Guitar Gear Forum

Modest Mike is wanting to connect two 8-ohm cabs to his Laney IRT, which only has 8-ohm and 16-ohm outputs. Daisy-chaining the speakers using the standard jacks on his 2x12 would put the cabs in parallel, resulting in a 4-ohm load that the amp can’t handle, so he needs to wire the cabs in series, which will make for a 16-ohm load.

There’s a few ways to accomplish this. He could rewire the connectors on the 2x12 to do series, but it’d take a little tricky work with switching jacks to allow the cab to be used without the second one attached. Plus, you could never use the two cabs in parallel (if needed) without rewiring the jacks. He could also rewire his outputs inside the amp, but it has similar limitations. The other option is to get a y-cable (not sure if these even exist) or a box to perform the wiring between amp and cabs.

For fun, I'm making him a little connector box to use. I had planned to use a (metal) utility box I had on hand for this, but realized when I was looking up the wiring that you can’t use a conductive box between the two jacks for the cabs, as it will cause a direct short across one of the speakers, which means you'll be back to half the expected load. Definitely not the best thing to do

Here’s a wiring diagram that I found (which also confirmed my realization that you can’t use a conductive box)



Went to Radio Shack and got the parts needed, and soldered it up with 16-gauge wire (should be fine for any amp). The following is a build diary, for anyone who may be interested in building one for themselves. It was really pretty simple - only took me about 45 minutes or so to build it up.

One of the cool things about building your own custom box is that you can place things wherever you want. I sent this to Mike, to see what he liked best - he picked option B. I told him that I could locate a second Amp jack on the other side of the box (it’d be wired in parallel with the first Amp jack), but he didn’t need it.



All the parts needed

Measuring for the jacks - the box is 4 inches long, 2 inches wide, and 1 inch tall (mamberg will probably note that I put 3x2 on the drawing, but I decided to go with the bigger one when I saw just how small the 3x2 one was at the store).

There were some grooves in the sides of the box (probably for holding circuit boards) that needed to be removed. A chisel made fast work of it.

Heating up the iron, getting ready for wiring



Closeup of the box before soldering



…and with the wiring completed

oops... double post

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Final testing using two of my 8-ohm speaker cabs. We’re measuring resistance of the coil, which translates to a bit less (around 6-ohms) resistance than the actual impedance that the speaker is actually rated for. Impedance acts just like resistance when you put speakers in series or parallel, so the calculations are the same. Where Z = Impedance:
* Z total (series) = Z1 + Z2
* Z total (parallel) = (Z1 * Z2) / (Z1 + Z2)

12.6-ohms = winner!

One thing I'm realizing is that you've got to be careful with this type of box. If the speaker cables have jacks with metal covers (which are generally connected to the 'sleeve' or ground terminal on the jack), and if they touched metal (like the handle hardware in the pic above) or were 90 degree plugs that touched, they could cause a short across one of the speakers, which would halve the load on the amp. Same goes with the amp plug - and I'm not certain what happens to the load if the Amp jack cover makes connection with one or both of the speaker jack covers. Will have to test

I would say that the safest thing to do is use straight jacks and zip-tie the serial box to the amp or one of the speaker cabs so it doesn't move around.

looks very nice

You mean to tell me soon I will be able to run my thiele and a BL80 cab at the same time!?!?!?

This is high level fucking around and it's awesome thanks man!!!

Ain't done yet. Told you, I gotta install the penor. It's on order, but it'll be here in time

I'm gonna watch some fuck'rs light up ! And I don't just mean mister smokey .

That's awesome. You are a great friend!

So it looks like in the pic that all 3 jacks are wired together?

Also lol at the Mamberg comment. Good call.

Some nice work in this thread. Good stuff Grime

fretless wrote:I'm gonna watch some fuck'rs light up ! And I don't just mean mister smokey .

Looking forward to hearing you guys at the jam next week Making a day of it in Santa Monica - gonna go by West LA Music (haven't been there since late 80s), True Tone (Mike told me I needed to check it out), and maybe check out the Venice Beach (never been there, and I've been in SoCal all my life).

Walt wrote:That's awesome. You are a great friend!

So it looks like in the pic that all 3 jacks are wired together?

Also lol at the Mamberg comment. Good call.

Thanks Walt - yep, all 3 wired together in a series loop. Amp output connects to first jack, Speakers connect to the two other ones.

JiveTurkey wrote:Some nice work in this thread. Good stuff Grime

Thanks JT

cool you coming by for the jam ? I thought WLA closed ?

GABroing at it's best!

You guys are awesome!

Nice work Steve! Busting out the calipers = not fuck!ng around.

Dude this is super cool! I always say GAB=bast web evar!

fretless wrote:cool you coming by for the jam ? I thought WLA closed ?

Hell yeah, been hoping I could get out to see you guys jam. I wasn't sure about West LA Music, but they still have a website up. Mike tells me the other store is the one to see, anyway.

If you guys know of a place to eat out there, let me know! I'm hoping to get out there by 10 or 11am.

ajaxlepinski wrote:GABroing at it's best!

You guys are awesome!

itchyfingers wrote:Nice work Steve! Busting out the calipers = not fuck!ng around.

When it comes to this stuff, I never fuck around - despite what my kids will tell you

JerEvil wrote:Dude this is super cool! I always say GAB=bast web evar!

GRIMESPACE wrote:

fretless wrote:cool you coming by for the jam ? I thought WLA closed ?

Hell yeah, been hoping I could get out to see you guys jam. I wasn't sure about West LA Music, but they still have a website up. Mike tells me the other store is the one to see, anyway.

If you guys know of a place to eat out there, let me know! I'm hoping to get out there by 10 or 11am.

ajaxlepinski wrote:GABroing at it's best!

You guys are awesome!

itchyfingers wrote:Nice work Steve! Busting out the calipers = not fuck!ng around.

When it comes to this stuff, I never fuck around - despite what my kids will tell you

JerEvil wrote:Dude this is super cool! I always say GAB=bast web evar!

Truetone is a nice store with kinda dopeyaholes running it

go here for all you can eat lunch $10 , food is fantastic
http://www.jaipurla.com/Japur-indian-food-delivery.html

hang out in the mall and WLA GC is right across the street

yeah I've never been happy with the staff at true tone necessarily but the gear they stock... man... really great stuff.

It's ok. Not like I'm buying anything. Just going to drool a bit

drooling happens when I unleash Laneys and BL80's and Thieles and Algal Blooms and Lukes and vape

with all that gear around it will be easy to lose weed