Running 16 ohm amp into 8 ohm load - couple of questions

CitizenCain

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I've got a Ceriatone JTM45 clone head. It's got hardwired 16 ohm output jacks. I read that it would be OK to run the amp into an 8 ohm load though.

First, is it really OK to do? I don't want to risk hurting it, it sounds so sweet!

Second, what could I expect to hear soundwise? Will it be brighter, darker, looser, tighter? :YinYang
 

rockstah

Member
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593
thats not right as far as everything i have every heard and read

8 ohm amp into 8 ohm cab fine, 8 ohm amp into 16 ohm fine

16 amp into 8ohm NOT fine yer okay giving the amp more resistence then it wants to see but giving less is asking for trouble _-BEWARE -=
 

king-albert

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567
CitizenCain- Do a search on this topic and you will find plenty of discussion/theories that may help you out.
 
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6,116
rockstah said:
thats not right as far as everything i have every heard and read

8 ohm amp into 8 ohm cab fine, 8 ohm amp into 16 ohm fine

16 amp into 8ohm NOT fine yer okay giving the amp more resistence then it wants to see but giving less is asking for trouble _-BEWARE -=




Actually, if this JTM45 clone has the correct output transformer primary
impedance, running it on an 8ohm load won't hurt a thing.
The amp will be a bit more aggressive sounding though.
 

rockstah

Member
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593
Roccaforte Amps said:
Actually, if this JTM45 clone has the correct output transformer primary
impedance, running it on an 8ohm load won't hurt a thing.
The amp will be a bit more aggressive sounding though.
what? with all due respect i thought this was a NO NO?
 
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6,116
rockstah said:
what? with all due respect i thought this was a NO NO?





With some amplifiers it can be, but the correct output transformer primary
impedance for a JTM45 is large enough (6.6K) that this shouldn't be an issue, provided his has the correct impedance?
A 50watt JMP is 3.4K at 16 ohms, and even lower at 8+4 ohms.
 

hasserl

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4,711
rockstah said:
thats not right as far as everything i have every heard and read

8 ohm amp into 8 ohm cab fine, 8 ohm amp into 16 ohm fine

16 amp into 8ohm NOT fine yer okay giving the amp more resistence then it wants to see but giving less is asking for trouble _-BEWARE -=
This is not generally true with tube amps. With tube amps it is worse to mismatch the load with the load being higher than the OT is designed for than with the load being lower. Flyback voltage can cause damage to the OT and/or tube sockets. Too low of a load will cause the tubes to work harder with worn tubes the result. Tubes worn to the point of failure could cause other problems.

With SS amps it is a different story, and the rule you stated does apply.
 
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6,116
hasserl said:
This is not generally true with tube amps. With tube amps it is worse to mismatch the load with the load being higher than the OT is designed for than with the load being lower. Flyback voltage can cause damage to the OT and/or tube sockets. Too low of a load will cause the tubes to work harder with worn tubes the result. Tubes worn to the point of failure could cause other problems.

With SS amps it is a different story, and the rule you stated does apply.




Also, a dead short on a tube amps speaker jack is safe.
Many companies actually wired their main speaker
jack to be closed (grounded) in the event no load
was connected. Every black and silver face Fender
amplifier came from the factory like this, so did Hiwatt,
Sound City, and many more.
 

sundaypunch

Member
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2,615
In the end it's easiest to just use the correct impedence. If you can't, spend the $80 or so on a Weber Z-Matcher. A one time investment that lets you mix and match w/ peace of mind.
 

waxnsteel

Member
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3,128
I remember John Phillips saying that a mismatch in either direction with a tube amp is OK so long as it's not more than a factor of two. Shouldn't be a problem. W/ solid state amps, consult the manual. I know for PA stuff, you don't generally want to show the power amp less than 4 ohms, though Crown's K series are OK down to 2.
 

CitizenCain

Member
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4,821
Thanks guys. The trannys in the Ceriatone are definately up to the task. I've got a Weber Z-Matcher that I use, my cab is actually a 4 ohm. Simple enough to switch the input load on teh Z-Matcher from 16 over to 8. I just wanted to make sure it wouldn't fry before I dod the deed.

I tried it last night, and can say that it does make the amp a little darker and more aggressive sounding. Woot! Even more flexibilty from an already incredible amp :D
 




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