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4/10/99 16:05
Trace
TonsOfTone@aol.com, traceallen@hotmail.com

Hey all;

I had a mess of emails asking about more mods for Marshall's. I'm certainly not
a expert on Marshalls by a long shot (maybe someday in a galaxy far, far
away--ha, ha) 

Many people were asking about mods for the JCM800 2203/2204 (basically the
same preamp) I posted 95% of them here so please take a looksy through the
archives. Richie and Carl posted some great sounding mods as well!!

I'll post the only other one I think is worth while. All resistors are 1/2 watt 2%
metal film (or whatever you prefer :-)

#1.) Locate R11 (470K) and replace it with a 120K.
#2.) Locate R10 (470K) and remove it from the board.
#3.) Grab a toggle switch and wire a 470K to it as well as a 120K. Solder the
leads to the board where where you removed the 470K (see#2)
#4.) You can remove the DI-output jack from the rear panel and mount the
switch in it's place.

The toggle switch allows you to switch between a good JCM800 distorted tone
and "richer", "wider" distorted tone. Yes, it does boost the gain and the lower
mids and bass frequencies are excentuated as well.

For a more "full tilt" tone that hard rock or heavy players would enjoy you can
do the following;

1.) Located R6 (10K cathode resistor) and replace it with a 4.7K
2.) Locate R15 (33K) and replace it with a 39K. The previous mod boosts the
lower frequencies but if you find you need more bass that what that provides
then you can use a 47K or even 56K for more bass yet. 
3.) Locate C1 (.68uF) and try a 47uF or 22uF cap here. The .68uF is very
Marshall'esq so you'll have to decide what you prefer.

So give these a try and see what you think. Let me know what you think and
feel to post it here.

Hope it helps someone;
Trace 


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4/19/99 15:35
Trace
TonsOfTone@aol.com, traceallen@hotmail.com

Hey all!

As you know I've been goofing about with JCM800's alot lately and I've posted
all the goodies I could think of. I came up another interesting mod that I doubt is
anything "revolutionary" or "brand-spankin'-new" but it sure does ALOT to juice
up or "brown-up" the tone of a Marshall.

These are just "hard-wired" mods and have no switching options.

JCM800 2203-2204 Model:

#1.) Change R6 (10K) to a 4.7K (a gain boost but not a radical one)

#2.) Change R10 & R11 (both 470K's) to 330K's. (a gain boost and a slight
increase in volume. You'll have more meaty lowend and some more lower mids)

#3.) Change R24 & R25 (both 220k's) to 100K's
(get a "browner" tone from the preamp)
Note: Make sure to re-bias the amp!

#4.) This is optional but I rather fancy changing R15 (33K) to a 39K value.

That's it. Like I said it's not revolutionary but it will give you some pretty
inspiring results! 

1987 circuit or the Plexi:

You can perform the #3 mod and it does "brown/warm" up the tone a great deal
on these amps as well. You will get a bit more gain but it's NOT the harsh/bitey
gain. It's extreamly pleasing to listen to even at higher volumes and doesn't seem
to fatigue the ears.

I've shared this with a few people and I believe Ken Fisher takes the credit for
this mod and it's listed in a book somewhere. it wouldn't surprise me since he's a
tone-guru and a then some! (ha, ha) It's a great mod none the less.

I wouldn't really bother with the #1 mod on this circuit since it's already a
gain-beast-from-hell circuit!! However, if the mood strikes you then PLEASE
experiment. 

Like Richie said, I think everyone's done just about everything to these sort of
models but to quote Richie.. "We'll keep experimenting."

I hope this helps someone's tone;

Trace 

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