JCM 900 tone opinions and known mods

[bnwitt]

I have a JCM 900 2100 in the shop with the owner complaining that something is missing in the tone.  I quiered him and the only substantial  thing I could gather is the lows and mids are wimpy.  So, I did some research on this model and it seems that complaint is a pretty constant one for this circuit.  It also seems that the diode distortion circuit is not held in high regard.  While the owner was here, I had him play the amp with the 1987 JMP50 turret board I installed in place of the original PCB 1986 50 watt bass board.  I had him playing with jumped channels and the V2a 0.68uf bypass cap boost switch on.  The tone blew him away so now I need to know if there are any mods out there for this 2100 to get the mids and bottom back into the output.  Anyone familiar with this amp?  I'd hate to tell him he needs to ebay it or gut it.  I did notice he had the output mode in low which I've read cuts lows.

[Ritchie200]

Other than a gut, I only have one recommendation...  I have a client that loves these buzzmeisters - PCB nightmares.  He swears by JJ's in the output.  They do sound pretty good, and I'm not a JJ fan.  Still, I keep thinking lipstick on a pig....   See if you can sell him a good amp!  He can pay you from the Fleabay proceeds....plus some extra!
Jim

[bnwitt]

You know Richie I'm beginning to think you are right on with your comment on this amp.  Everything I read says it sucks.  I cranked it up next to the 1987 amp I just built and talk about anemic tone.  Still, I'm going to run through it and make sure nothing is wrong with it before I pronounce it crapola.

[HotBluePlates]

I played a JCM900 Dual Reverb once back in maybe 1994. I can't imagine a great sound coming out of it. It does work well for grunge/noise rock/etc.

[Backwoods Joe]

My son had JCM900. The key word here is "HAD". Wish i could help you out but that has got to be one Marshalls biggest "clunkers". joe

[tubenit]

A friend of mine who is an excellent player had one and never used it. It was literally gathering dust. I converted it into a Plexi 50 with reverb. He loves it now. I heard him play it with a loud band and it cut thru the mix excellent. He wanted to make the conversion as cheaply as possible so I ended up using the original PCB type pots.

Here is a photo of the conversion:

http://s28.photobucket.com/albums/c216/tubenit/?action=view&current=CPlexi50chassisinteriordescription.jpg

With respect, Tubenit

[bnwitt]

The consensus grows.

Nice conversion on a tight budget Tubenit.

[tubenit]

 I can not remember for sure, but I think the conversion only cost around a $100 or so?  About as cheap as a good effects pedal. 

I originally wired it with Hoffman's "add reverb to a western unit" and later converted the reverb into the "one tube reverb" insertion prior to the LTPI. 

He also wanted less volume and I installed a pentode/triode switch and converted it to cathode biased which he ended up preferring over the original fixed biased design. So the cathode biased got left in there.

The band he was with had keyboards and the other guitarist used either a Mesa Boogie or a Deluxe Deville which both sounded like mush to me in the mix compared to the Plexi 50 which cut thru clear as a bell even overdriven.

With respect, Tubenit