JC40 Extension Cabinet? (Tech advice wanted!)

b_dj · August 2023

Hey!

I’ve got a JC40 that I love as a pedal platform, however I find it can sound boxy and lacks low end due to the 10” speakers.

I’m a little bit handy with a soldering iron, so wondered if anyone had any advice if it was possible to use an extension cabinet with it?

I know the speakers are 4Ohm, so if I wired a female Jack in parallel into a 212 with two 8ohm also in parallel that shouldn’t be too much strain on it?

My other option would be to jam 2 12inch speakers in it, which I’ve measured and could be do-able with some mini modding to the mounting rings (it just about fits!)

Any advice from techs etc would be fab.

Sadly selling it and getting a JC120 isn’t an option as frankly it’s beaten to hell after many many tours!

thanks!

ICBM · August 2023

I’ve never seen one in person but I’m reasonably sure it’s a stereo amp, ie you need two separate speakers not a pair wired in parallel. That’s not a problem, other than needing two cables if you want to use an extension cab - 8-ohm speakers are fine, although they will reduce the maximum power available, but probably offset by the greater efficiency of the 12” speakers.

I do think you need an extension cabinet - the boxiness is more likely due to the cabinet size rather than the 10” speakers… think about bass amps with multiple 10s, they don’t lack low-end. Fitting 12s to the existing cabinet might actually make it worse, surprisingly. Or even just find some better 10s - there are a fair number available in 4-ohm if you look for bass speakers rather than guitar.

I would see if you can borrow a 2x12” cab with stereo inputs and lash up some sort of connection to the amp before you set about modifying anything - it might give you a better idea of how much you can achieve or whether that’s even the right direction.

b_dj · August 2023

Thanks ICBM! Was hoping you’d be able to comment aha.

Re fitting new 10”, is there any in particular you’d recommend? I was looking at some 10” greenbacks but wasn’t sure if they’d do the job, or make any difference!

Reducing the output isn’t too much of a concern, considering I already barely run it above 5 before sound guys complain.

ICBM · August 2023

I don’t think the Greenback will do what you want - if anything it’s quite a midrangy speaker. I was think of something more like an Eminence Beta, but they seem to be not available in 4 ohm now. (I thought they were, but I might be wrong.)

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JC40 Extension Cabinet? (Tech advice wanted!)

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