B52 AT-212

[puckerstring]

I have a B52 AT212.. IT has 2-16ohm spks. If I use one cable out, how do I wire it to both speakers and what do I set the load on ? Also, if I use two cables out of both jacks, one to each speaker, what do I set the load on ?

[WRGKMC]

The impedance selector is set to match your total speaker load. The jacks are in parallel.

 

You use ohms law to figure this out. Series and parallel are different formulas. You can Google up on line calculators to figure these out.

you have to be specific however. You mention using two cables but what are the impedance or the cabs you plan to connect?

 

If you have two internal speakers which are 16 ohms each - wired in parallel the impedance is cut in half to an 8 ohm load.

 

Unless you disconnect the internal speakers - you have to include them when calculating your total load adding additional speakers to the external jack.

 

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.

 

 

That amp only has 4, 8 and 16 ohm selections. You have to know what your cabs are rated for in order for the math to work. Since your internal speakers total 8 ohms, the external can only be 8 ohms because the amp only goes down to 4 ohms. The external cab can have multiple speakers wired for 8 ohms however.

 

It can have 4 x 8 ohm speakers wired in series parallel for example. Two sets wired in series. Each set is in series - 8 + 8 = 16 ohms in series. Then you wire those two sets in parallel 16 + 16 = 8 ohms total for the cab. This way you have 4 X 8 ohm speakers totaling 8 ohms.

 

If the external cab has 4 X 16 ohm speakers you can only get either 4 ohms wiring all four in parallel (16 + 16 + 16 + 16 ohms in parallel = 4 ohms) or you can use two sets in series (16 + 16 = 32) then parallel them to get 16 ohms total.

 

Where you run into problems is when you try and combine unlike impedances. If your internal speakers total 8 ohms - then you try to combine say a 16 ohm cab as an extension you would have a total of 5.3 ohms. you can probably run the amp at 4 ohms and be safe but its not an exact match so your tone may be affected and you may have unwanted distortion. Its possible the outputs of the speakers may not be even too.

 

What you cant do is add a 4 ohms speaker to the amp while its running the internal speakers. The output jacks are in parallel with the internal speakers so the total is always going to be lower then the lowest impedance speaker. 4 + 8 in parallel will give you 2.6 ohms which is too low for the amp head. You will either blow the tubes or the output transformer when you push the amp hard. May not happen right away either.

 

This on line calculator can be used to figure out your combinations. http://www.speakerimpedance.co.uk/?act=two_parallel&page=calculator

The totals have to match your selector switch and you have to know what your cabs are rated for.