OHMS mismatch mishap...

[mountain2012]

So, I just got my brand new JCM800 2204 Ceriatone clone in the mail. I hooked it up and played through my 8 ohm cab for about 15-30 mins and could have sworn I set the amp to 8 ohms as well. Well, today I looked at the ohm switch on the amp and it was set to 16 ohms instead of 8 to match my cab. Also, I had the amp cranked. Master and gain both on 6.5, if that makes a difference.

So to clarify, my amp was set on 16 ohms, connected to an 8 ohm cab.

My questions:

What damage could this have caused?

Could any damage affect the tone of the amp?

Does this warrant a visit with the amp doctor?

I seem to have the new amp curse. My brand new Orange Rocker 30 was left on overnight by my friend when I first got it.

thanks

 

[mickeydg5]

Well that was not good. How does it sound now with the selectors in the proper positions?

Most OT's are built with a good bit of tolerance. 15 minutes probably did not hurt it, hopefully. The OT may be well broken in now though.

Always good habit check your selectors, knobs and speaker connections before powering up.

 

[Fe911]

You probably didn't do any harm. In the past some amp manufacturers actually would put 8ohm speaker loads on a 4 ohm tap, so when you added an extension 8ohm speaker with the added load, it would match. Most problems happen when you put a bigger mismatch, like a 4ohm cab on a 16ohm tap.
How do you like the amp? I've played and built a few of Nik's amps, but not that one. And I've enjoyed pretty much every one. Give us a review!

 

[Wiking]

Ooooh, not good. But if it still works theres no problem at all.
Your ot warms up too much because of mismatch and in the end it just fails due to heat.
If yoy ool it down before that happens; no problemo.
Try to avoid it in the future, cause the bill for repair is a hefty one.

Lucky basterd you, lol.

 

[GIBSON67]

That Sucks! But, since you didn't dime it, hopefully everything will be fine.

 

[MKB]

I wouldn't be the slightest bit worried about running an amp set at 8 ohms into a 16 ohm load for a short period of time. Not the least bit. I am not sure where most players sensitivity to impedance mismatches has come from, but I would be shocked if any amp has blown with a 8-16 ohm mismatch. A standard 16 ohm guitar speaker's impedance will vary from around 12 ohms to as much as 30-40 ohms or more, depending on the frequency you measure it at.

Transformers are far more rugged that folks give them credit for. Fenders are routinely used with 50% or more mismatches, and I knew a guy that used a Marshall set for 16 ohms with a 32 ohm load for years with no issues (I wouldn't use one that long, but he did with no problems). I have seen a 2 ohm Super Reverb cook a tube socket when cranked for a good while into a 16 ohm cab, but that is an extreme case. The transformer survived just fine though.

Another thing about output transformers; in the thirty years I have been working on amps, I have only seen a single partial OT failure. All other failed OT's were shorted and immediately blew B+ fuses. The point is if your amp is working OK after the impedance mismatch is corrected, it is most likely OK.

A output transformer will blow when operated at high power with no load, which can happen if a cable is disconnected or a speaker in a series connection fails open. However I have by mistake powered up tube amps with no speaker cable plugged into the back of the amp, and have never had a problem. I do make it a point to slowly bring up the volume when starting an amp; you can tell quickly at low volume if there is an issue and avoid any damage.

 

[mountain2012]

^ To clarify, my amp was set on 16 ohms into an 8 ohm load.

 

[Keeb]

^ To clarify, my amp was set on 16 ohms into an 8 ohm load.

Does it work still?

 

[mountain2012]

^Yep, still works.

 

[WinterOrb]

You would probably have just blown the transformer.

 

[diesect20022000]

don't do it again. If it sounds fine and works alright it's probably fine and as was previously stated it CVOULD cause you to blow the Output Transformer but you clearly didn't but you did stress it most likely and "broke it in". so it should be alright if you refrain from further accidental abuse.

 

[1337storm]

Of course it differs from amp to amp, depending on what margins and tolerances the designers used for a particular amp, but I wouldn't worry.
When I was thinking about this subject regarding my JVM, Santiago said that a one step mismatch (up or down) is no problem at all, he even encouraged us to try it out, just to explore the difference in sound.
But then again what is true for one particular amp might not be true for another.

 

[titan7]

Glad your amp is okay. I always double check before powering up. I only run 16 ohms, but I alway double check when switching heads. Actually I am thinking of putting plastic plugs in the other jack holes just for extra insurance, but I have bad OCD.

 

[Roadburn]

Amp Imp > Cab Imp = ok
Amp Imp < Cab Imp = bad

You want it matched though...

 

[bulldozer1984]

Amp Imp > Cab Imp = ok
Amp Imp < Cab Imp = bad

You want it matched though...

Man i think you have it the wrong way around unless im reading it wrong. Its better to put more load on the amp than not enough load.

So its better to have say an amp set to 8 and a cab set to 16 than the other way around.

 

[Bieling3]

My Fender PA 100 has two 8 ohm taps, running one will give you four ohms. I run that 4 ohm into a 8 ohm 1x12 regularly and have no issues what so ever. Even cleared it with a notable local amp builder/modder who said it would be no issue. It's when you go from 16 on the amp to 4 on the cab that you run into problems...

 

[Ken]

Man i think you have it the wrong way around unless im reading it wrong. Its better to put more load on the amp than not enough load.

So its better to have say an amp set to 8 and a cab set to 16 than the other way around.

No, this is wrong for a tube amp. For SS yes, but tube amps are far better to have less than more load.

Think of it this way: You can short the output of a tube amp and the amp will live, but no load and the amp will die. So 8ohms is more like a short than 16 ohms.

If you short a SS amp's output it will fry right away, but no load won't harm it in the slightest. A 2 ohm load on a 4 ohm out will kill the SS amp in short order.

The OP mismatched in the less critical way, so for only 15 min. I'm sure he's fine. But like everyone says, ALWAYS match a tube amp correctly.

Ken

 

[charveldan]

A cab with more ohms than the head is better than less ohms, neither one is good.

If your amp works, keep an eye out for anything overheating like tubes or trannies, a burning smell, otherwise you may be OK.

Always match impedance for best results.

 

[bulldozer1984]

No, this is wrong for a tube amp. For SS yes, but tube amps are far better to have less than more load.

Think of it this way: You can short the output of a tube amp and the amp will live, but no load and the amp will die. So 8ohms is more like a short than 16 ohms.

If you short a SS amp's output it will fry right away, but no load won't harm it in the slightest. A 2 ohm load on a 4 ohm out will kill the SS amp in short order.

The OP mismatched in the less critical way, so for only 15 min. I'm sure he's fine. But like everyone says, ALWAYS match a tube amp correctly.

Ken

Puttin half the load on the amp is closer to NO LOAD than putting double the load on the head. Cab at 16 ohm with amp on 8 is safer than cab at 8 and amp on 16.

No ??

 

[Bieling3]

Puttin half the load on the amp is closer to NO LOAD than putting double the load on the head. Cab at 16 ohm with amp on 8 is safer than cab at 8 and amp on 16.

No ??

Basically, yes. But you'd better have a beefy transformer. With an ohms mismatch you're rolling the dice. I play my 4 ohm head into 8 ohm cab sparingly at low level home practice volumes. Trying to get together an 8 ohm 2x12 closed back cab to go with my 8 ohm open back an eliminate any possibilities of shortening the life of my transformer.