hey amp techs...combo to head conversion?

[korovamilkdud]

I've got my JC-120, I actually like running it into my Marshall. I was just wondering if there was a way to convert from a combo to a head so that the only speakers running were from the cab.

[Davey]

Re: hey amp techs...combo to head conversion?

remove guts, stick it into a box ...

essentially what it boils down to

[ErikH]

Re: hey amp techs...combo to head conversion?

Yup, that's pretty much it. Only difference between it and say a Marshall type head is the tubes would be sticking down still, unless you don't mind the face plate being upside down or plan on changing it. Don't forget to leave space for the reverb pan.

[ES350]

Re: hey amp techs...combo to head conversion?

JC 120 is a top-mounted chassis, right?---like a Fender; bolts through the top of the cab and the sides. No tube clearance to worry about, no big PT or OT for tube current draw. There are loads of cab builders out there who will make you one if you send very good dimensions, or you can send the head if you want it right. This conversion is not really a standard off the shelf item for most cab builders, tho. You can build your own if you have the tools and a little skill...just a box.

[itbepopples]

Re: hey amp techs...combo to head conversion?

Isn't a JC-120 a Roland Jazz Chorus? There shouldn't be any tubes in there IIRC.

[ES350]

Re: hey amp techs...combo to head conversion?

Right, JC 120---no tubes, no way heavy PT, but top mounted like a Fender. Don't need a real heavy duty cab to keep it in one piece...might be some empty Fender head cabs (ala SF Showman, etc) floating around that might work if they're wide enough for the JC 120 chassis. White Tolex might look pretty cool...

[korovamilkdud]

Re: hey amp techs...combo to head conversion?

Well, here's the deal. I'm not exactly sure what you all all referring to when you say "guts" but I did try disconnecting the speakers on the amp and using the two ext. speaker jacks on the amp to connect the cab, but that didn't work. For some reason the speakers on the amp needed to be connected in order to enable the amp to run into the cab.

[ES350]

Re: hey amp techs...combo to head conversion?

Do you know what output impedence the JC 120 is looking for? I'm guessing, but since it's got two seperate output sections (60 w each), it probably wants 4 or 8 ohms each side (I tried downloading a manual, but it didn't work). Check the back panel, the specs may be printed there. If you have a multimeter, check the stock speakers to find out what the amp wants to see for each output section (SS can be very picky about lower impedance loads).

Chances are that you need to use the main speaker output jacks (a shorting type) instead of the ext outputs (which don't work unless the main output is also plugged in, a little safety feature). So, the correct load is important if you want to avoid damage to the output section. It can be done, it's pretty simple...maybe get some local help on this from a tech or a friend with some good electronics or sound reinforcement experience.

[korovamilkdud]

Re: hey amp techs...combo to head conversion?

Do you know what output impedence the JC 120 is looking for? I'm guessing, but since it's got two seperate output sections (60 w each), it probably wants 4 or 8 ohms each side (I tried downloading a manual, but it didn't work). Check the back panel, the specs may be printed there. If you have a multimeter, check the stock speakers to find out what the amp wants to see for each output section (SS can be very picky about lower impedance loads).

Chances are that you need to use the main speaker output jacks (a shorting type) instead of the ext outputs (which don't work unless the main output is also plugged in, a little safety feature). So, the correct load is important if you want to avoid damage to the output section. It can be done, it's pretty simple...maybe get some local help on this from a tech or a friend with some good electronics or sound reinforcement experience.

It has a pair of jacks that read "main in". Is that what I'm looking for?

I had a funny thought, if I reconnected the wires that are now connected to the speakers to a pair of jacks, then ran speaker cables from the jacks to the cab, would that work to eliminate the combo speakers?