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B-52 AT-212 Impedance Question ....


bsumpter

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Hello all.

 

I picked up one of the B-52 AT-212 combos at GC last night, and thus far I'm thoroughly impressed. I wasn't really expecting it to sound as good as it did -- especially on the clean channel.

 

Anyway, for those that have this amp, could you clear up some mud for me concerning the impedance switch? The manual is basically crap, and barely even described it.

 

Question 1: Does the selector have anything to do w/ the built in speakers? Do I need to worry about where it is set if I do not have an extension cabinet hooked up? If I do need to worry about it, what should it be set on?

 

I put a meter on the stock speakers, and they show 7.2 ohms, so I'm assuming it's a 8 ohm load.

 

Question 2: If I do hook up an extension cab, do I need to take into account the impedance of the built in speakers? Or just set the switch to the impedance of the cabinet I'm hooking up?

 

Sorry if these questions are dumb -- I just can't seem to find this info in the manual anywhere. I have a big fat Fender 4x12 here that I'm dying to hook up, but I don't want to damage anything. Hell I'm unsure if I'm damaging it by having the wrong selection for the built in speakers, much less hooking up anything new!

 

All thoughts would be appreciated.

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OK, I'm officially impressed by this company.

 

Avi Elkis (B-52 Vice President) just responded to my email answering this question. I never expected the VP to respond to a tech support question, and on a Sunday nonetheless!!! Bravo to B-52 for thier customer support.

 

If anyone else needs an answer to this question, you DO have to worry about the switch on the stock speakers. They are 16 ohms each wired in parallel, yeilding a combined ohm rating of 8 ohms. So when running the combo alone, the switch should be set to 8 ohms, and not 4 ohms like mine came out of the box.

 

You also have to caculate the combined ohms when you hook up an extension cab. I was under the mistaken impression that you simply set the selector to match the cabinet you hook to it, but that is not the case.

 

If for no other reason, this company deserves support due to the way they handle their customers. I have to say I've never been so impressed by an amplifier company before. Not to mention that this thing sounds amazing as well!!!

 

Internal "gut" photos of the amp coming soon ....

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Originally posted by bsumpter

Hello all.


I picked up one of the B-52 AT-212 combos at GC last night, and thus far I'm thoroughly impressed. I wasn't really expecting it to sound as good as it did -- especially on the clean channel.


Anyway, for those that have this amp, could you clear up some mud for me concerning the impedance switch? The manual is basically crap, and barely even described it.


Question 1: Does the selector have anything to do w/ the built in speakers? Do I need to worry about where it is set if I do not have an extension cabinet hooked up? If I do need to worry about it, what should it be set on?


I put a meter on the stock speakers, and they show 7.2 ohms, so I'm assuming it's a 8 ohm load.


Question 2: If I do hook up an extension cab, do I need to take into account the impedance of the built in speakers? Or just set the switch to the impedance of the cabinet I'm hooking up?


Sorry if these questions are dumb -- I just can't seem to find this info in the manual anywhere. I have a big fat Fender 4x12 here that I'm dying to hook up, but I don't want to damage anything. Hell I'm unsure if I'm damaging it by having the wrong selection for the built in speakers, much less hooking up anything new!


All thoughts would be appreciated.

I would think that the manual would run you through all that. A decent company certainly would explain it there. Anyway,ordinarily,you would set your selector to the correct impedence of the internal speakers if that's all you were running through. If you add a cab,you'd set it on the total impedence of all speakers being used. That means that if using the extension speaker out cuts the internal speakers you'd just set it to matct the extension cab. If the speakers stay in the circuit when using the extension jack,you'd go with the overall impedence. So in a nutshell,you obviously want to set it to match the total impedence of all speakers being provided a signal from the amp. Pretty basic.

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Originally posted by tlbonehead

I would think that the manual would run you through all that. A decent company certainly would explain it there. Anyway,ordinarily,you would set your selector to the correct impedence of the internal speakers if that's all you were running through. If you add a cab,you'd set it on the total impedence of all speakers being used. That means that if using the extension speaker out cuts the internal speakers you'd just set it to matct the extension cab. If the speakers stay in the circuit when using the extension jack,you'd go with the overall impedence. So in a nutshell,you obviously want to set it to match the total impedence of all speakers being provided a signal from the amp. Pretty basic.

 

 

I would have thought the manual would have mentioned it as well, but it doesn't say anything at all about it.

 

The VP responded to my email however, and pretty much echoed everything you said here. This is my first "new" tube amp, and the first one I've owned with an impedance selector. See my post above for more elaboration on his response.

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The impedance selector if for the total load.

 

If you have two internal speakers wired in parallel that gives you an 8 ohm load.

 

If you add an additional cab that's 8 ohms you will need to change the impedance selector to 4 ohms 8 + 8 ohms in parallel = 4 ohms total

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