How do you hook up your extension cab w/ a LSS?

[mtmartin71]

I've got a 1x12 LSS. Bought a closed-back 1x12 Vintage Cab with a V30 from Avatar (8ohm). I have a few hookup options in the back (8ohm and 4ohm) with the main speaker hanging off of one of the 4ohm jacks). Which one am I "supposed" to hook up to as the "optional" is 8ohm? Also, how do you guys typically handle your cabs? Stacked or side-by-side? Can't do across the stage because I'm in a two guitarist band. The Avatar is big enough for me to plop the LSS on top of.

Matt

 

[ToneAddictJon]

Plug the extension into the other 4ohm speaker out as well. I always like setting my cabs up side by side a few feet from each other, it helps spread the sound out and just feels bigger to me.

 

[rickc007]

yup, and I once called Boogie on this

basically, the 8 ohm out is optimal for 30watt mode

the 4ohm outs are optimal for 5 and 15 watt mode

if internal speaker is 8, and cab is 8, each go into
each of the 4 ohms

it won't hurt anything if you do diff, you get
optimal performance, aka max power transfer
when matched optimally

but Boogie clearly states that this amp is designed
to allow mismatches.

When you mismatch, you may just hear a slight
difference. One setting may be a little punchier....

 

[simonich]

Hold On! :!:

The amp (and most amps) can be used with a SAFE mismatch. Essentially that means that the speaker load is HIGHER than what the amp is set to drive. (e.g. the 4 ohm jack driving an 8 ohm speaker).

An UNSAFE mismatch is where you're driving a LOWER speaker impedance than your amp is set for (e.g. the 8 ohm jack driving a 4 ohm speaker). What happens in an unsafe mismatch is the speaker will try and pull more current than the transformer can produce and you can damage the transformer.

The 4 ohm jacks are hooked up in parallel. So correct, plug each 8 ohm speaker into one of the 4 ohm jacks. your total load is 4 ohms since it's effectively wired in parallel. You will be "matched" in this config.

 

[rickc007]

Wait Wait Wait one minute :lol:

I know what you are saying, and I know ohms law (I should, I'm an electrical engineer)

and I agreed with your description as well, but heard another one
that had me going .... check this out

watts=watts on each side of the transformer ( watts is voltage x current )

when you go to a twice higher ohm load it is half the current, but the voltage doubles. This is safe current wise, but what about voltage...

if this voltage builds, it can arc across the transformer windings ,and blow the transformer

if your load is too high in ohms, very little current is produced, but the voltage rises ( just like in the big electrical wires overhead, they jack the voltage up big time, so the current is low, thus less heat from the resistance, and the more effecient the energy system is. Same wattage all over the place, but less current down the wire)


I've read this is the theory about running an amp without a load at all.
If you have no speakers connected, this represents and infinite load.
No current, but the Voltage raises and can wipe out the transformer, by
having enough umph to jump across the windings.

Thus plugging an 8 ohm out to a 16 load may appear safe from
a current perspective, it's the voltage that can get you
This example is probably safe, but you get the point
Think Mesa are designed to be safe either way, within reason

You probably wouldn't want to put a short or a very high load across the output
If you stay between 4 ohms and 16ohms you're probably safe

I'm no expert on this...but it's what I've gathered reading into this
feel free to correct this theory if it is wrong

cheers,

Hold On! :!:

The amp (and most amps) can be used with a SAFE mismatch. Essentially that means that the speaker load is HIGHER than what the amp is set to drive. (e.g. the 4 ohm jack driving an 8 ohm speaker).

An UNSAFE mismatch is where you're driving a LOWER speaker impedance than your amp is set for (e.g. the 8 ohm jack driving a 4 ohm speaker). What happens in an unsafe mismatch is the speaker will try and pull more current than the transformer can produce and you can damage the transformer.

The 4 ohm jacks are hooked up in parallel. So correct, plug each 8 ohm speaker into one of the 4 ohm jacks. your total load is 4 ohms since it's effectively wired in parallel. You will be "matched" in this config.

:lol: :lol:

 

[simonich]

Yep, I was pulling on that EE training from years back too. Though I must confess most of my time was spent in the digital world.

What you describe is true for an ideal transformer. I'm clearly not an expert, but I'd think a 2x voltage overage would have a lower probability of causing the damage you describe vs. a 2x current issue. Of course the issue with current is that you'll just melt the windings.

Though I suppose one could call Mesa and get the story straight from the horses mouth so to speak. I'd trust them more than my 20 yr old memories. 8)

 

[rickc007]

That's funny....I specialized in Digital Signal Processing
Not interested in that old tube technology, or stupid magnetic fields hocus pocus

Now, my only electrical interest is pickups, and tube amps, go figure

and ya, I don't think a 2x voltage would hurt anything, or a 2x current
they could probably fuse for that pretty easy.

And I phoned Mesa at one point, and they seemed very lax about
small mismatches, used the word "optimal" to use equal ohms (8 ohm out to 8 ohm speaker)

but were also very quick to recommend trying the mismatches.
"won't hurt anything, you'll just get a different feel"

Yep, I was pulling on that EE training from years back too. Though I must confess most of my time was spent in the digital world.

What you describe is true for an ideal transformer. I'm clearly not an expert, but I'd think a 2x voltage overage would have a lower probability of causing the damage you describe vs. a 2x current issue. Of course the issue with current is that you'll just melt the windings.

Though I suppose one could call Mesa and get the story straight from the horses mouth so to speak. I'd trust them more than my 20 yr old memories. 8)