I posted this on TGP as well but i wanted to get the opinion of the Marshall experts. I have a JCM 800 4104 that i really like the sound of. I replaced the V30's thatwere in it with ET65's and it made a huge difference but I still much prefer it though into a 212 closed back cab. I'd like to make the combo a closed back but instead of butchering the original white combo i thought i'd get a new closed back combo cab made. I have a guy that makes cabs looking into it as well. I've looked at some closed back combo's such as the 5150 and Mesa Roadster and they don't seem much larger than mine other than a couple inches taller and a few inches deeper. I'll need to keep the top part open to allow the tubes to circulate of course. Does the depth of the cab make a huge difference in the bottom end? Most of the closed combos seem to be about 12 inches. Has anyone ever done this before? Any ideas?
Has anyone made their own closed combo design?
- Thread starter rpurdue
- Start date
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The easiest thing to do is make your combo into a 3 piece back. I have done it with 2 of my combo's. The top board on a 4104 can be turned upside down to allow more heat from the tubes to escape. Just turn that board around so you get less heat and make your own 3rd piece for the back of your combo. This also gives you the option to leave it on, or take it off to tune your sound alittle bit for where you are playing. Good luck, man.
P.S You said your amp is white, I don't suggest you drill into it to mount the board. I use velcro strips the width of the board. They also make velcro in white, so you don't even notice it's there when you remove the center board.
P.S You said your amp is white, I don't suggest you drill into it to mount the board. I use velcro strips the width of the board. They also make velcro in white, so you don't even notice it's there when you remove the center board.
Awesome Man! Thanks for the info. I'm going to try it to see how i like it. If i like it i think i'll still make a new combo cab with a closed back and leave it open where the tubes are. I use an Alex Attenuator so it gets HOT!!!
The velcro strips don't have enough holding power to hold a small panel on the back of a cranked JCM800 combo. If you leave a portion open, then you should not have a problem with the panel but it still won't be a closed back cab.
Hillcountry
Active Member
You can make these, but there is a trick. You will need a larger cab like a blues breaker size. Then you can have the 2x12 portion on the bottom closed off, and you can have the amp portion open on the top and back so air can circulate - making two separate enclosures within the one. You will get weird phasing issues of you make a closed back combo with a vent in the top.
Yeah i think that's what i'm going to do! What do you mean by "Phase issues"?
Hillcountry
Active Member
Well...I had been experimenting with a design and I just closed the back in to see what would happen. There was a tremendous amount of air pressure coming out of the vent in the top of the cab and it tended to be out of phase with the sound from the speakers. You probably wouldn't notice in the house, but up on stage it had a really weird effect on what I could hear. On top of that, the amp couldn't breathe.
I like having good circulation for the head and an appropriate space for the speakers. What I built was 28"wide by 24"tall by 11.25 inches deep. The baffle was inset 1" at the bottom and 2" at the top and mounted from the front like a fender combo. The space for the head was 8" from the top of the cab leaving a 2x12 cab space below that was roughly 28x16.
I ended up re-making it with 1 of the 12s closed (an anniversary G12H) and the other side open (Celestion Gold). It was a killer combo. The amp was a JTM45.
I like having good circulation for the head and an appropriate space for the speakers. What I built was 28"wide by 24"tall by 11.25 inches deep. The baffle was inset 1" at the bottom and 2" at the top and mounted from the front like a fender combo. The space for the head was 8" from the top of the cab leaving a 2x12 cab space below that was roughly 28x16.
I ended up re-making it with 1 of the 12s closed (an anniversary G12H) and the other side open (Celestion Gold). It was a killer combo. The amp was a JTM45.
Awesome! So did this give you the bottom end THUMP that a normal closed cab would. Would you happen to have any pics?
Hillcountry
Active Member
I'll take a pic of my standard open back cab that I kept for myself - looks like a Blues breaker. Yes the cab I built for that guy did have some serious thump. The G12H anniversary seems like a great speaker, and the Gold added sweetness to the mix. I have some crazy work this week...If I get a chance I'll take a few pictures of my cab.
-Geoff
-Geoff
