Using an MG30DFX as a cab

[Pointy]

I've got a Marshall MG30DFX lying around that i hardly ever use anymore, and i am thinking of using it as a cab, probably with a Blackheart BH15H for a practice/bedroom setup, maybe recording too.

The Marshall only has a "CD IN" input. Acording to the manual (link) the CD IN is 3.3kΩ, and i think the speaker is 4Ω.

So, i am guessing i can't just plug the head's 4Ω output into the 3.3kΩ (which is 3300Ω) CD IN, is that right? And, for educational purposes, will this ruin the amp head or just produce no sound?

Second question, can i just get rid of the Marshall's amp section and connect the speaker to an input jack to use it as a cab or does there need to be some sort of circuit involved?

Don't know if any of the above sounds stupid, but hey, i am only learning!

[Hellbat]

Do not connect your head to the CD in in your Marshall unless the head has a line level output. You stand a good chance of melting both if you try. Assuming the speaker in the Marshall is an impedance that the head supports, you could connect it directly, but I don't know if the speaker is directly wired or plugged in with a 1/4" jack or not.

[Pointy]

Thanks for the reply. The description in the manual and on the amp's back is "Power output: "30W RMS into 4Ω". I take it that means the speaker is 4Ω? Can the speaker's impedance be measured directly with a multimeter?

I have no problem yanking out the cables and connecting/soldering an 1/4" jack, but does it matter which cable goes to the tip and the shaft? Since two speakers can be wired out of phase with each other i am guessing it doesn't matter for a single speaker, is that correct?

[Hellbat]

Check the speaker to see whether it is marked with impedance. Most multimeters will not read impedance. While it is measured in Ohms, it's not the same thing as resistance. You are generally going to want to wire + to the 1/4" tip and - to the barrel.

I don't know the BH heads at all but if it has a 4 ohm mode you are going to want to switch it to that mode.

[Pointy]

It does have 4Ω output. Thanks again!