Speaker cabinate hookup - Mark V Amp Head

[richiedoc]

I think this configuration will work, but I wanted to be sure before buying everything.

2 Mesa 8 ohm cabs chained to make one 4 ohm amp connection x 2
(4 speaker cabs in total)

1 8 ohm rotating cab.

My concern is that those input jacks in the brain are (or are not!) all discreet: meaning they are rated at those ohm values even if all 4 input jacks are being used. Thanks for any input.

 

[MrMarkIII]

"... 2 Mesa 8 ohm cabs chained to make one 4 ohm amp connection x 2
(4 speaker cabs in total)..."

This won't work, as the total load will be 2 ohms, too low.
It's four 8 ohm loads in parallel, which is 2 ohms.

All those speaker jacks are parallel. It's confusing, but the "4 ohm" label means the when you use both jacks, the total load is 4 ohms, NOT 4 ohms each.
Ignore the "4 ohm" label.
Pay attention to the label between the jacks which says "2 x 8 ohm cabs". Two 8 ohm cabs plugged into these jacks will yield a total load of 4 ohms.
Complain to Mesa.
You'll have to re-wire those cabs to 16 ohms each. That will give you a total of 4 ohms, an acceptable mismatch.
Isn't the Motion Sound a powered cab? In that case, it wants a line signal. A speaker signal will damage it. IMHO, sixteen 12 inch speakers is going to totally bury the Motion Sound. Hope this helps

 

[LPJunky]

Well I did investigate these issues (see all the dirty details here http://forum.grailtone.com/viewtopic.php?f=33&t=45637 if you want).

First, you should not use both the 8 ohms and 4 ohms at the same time. Mesa did not want to acknowledge any other combination than what is in the manual. There are two tap windings out of the output transformer (4 ohms and 8 ohms) and to calculate (or figure out) the exact power output is not simple. One would also need to know if the MkV OT can handle 90watts total or per output taps. You actually might risk melting it if you perform at gig volume.

Second, Both 8 ohms output is nothing other than 2 connector in parallel. Same for the two 4 oms connectors. If I understand the 4 ohms connections your suggesting, 2 x (2x8 ohms cabs connected to give a 4ohms overall load) each connected in the 4 ohms would produce a 2ohms load which is in itself an UNSAFE mismatch.

Look at the manual again for the different combinations. Unfortunately, you should stay away of using both 8 ohms and 4 ohms outputs simultaneously.

 

[richiedoc]

OK, so I eliminate 2 of the Mesa cabs.
Each plugs into one of the 4 ohm outputs on the amp.

Now I am left with the two 8 ohm (combo) outputs staring me in the face, begging to be used.

But are these really 8 ohms - now that there are two 4 ohm outputs being used...

The Motion Sound cab is powered but only to rotate the drum. There is no amp inside from what I remember. So it is 8 ohms.

So...the question is - "is it safe". (can I have some of that liquid Novocaine Zell? My teeth hurt.)

 

[richiedoc]

Let me answer my own question: no, it is not safe.

4 ohms total is the limit.
The output jacks are there for convenience.

Slave out to the amp powering the Motion sound is the workaround.

 

[LPJunky]

But are these really 8 ohms - now that there are two 4 ohm outputs being used...

Yes they are 8 ohms BUT Mesa doesn't want us to used them at the same time as using the 4 ohms. They are two different windings. Electrically separated (I checked).

Slave out to the amp powering the Motion sound is the workaround.

Sounds like a good idea

 

[richiedoc]

Thanks gentlemen. You just saved me 2 grand.