.

What I don't understand is why there's a "sweet spot". How is it that going with a lower impedance is fine, until you remove the load entirely and have zero ohms, then it's a recipe for disaster?

Quote by cedricsmods
Wouldn't a short to ground be zero resistance? An open circuit (one with no connection to ground) would have infinite resistance. You have it backwards Bob.
After this discussion I realize that I was incorrect in my first post. Going to edit a disclaimer in there.


That's just it, when there's no load connected, there would be a short to ground at the shorting jack and no resistance.
#24
Quote by Blaster Bob
That's just it, when there's no load connected, there would be a short to ground at the shorting jack and no resistance.



Not all amps have a shorting jack though.
#25
Quote by Blaster Bob
Allright, I believe you, but I specifically remember reading my backwards rule in on one of the stickies on UG, which I now can't find. Anyone know where that would be? Because it needs to be fixed.

What I don't understand is why there's a "sweet spot". How is it that going with a lower impedance is fine, until you remove the load entirely and have zero ohms, then it's a recipe for disaster?


That's just it, when there's no load connected, there would be a short to ground at the shorting jack and no resistance.
Look dude, I don't know where this rule is you're talking about in the stickies, but you have a SERIOUS confusion in the use of the term load. You post is a complete mess because of that.


Heavy load = High conductance = Low resistance.
Light load = Low conductance = High resistance.
No load = Zero conductance = Infinite resistance.
Meadows
Quote by Jackal58
I release my inner liberal every morning when I take a shit.
Quote by SK8RDUDE411
I wont be like those jerks who dedicate their beliefs to logic and reaosn.