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Converting a combo. GK MB112

Stimpy

Stimpy

Guest
Nov 17, 2012
47
10
Manchester
neilsutcliffe.com
#1
I have a GK MB112, which cut out on me during rehearsal. At the moment I have no idea what is wrong with it, but was looking to upgrade to a head and amp using my MB112 as a cab.

Now the build quality of the combo is exceptional, lightweight all that. I have my heart set on the Ashdown Rootmaster 420W, due to the rugged design, ease of use, and ballsy sound. Then modding the combo (200W) to have a speaker connector where the amp block was, or getting a tech to mod this for me.

Inside there is are two cables coming through a sealed hole, which connect to a motherboard style header on the board. I was thinking the tech could either put a speakon connection from inside the cab, or drill a hole in the existing metal amp panel and connect it somehow.

I was wondering though how safe this would be, given I would be running a 420W head into a 4ohm cab with a 200W speaker. The Ashdown advertises as 4ohms minimum on the back-panel, but the matching cabs they sell are 8ohms, so would this overload the speaker, or would it double the wattage I could effectively use?

Thanks
 
#2
I would put two jacks on the back of the combo, somewhere through the wood and leave the amp metal part alone.

One jack would be the power amp output.
The other jack would be the speaker input.
Label them both clearly!!!
To use it as a combo you would run a short speaker cable between the two.
To use it as a speaker cab leave the power amp off and it's jack unplugged and run a speaker cable from your head into the speaker input.
Do not ever run your cable from your new head into the power amp output. You will blow up at least one and possibly both of the amps.

Could be either speakon or 1/4 inch.

As to the power mismatch it will work but you won't be able to crank the new head up. Back off before you hear the speaker having difficulties.
 
#4
jthisdell said:
I would put two jacks on the back of the combo, somewhere through the wood and leave the amp metal part alone.

One jack would be the power amp output.
The other jack would be the speaker input.
Label them both clearly!!!
To use it as a combo you would run a short speaker cable between the two.
To use it as a speaker cab leave the power amp off and it's jack unplugged and run a speaker cable from your head into the speaker input.
Do not ever run your cable from your new head into the power amp output. You will blow up at least one and possibly both of the amps.

Could be either speakon or 1/4 inch.
Click to expand...

+1 This is exactly what I did with an Ampeg BA115 and it works great. I added a third speakon soldered to the speaker speakon so I could daisy chain to other cabs as well since I replaced the original BA115 4ohm speaker with an 8ohm speaker. The possibilities are endless.
 
#7
anderbass said:
The reason your combo cut out; might just be dirty/stuck switching contacts in your headphone jack. Sometimes, all that's needed to correct this problem is to simply insert a guitar/headphone plug in and out of the headphone jack a few times.

Does your combo have an fx-loop?
Click to expand...

Why didn't I think of that. It matches all the symptoms, and putting in some headphones does create a crackling noise very similar to the one just before it cut out.

I'm probabaly not going to convert it now under Jools recommendations. The money would be better served going towards a cab I really want, I will end up keeping it for home/practice and rehearsals where there is a backup amp. It may never cut out again now I've put some compressed air in the headphone socket.
 
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