JCM 800 50 watt 2204 mods w/pics

[afmobius]

FYI, my JCM has the VERTICAL inputs. For everyone with this set up I wanted to post pics that might make the task a little easier. All the instructions, how to's, etc. were gathered right here on marshallforum from the more knowledgeable techs.

If there are any errors, missed steps, etc. let me know and I will make the change EXCEPT for spelling chassis wrong in the pics… I hate editing text on photos. =)

Covering the primary mods: Clip 1 leg or remove both the C4 (treble peaking circuit) and C5 (bright cap). Also replacing R 5 with 68k (from 470k). Together, these mods reduce the tin like highs while getting the amp to produce a more traditional Marshall tone as well as more functionality at lower volumes. This was my 1st time working on an amplifier and start to finish, the job took about 30 minutes. Further, these mods create a lot of improvement for minimal effort.

Items needed: screwdriver, wire snips, a 600 volt rated jumper wire with shielded alligator clips on both ends, digital multimeter that can check up to 600 v dc, solder/soldering iron, a 68 k resistor, canned air, (2) same size blocks (not made of metal), contact cleaner spray and possibly a bleeder tool (will address later).

 

[afmobius]

[FONT=&quot]1) [/FONT][FONT=&quot] To get started, turn the power and standby switches to the on position. [/FONT]

[FONT=&quot]2) [/FONT][FONT=&quot] Remove the 4 screws from the base and CAREFULLY slide the amp rack out of the [/FONT]
[FONT=&quot] head. It should be quick and easy--like your sister! Now is a good time to spray[/FONT]
[FONT=&quot] some compressed air around to dust things off. Have 2 same size blocks (NOT made[/FONT]
[FONT=&quot] out of metal) to put at either end then turn rack upside down.[/FONT]

[FONT=&quot]3) [/FONT][FONT=&quot] If this is new ground for you, check out the pic below labeled 2204BleedNTest that [/FONT]
[FONT=&quot] shows what you can expect to see when you open the amp and identifies the [/FONT]
[FONT=&quot] location of the parts being modified.[/FONT]

[FONT=&quot]4) [/FONT][FONT=&quot] Attach one end of your jumper to the chassis and, with one hand behind your back, the other to Pin 1 of the preamp closest to the caps. (for location see top center of pic labled 2204BleedNTest). Take 5 minutes-- go smoke a cigarette, play a deathmatch on Call of Duty, etc to let the caps drain. It does not really take that long but hey, it was a good time for a break.[/FONT]

[FONT=&quot]5) [/FONT][FONT=&quot]Attach the ground from your multimeter to the chassis and, with one hand behind your back, carefully check the voltage on the positive terminal of each cap.[/FONT]
[FONT=&quot](for location see top right of pic labled 2204BleedNTest)[/FONT][FONT=&quot]. If for any reason the voltage did not drain click here-[/FONT]à

http://www.marshallforum.com/workbench/14545-draining-filter-caps-jcm800-2.html

[FONT=&quot]6) [/FONT][FONT=&quot]Clip a leg or remove C5… when you clip R5, C4 goes with it… solder in your 68k resistor. (for location see top left side of pic labled 2204BleedNTest). For a close up of the resistors see pic labled 2204ModLocations.[/FONT]

[FONT=&quot]7) [/FONT][FONT=&quot]As long as you everything opened up, spray some air around and spray contact cleaner on the pots.[/FONT]

[FONT=&quot]8) [/FONT][FONT=&quot]Reassemble, play and be depressed that while your amps sound has improved, your playing has not... =)[/FONT]

 

[afmobius]

Pic 2204BleedNTest

 

[afmobius]

Pic 2204ModLocations

 

[impetus maximus]

glad to see your modding for taste

check out imgur for image hosting. then we can get a better look at your work

 

[afmobius]

Is imgur the standard or will any photo upload site (flickr) work?

 

[impetus maximus]

i just suggest them as they seem to last. unlike like phototoilet err bucket
so many threads i see "this photo has been deleted from photobucket" etc.

 

[Jonathan Wilder]

Out of curiosity, what is the purpose behind turning the power and standby switches to "on"?

 

[afmobius]

impetus, Ok here is a link to flickr... my other pix have been up for a while without any problems..

lvheretic's photosets on Flickr

Wilder, I believe this is to ensure any remaining charge in the caps can complete the circuit when you clip onto the preamp to drain... I did this following Lane's instructions-- I am no tech (and do not plan to be) so for me, once I got the "how" I didnt really need the "why"... except in learning Ohm's Law.

 

[sweethouze28]

I have the Canadian model 2204 and i m gonna check if the inside of my amp look like your and if yes , i m gonna mode mine too cauz i found it realy trebbley but i have a lot of bass so...

 

[demonufo]

Well, go easy on it, do it one mod at a time and try to live with the results before moving on to the next one.

Personally I think most of the common mods (such as these are) to a 2203/2204 platform mess up the character and the response waaaaay too much. Clipping the brite cap alone causes other side effects, and the amp doesn't clean up too nicely on the guitars volume pot from then on.
Many other mods just make the amp mushy.

 

[SmokeyDopey]

WHO's sister is quick n' easy? Yours?

Please, introduce us

 

[sweethouze28]

Ohhhhh i just finish to mod my amp ( 1989 2204 Canadian model ) like you mentioned and... THANKS YOU !!! This mod kick ass !!! The glassy top end have dissapear and the amp sound much bigger !!!

 

[Joey Voltage]

Well, go easy on it, do it one mod at a time and try to live with the results before moving on to the next one.

Personally I think most of the common mods (such as these are) to a 2203/2204 platform mess up the character and the response waaaaay too much. Clipping the brite cap alone causes other side effects, and the amp doesn't clean up too nicely on the guitars volume pot from then on.
Many other mods just make the amp mushy.

You know I agree 100% and if you do the silly 68k mod at least put a 1m resistor from wiper to ground of the gain pot, and then lower the value of the first coupling cap to .0022uf...,......,. And while your at it wtf just permantantly install resistive bleeders while your at it, save yourself the trouble.

 

[JTyson]

Any clips?
would love to hear the results

 

[afmobius]

Sweethouze, Glad the mods worked for you... I have had my amp since the 80's (wow..) and my only regret is not knowing about this and doing it a long time ago...and your right--the tinny highs are replaced with a heavier, balanced tone...