modding a jcm900 to something usable

[Machinated]

basically to cut a long story short i was given a jcm900 4100 for free from one of my dads mates, and i cant really sell it as i could see him coming round and asking how im getting on with it and all that goes with it.

so basically im up for changing as much inside the amp as possible to get it close to a jcm800 (or at least something more usable than the 900 is).

I know the schematics are really different between them, but would it be possible to get something done? I'd be prepared to spend about £400/500 on it.

are any of you schematic guys able to give any info on how much stuff would need to be done?

Marshall Schematics

that site says the 4100 is based on the 2205/2210 series amps - how much work would it take to get it to one of those?

cheers!

 

[korpse pop]

I think it's usable the way it is. I've played one of those and got a nice sound with a overdrive pedal in front and turning the bass knob to 10. Of course not as good as JCM 800 but not as bad people often think they are IMO

 

[Lasse Lammert]

I've modded that thing twice....got nice results.
I had a nice mod-guide for it, I'll see if I can find it

 

[samih]

From what i've heard would be easier to buy diy jcm800 kit and use only 900 headshell. Ok, anyway try boss sd-1 in front and eq in fx loop to get bass and high freq's to decent level. Have to get my 4100 model repaired and try this also.
-Samih

 

[Machinated]

yeah i remember you saying lasse - what did the mods do?

id love to have a 2205-esque amp and then pick up a 2203 later down the line.

 

[The spark]

Run an external preamp (JMP-1 or ADA MP1?) into the effects return.

 

[samih]

Lasse. I would like to see those mods if you can find them.
-Samih

 

[drew_drummer]

C'mon.... sell it to me... you know you want to Since you got it free, I'll even give you £50

 

[samih]

http://www.ceriatone.com/productSubPages/BSJCM800_2204/BSJCM800_2204.htm

 

[samih]

sorry this http://www.ceriatone.com/productSubPages/BSJCM800_2204/BSJCM800_2204Kits.htm

 

[mick thompson]

nothing beats the 800 series - i loved them so much, my old guitar teacher was trying to sell me his one a few years back but i was cash short - such a kick in the nuts.

anyway Machinated - check these:

http://www.thegearpage.net/board/archive/index.php/t-214286.html

http://www.fjamods.com/Marshall.html

http://tubeworks.tistory.com/entry/JCM900-Mods

you could try playing with some crossovers too.

this is just theoretical (i never tried it) but crack open the jcm, take the pre send, split it into a few different sections, throw a crossover onto 1 or 2 of them (or eq em), build a simple fuzz circuit, mid gain circuit or octave circuit, effect the crossover signal, join the signals back together and send them to the power amp, throw a few switches and potentiometers onto the circuits you built, drill some holes on the 900 and feed the knobs through, then you can have a effected signal on a specific eq band - eg: your high end can be octaved, your low end can be fuzzed and your mids stay normal. it might sound a little weird but you might end up with a fucking funky ass sound. - or try throwing an mxr phase 90 onto a mid ranged crossover signal and join them back up so you'll have a constant swell on your mid frequencies but your bass and high end will stay normal. (make sure you throw in a bypass switch so you can turn it off if its shit)

just a few ideas - there pretty simple without having to get into a great deal of schematics and resistors and shit - last thing you want to do is blow the shit out of the 900 because of a removed resistor or a new capacitor. if i were you i would play with small circuits and attempt to integrate the current signal into the circuit you build and then send it to the power amp, at least you'll only fry the circuit you build and not potentially the whole 900's board

 

[Machinated]

cheers guys

lasse, would love to see those mod guides. did you do them yourself? fancy coming to milton keynes and doing mine?

im in 2 minds whether or not to mod this or just save towards a 2203