Restoring a JCM 800 Lead 1960

chuck · Post by **chuck** » Sat Apr 01, 2006 1:48 pm

I just bought a JCM 800 Lead 1960 but it had been modified a previous owner. It was re-wired to 8 ohms, 2 3" wood strips running top to bottom inside the cab on the back piece were added (i guess as baffling of sorts?) and there's a white cotton-like material on the back as well. I've seen the material in Ampeg 8x10's and some others but i didn't know if Marshall's has them as well. I'm just trying to get it back to stock. I took out the wood and filled the screw holes (fairly small ones) with a strong wood epoxy. I'm just wondering about the fabric. anyone know? The 8ohms doesn't really bother me but is there anything else to look for?

thanks.

Bainzy · Post by **Bainzy** » Sat Apr 01, 2006 1:51 pm

They (apart from 8ohm mod) might actually have been to improve the sound of the cab - are you sure you want to take them out?

chuck · Post by **chuck** » Sat Apr 01, 2006 2:03 pm

Well the work was defiantly not professionally done. It was apparently young guy in a band that threw it together. Mind you, it doesn't mean he's not capable of good work, it just looks a little like a hack job to me. To be honest i though the cab sounded a little stuffy, the guy i got it off said he didn't hear a difference but i think by removing some of the add ons she might breathe a little better.

Good point tho, i'm just used to a certain sound from years of playing with them and i think (in my opinion) that the sound i enjoy come from a stock setup. I've never used a moded one before so i may be wrong. It might sound worse after! hah.

chuck · Post by **chuck** » Sat Apr 01, 2006 2:09 pm

Also, would you suggest re-wiring back to 16 ohms?

Bainzy · Post by **Bainzy** » Sat Apr 01, 2006 2:39 pm

In that case it's probably best to return it to stock then. I'd recommend wiring it to 16 ohms if you like the 16ohms setting on your amp, but it's mostly personal taste really. I prefer 16ohms.

chuck · Post by **chuck** » Sat Apr 01, 2006 3:04 pm

Sounds good. I want to put this guy back together but i still don't know if Marshall's use that white material on the particle board back. Anyone know?

daneswede · Post by **daneswede** » Thu Apr 06, 2006 11:47 am

chuck wrote:Also, would you suggest re-wiring back to 16 ohms?

Rewiring the cabinet to 8 ohms will create a more resonent negative feedback. Anotherwords, RUnning at 8 ohm impedance out of the head into the cab at 8 ohm will give you a bit more resonoance in the low end and a bit more "hair" around the notes I think anyway. The higher the iumpedance the tighter, the less the imp. the looser and fluffier or hairy if you will :>) . Has to do with the negative feedback circuit , im no tech just what I eread and I do hear a differance when running at 8 ohm impedance rather than 16 ohm imp.

Not saying one is better than the other. For instance, My 1981 Marshall JCM800 runs at 8 ohm impedance into a BOgner Uberkab which was wired at 8 ohm impedance from the Bogner Factory. My Marshall 1959HW runs straight at 16 ohm impedance negativer feedback into the 1978 Marshall slant check cab with the Blackbacks. SOunds somewhat tighter around the notes. THats what im hearing any way.

daneswede · Post by **daneswede** » Thu Apr 06, 2006 11:48 am

chuck wrote:Sounds good. I want to put this guy back together but i still don't know if Marshall's use that white material on the particle board back. Anyone know?

Marshall, during the 1970s or at somw point during the construction period of the 4x12" cabs DID USE a material like foam looking almoszt to LINE the back and COMPLETE INSIDE OF the cabinet YES. THis would deaden the sound a biot I would think. I forget exactly what this accomplished?

sub · Post by **sub** » Fri Apr 07, 2006 10:38 pm

How you can wiring 4 16 ohm speakers to 8 ohm???

Billy Batz · Post by **Billy Batz** » Fri Apr 07, 2006 10:49 pm

daneswede wrote:
chuck wrote:Also, would you suggest re-wiring back to 16 ohms?

Rewiring the cabinet to 8 ohms will create a more resonent negative feedback. Anotherwords, RUnning at 8 ohm impedance out of the head into the cab at 8 ohm will give you a bit more resonoance in the low end and a bit more "hair" around the notes I think anyway. The higher the iumpedance the tighter, the less the imp. the looser and fluffier or hairy if you will :>) . Has to do with the negative feedback circuit , im no tech just what I eread and I do hear a differance when running at 8 ohm impedance rather than 16 ohm imp.

Thats only in amps that have the NFB connected to the output jack tips. Many marshalls are wired like that. I guess the idea is when your using 8 ohm youll have a full stack and so a cleaner low end responce and when you have 16 ohms youll have a half stack so the extra voltage in the NFB will clean it up a bit. The much better way to do it is to connect the NFB wire directly to the OT secondary tap on the impedance switch. Then your set to a certain amoutn of NFB regardless of the cab you use. As far as I know marshall has done it like this a lot as well and it seems most people here do it to. It makes sense. Then you have more control over your NFB. If you wanted it on 4ohm for the least NFB and the hairiest sound you could do taht as well otherwise youd never set the selector there unless you had a 4 ohm cab of coarse

Metropoulos Forum

Restoring a JCM 800 Lead 1960

Restoring a JCM 800 Lead 1960

impedance 16 or 8?

Re: impedance 16 or 8?