Used amp on wrong Ohm

[carlos840]

I all,

Quick question, i just noticed i had been using my Orange bass terror on 8 Ohm with a 4 ohm cab for a few hours!
Could i have done some damage to something?
It was at bedroom level and everything still works fine, just a bit paranoid as its my first amp with an impedance switch...

Cheers

[i_got_a_mohawk]

If it's still working fine, you should be alright

With a tube amp, running at a lower impedance is a slightly lesser evil than running higher impedance.

[GCool]

at very low levels the TB will be fine... Iv don't it to my TB head and I did not even notice, but it works fine... Im sure if it was at hight volume it would have damaged something.

[carlos840]

Cool, thanks...
Didnt even notice the switch was on 8 ohm when i turned it on! Glad it didnt spontaneously combust or something...

[okcrum]

Originally Posted by i_got_a_mohawk

If it's still working fine, you should be alright

With a tube amp, running at a lower impedance is a slightly lesser evil than running higher impedance.

Really? Why?

[rpsands]

The Terror bass is not a tube amp anyway so it's pretty much meaningless.

[kosmicwizard]

Originally Posted by okcrum

Really? Why?

because all tube amps (which this Orange isn't anyway) need to be attached to a load or they self destruct. Running it on 8 ohms attached to a 4 Ohm cabinet is better that the reverse as all the juice will be used by the cab and not have any come back to the head. Think of the head trying to push out water, down a stream bed that is already established but only a certain size, it is okay to run a trickle into that stream bed, but the volume of a river going down it is going to cause flooding and backup. In like manner if the head is pushing too much at the cab, there is no bank per say so it becomes harder for the head to push the given watts at a lower Ohm rating than the cab can take, and will have to work extra hard to push all of it to the cab and may get some of it coming back at it. That is my understanding of it anyway. Cheers.

[okcrum]

Originally Posted by kosmicwizard

because all tube amps (which this Orange isn't anyway) need to be attached to a load or they self destruct. Running it on 8 ohms attached to a 4 Ohm cabinet is better that the reverse as all the juice will be used by the cab and not have any come back to the head. Think of the head trying to push out water, down a stream bed that is already established but only a certain size, it is okay to run a trickle into that stream bed, but the volume of a river going down it is going to cause flooding and backup. In like manner if the head is pushing too much at the cab, there is no bank per say so it becomes harder for the head to push the given watts at a lower Ohm rating than the cab can take, and will have to work extra hard to push all of it to the cab and may get some of it coming back at it. That is my understanding of it anyway. Cheers.

I agree that it's bad to run a tube amp open (or short) circuited, and an impedance mismatch high is usually better than one low. But...

The reflected power from an 8 ohm output into a 4 ohm load will be the same as that from a 4 ohm output into an 8 ohm load, and it will be 11% of the total power delivered, neglecting the effects of the speaker cable. That power has to go somewhere, and is dissipated by the output transformer, the speaker cable, and by reflection back to the speaker itself. More current will flow (with a correspondingly lower voltage) in the first case, for the same amount of power output from the amp. This might be a factor in overheating if the output transformer's wire or output tubes are undersized. OTOH you'll see higher voltage and lower current in the second case. This could also cause problems in some output stage or OT designs.

Normally, less than 2:1 impedance mismatch is not a problem in either case unless the amp is marginally designed. In the real world, you'd also consider the losses and mismatch of the speaker cable, which actually help in these cases.

But the point is moot, as you and rpsands noted, since we're talking about a solid state amp.

[GCool]

BTW it's tube pre!

[Tim1]

It's the power amp section that counts for speaker matching.

[carlos840]

So does that mean my amp is ok?

[okcrum]

Originally Posted by carlos840

So does that mean my amp is ok?

Yep, sure looks that way. The Impedance switch on the Bass Terror appears to change only the Limiter threshold to prevent damage to the Class D power amps. It looks like having it in the wrong position will only affect the amp if you are playing very loudly.

[GCool]

Does it work at full volume now? If the answer is yes then you should be fine.