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1,727 Posts
Discussion Starter · #1 ·
As outlined here, I picked up a spiderII 150h head and a peavy XXL 4x12 cab for dirt off craigslist to hold me over until I can afford/find better gear.

both items are crap. I know this. :)

But, i'd like to get the best out of it while I have it running. Playing with a dummer the other day, I found that about 1/2 volume is as high as it will go. Beyond 12 o'clock to 6, it doesn't get any louder at all.

The 150h is set up for 2 cabs, 8 ohms each, in stereo (l/r channels, not 'top/bottom'), effectively 75x2

The xxl cab is wired for 16 ohms, mono (1 jack)

From my car audio days, I realize this means that I'm using the left (or right, whatever i'm plugged into) 75 bank at effectively 1/2 draw, or 37.5 watts. And that explains why a dummer in a basement is basically drowning me out at full volume.

I likely will never have/use a full stack with this head (or this cab) so sending both amp outputs to 1 cab seems to be the smartest/cheapest thing to do.

The cab is rated for 300 watts, so i'm thinking about making it stereo, get a new back plate, re-write the inside to 2 banks, 8 ohms each.

Can I do this?

The specs don't list what the speakers are each ohm wise. All i can find is "4 - 12" model 144 Blue Marvel speakers" but no more details about those individual speakers themselves. The XXL isn't even listed on here: so i'm out of ideas.

If they are 8 ohm speakers, I can do series-parallel, giving me an 8 ohm load on 2 speakers.
If they are 16 ohm speakers, I can series them to get 8 ohms per side.

This will effectively quadrouple my output if I am doing the math right. This will give me a full 8 ohm draw, and be able to get both sides running at 75 each, for 150 solid state line 6 wattage of DOOM! :scream:

Sound right? Anyone have any pointers for doing something like this? Or should I just scrap it and get a real cab?

Good news, Everyone!
1,528 Posts
Get a multimeter, They're invaluable for doing all sorts of work like that. Measure the speakers, and see what comes up. I'm fairly sure the Blue Marvels exist in both 8 and 16-ohm models. Wiring a cab stereo is fairly easy, too. At least if you have a fundamental knowledge of how Series and Parallel circuits work...

Mod Britannia
7,233 Posts
Wiring a cab in stereo isn't hard if you're handy with a soldering iron and wire snips. The speakers will most likely have their resistance on the back of the magnet. With two speakers putting them into series adds the values (so two 8ohm speakers would give a 16ohm total) and having them parallel halves the values (so two 8ohm speakers would give a 4ohm total). For more than one two speakers in parallel the resistance "x" is given by adding the inverses of the speakers resistances:

1/x = 1/(speaker a) + 1/(speaker b) + 1/(speaker c) etc.
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